Mechanism‐Guided Thermoelectric Strategies for Smart Fire Prevention

Abstract

Fire prevention and early warning systems are essential to minimize fire risks. Thermoelectric (TE) materials that convert temperature gradients into electrical signals offer a promising pathway for designing self‐powered fire‐warning technologies and devices; however, their practical applications are often impeded by their low output power, inefficient charge transport, and poor interfacial compatibility. Despite several relevant reviews focusing on material types, it has remained underexplored from a mechanism‐driven perspective to enhance the fire prevention performance of TE strategies to date. To fill this knowledge gap, this work aims to systematically review TE materials and design strategies, e.g., structural design, energy filtering, ion doping, ionic thermoelectric effects, and interfacial engineering. This work highlights typical applications of TE‐driven fire prevention systems, such as wearable sensors, distributed forest fire monitoring networks, and intelligent building safety systems. Finally, future directions are discussed, which include multifunctional integration, durability under harsh conditions, and AI‐driven fire prediction, paving the way for developing intelligent, self‐powered fire safety technologies. This work underpins how mechanism‐oriented material design advances next‐generation fire warning systems with enhanced sensitivity, environmental adaptability, and autonomous operation, thereby expediting the creation of next‐generation fire‐prevention system and platform.

This review highlights recent advances in thermoelectric materials for smart fire prevention and early warning. Mechanism‐guided strategies—such as structural design, energy filtering, ion doping, and ionic thermoelectric effects—are systematically discussed, offering insights into the development of self‐powered, high‐sensitivity fire warning systems and their integration into next‐generation intelligent fire safety technologies.

1. Introduction

Fires are among the most devastating disasters worldwide, posing severe threats to human life and causing immense economic losses. For example, the 2019–2020 Australian bushfires burned over 18.6 million hectares of land, directly caused 34 deaths, and indirectly led to the deaths of 445 people due to smoke inhalation. Economic losses were estimated to be as high as USD 69 billion.^{[ 1} , ² , ³ , ⁴ , ⁵ , ^{6 ]} The 2025 wildfires in Los Angeles were considered among the most destructive in U.S. history, with economic damages estimated between USD 52 and 57 billion.^{[ 7} , ⁸ , ⁹ , ¹⁰ , ^{11 ]} Fire incidents are particularly frequent in high‐density urban areas, industrial zones, and forest‐urban interfaces, where uncontrolled fires can lead to extensive infrastructure damage and widespread environmental destruction.^{[ 12} , ¹³ , ^{14 ]} In buildings, fire risks are especially pronounced in residential and commercial structures where wood‐based materials are widely used. Due to the inherent flammability of wood, fires in such structures can spread rapidly, creating significant challenges for evacuation and firefighting operations.^{[ 15} , ¹⁶ , ¹⁷ , ¹⁸ , ^{19 ]} This highlights the urgent need for advanced fire prevention and early warning systems to mitigate fire hazards and enhance safety in vulnerable areas.

Early fire prevention research aimed to develop materials capable of withstanding high temperatures and suppressing flame propagation.^{[ 20} , ²¹ , ^{22 ]} This endeavor was driven by the urgent need to enhance fire safety in high‐risk environments such as building construction, textile manufacturing, and the production of electrical components.^{[ 23} , ²⁴ , ^{25 ]} Consequently, extensive efforts were made to explore various chemical and physical mechanisms by which materials could resist ignition or slow down the fire spread. One of the earliest milestones was the formulation of basic flame‐retardant coatings that incorporated brominated flame retardants (BFRs) as key components.^{[ 26} , ²⁷ , ²⁸ , ^{29 ]} These compounds became central to early fire‐resistant systems due to their high efficiency in interrupting the combustion process. As the understanding of environmental and health risks advanced, growing concerns emerged over toxicity, persistence, and bioaccumulation associated with halogenated flame retardants, particularly BFRs. This prompted a significant shift in research focus toward the development of nontoxic, biodegradable, and environmentally friendly flame retardant alternatives.^{[ 30} , ³¹ , ^{32 ]} Building on this shift, a new generation of nanostructured flame retardants has garnered considerable attention. Nanomaterials, with their unique size‐dependent properties, high surface areas, and interfacial interactions, have demonstrated excellent potential for enhancing flame retardancy at relatively low loadings.^{[ 33} , ³⁴ , ³⁵ , ³⁶ , ³⁷ , ³⁸ , ³⁹ , ⁴⁰ , ⁴¹ , ⁴² , ⁴³ , ⁴⁴ , ⁴⁵ , ⁴⁶ , ⁴⁷ , ⁴⁸ , ^{49 ]} Moreover, they often contribute to the improved mechanical strength and thermal stability of host materials. This evolution represents a critical step toward achieving a balance between fire protection performance and environmental sustainability, while also paving the way for the multifunctional and intelligent design of next‐generation flame retardant systems.

Despite the critical role in slowing fire spread and reducing combustion intensity, flame retardants primarily serve as the last line of defence in fire protection. Early fire warning and intervention are more effective in reducing fire risks and preventing severe damage. Studies have shown that detecting and responding to fires at an early stage can significantly minimize fire‐related hazards.^{[ 50} , ^{51 ]} However, traditional fire alarm systems, which rely mainly on smoke and temperature sensors, often suffer from detection delays. These technologies typically trigger alarms only after a fire has developed significantly, resulting in lost critical time for evacuation and firefighting efforts.^{[ 52} , ⁵³ , ^{54 ]} Therefore, the development of more sensitive and reliable fire warning technologies that offer faster response times and higher detection accuracy has become a key research focus for enhancing fire safety and risk mitigation. To enable efficient and early stage fire detection, a variety of novel fire sensing mechanisms have been proposed and investigated. Currently, common strategies include fire emission detection, resistance modulation, colorimetric response, thermal‐responsive transformation, and thermoelectric fire sensing. Fire emission detection relies on the rapid identification of combustion byproducts, such as carbon monoxide or carbon dioxide, released during the early stages of a fire, offering high sensitivity.^{[ 55} , ⁵⁶ , ^{57 ]} Resistance modulation utilizes the change in the electrical resistance of certain conductive or semiconductive materials when exposed to elevated temperatures or specific fire‐related gases, providing a direct electrical signal for fire detection.^{[ 58} , ⁵⁹ , ^{60 ]} Colorimetric response systems employ materials that undergo distinct and often irreversible color changes upon exposure to thermal or chemical stimuli, enabling low‐power or passive visual fire alerts.^{[ 61} , ⁶² , ⁶³ , ^{64 ]} Thermal‐responsive transformation involves shape or structural changes in thermally sensitive polymers or smart materials, which can be designed to trigger mechanical or electronic alarm systems.^{[ 65} , ^{66 ]}

More recently, thermoelectric fire sensing has emerged as a promising approach that exploits the Seebeck effect of thermoelectric materials to generate electrical signals under temperature gradients, enabling self‐powered continuous monitoring even under extreme conditions.^{[ 67} , ⁶⁸ , ⁶⁹ , ⁷⁰ , ^{71 ]} As summarized in Figure 1 , diversified fire sensing mechanisms, including resistance modulation, colorimetric response, fire emission detection, thermal‐responsive transformation, and thermoelectric fire sensing, collectively contribute to early fire warnings by improving detection sensitivity, response speed, and system autonomy. These strategies are becoming integral components in the development of next‐generation intelligent fire safety technologies.

Figure 1.

Fire detection and fire retardant mechanisms across different stages.

However, the application of conventional thermoelectric materials in fire‐warning systems still faces several challenges. Conventional inorganic thermoelectric materials, such as bismuth telluride (Bi₂Te₃) or lead telluride (PbTe), exhibit high thermoelectric conversion efficiency but suffer from brittleness and poor mechanical stability, making them unsuitable for long‐term use in complex environments.^{[ 72} , ^{73 ]} On the other hand, organic thermoelectric (OTE) materials offer excellent flexibility and processability but require further improvement in thermoelectric performance.^{[ 74} , ⁷⁵ , ^{76 ]} Therefore, optimizing thermoelectric materials through modification strategies, such as nanocomposites, doping engineering, and interface optimization, is crucial for enhancing their sensitivity, stability, and practical applicability in fire early warning systems. Although recent reviews have summarized the progress in thermoelectric fire warning materials, they primarily focus on material types or performance metrics.^{[ 77} , ⁷⁸ , ^{79 ]} Few studies have systematically analyzed how specific modification strategies, such as doping, nanostructuring, or interfacial engineering, improve thermoelectric performance and sensing behavior. This gap hinders the rational design of next‐generation materials tailored for smart fire‐warning applications.

This review aims to address this critical knowledge gap by focusing on thermoelectric material modification strategies that target enhanced early fire‐warning performance. We analyze how structural design, energy filtering, ionic doping, and ionothermal effects improve the Seebeck coefficients, response speed, and stability. Additionally, we explore the integration of these materials into wearable sensors and large‐area networks. By shifting from a purely material‐centric view to a mechanism‐driven approach, this study provides technical guidance for the development of intelligent, self‐powered fire‐warning systems and promotes the advancement of next‐generation smart active materials.

2. Thermoelectric Materials For Smart Fire Warning

With the rapid development of the thermoelectric field, an increasing number of novel materials are being applied to fire early warning systems. Existing review articles have extensively and thoroughly discussed the applications of specific materials, such as graphene oxide (GO) and MXene, in the fields of fire warning and flame retardancy, as well as the flame‐retardant properties and fire‐warning functionalities of thermoelectric materials. For instance, a recent review by Song systematically explored the role of MXene materials in flame retardancy and fire early warning systems.^{[ 77 ]} Their work covered the conceptual design, characterization methods, modification strategies, performance optimization, practical applications, and potential mechanisms of MXene. Similarly, Wang et al. provided a comprehensive review of thermally responsive fire early warning systems, detailing their working mechanisms, response times, signal conversion processes, and feasibility for practical applications.^{[ 80 ]} These reviews offer critical theoretical support and practical guidance for the application of thermoelectric materials in fire warning systems.

Compared with inorganic materials, OTE materials offer advantages such as flexibility, strong adhesion, and ease of processing, making them highly promising for fire warnings, particularly in flexible and wearable devices. The unique characteristic of OTE materials lies in their molecular chain structure or charge transport pathways, which dynamically adjust at high temperatures, allowing smoother electron migration, reduced resistance, and increased conductivity. This property enables OTE materials to respond rapidly to fire signals, making them suitable for complex application scenarios. Additionally, ionic thermoelectric materials, such as ionic hydrogels, exhibit asymmetric ion migration under temperature gradients, generating significant potential differences. Their Seebeck coefficients are notably higher than those of traditional electronic thermoelectric materials. This feature provides ionic thermoelectric materials with broad application prospects in flexible electronics and sensing, making them an important focus in fire warning research.

Figure 2 summarizes the thermoelectric working principles of these materials and their specific applications in early fire warning systems. Tables 1 and  2 summarize the thermoelectric and flame‐retardant properties of the reported fire‐warning materials, respectively. The diverse mechanisms demonstrated by these materials provide a critical scientific foundation and design inspiration for the future development of more efficient and intelligent thermoelectric fire‐retardant systems.

Figure 2.

Thermoelectric materials for fire sensing and early warning.

Table 1.

Comparison of thermoelectric fire‐warning materials: Key performance parameters.

	Key component	ZT	Seebeck coefficient	Response time (s)	Continuous alarm time (stability)	Operating temp. range
Inorganic	GO[ 81 ]	N/A	–	2.0	168 s	50–350 °C
	Ag₂Se[ 82 ]	N/A	–	2.	Sustained	100–300 °C
	Ag₂Se[ 83 ]	N/A	–	1.9	14 s	100–500 °C
	SWCNT[ 84 ]	N/A	62.5 ± 1.7 µV K−1	2.5	>60 s	25–75 °C
	MXene[ 67 ]	9.27 × 10 −3	–	0.1	< 5.5 s	100–500 °C
	MXene[ 85 ]	N/A	0.0141 mV °C−1	1.6	40 s	100–400 °C
	MXene[ 86 ]	N/A	–	1.43	Repeatable	100–400 °C
Organic	PEDOT[ 87 ]	N/A	32.6 µV K−1	1.5	100 cycles	50–350 °C
	PPy[ 88 ]	0.62 × 10 −3	–	0.8	50–165 s	–
	PPy[ 89 ]	N/A	–	1.9	>60 s	10–300°C
	PPy[ 90 ]	N/A	10.2–10.9 µV K−1	1.0–1.7	>5 s	Linear at 50–100 °C
	Ionic hydrogel[ 91 ]	N/A	10.1 mV K−1		Repeatable	Stable at 90 °C
	Ionic hydrogel[ 92 ]	N/A	1.31 mV K−1	1.1	Sustained	−70 °C to 100 °C
	Ionic hydrogel[ 93 ]	N/A	24.7 mV K−1	1.5	Sustained	–

Table 2.

Comparison of thermoelectric fire‐warning materials: flame‐retardant characteristics.

	Key component	LOI	UL‐94	Char yield	Mechanical flexibility
Inorganic	GO[ 81 ]	–	V‐0	20.7% (700 °C)	Bendable, foldable, strong adhesion
	Ag₂Se[ 82 ]	32.2%	V‐0	21.2%	Compatible with flexible substrates
	Ag₂Se[ 83 ]	35.8%	V‐0	47.6% (800 °C)	Withstands 15 g load, σ t = 2.9 MPa
	SWCNT[ 84 ]	–	–	–	Stable after 500 bending cycles
	MXene[ 67 ]	36.0%	–	25.5% (600 °C)	Bendable to 1.5 mm radius
	MXene[ 85 ]	28.0%	–	73.8%	σ t = 6.7–10.7 MPa
	MXene[ 86 ]	35.0%	–	–	ɛ t = 12.4–12.7%
Organic	PEDOT[ 87 ]	33.7%	V‐0	94.3%	Bendable, twistable, foldable
	PPy[ 88 ]	–	V‐0	High	–
	PPy[ 89 ]	31.4%	V‐0	96.4%	Bendable, twistable
	PPy[ 90 ]	–	–	45.2% (900 °C)	–
	Ionic hydrogel[ 91 ]	–	V‐0	11.6% (800 °C)	ɛ t = 842.5%, σ t = 0.77 MPa
	Ionic hydrogel[ 92 ]	45.5%	–	17.4%	Maintains flexibility at −45 °C
	Ionic hydrogel[ 93 ]	54.0%	V‐0	–	ɛ t = 4270%, stretchability, ɛ c = 90%

σ _t: tensile strength, ɛ _t: tensile strain, ɛ _c: compression strain

However, as research progresses, the focus has shifted to how material modifications can further enhance performance. Key challenges include optimizing the thermoelectric effects, improving the interface compatibility between different materials, and enhancing processing and application stability. Addressing these issues has become central to research on thermoelectric materials. Therefore, this chapter systematically summarizes the application of thermoelectric materials in fire early warning systems from the perspective of material modification, with a focus on strategies such as structural design, doping modifications, energy‐filtering effects, and interface optimization. This systematic analysis aims to provide researchers with new perspectives and design approaches, driving the further advancement of thermoelectric materials in fire early warning and related fields.

3. Materials Design Strategies For Thermoelectric Fire Warning

3.1. Structural Design

Structural design is a widely adopted approach for material modification, with its core principle centered on constructing a conductive network. This involves establishing conductive pathways at the structural level to facilitate efficient charge carrier transport within the material, ultimately improving its electrical conductivity and thermoelectric performance.

For GO‐based composites, structural design strategies primarily leverage the reduction‐induced conductivity of GO and can be classified into two key mechanisms. The first involves the incorporation of reducing agents to accelerate the high‐temperature reduction of GO into highly conductive reduced graphene oxide (rGO). The second strategy employs functional molecular coassemblies to construct conductive networks. For instance, as shown in Figure 3a, ascorbic acid (LA) can be used as a reducing agent to partially reduce GO, enabling a rapid transition from an insulating to a conductive state under elevated temperatures, thereby significantly enhancing the fire alarm sensitivity (Figure 3b–e). Furthermore, the introduction of phenoxycyclophosphazene (HP) reinforced π–π stacking interactions between the GO layers, which not only improved the electrical conductivity but also enhanced the thermal stability of the composite. Under high‐temperature conditions, HP promotes the formation of a carbonized layer, effectively preserving the circuit integrity and further augmenting the fire resistance through thermal insulation and flame‐retardant effects.^{[ 81 ]} Additionally, the combination of pyromellitic acid (PyA) and phosphoric acid (PA) contributed to fire retardancy by catalyzing carbonization and facilitating gas‐phase dilution, providing a chemical safeguard for improved flame resistance (Figure 3f).

Figure 3.

Interfacial design of graphene oxide (GO) with LA and HP for synergistic fire warning and protection, reproduced with permission.^{[ 81 ]} Copyright 2024, Elsevier.

The design of hierarchical heterostructures is another effective approach to constructing conductive networks in materials. In Figure 4a, the in situ polymerization of 3,4‐ethylenedioxythiophene (EDOT) on the surface of GO results in the formation of thermoelectric graphene (TEG) composed of poly(3,4‐ethylenedioxythiophene) (PEDOT) and rGO.^{[ 87 ]} By assembling TEG nanosheets with carboxymethyl cellulose (CMC) into a layered structure, a stable conductive network was established. This hierarchical heterostructure optimized the electron transport pathways, significantly enhancing the charge carrier mobility (Figure 4b–e). Under high‐temperature conditions, the carbon frameworks of PEDOT and rGO synergistically formed a stable carbonized protective layer, providing thermal insulation and preventing oxygen penetration (Figure 4f). Consequently, this structure substantially enhanced both the fire alarm sensitivity and flame‐retardant properties of the composite material.

Figure 4. P.

oly(3,4‐ethylenedioxythiophene) (PEDOT) functionalized reduced graphene oxide (rGO) with carboxymethyl chitosan (CCS) for fire‐resistant thermoelectric coatings, reproduced with permission.^{[ 87 ]} Copyright 2024, Elsevier.

The design of porous structures has also been demonstrated to be an effective strategy for optimizing charge‐carrier transport pathways and further enhancing material performance. As shown in Figure 5a, the synergistic combination of GO, MXene, and chitosan (CS) enabled the construction of a three‐dimensional porous aerogel with a high specific surface area. The layered structure of GO forms a stable conductive network through π–π stacking interactions with MXene, thus ensuring strong interlayer bonding. CS, acting as a network stabilizer, reinforces the aerogel structure via intermolecular hydrogen bonding.^{[ 94 ]} This design facilitates rapid thermoelectric response pathways, as the thermal reduction of GO at high temperatures results in the formation of highly conductive rGO. MXene further enhances the overall electrical and thermoelectric properties owing to its high conductivity and thermoelectric responsiveness (Figure 5b,c). Additionally, CS decomposes at elevated temperatures, forming a dense carbonized layer that ensures long‐term stability during the fire alarm process (Figure 5d). Through synergistic effects, the multicomponent material achieves a balance between the flame retardancy, fire alarm sensitivity, and structural stability.

Figure 5.

Hierarchical graphene oxide (GO)/MXene/chitosan (CS) composite for fire‐resistant thermoelectric applications, reproduced with permission.^{[ 94 ]} Copyright 2024, American Chemical Society.

Similarly, the construction of a three‐dimensional porous structure using composite aerogel fibers composed of flexible polyimide (PI), hydroxyapatite (HAP), and silver selenide (Ag₂Se) has been shown to effectively extend heat transfer pathways (Figure 6a). In this structural design, PI serves as the fundamental framework, providing excellent mechanical flexibility and thermal stability. HAP acts as a flame‐retardant cross‐linking agent, introducing abundant cross‐linking points that prevent the collapse of the aerogel structure at high temperatures. Additionally, its carbonized byproducts enhance the physical barrier properties of the material.^{[ 83 ]} Ag₂Se contributes to outstanding thermoelectric performance, generating a significant thermoelectric voltage output under high‐temperature conditions (Figure 6b–d). This enables a self‐powered fire alarm function, which further enhances fire safety applications.

Figure 6.

Fire‐resistant and thermoelectric performance of Ag₂Se‐modified polyimide aerogels, reproduced with permission.^{[ 83 ]} Copyright 2024, Elsevier.

In the development of conductive networks, the hierarchical heterostructure design strategy effectively optimizes electron transport pathways by establishing continuous conductive networks within the material. Additionally, under high‐temperature conditions, it forms a stable carbonized protective framework, offering excellent conductivity and flame retardancy. However, this approach typically requires complex synthesis conditions and stringent process control. In contrast, improving the material conductivity and thermal stability through chemical interactions (such as π–π stacking or hydrogen bonding) is a more straightforward approach that can also achieve high sensitivity. However, as this strategy relies primarily on weak intermolecular interactions, its structural stability may be compromised, potentially leading to performance degradation under repeated cycling or extreme environmental conditions. On the other hand, the porous structure design strategy focuses on constructing a high‐specific surface‐area three‐dimensional network, which significantly enhances the electrical conductivity by providing abundant transport pathways. Additionally, it forms multiple physical barriers at high temperatures, thereby improving flame retardancy. Although this method balances lightweight properties and multifunctionality, it may encounter challenges such as insufficient mechanical strength or nonuniform pore size distribution in practical applications.

3.2. Energy Filtering Effect

The energy‐filtering effect is a key strategy for enhancing the performance of thermoelectric materials through structural regulation. Its core principle involves the construction of energy‐selective transport interfaces or barriers that effectively suppress the transmission of low‐energy charge carriers, while optimizing their migration pathways (Figure 7 ). This mechanism significantly enhances the Seebeck coefficient and overall thermoelectric performance of the material and has demonstrated considerable application potential in inorganic materials.

Figure 7.

Mechanism of energy filtering effect in thermoelectric materials.

In inorganic thermoelectric materials, the energy filtering effect is primarily achieved by constructing nanocomposite structures that leverage the energy level differences between materials to optimize selective charge carrier transport. In Figure 8a–d, in the multiwalled carbon nanotube (MWCNT) composite system, Schottky barriers are formed at the interfaces, effectively scattering low‐energy charge carriers while preserving the transmission of high‐energy carriers. This interfacial barrier design not only enhances the Seebeck coefficient but also improves the thermal insulation and flame retardancy through the formation of a carbonized layer from MWCNTs at high temperatures. Specifically, MWCNTs provide one‐dimensional conductive pathways, while their coupling with the two‐dimensional layered structure of MXene optimizes charge carrier migration pathways and reduces the thermal conductivity of the material, significantly enhancing the thermoelectric performance (Figure 8b,c). Additionally, the formation of the carbonized layer serves as a barrier against oxygen and heat transfer, further improving the mechanical stability and durability of the material. These findings highlight that the synergistic enhancement of the electrical conductivity, thermoelectric efficiency, and flame retardancy through interfacial barrier engineering is a key feature of MXene‐based composites. However, due to the tendency of MXene nanosheets to aggregate, prolonged high‐temperature exposure may lead to interfacial barrier degradation. Therefore, further research is needed to improve the dispersion and interfacial stability of MXene‐based composites.^{[ 95 ]}

Figure 8.

a–d) Sandwich‐like structures for thermoelectric performance enhancement, reproduced with permission.^{[ 95 ]} Copyright 2024, Elsevier. e–g) Hybrid energy filtering structures for thermoelectric performance enhancement, reproduced with permission.^{[ 96 ]} Copyright 2022, Elsevier.

The unique porous structure of Ag₂Se exhibits a significant energy‐filtering effect.^{[ 82 ]} The porous interfaces effectively scatter low‐energy charge carriers while selectively transmitting high‐energy carriers, leading to a substantial increase in the Seebeck coefficient and achieving an optimal balance between the thermal and electrical conductivities. In its composite design with MXene, Ag₂Se further enhances charge carrier migration pathways through its intrinsic energy filtering mechanism, significantly improving the thermoelectric performance.^{[ 96 ]} Notably, the porous structure of Ag₂Se not only provides efficient charge carrier filtering but also ensures excellent thermal stability under high‐temperature conditions. Additionally, Ag₂Se can synergize with the interfacial charge transfer mechanism of MXene, further boosting the overall thermoelectric output (Figure 8e–g). This composite strategy endows the material with outstanding thermoelectric properties in high‐temperature environments as well as superior oxidation resistance and flame retardancy.

3.3. Doping Modification

Doping modification is a widely used strategy for improving the performance of thermoelectric materials. Its core principle lies in precisely tuning the charge carrier concentration to achieve a dynamic balance between the electrical conductivity and thermoelectric performance. When the carrier concentration was too high, the electrical conductivity increased; however, the Seebeck coefficient decreased significantly, ultimately reducing the overall thermoelectric efficiency. Conversely, when the carrier concentration was too low, the Seebeck coefficient improved; however, the decline in the electrical conductivity weakened the overall performance of the material. Therefore, identifying the optimal balance between these two factors remains a key challenge in doping–modification research.

Doping with metal ions (such as Al³⁺, Ca²⁺, and Na⁺) and halogen ions (such as Cl⁻ and F⁻) has been widely applied to inorganic materials. By introducing additional electrons or holes, the number of free charge carriers is increased, thereby enhancing the electrical conductivity of the material. Metal ions and polymer matrices form stable composite structures through ionic bonding or coordination interactions, which provide continuity in the conductive network and protect the mechanical integrity of the material at high temperatures. Ca²⁺, a divalent metal ion, can fill vacancies or defects within the crystal structure, stabilize the lattice, and reduce the risk of structural collapse under high‐temperature conditions. In related studies, Ca²⁺ formed stable cross‐linking points through coordination with MXene and tannic acid (TA).^{[ 97 ]} This dense and continuous structure effectively preserved the integrity of the carbonized layer during combustion, thereby enhancing the flame‐retardant properties of the material (Figure 9a). Furthermore, the synergistic effect of Ca²⁺ and Cl⁻ generates a higher thermoelectric voltage through the ion thermoelectric effect (where Cl⁻ migrates toward the cooler end under a temperature gradient), ensuring improved sensitivity to fire alarms and long‐term material stability (Figure 9b–c).

Figure 9.

a–c) Effect of ionic coordination on charge transport and thermal stability, reproduced with permission.^{[ 97 ]} Copyright 2022 Elsevier. d) Doping‐induced charge transport in conductive polymer chains, reproduced with permission.^{[ 90 ]} Copyright 2023 Springer Nature. e) Improved fire warning voltage and repeatability with flame retardant doping, reproduced with permission.^{[ 88 ]} Copyright 2023, Springer Nature.

The doping mechanism of halogen ions enhances the electrical conductivity by creating electron‐rich regions within the material. For example, in the synthesis of polypyrrole (PPy), Cl⁻ acts as a dopant by integrating with the PPy backbone, forming a stable conductive network that optimizes the charge transport pathways and significantly improves the thermoelectric performance.^{[ 90 ]} Further studies have explored alternative doping approaches, such as the use of small‐molecule dopants such as p‐toluenesulfonic acid (PTSA), which presents a promising modification strategy (Figure 9d). Compared to larger ionic dopants, PTSA has a smaller molecular size, causing minimal disruption to PPy chain stacking. This preserves the efficient charge transport channels and avoids the trade‐off between the conductivity and Seebeck coefficient. The experimental results demonstrate that as the PTSA concentration increases, the maximum thermoelectric voltage (VTE) increases, while the fire alarm response time decreases (Figure 9e), directly indicating the simultaneous enhancement of the Seebeck coefficient and electrical conductivity. This synergy leads to a substantial optimization of the thermoelectric performance.^{[ 88 ]}

Although doping strategies have shown remarkable success in enhancing thermoelectric and fire‐alarm performance, they also present inherent trade‐offs that require careful optimization. For instance, increasing carrier concentrations through doping can improve electrical conductivity but often leads to a decline in the Seebeck coefficient due to reduced energy filtering effects. Additionally, excessive dopant levels are likely to disrupt the polymer chain alignment or crystal symmetry, resulting in decreased carrier mobility and mechanical instability.^{[ 98} , ^{99 ]} Moreover, some dopants can introduce defect sites or localized traps, further hindering charge transport.^{[ 100 ]} Therefore, the effectiveness of doping depends on not only the type and concentration of dopants, but also their compatibility with the host matrix and the preservation of long‐range conductive pathways. Hence, a balanced approach is essential for enhancing one performance metric without compromising another one.

In summary, doping plays an irreplaceable role in optimizing the performance of thermoelectric materials. Whether through the incorporation of metal and halogen ions to construct conductive networks or the use of small‐molecule dopants for the precise control of the charge carrier concentration, these strategies offer new possibilities for the efficient design of thermoelectric materials. However, achieving an optimal balance between the electrical conductivity and Seebeck coefficient remains a critical challenge that needs to be addressed. This ongoing challenge opens vast opportunities for further innovation in material design and applications.

3.4. Ionic Thermoelectric Effect

In inorganic thermoelectric materials, ion‐doping modification primarily optimizes the performance by regulating the electron or hole concentrations. However, the ionic thermoelectric effect is more pronounced in OTE materials. The Soret effect describes the migration of ions under a temperature gradient, where the ions move differently based on their mass and charge distributions. Typically, positively charged ions have smaller masses and higher thermal diffusion coefficients, gaining greater kinetic energy at the high‐temperature end and tending to migrate toward the low‐temperature region. Conversely, negatively charged ions accumulate at the low‐temperature end and diffuse toward the high‐temperature region owing to the differences in the diffusion dynamics (Figure 10a). This effect provides a unique pathway for enhancing the thermoelectric properties of materials, with particularly notable performance in ionic hydrogels.

Figure 10.

a) Mechanism of ionic thermoelectric effect, b) ion migration and thermodiffusion behavior in sulfonated polymer matrix, reproduced with permission.^{[ 101 ]} Copyright 2022, Royal Society of Chemistry. c) Stepwise stages of ionic thermoelectric conversion, adapted from elsewhere.^{[ 92 ]} Copyright 2023 Elsevier.

In the design of thermosensitive ionic hydrogels, multicomponent systems leverage thermally responsive ion channels to exhibit significant ionic thermoelectric potential. For example, a composite material composed of gelatin, poly(acrylamide‐acrylic acid) copolymer, CaCl₂, spindle‐shaped aluminum hydroxide nanosheets, and glycerol achieves high thermoelectric efficiency through the precise control of ion migration pathways. In this system, Ca²⁺, due to its high charge density and strong driving force, migrates significantly faster than Cl⁻ under a temperature gradient. Asymmetric ion migration results in a spatial charge distribution difference, generating a thermally driven potential difference, leading to a Seebeck coefficient of 10.1 mV K⁻¹. This design strategy not only enhances the thermoelectric performance through ion migration but also provides a new direction for developing high‐efficiency ionic thermoelectric materials.^{[ 91 ]}

Similarly, the design of high‐performance ionic hydrogels further strengthens the advantages of the ionic thermoelectric effect in practical applications. By introducing the cationic polymer PDDA (poly(diallyldimethylammonium chloride), a quaternary ammonium salt containing N⁺) into the hydrogel system, PDDA's N⁺ forms stable electrostatic cross‐links with sulfonate groups (−SO₃⁻) within the gel network (Figure 10b). This partially replaces Ca²⁺, which would otherwise bind to −SO₃⁻, reducing the constraints on Ca²⁺ and allowing freer migration under a temperature gradient, thereby increasing the ionic thermoelectric gradient. Additionally, the cationic network of PDDA effectively restricts Cl⁻ diffusion, reducing its random migration in the thermal gradient field and further enhancing the thermoelectric potential difference, thereby increasing the Seebeck coefficient. This strategy not only optimizes thermoelectric conversion efficiency but also improves the mechanical stability of the hydrogel, offering a novel design approach for high‐performance ionic thermoelectric materials.^{[ 101 ]}

The combination of phosphate ionic liquids (PILs) and ionic gels (PILGs) further validates the role of asymmetric ion migration in thermoelectric performance enhancement. Under a temperature gradient, different types of ions (cations and anions) exhibit distinct migration rates and directions during thermal diffusion, significantly contributing to thermoelectric optimization.^{[ 92 ]} As shown in Figure 10c, at the initial stage (Stage 1), the presence of a temperature gradient (ΔT > 0) induces the thermal diffusion of ions, with cations migrating toward the low‐temperature region and anions moving toward the high‐temperature region. This asymmetric ion distribution leads to the formation of a potential difference (ΔV > 0), generating a thermoelectric signal. As thermal diffusion progresses (Stage 2), positive and negative ions gradually accumulate at opposite ends, further increasing the potential difference. At this stage, the electrons begin to flow through an external load, generating an external current. However, as the current flow depletes the potential difference, ΔV gradually approaches zero. When the heat source is removed or the temperature gradient disappears (Stage 3), the system undergoes a spontaneous relaxation process due to the nonuniform ion distribution. This leads to a reversal in the polarization, causing the potential difference to become negative (ΔV < 0). Finally, as the system fully returns to equilibrium, with ΔT = 0 and ion distribution restored (Stage 4), the potential difference (ΔV) gradually returns to its initial state. During this process, the direction of the external current may change before the system stabilizes.

By precisely controlling the migration behavior of cations and anions, this system successfully establishes a stable thermoelectric potential difference, significantly enhancing the Seebeck coefficient. Additionally, the material exhibits multifunctional properties, including flame retardancy, self‐powered capability, and thermoelectric responsiveness. This ionic thermoelectric effect‐based design not only expands applications in intelligent fire alarm systems but also serves as a reference model for functional composite materials in complex environments.

Compared to the above strategies based on inorganic ions, the regulation of ionic liquids in organic materials provides a unique perspective for the development of flexible and wearable devices. In another study, coating PEDOT:PSS and other OTE materials with the ionic liquid EMIM:DCA was shown to enhance performance.^{[ 102 ]} In this system, EMIM⁺ (1‐ethyl‐3‐methylimidazolium, C₆H₁₁N₂⁺) contains an imidazolium ring, which offers high charge stability and effectively forms stable ion pairs with various anions. The dicyanamide anion (DCA⁻, N(CN)₂⁻) possesses two cyano (−CN) groups, providing high polarity and excellent charge transport capability, which improve both the mobility and conductivity of the ionic liquid. By facilitating ion migration, this system generates a potential difference, thereby enhancing thermoelectric conversion efficiency. Additionally, the built‐in electric field leverages the energy filtering effect to effectively block the transport of low‐energy charge carriers, further optimizing the Seebeck coefficient. This mechanism not only significantly improves the thermoelectric conversion efficiency but also enables flexible designs suitable for wearable applications. These findings indicate that the integration of ionic liquids can enhance the thermoelectric performance while improving the environmental adaptability and long‐term stability, making them promising candidates for next‐generation flexible and wearable thermoelectric devices.

Table 3 summarizes the key differences between ionic thermoelectric effects and ionic doping. Unlike ionic doping, the ionic thermoelectric effect leverages temperature gradients to directly generate potential differences, significantly enhancing the thermoelectric performance while providing a promising direction for the development of intelligent flexible materials.

Table 3.

Comparison of ion thermoelectric effect and ion doping.

Characteristic	Ion thermoelectric effect	Ion doping
Mechanism	Temperature gradient induces ion migration, generating an electric potential difference	Doped ions alter charge carrier concentration, crystal structure, or electronic structure
Charge carrier	Ions	Electrons, vacancies (indirectly affecting ion migration)
Objective	Thermoelectric energy conversion, sensing	Enhancing electrical conductivity, optimizing thermoelectric performance, improving stability
Applicable materials	Organic thermoelectric materials (e.g., ionic hydrogels)	Applicable to both inorganic and organic materials
Preferred applications	Used in flexible, lightweight materials	Applied in high‐performance thermoelectric materials

3.5. Interface Optimization

Interfacial optimization is a key material modification strategy, typically employing methods such as layer‐by‐layer assembly (LbL) or layer‐by‐immersion, to enhance the interfacial adhesion between different material components, optimize charge carrier transport pathways, and improve overall thermoelectric and flame‐retardant performance. The core of this strategy lies in precisely tuning interfacial interactions to reduce interfacial scattering, promote efficient electron and ion transport, and construct a stable protective layer under high‐temperature conditions, enabling intelligent response capabilities (Figure 11 ).

Figure 11.

Schematic of multilayer assembly strategy for interfacial optimization in flame‐retardant thermoelectric coatings, reproduced with permission.^{[ 89 ]} Copyright 2022, Elsevier.

In multiphase composite systems, the interface not only serves as a pathway for electron and phonon transport, but also acts as a critical region for regulating the band structure and carrier dynamics. Through deliberate band engineering and interfacial design, TE performances can be effectively enhanced by improving the charge transport and energy conversion efficiency. When materials with mismatched work functions or band structures, such as organic/inorganic or polymer/nanofiller systems, are combined, an internal electric field or potential barrier can form at the interface. This enables energy filtering, wherein low‐energy carriers are selectively scattered, while high‐energy carriers contribute to electrical conduction, thereby increasing the Seebeck coefficient without significantly compromising the electrical conductivity.^{[ 103} , ^{104 ]} In addition to band structure optimization, interface‐induced carrier scattering mechanisms are equally critical. TE materials require strong phonon scattering to reduce thermal conductivity (κ) but weak electron scattering to maintain high electrical conductivity (σ). By tailoring interfacial scattering, the selective transport of high‐energy carriers can be achieved while minimizing backscattering and carrier losses.^{[ 105} , ¹⁰⁶ , ^{107 ]}

The layer‐by‐layer assembly strategy is commonly applied in MXene/carboxymethyl chitosan (CCS) composite systems, where the carboxyl and hydroxyl functional groups in CCS form hydrogen bonds with the MXene nanosheets. This hydrogen‐bonded network not only enhances mechanical adhesion but also induces a mild interfacial dipole, which facilitates low‐energy carrier scattering. Such interfacial enhancement not only improves the uniformity of the conductive network and enhances the charge carrier mobility, but also enables rapid fire alarm activation in fire environments. Additionally, during combustion, the structure forms a dense carbonized layer, effectively blocking oxygen diffusion, thereby achieving a synergistic effect between flame retardancy and fire warning.^{[ 108 ]}

In the heterostructure optimization, the integration of one‐dimensional single‐walled carbon nanotubes (SWCNTs) with two‐dimensional MXene results in bridged layered heterostructures with outstanding multifunctional properties. This structure primarily relies on van der Waals forces, π–π electronic interactions, and potential covalent bonding between SWCNTs and MXene, which optimizes the charge transport pathways, enhances the electrical conductivity, and improves the mechanical strength and thermal stability of the composite.^{[ 67 ]} The van der Waals gap between SWCNT and MXene creates phonon scattering hotspots while maintaining a high carrier mobility through quantum tunneling. This decoupled scattering of phonons and electrons is a typical characteristic of ideal thermoelectric interfaces. Consequently, the material exhibited enhanced durability and stability in extreme environments. Furthermore, at high temperatures, the layered interface induces localized carbonization, strengthening the oxygen barrier effect and further enhancing the flame retardancy and long‐term durability of the material.

In practice, interfacial optimization is best understood as a synergistic strategy (synergistic interface engineering), where multiple interfacial interactions are leveraged to comprehensively enhance the overall performance of composite materials. For instance, in the polypyrrole (PPy)–MXene composite system, the coassembly of cellulose‐modified PPy nanowires with MXene nanosheets not only significantly improves the interfacial adhesion strength but also effectively regulates thermoelectric charge carrier transport pathways, thereby increasing the thermoelectric response sensitivity. Additionally, this interfacial optimization strategy enhances the adhesion of the material to various substrates, improving the reusability and extending the lifespan of fire alarm materials.^{[ 89 ]}

Furthermore, in the phytic acid (PA)‐MXene‐metal ion (Co²⁺) interfacial assembly system, interfacial optimization demonstrates multifunctional characteristics. Phytic acid molecules exhibit strong coordination abilities, forming stable interfacial complexes with Co²⁺, which further establishes a cross‐linked network on the surface of MXene nanosheets, thereby enhancing the structural stability and electrical conductivity. This strategy not only strengthens the interfacial bonding but also utilizes the catalytic effect of Co²⁺ to promote efficient carbonization reactions under fire conditions, thereby improving the flame‐retardant performance of the material. Additionally, the MXene–PA interface exhibits a gas barrier effect, effectively inhibiting the diffusion of combustion gases, which further enhances the durability and stability of fire alarm materials.^{[ 109 ]}

4. Applications of Thermoelectric Effects—Enabled Smart Fire Warning

To translate material‐level innovations into practical fire‐warning systems, it is essential to understand how each modification strategy contributes to performance enhancement at the device and system levels. Ion doping effectively tunes the carrier concentration and Seebeck coefficient, improving the sensitivity and power output of thermoelectric elements under thermal stimuli. Interfacial engineering reduces carrier scattering and enhances charge transport pathways, thereby increasing signal stability and response speed. Structural designs, such as layered assemblies, porous architectures, and hybrid composites, provide mechanical flexibility and thermal resilience, ensuring that the material can withstand deformation, high temperatures, and environmental fluctuations. These enhancements enable reliable real‐time fire detection, rapid signal generation, and long‐term reliability when integrated into functional devices. Therefore, the synergy between material optimization and system design plays a pivotal role in advancing thermoelectric fire‐warning technologies from laboratory studies to real‐world deployment in wearables, smart buildings, and distributed forest monitoring systems.

4.1. Thermoelectrically Wearable Warning Device

In recent years, wearable electronic devices have rapidly evolved in the fields of smart protection, health monitoring, and motion sensing. Wearable thermoelectric materials (WTEs) have garnered significant attention as functional materials capable of directly utilizing human body heat or environmental temperature differences for energy conversion and signal detection. The core mechanism of WTEs is based on the Seebeck effect, where charge carriers within a thermoelectric material undergo directional migration under a temperature gradient, generating a measurable thermoelectric potential difference. This unique property enables wearable thermoelectric materials to perform real‐time temperature monitoring without the need for an external power source, while maintaining high sensitivity and stability. Wearable thermoelectric materials exhibit tremendous application potential for fire safety and motion monitoring, paving the way for next‐generation self‐powered sensing technologies.

In the field of fire safety, the core requirements of firefighting gears extend beyond flame resistance and high‐temperature protection. They must also provide real‐time temperature monitoring and rapid alarm functionality to significantly enhance firefighter safety in extreme environments. Following the introduction of the active fire protection concept by He et al.,^{[ 111 ]} extensive research has been conducted to explore material design strategies for achieving multifunctional integration in firefighting apparel. Modifying fibers or textiles to impart flame resistance, thermoresponsiveness, and self‐cleaning capabilities has become the primary direction for improving the comprehensive performance of firefighting gear.^{[ 112 ]} For instance, a wearable self‐powered fire alarm electronic textile (MAA e‐textile) has been developed using MXene/silver nanowires/aramid nanofiber (ANF) aerogel fibers. This textile exhibits precise temperature sensing capabilities in the range of 100 °C to 400 °C, utilizing the thermoelectric properties of MXene to trigger a fire warning signal within 1.6 s, all without an external power source.^{[ 85 ]} This design not only enables real‐time monitoring but also enhances flame retardancy through the formation of a protective carbonized layer during fire exposure.

Additionally, the integration of Ag₂Se thermoelectric materials, PI, and HAP has led to the development of aerogel fiber‐based fire alarm sensors.^{[ 83 ]} This sensor demonstrates accurate temperature sensing from 100 °C to 500 °C and provides a rapid response within 1.9 s, marking a significant advancement in fire monitoring capabilities for extreme environments. By leveraging the high‐efficiency thermoelectric conversion properties of Ag₂Se, this sensor achieved the dual functionality of flame retardancy and thermally driven fire alarms. With regard to material fabrication techniques, the introduction of a novel alternating coaxial wet‐spinning strategy has expanded the application potential of firefighting textiles. By fabricating p‐n structured thermoelectric fibers composed of n‐type MXene and p‐type MXene/SWCNT‐COOH (Figure 12a), with ANFs serving as a protective shell, this approach enhances the fiber flexibility and thermoelectric performance.^{[ 86 ]} The design effectively optimized the thermoelectric response by regulating the interfacial charge‐carrier transport pathways while ensuring mechanical stability under high‐temperature conditions.

Figure 12.

a) The design of p‐n segment fire‐resistant suit, reproduced with permission.^{[ 86 ]} Copyright 2023, Springer Nature. b) Self‐healing behavior via molecular migration, reproduced with permission.^{[ 110 ]} Copyright 2022, Elsevier.

These studies demonstrate that by combining various modification strategies, it is possible to achieve an integrated design that simultaneously enhances the thermoelectric performance, flame retardancy, and multifunctionality of firefighting gears. However, several challenges remain to be addressed in future research. Long‐term stability is a critical concern because prolonged exposure to high temperatures or flames may lead to performance degradation. Therefore, optimizing the durability and thermal resilience of these materials remains a key research focus. A promising approach to address this challenge is the incorporation of self‐healing materials that rely on dynamic chemical bonds to enable molecular reassembly after damage^{[ 69} , ^{110 ]} (Figure 12b). In many cases, water molecules play a crucial role by breaking old bonds and facilitating the formation of new bonds, thereby enabling material repair. The overarching goal of self‐healing materials is to extend the operational lifespan of firefighting gear in extreme environments while enhancing the overall safety performance. Given their exceptional applicability in fire protection, self‐healing materials provide a promising pathway for the development of next‐generation smart protective materials.

In addition to fire protection, multifunctional wearable materials have demonstrated significant potential for motion‐detection applications (Figure 13 ). Based on the piezoresistive sensing mechanism, these materials undergo dynamic changes in their internal conductive pathways under mechanical stress or deformation, leading to corresponding resistance variations. This property enables the precise detection of stress changes induced by different movements. For instance, experimental observations revealed distinct resistance variation curves for finger and wrist bending, with wrist bending inducing a significantly higher rate of resistance change than finger bending. This finding highlights the material's high signal sensitivity and capability to distinguish between different motion types, indicating its potential for pattern recognition applications.^{[ 113 ]}

Figure 13.

Thermoelectric sensor for motion detection.

To meet the demands of multifunctional and multienvironmental applications, these materials integrate flame resistance, thermoelectric properties, and high‐sensitivity piezoresistive characteristics. Under various levels of mechanical pressure or movement stimuli, the material responds rapidly and generates stable resistance signals, demonstrating its potential for real‐time dynamic monitoring.^{[ 97 ]} Optimizing the material's porous structure and ionic composite interfaces has significantly enhanced charge carrier mobility and the stability of conductive pathways, ensuring that the material maintains high‐performance sensing capabilities even after multiple cyclic stress tests. Furthermore, this design enables stable operation in extreme environments (e.g., high‐temperature or fire scenarios), expanding its applicability under specialized conditions.

The long‐term operational stability of wearable thermoelectric devices strongly relies on their ability to withstand mechanical deformation and environmental stress while maintaining performance. Liu et al.^{[ 114 ]} reported CNT/PLA composite fabrics fabricated via an innovative electrospray‐on‐electrospinning technique, forming an interpenetrating CNT network within a biodegradable PLA matrix. This structure exhibits excellent durability, retaining thermoelectric performance after 500 bending cycles and 100 washing cycles, and delivering a power density of 37.3 µW cm⁻² at ΔT = 17 K. The observed stability is attributed to strong interfacial adhesion between CNTs and PLA nanofibers, along with the inherent moisture resistance of the polymer matrix. In a complementary study, He et al.^{[ 115 ]} developed CNT/PVP/PU composites using an alternating electrospinning–spraying process, yielding fabrics with remarkable mechanical resilience. The materials can maintain stable electrical conductivity after 1000 bending cycles and under strains up to 250%, enabled by PVP's dual function as a dispersant and interfacial binder. While the CNT/PLA system demonstrates superior washability (maintaining performance after 100 washing cycles) and environmental stability due to its hydrophobic PLA matrix, the CNT/PVP/PU architecture exhibits enhanced stretchability (up to 250% strain) and cyclic fatigue resistance (1000 bending cycles), leaving its water resistance uncharacterized.

These examples collectively show that addressing both mechanical and environmental challenges is a prerequisite for achieving long‐term stability in wearable thermoelectric systems. Mechanical fatigue from repeated deformation, as well as exposure to humidity, sweat, or washing, can significantly degrade material performance over time. Therefore, enhancing interfacial adhesion, selecting moisture‐resistant polymer matrices, and optimizing fabrication strategies are critical for maintaining consistent thermoelectric output in real‐world applications. Further research on encapsulation methods, robust fiber architecture, and hydrophobic coatings is needed to improve the operational reliability and environmental tolerance of wearable thermoelectric sensors.

Notably, the innovative aspect of these materials lies in their integration into smart systems. By incorporating wireless data transmission technologies (such as Bluetooth or LoRa), real‐time remote monitoring of motion signals can be achieved, offering new solutions for smart wearable devices in human‐computer interaction, health monitoring, and beyond. Moreover, the combination of flame retardancy and thermoelectric properties ensures reliable signal transmission and functional output even under extreme conditions, making these materials ideal for high‐risk occupational protective gears, such as firefighter uniforms. The integration and adaptability of such multifunctional materials provide valuable research directions and technological advancements for the next generation of smart clothing.

4.2. Forest Fire Warning System

Forest fires are highly unpredictable and destructive natural disasters, causing severe impacts on ecosystems and human society. Although traditional fire warning systems (such as smoke detectors and infrared thermal sensors) are widely used in urban and industrial settings, they often face significant limitations in complex outdoor environments, such as forests. These limitations include long response times, susceptibility to environmental interference, and operational difficulties under extreme conditions. In forest fires, factors such as high wind speed, extensive vegetation combustion, and complex terrain exacerbate the challenges of fire detection. Traditional detectors are typically activated only when the smoke concentration or temperature reaches a critical threshold, leading to delayed fire warnings and increased disaster severity. In recent years, advancements in smart sensor technology and self‐powered systems have led to the development of thermoelectric‐based fire‐monitoring systems, offering a promising solution for early fire detection.^{[ 50} , ¹¹⁶ , ^{117 ]} By integrating high‐sensitivity thermoelectric sensors with wireless communication networks, these systems enable remote real‐time monitoring and data analysis, thereby significantly improving the sensitivity and reliability of forest fire warnings (Figure 14 ). Furthermore, their low power consumption and self‐sustaining capabilities make them particularly well suited for deployment in remote and off‐grid areas.^{[ 118} , ^{119 ]}

Figure 14.

Thermoelectric sensor for forest fire early warning.

Thermoelectric sensors utilize temperature gradients to generate electrical potential variations, enabling efficient low‐power temperature monitoring without the need for an external power source. This makes them particularly suitable for long‐term operation in remote or energy‐limited environments, such as forests. Owing to their excellent thermoelectric properties, MXene‐based sensors can rapidly generate electrical signals in response to temperature fluctuations, enabling real‐time monitoring and remote fire alarms.^{[ 108 ]} Structurally, these sensors can function as intelligent nodes in a distributed fire monitoring network, integrating the Internet of Things (IoT) and cloud computing to facilitate multiscenario data collection and analysis. With a response time of only 3.8 s, these sensors significantly enhanced the timeliness of fire warnings. Additionally, they feature repeatable activation, ensuring continuous monitoring, making them highly suitable for high‐risk applications, such as forest fire early warning systems.

Windy and humid environmental conditions significantly influence forest fire behavior and present major challenges for early warning systems. High wind speeds can accelerate flame propagation, while low relative humidity decreases fuel moisture content (FM_a), often pushing forest ecosystems past critical flammability thresholds (e.g., FM_a < 12%). However, widely used empirical fire danger indices, such as the Fire Weather Index (FWI), often fail to account for such dynamics, as evidenced by the 2017 Pedrogão Grande fire, where FM_a dropped below 12% but FWI values remained moderate. To improve prediction accuracy, integrating real‐time environmental sensor data—such as wind speed, ambient humidity, and temperature—with physically based models (e.g., FM_a = FM₀ + FM₁e^−mD) is essential. This highlights the need for robust weather‐tolerant sensing materials capable of long‐term operation under various outdoor conditions.^{[ 120 ]} Therefore, ideal thermoelectric fire‐warning materials deployed in forest environments should maintain a stable output under fluctuating humidity, airflow, and temperature gradients. Future effort should be devoted to enhancing hydrophobicity, encapsulation, and energy‐harvesting resilience to ensure reliable fire risk monitoring in such complicated environmental settings.

In addition to electronic sensing, novel visual fire warning systems have gained attention. For example, thermochromic materials provide a direct and efficient fire‐detection strategy that does not require electronic conversion.^{[ 122 ]} POSS‐metal composite films (PMFs) exhibit distinct color changes between 20 °C and 150 °C and can self‐recover through moisture absorption upon cooling, enabling repeated use^{[ 121 ]} (Figure 15a). Compared to traditional fire alarms, which rely on smoke detection or temperature threshold activation, this system offers early stage visual fire warnings during incipient fire conditions or abnormal temperature increases. Because these systems do not require an external power source, they can be seamlessly integrated with remote‐surveillance cameras, drones, and other monitoring devices for real‐time observation. This strategy provides an efficient and sustainable fire warning solution that is particularly suited for forest monitoring, smart buildings, and industrial environments where passive fire detection is critical.

Figure 15.

a) Colorimetric materials for forest fire early warning, reproduced with permission.^{[ 121 ]} Copyright 2021, Elsevier. b–d) Shape memory materials for forest fire early warning, reproduced with permission.^{[ 122 ]} Copyright 2021, Elsevier.

4.3. Residential Building Fire Warning System

The design of forest fire early warning systems primarily focuses on large‐scale monitoring and early detection, considering environmental factors that influence fire behavior, such as wind speed and humidity. These systems are designed to provide sufficient warning time before a fire spreads, allowing for timely firefighting interventions. In contrast, fire early warning systems for residential buildings prioritize occupant safety and minimize property damage. These systems emphasize high‐precision indoor detection, rapid response, and integration with smart home devices to reduce direct fire‐related losses and ensure the timely evacuation of residents.^{[ 123} , ¹²⁴ , ^{125 ]}

Modern home fire prevention systems typically employ multisensor collaboration rather than relying solely on thermoelectric sensors. These systems integrate smoke, temperature, humidity, gas sensors (CO and CO₂), and infrared optical sensors to form a more precise fire detection mechanism. As part of a smart home network, these sensors can connect via Wi‐Fi, Bluetooth, or LoRa wireless communication modules, creating a comprehensive fire early warning system. Sensor nodes are strategically placed in high‐risk areas, such as kitchens (high‐temperature risk), living rooms (electronic device concentration), and bedrooms (nighttime safety concerns), to enable comprehensive fire monitoring. For example, expandable graphite (EG) embedded in elastic polymer surfaces has been utilized to achieve multimode fire detection, including resistance changes, morphological transformations, and thermoelectric responses (Figure 16 ). This approach also introduces the concept of building‐integrated fire‐monitoring systems, where fire warning materials are embedded in building structures and linked to IoT‐based remote monitoring via wireless communication modules.^{[ 126 ]} Additionally, Fawad et al.^{[ 127 ]} reported a graphene‐based nanocoating sensor capable of covering large building structures, making it suitable for applications on interior walls, carpets, ceilings, and other surfaces. When applied to a sensing fabric measuring 33 cm in length and 5 cm in width, the sensor triggered a fire alarm within 3 s and exhibited strong self‐extinguishing properties, effectively preventing the fire spread.

Figure 16.

Fire detection and early warning system for residential buildings, reproduced with permission.^{[ 126 ]} Copyright 2023, John Wiley & Sons Ltd.

For further advancements, home fire early warning systems require rapid transmission of alarm signals, which can be achieved using wireless communication technologies such as Wi‐Fi, Bluetooth Mesh, NB‐IoT, and Zigbee.^{[ 128} , ^{129 ]} When the sensor detects an abnormal temperature rise, it can directly send alerts to smart home devices (e.g., smart speakers and home security systems) via Bluetooth or Wi‐Fi. In addition, through a cloud‐based data platform, users can receive fire alerts on a mobile app and remotely monitor the temperature data, alarm records, and other relevant information. In the event of a severe fire, the system can utilize 4G/5G or LoRaWAN to directly notify the fire department, ensuring timely emergency response.^{[ 130 ]}

5. Conclusion and Outlook

Thermoelectric fire‐warning materials represent an emerging class of smart functional systems that not only provide self‐powered temperature sensing but also offer synergistic flame‐retardant capabilities. This review comprehensively summarizes the current progress in material‐level modification strategies, including structural design, energy filtering effect, ion doping, ionic thermoelectric effect, and interfacial engineering. These approaches have demonstrated significant improvements in thermoelectric conversion efficiency and fire warning sensitivity, while enhancing the mechanical robustness and environmental adaptability of the materials. The integration of these modified materials into practical applications, such as fire‐retardant firefighter suits, distributed forest fire detection networks, and smart building alarm systems, has further highlighted their versatile potential in addressing real‐world fire hazards.

The future development of thermoelectric fire‐warning materials should prioritize multifunctional integration. This includes not only a combination of flame retardancy, thermoelectric responsiveness, and structural flexibility, but also integrated features such as self‐healing behavior, thermochromic visualization, anti‐corrosion properties, and wireless signal transmission within a unified system. Incorporating self‐healing ability, hydrophobicity, stretchability, and colorimetric responsiveness into thermoelectric systems can yield next‐generation materials that can operate reliably in complex and dynamic environments. Meanwhile, optimization should not be limited to the material level but should be extended to device‐level and system‐level design. Coordinated strategies involving material architecture, sensor packaging, and signal transmission modules are essential for realizing stable, durable, and highly sensitive devices with low false‐alarm rates.

Scalability and cost‐effectiveness are critical concerns for practical deployment. Thus, developing solution‐processable materials compatible with large‐area fabrication methods, such as spray‐coating, dip‐coating, and inkjet printing, will be vital. These techniques not only facilitate industrial‐scale production but also maintain compatibility with flexible substrates required for wearable and textile‐based applications. Furthermore, durability tests should include a broader range of environmental conditions, such as UV radiation, wind, acid rain, and biological fouling, especially for long‐term outdoor deployments such as forest or marine sensors. Moreover, the long‐term stability under repeated thermal cycling, humidity exposure, and mechanical deformation must be thoroughly evaluated to ensure reliability in real‐world scenarios.

Finally, the integration of artificial intelligence (AI) and wireless communication technologies presents new opportunities for system‐level innovation. By combining thermoelectric sensors with IoT frameworks, cloud‐based data processing, and real‐time analytics, it is possible to establish intelligent, autonomous fire warning networks that operate across multiple environments, from homes to forests and industrial settings. In particular, AI can enable predictive fire analytics based on historical sensor patterns, environmental trends, and machine learning algorithms, allowing early stage fire risks to be detected even before the temperature thresholds are crossed. Such systems will enable early risk identification, predictive alerts, and a coordinated emergency response.

In summary, the convergence of advanced material engineering and intelligent system integration will accelerate the transformation of thermoelectric fire warning materials from laboratory research to practical safety solutions. With continued interdisciplinary collaboration, these materials are expected to play a pivotal role in the next‐generation fire prevention and disaster mitigation strategies.

Conflict of Interest

The authors declare no conflict of interest.

Biographies

Boyou Hou is currently pursuing his Ph.D. degree at the University of Southern Queensland under the supervision of Prof. Pingan Song. He received his M.S. degree from Beijing Institute of Technology, China, under the supervision of Prof. Ye‐tang Pan. His current research focuses on the development of thermoelectric fire‐retardant coatings. He has authored several peer‐reviewed articles in the field of flame‐retardant nanomaterials.

Min Hong received his Ph.D. from The University of Queensland, Australia in 2016 under the supervision of Prof. Jin Zou and Prof. Zhi‐Gang Chen. Currently, he is a professor and ARC Future Fellow at the University of Southern Queensland, Australia. His research includes thermoelectric materials and devices, electron microscopy characterizations, and theoretical calculations and modeling.

Pingan Song received his Ph.D. from Zhejiang University in 2009 under the supervision of Prof. Zhengping Fang. He is currently a full professor at the School of Agriculture and Environmental Science and Centre for Future Materials of University of Southern Queensland, Australia. His research interests involve fire retardants, sensors, polymers, and polymer composites as well as their structure–property correlations, plastic upcyclying, and microplastics impacts on soil property and crop production.

Hou B., Guo Y., Yang Q., et al. “Mechanism‐Guided Thermoelectric Strategies for Smart Fire Prevention.” Adv. Mater. 37, no. 39 (2025): 37, 2508628. 10.1002/adma.202508628