Origami Solar Interfacial Evaporator for Water‐Electricity Co‐Generation

ABSTRACT

Water scarcity represents a critical challenge to global sustainable development. While solar interfacial evaporation offers an eco‐friendly approach to desalination, its widespread application has been limited by the high cost of materials, energy inefficiency in 2D evaporators, and complex fabrication for 3D evaporators. In addition, the streaming potential generated during evaporation remains largely untapped in existing systems. To address these limitations, we present an integrated water‐electricity co‐generator based on low‐cost activated carbon fiber felt (ACFF). The planar ACFF achieves evaporation rates of 0.67–1.80 kg m⁻² h⁻¹ under solar intensities from 0.5 to 1.5 sun, while delivering electrical outputs of 0.50–0.60 V and 6.90–34.55 µA cm⁻². Through origami structuring that enhances light trapping and ion transport, performance is elevated to 0.76–1.93 kg m⁻² h⁻¹ and 0.52–0.61 V with 8.65–68.77 µA cm⁻², representing a 7.22%–14.50% improvement in solar evaporation rate and a 99.72% increase in maximum power output. The origami ACFF system not only rivals state‐of‐the‐art 3D evaporators in performance but also provides exceptional advantages in scalability, cost, and ease of fabrication, while simultaneously generating substantial electricity. This work provides an efficient and scalable strategy toward integrated water‐energy sustainability.

A low‐cost activated carbon fiber felt origami evaporator boosts solar evaporation from 1.31 to 1.50 kg m⁻² h⁻¹ and efficiency from 79.09% to 92.16% versus flat counterparts via enhanced light trapping. The evaporation‐driven streaming potential simultaneously delivers 0.52 V and 8.65 µA cm⁻², with stable performance under high salinity for scalable water–energy co‐generation.

1. Introduction

Water scarcity poses a pressing challenge affecting billions of people worldwide. Driven by climate change, population growth, and deteriorating water quality, this issue is expected to impact an even larger number of individuals in the coming decades. Although the Earth holds vast water reserves–approximately 1.4 × 10¹⁸ tons in total [1] only about 2.5% is freshwater, while over 97% is saline and largely confined to the oceans. Converting seawater into potable water has thus emerged as a critical strategy to mitigate global water stress. Among the various approaches, solar interfacial evaporation stands out as a highly promising technology [2, 3]. This technology employs a photothermal evaporator to generate steam directly from seawater or wastewater using solar energy, which is then condensed and collected as freshwater. In contrast to conventional solar stills that rely on heating the entire water volume, solar interfacial evaporation localizes heat at the water‐air interface, significantly improving energy efficiency [4]. Recent years have witnessed remarkable advancements in this field, particularly in material design [5, 6, 7] and structural engineering [8, 9, 10] positioning solar interfacial evaporation as an increasingly vital contributor to global water sustainability.

Effective thermal management is crucial for achieving high‐efficiency solar interfacial evaporation. The overall system efficiency is largely determined by the evaporator's ability to convert solar energy into heat for steam generation. Significant energy loss occurs through heat conduction to the underlying water and heat dissipation via convection or radiation to the ambient environment. Although insulating materials such as foam can reduce conductive loss in two‐dimensional (2D) evaporators, dissipation via convection, radiation, and reflection persists, typically limiting the solar vapor conversion efficiency to around 70%. In response, various three‐dimensional (3D) evaporators have been developed [11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30] By providing a larger surface area, these structures lower the steady‐state evaporation temperature under equivalent solar irradiation, thereby reducing convective and radiative losses and achieving higher energy efficiency [31]. However, the fabrication of such 3D evaporators often involves complex processes such as precise chemical treatments or high‐temperature carbonization. Moreover, commonly used raw materials–including carbon nanotubes (CNTs), MXene, and graphene–tend to be costly, hindering scalable deployment. Thus, it is imperative to develop 3D evaporators based on low‐cost materials through simple and scalable fabrication routes. In addition, the water evaporation process inherently produces a streaming potential between the evaporation interface and the bulk water [32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52], yet this effect remains underexploited in most existing studies.

In this work, we present a water‐electricity co‐generator based on low‐cost, commercially available activated carbon fiber felt (ACFF), as schematically illustrated in Figure 1A. Under one‐sun illumination, the ACFF rapidly heats up and enables efficient steam generation, achieving an evaporation rate of 1.31 kg m⁻² h⁻¹ with a solar vapor efficiency of 79.09%. By further shaping the ACFF into a 3D origami structure through a simple molding process–which enhances light trapping through multiple internal reflections (Figure 1B)–the evaporation rate and energy efficiency were increased to 1.50 kg m⁻² h⁻¹ and 92.16%, respectively. Simultaneously, the evaporation process drives the formation of a streaming potential along the internal water transport paths (Figure 1C), which can be harvested as electrical energy using integrated electrodes. The origami ACFF evaporator delivered an average electrical output of 0.52 V and 8.65 µA cm⁻² in pure water. Remarkably, the evaporator maintained stable performance under high‐salinity conditions, while the electrical output improved slightly due to increased ion concentration. This study aims to address critical limitations in solar evaporation technology, including energy loss in 2D evaporators, scalability and fabrication complexity of 3D systems, and the untapped potential of evaporation‐induced electricity. Compared to conventional 2D evaporators, the origami ACFF achieves higher water evaporation rates at a significantly lower cost. Although certain bio‐based materials and pencil‐drawn paper (PDP) [17] are also inexpensive, they have yet to demonstrate feasibility for large‐scale production and commercial availability. When compared with state‐of‐the‐art 3D evaporators, the origami ACFF offers distinct advantages in terms of lower cost and simpler fabrication, while maintaining a comparable evaporation rate. Furthermore, most existing hydrovoltaic systems focus solely on electricity generation, with no reported capacity for freshwater production. In contrast, the origami ACFF system not only delivers competitive power output but also enables efficient water evaporation, providing a scalable and sustainable solution to the intertwined challenges of water and energy.

FIGURE 1.

Setup and working principle of the ACFF‐based water‐electricity co‐generator. (A) Schematic illustration of the ACFF‐based water‐electricity co‐generator. (B) Comparison between origami ACFF and flat ACFF concerning sunlight absorption. (C) Schematic illustration of the potential difference between two sides of the evaporator during evaporation.

2. Results and Discussion

2.1. Design and Characterization of ACFF Evaporators

The solar evaporator used in this study was a commercially available ACFF with a thickness of 2 mm and a high specific surface area of ∼1400 m² g⁻¹, which facilitates efficient water sorption and transport. Brunauer‐Emmett‐Teller (BET) analysis revealed a nanoporous structure with a total pore volume of 0.59 cm³ g⁻¹ and an average pore diameter of 2.56 nm. To enhance light absorption beyond that of the flat configuration, we developed a three‐dimensional (3D) origami ACFF evaporator using a facile fabrication process (Figure 2A) [2]. This involved first designing and 3D printing an origami mold (Note S1, Figure S1). A pristine ACFF sheet was then shaped using this mold with silica sol as a binder. The molded structure was subsequently dried at 70°C for 6 h to form the final, self‐supporting origami evaporator.

FIGURE 2.

Design and characterization of ACFF evaporators. (A) Preparation process of origami ACFF evaporator. (B) EDS mapping of raw ACFF and origami ACFF evaporators. (C) FTIR results of raw ACFF and origami ACFF evaporators. (D) Contact angles between water and ACFF evaporators. (i.) Raw ACFF; (ii.) Origami ACFF. (E) Solar absorption spectrum of raw ACFF evaporator.

The incorporation of silica sol led to the adhesion of silicon dioxide (SiO₂) nanoparticles onto the internal fibers of the ACFF, as evidenced by SEM imaging (Figures 2A and S2) and confirmed by Energy dispersive spectroscopy (EDS) elemental mapping (Figures 2B and S3) and quantitative analysis (Figure S4), which showed a significant increase in oxygen and silicon signals. This successful integration was further verified by Fourier Transform infrared (FTIR) spectroscopy (Figure 2C), where new characteristic peaks were formed (464.30 and 1064.08 cm⁻¹) aside from that of the pristine ACFF (400.17 cm⁻¹), indicating the introduction of O‐ and Si‐ bonds. Consequently, the modified ACFF exhibited improved mechanical properties. BET analysis revealed that the silica sol treatment reduced the total pore volume to 0.32 cm³ g⁻¹ but increased the average pore diameter to 4.38 nm, indicating that the material retained its nanoporous structure (Figures S5 and S6).

Both the pristine and silica sol‐modified origami ACFF exhibited superhydrophilic properties. When brought into contact with water, a 5 × 5 cm² sample of pristine ACFF was fully wetted within seconds, while the silica sol‐loaded sample achieved complete wetting within 30 s. Contact angle measurements confirmed this superhydrophilicity, with a value of 0° for both materials (Figure 2D). Further water transport experiments revealed that the water rising height of the origami ACFF reached 15 cm within 10 min, compared to 11 cm for the raw ACFF, indicating enhanced hydrophilicity of the origami structure due to the introduction of hydrophilic silanol (Si–OH) groups (Figure S7) [2]. Both origami and raw ACFF enabled complete wetting of a tissue paper within 120 s, demonstrating excellent water delivery ability (Figure S8). Moreover, when excess NaCl was deposited on the evaporator surface, both samples facilitated full dissolution of the salt within 5 h, highlighting their efficient water diffusion capability (Figure S9). In terms of optical performance, the ACFF evaporator demonstrated excellent light absorption, maintaining a rate exceeding 90% across the wavelength range of 280–2500 nm, with an average absorption of 97.03% (Figure 2E). Under one‐sun illumination, the surface temperature of the dry, flat ACFF reached 45°C within 10 min and 56°C after 20 min. In comparison, the origami ACFF showed enhanced photothermal performance, attaining 55°C and 60°C over the same intervals, further validating its superior solar‐thermal conversion capability (Figure S10).

2.2. Water Evaporation Performance of Flat ACFF Evaporators

A schematic of the typical experimental setup for solar interfacial evaporation using ACFF is shown in Figure 3A. To minimize conductive heat loss to the bulk water, the ACFF evaporator was thermally insulated from the underlying water using a layer of expanded polystyrene (EPS) foam (Figure S11). Under simulated solar irradiation at intensities of 500, 800, 1000, 1200, and 1500 W m⁻², the flat ACFF evaporator achieved water evaporation rates of 0.67, 1.06, 1.31, 1.53, and 1.80 kg m⁻² h⁻¹, respectively (Figure 3B). These experiments were conducted in an ambient environment of approximately 24°C with 50%–60% relative humidity (RH) (Figures S12 and S13). For reference, the evaporation rate measured without illumination was 0.16 kg m⁻² h⁻¹.

FIGURE 3.

Water evaporation performance of flat ACFF evaporators. (A) Schematic illustration of the device setup of flat ACFF‐based solar interfacial evaporation. (B) Mass change of the flat ACFF evaporator under different solar illumination intensities. (C) Temperature variation of the flat ACFF evaporator under different solar illumination intensities. (D) Infrared images of the flat ACFF evaporator after being illuminated under one‐sun illumination for 10 min. (E) Evaporation rate and efficiency of the flat ACFF evaporator under different solar illumination intensities. (F) Mass change of the flat ACFF evaporator in pure water and in NaCl solution of different concentrations.

The enhancement in evaporation rate with increasing solar intensity is directly attributable to the rise in the evaporator's surface temperature. After 10 min of illumination, the surface temperature of the flat ACFF, measured by both thermal probe and infrared imaging, increased consistently with solar intensity (Figure 3C,D), reaching 32.9°C, 36.2°C, 40.2°C, 41.5°C, and 44.2°C, respectively, under irradiances from 500 to 1500 W m⁻². This temperature elevation accelerates the phase change of water, thereby boosting the evaporation rate. The solar vapor efficiency η was calculated to evaluate the performance of flat ACFF evaporator by the following Equation (1) (Note S2) [3, 17]

$$\eta =\frac{\dot{m}\times h_{lv}}{C_{opt}{I}_o}$$ (1)

where $\stackrel{.}{m}$ is the water evaporation rate under different solar illumination intensities minus dark evaporation, h_lv is the enthalpy change of liquid to vapor (sensible heat and latent heat of vaporization at evaporator surface, kJ kg⁻¹) [19], C_opt is the optical concentration, and I_o is the solar irradiance (kW m⁻²). The corresponding evaporation efficiencies, calculated using Equation (1), were 70.15%, 77.38%, 79.09%, 78.52%, and 74.28% under irradiances from 500 to 1500 W m⁻², demonstrating high performance across a wide range of conditions (Figure 3E). Furthermore, the evaporator exhibited remarkable resistance to salt accumulation. Under one‐sun illumination (1000 W m⁻²), the evaporation rate remained stable at approximately 1.20–1.30 kg m⁻² h⁻¹ even as water salinity increased from 1% to 10% NaCl (Figure 3F), indicating excellent salt‐resistance capability.

2.3. Water Evaporation Performance of Origami ACFF Evaporators

The origami ACFF evaporator demonstrated a superior solar absorption capability compared to its flat counterpart, as quantified by ultraviolet‐visible‐near‐infrared (UV‐Vis‐NIR) spectroscopy. The average absorption rate across the solar spectrum was 96.59% for the origami structure, higher than the 95.53% achieved by the flat ACFF with silica sol (Figure 4A). Although both values are marginally lower than that of the pristine ACFF (97.03%) due to the introduction of the light‐colored silica sol, the unique topography of the origami structure compensates for this through enhanced light‐trapping. Specifically, the valleys within the origami design promote multiple internal reflections of sunlight, significantly improving solar energy utilization compared to the single reflection on a flat surface (Figure 1B). Consequently, under similar experimental conditions (∼24°C, 50%–60% RH), the origami evaporator achieved significantly higher water evaporation rates across all tested solar intensities (500 to 1500 W m⁻²), reaching 0.76, 1.21, 1.50, 1.66, and 1.93 kg m⁻² h⁻¹, respectively (Figures 4B and S14). These rates represent an enhancement of 7.22% to 14.50% over the flat evaporator (Figure S15).

FIGURE 4.

Water evaporation performance of origami ACFF evaporators. (A) Solar absorption rate of flat ACFF and origami ACFF loaded with silica sol. (B) Mass change of origami ACFF evaporator under different solar illumination intensities. (C) Temperature variation of the valley of origami ACFF evaporator under different solar illumination intensities. (D) Temperature variation of the mountain of origami ACFF evaporator under different solar illumination intensities. (E) Infrared images of origami ACFF evaporator after being heated for 10 min under different solar illumination intensities. (F) Mass change of origami ACFF evaporator in DI water and in NaCl solution of different concentrations. (G) Simulation results of single origami units of different structures: (i.) Schematic illustration; (ii.) α = 45°; (iii.) α = 56.3°; α = 63.4°. (H) Simulation result of origami ACFF evaporator composed of three units. (I) Simulation result of origami ACFF evaporator composed of six units. (J) Cycling water evaporation performance of the origami ACFF evaporator in 3.5 wt% NaCl solution. (K) Water quality of the evaporator water and tap water. (L) Comparison of evaporation rate and cost between origami ACFF evaporator and other 3D evaporators.

The superior evaporation performance of origami ACFF under increasing solar intensity is also attributed to its higher surface temperatures. After 10 min of illumination, the temperature in the valleys–which benefit from multiple light reflections–reached 35.4°C, 37.8°C, 42.7°C, 43.6°C, and 46.1°C under irradiances from 500 to 1500 W m⁻², respectively (Figure 4C). These values are generally 2–3°C higher than those of the flat evaporator. In contrast, the mountain regions, which primarily experience single reflection, exhibited a temperature profile similar to the flat ACFF, measuring 34.1°C, 37.0°C, 40.0°C, 41.2°C, and 44.6°C under the same conditions (Figure 4D). This thermal distribution, further visualized by infrared imaging (Figure 4E), directly contributes to enhanced efficiency. Calculations using Equation (1) confirmed that the origami structure achieved evaporation efficiencies of 82.53%, 90.27%, 92.16%, 85.97%, and 81.16%, respectively, across the tested intensity range, representing an improvement of 6.88% to 13.07% over the flat design (Figure S16). Furthermore, the origami evaporator maintained stable evaporation rates (approximately 1.32–1.40 kg m⁻² h⁻¹) in saline solutions with concentrations up to 10% NaCl under one‐sun illumination, demonstrating robust salt resistance capability (Figure 4F).

To further validate the enhanced solar utilization of the origami ACFF evaporator, we performed numerical simulations using COMSOL Multiphysics. The investigation began by evaluating the light absorption and evaporation capabilities of three distinct single‐origami units (Figure 4G, Note S3). Under one‐sun illumination, Origami i (α = 45°, β = 79.6°) achieved the highest surface temperature (33.0°C) and a competitive evaporation rate (1.10 × 10⁻⁷ kg/s), outperforming the other two designs (Origami ii: 30.2°C, 1.17 × 10⁻⁷ kg/s; Origami iii: 29.4°C, 9.40 × 10⁻⁸ kg/s) and indicating superior overall solar utilization. Simulations of other structures further confirmed this trend (Figure S17). Crucially, scaling up the design by arraying multiple Origami i units significantly enhanced performance due to intensified inter‐unit light reflection. The simulated surface temperature rose to 36.4°C for a three‐unit array and further to 43.0°C for a six‐unit array (Figure 4H,I), a trend consistent with our experimental measurements. Furthermore, the origami evaporator demonstrated excellent stability, maintaining its evaporation rate without degradation over multiple cycles in a 3.5 wt% NaCl solution (Figure 4J). After 50 h of operation in 10 wt% NaCl solution, only slight salt deposition was observed on the ACFF surface, and the fiber gaps remained largely unblocked (Figures S18 and S19). Furthermore, 24 h of continuous operation in real seawater resulted in no apparent salt deposition or significant decline in evaporation performance, demonstrating excellent salt resistance (Figure S20). Although some loss of the silica sol binder occurred during long‐term operation (Figure S21), the origami ACFF was still able to maintain its shape after one month of use, indicating adequate structural stability. Given that the mechanical robustness may gradually weaken with extended operation, it is estimated that a newly fabricated origami ACFF could withstand at least one month of usage before replacement is needed.

To assess the practical viability of the ACFF evaporators, an outdoor desalination experiment was conducted using natural seawater on a balcony at City University of Hong Kong. On September 4, 2025, two prototypes (15 × 15 × 11 cm³)–one equipped with the origami ACFF and the other with a flat ACFF (both with a surface area of 9 × 9 cm²)–were tested under real sunlight from 9 a.m. to 6 p.m. (Figure S22). The origami‐based device collected 22.55 g of condensed water, significantly outperforming the flat‐based device, which collected only 13.68 g (Figure S23). This corresponds to a daily water collection rate of 2.78 kg m⁻² for the origami evaporator, which is 64.49% higher than the flat evaporator's rate of 1.69 kg m⁻². Critically, the quality of the produced water was excellent: post‐distillation values for pH, electrical conductivity (84 µS cm⁻¹), total dissolved solids (41 ppm), hardness (42 ppm), and salt percentage (0.00%) all met stringent drinking water standards, a marked improvement from the raw seawater and tap water (Figures 4K and S24). Notably, the origami ACFF achieves this competitive evaporation performance (Figure 4L) with a significantly lower material cost and a much simpler fabrication process compared to most reported 3D evaporators [17, 29, 53, 54, 55, 56, 57] (Tables S1 and S2).

2.4. Electricity Generation Performance of ACFF Evaporators

The ACFF material in a dry state exhibits a surface zeta potential of −0.402 mV at pH ∼7, indicating a negatively charged surface. When water is adsorbed, an electric double layer (EDL) forms along the internal fiber surfaces. The subsequent upward transport of counterions, driven by continuous evaporation, establishes a streaming potential–a measurable voltage difference across the thickness of the ACFF. To harness this effect, a pair of silver (Ag) electrodes was integrated with the evaporator to create a water‐electricity co‐generator. Owing to the excellent water sorption and transport properties of the ACFF, a potential difference of approximately 0.35 V is rapidly generated upon water contact even without illumination. Under one‐sun illumination, this potential difference increases to about 0.5 V, a modest enhancement attributed to the accelerated water evaporation rate (Figure 5A). The theoretical voltage output of a capillary tube during evaporation can be calculated as [38]

$$V_s=\frac{{\epsilon }_0{\epsilon }_r\mathrm{\Delta }P\zeta }{\sigma \mu }$$ (2)

where ε₀ε _r , ΔP, ζ, σ, μ are the dielectric constant (8.85 × 10⁻¹² C² N⁻¹ m⁻²) (78.5 for water, 78.6 for NaCl solution), the pressure difference between the upper and lower tube surface, the inner zeta potential (increase with salinity), solution conductivity (increase with salinity, ∼0.5 for pure water), and solution viscosity (increase with salinity), respectively. The theoretical current output can be expressed as:

$$I_s=\frac{A\sigma V_s}{L}=\frac{A{\epsilon }_0{\epsilon }_r\mathrm{\Delta }P\zeta }{\mu L}=\frac{\pi d^2{\epsilon }_0{\epsilon }_r\mathrm{\Delta }P\zeta }{4\mu L}$$ (3)

where A is the cross‐sectional area of the tube, and L is the length of capillary tube. The pressure difference ΔP can be calculated as:

$$\mathrm{\Delta }P=\frac{4\gamma \cos \theta }{d}$$ (4)

where γ is the surface tension of water, θ is the contact angle between water and the capillary tube, which is 0 for ACFF evaporators, and d is the diameter of the capillary tube.

FIGURE 5.

Electricity generation performance of ACFF evaporators. (A) The voltage output of flat ACFF evaporator with/without solar illumination. (B) Voltage output of flat ACFF evaporator in DI water and in NaCl solution of different concentrations. (C) Current output of flat ACFF evaporator in DI water and in NaCl solution of different concentrations. (D) Comparison of voltage output between flat ACFF evaporator and origami ACFF evaporator. (E) Comparison of current output between flat ACFF evaporator and origami ACFF evaporator. (F) Voltage output of a single ACFF‐based water electricity co‐generator and that of its series connection (3 and 6). (G) Voltage and current variation of 6 ACFF‐based water electricity co‐generators connected in series. (H) Voltage and current outputs of flat ACFF evaporator with different external load resistances. (I) Power output of flat ACFF evaporator with different external load resistances.

Under one‐sun illumination, the electrical output of the flat ACFF evaporator showed a clear dependence on water salinity, with the average voltage output reaching 0.501, 0.601, 0.581, 0.562, and 0.539 V, at 0, 1, 3.5, 7, and 10 wt% NaCl solution respectively (Figure 5B), while the average current output reaching 6.90, 11.33, 28.87, 34.55, and 17.26 µA cm⁻² (Figure 5C), respectively. The voltage output reached a maximum of 0.601 V at 1 wt% NaCl, while the current output peaked at 34.55 µA cm⁻² at 7 wt% NaCl before both decreased at higher concentrations (Figure 5B). This behavior arises from the interplay of several salinity‐dependent factors, as governed by Equations (2) and (3). Although a higher salinity increases the surface zeta potential (which favors higher output), it simultaneously increases the solution's conductivity and viscosity (which dampens it). The average power output P during a period T can be calculated as:

$$P=\frac{1}{T}\underset{-\frac{T}{2}}{\overset{\frac{T}{2}}{\int }}U\left(t\right)·I\left(t\right)dt$$ (5)

where I is the output current and U is the output voltage. When T is small enough, the average power output is equal to the maximum power output, which can be calculated as [58]

$$P_{max}=I\times U$$ (6)

Using Equation (6), the maximum power outputs of the flat ACFF evaporator under one‐sun illumination across different salt salinities (DI water, 1%, 3.5%, 7%, and 10%) were calculated to be 3.46, 6.81, 16.77, 19.42, and 9.30 µW cm⁻², respectively. Overall, the electricity output of ACFF evaporators peaked at 7 wt% NaCl solution.

The origami evaporator exhibits a higher net zeta potential (0.593 mV) and a larger average pore diameter compared to the flat ACFF, attributable to the incorporation of silica sol. Consequently, while the voltage output of the origami design remains similar to that of the flat evaporator (Figures 5D and S25), its current output is significantly enhanced. Under one‐sun illumination in NaCl solutions ranging from 0% to 10%, the current density increased substantially, reaching values of 8.65, 16.11, 40.67, 68.77, and 32.88 µA cm⁻², respectively (Figures 5E, S26, and S27). Furthermore, connecting multiple ACFF co‐generators in series resulted in a stepwise increase in the overall voltage output (Figures 5F,G and S28), demonstrating the ability to power small electronic devices such as an LED light and a calculator (Figure S29). When tested under varying load resistances, the system achieved a peak power density of over 10.32 µW cm⁻² at a load resistance of ∼200 Ω (Figure 5H,I), indicating the low internal resistance of ACFF ascribed to its excellent intrinsic carrier transport properties (Figure S30). Compared with existing hydrovoltaic systems, the origami ACFF exhibited competitive power output (Table S3).

3. Conclusion

In summary, we have developed a scalable and cost‐effective water‐electricity co‐generation system based on ACFF that integrates efficient solar‐driven evaporation with concurrent power harvesting. The flat ACFF evaporator achieved high evaporation rates, ranging from 0.67 to 1.80 kg m⁻² h⁻¹ under solar intensities of 500–1500 W m⁻², while maintaining robust performance in saline environments–demonstrating strong potential for desalination applications. By further engineering the ACFF into an origami structure, light absorption and thermal management were significantly enhanced, leading to an evaporation rate of 0.76–1.93 kg m⁻² h⁻¹ and a peak solar vapor efficiency of 92.16%, representing a 13.07% improvement over the planar configuration. In parallel, the evaporation‐induced potential difference was effectively harnessed for electricity generation. The flat ACFF delivered a stable voltage of 0.50–0.60 V and a current density of up to 34.55 µA cm⁻² in saline water. Benefitting from an enlarged zeta potential and average pore diameter, the origami structure further increased power output by 30.3–99.7% across salt concentrations from 0 to 10 wt% NaCl. Unlike conventional 2D evaporators limited by heat loss or complex 3D systems constrained by cost and fabrication, the origami ACFF system combines high performance, material accessibility, and simple manufacturing with the ability to harness evaporation‐induced electricity. This integrated approach provides a practical and sustainable pathway toward addressing the intertwined challenges of water scarcity and energy demand, advancing the real‐world applicability of solar interfacial evaporation technology.

4. Materials and Methods

4.1. Preparation of Origami ACFF Evaporator

The origami ACFF evaporator was fabricated using a 3D‐printed mold and silica sol binder. The mold was designed in a two‐step computational process: first, the origami pattern with specific mountain and valley folds was created using the ORIPA: Origami Pattern Editor software. This pattern was then imported into Freeform Origami software to generate a foldable 3D model, which was subsequently printed to produce the physical mold. The size of the printed mold was scaled according to the desired final evaporator size; for instance, a 10 × 10 cm² mold was used to fabricate a 5 × 5 cm² evaporator, and an 18 × 18 cm² mold for a 9 × 9 cm² evaporator. To shape the evaporator, a raw ACFF sheet was first placed on the mold for preliminary forming. A suitable amount of 20% concentration silica sol was then applied as a binder to fix the shape. The assembly (mold and ACFF) was finally dried in an oven at 70°C for 6 h to solidify the structure.

4.2. Material Characterization

The morphological characteristics of the ACFF evaporators were examined using a TESCAN MIRA LMS scanning electron microscope. The specific surface area and pore structure were analyzed by nitrogen adsorption‐desorption isotherms obtained with a Micromeritics ASAP 2020 instrument. FTIR spectra were collected on a Thermo Fisher Scientific Nicolet iN10 spectrometer. Water contact angles were measured with a Lauda Scientific LSA100 instrument. Thermal images were recorded using a Fluke Ti860 thermal imager. The zeta potential was determined with an Anton Paar Surpass 3 electrokinetic analyzer. UV‐Vis‐NIR spectra were acquired using a PE Lambda 1050+ spectrophotometer. The quality of the water samples was analyzed with an EZ‐9909A device.

4.3. Solar Vapor Evaporation Experiment

Indoor water evaporation tests were conducted under ambient conditions of approximately 24°C and 50%–60% RH. A flat ACFF sample with a projected area of 5 × 5 cm² was placed on an expanded polystyrene (EPS) foam float, which was placed on a container of deionized (DI) water or NaCl solutions at various concentrations (1%, 3.5%, 7%, and 10%). A SCIENCETECH SciSun‐300 solar simulator provided illumination at intensities ranging from 500 to 1500 W m⁻². The surface temperature of the evaporator was monitored using a Fluke TiS60 thermal imager, and the mass change of the water was recorded in real‐time using a Mettler Toledo electronic balance.

For outdoor testing, a custom‐designed device (15 × 15 × 11 cm³) containing seawater and a 9 × 9 cm² origami or flat ACFF evaporator was placed on a balcony at the City University of Hong Kong. The condensed freshwater was channeled via tubing into collection bottles for quantification. Ambient temperature and humidity during the experiments were recorded using a ROS‐03 sensor.

4.4. Electricity Generation Experiment

The water‐electricity co‐generation setup comprised an ACFF evaporator, two silver (Ag) electrodes, an EPS foam insulator, bulk water, and a containing beaker. One Ag electrode was positioned on top of the ACFF evaporator, and the other was immersed in the underlying water. The real‐time voltage and current outputs were measured using a Keysight DAQ970A Data Acquisition System, with data recorded via the accompanying Keysight BenchVue software.

Author Contributions

W. W. and W. Z. conceived and designed the study. W. W. supervised the project. W. Z. and F. L. performed the experiments. W. Z. analyzed the experimental results. W. Z. wrote the manuscript with support from W. W., T. Y., and H. C. W. W., T. Y., H. C, W. Z., H. L., and G. L. edited and revised the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File 1: smll74678‐sup‐0001‐SuppMat.pdf.

Data Availability Statement

The data that support the findings of this study are available within the paper and Supplementary Information. Additional supporting data generated during this study are available from the corresponding authors upon reasonable request.