Supercritical CO₂‐Modulated Surface Amorphization and O_V Defect in CaSnO₃ for High‐Efficiency Electrocatalytic H₂O₂ Production

ABSTRACT

The electrochemical two electron water oxidation reaction (2e‐WOR) offers a promising route for hydrogen peroxide (H₂O₂) production, but its efficiency is limited by the lack of high performance electrocatalysts. Herein, we report a supercritical carbon dioxide (SC CO₂) modulation strategy to synergistically engineer surface amorphization and oxygen vacancy (O_V) defects in orthorhombic CaSnO₃. Under an optimal SC CO₂ pressure of 16 MPa, the treated CaSnO₃ exhibits a partially amorphized surface, abundant O_V, and concomitant Sn³⁺ defects. These features collectively increase unsaturated coordination sites, accelerate interfacial charge transfer, and lower the reaction overpotential. Consequently, the optimal catalyst achieves a H₂O₂ production rate of 26.6 µmol cm−² min⁻¹, a Faradaic efficiency (FE) of 82% at 2.9 V versus RHE, and a cumulative yield over 300 min approximately eight times that of pristine CaSnO₃, with stable operation for 24 h. This work demonstrates that SC CO₂ treatment is an effective tool to construct defect coupled surface amorphous regions, providing a new paradigm for designing high ‐ performance 2e‐WOR electrocatalysts for green H₂O₂ synthesis.

In this study, SC CO₂ has been used to treat orthorhombic CaSnO₃, and a synergistic combination of surface amorphization and O_V generation can be obtained. The amorphous layer provides unsaturated coordination sites, while the O_V and associated Sn³⁺ defects optimize local electronic structure and accelerate interfacial charge transfer. This synergistic effect enables efficient 2e‑WOR to H₂O₂, achieving a production rate of 26.6 µmol cm⁻² min⁻¹ and a Faradaic efficiency of 82%, providing a new paradigm for the development of high‐performance electrocatalysts for synthesis of H₂O₂.

1. Introduction

With the increasing global demand for sustainable energy systems and green chemical processes, the development of efficient and environmentally friendly energy conversion technologies has emerged as a frontier research hotspot. H₂O₂ is an important inorganic chemical widely used in sterilization [1], wastewater treatment [2, 3], chemical synthesis [4], and healthcare [5]. Currently, commercial H₂O₂ is mainly produced via the multi‐step anthraquinone process [6]. Although this method enables production at large scale and high concentration, it suffers from complex procedures, high equipment investment, significant organic waste generation, and substantial safety hazards during transportation [7]. To minimize subsequent treatment steps and unnecessary transport costs, there is an urgent need to develop a safe, green, and direct approach for producing H₂O₂.

Among various alternatives, electrochemical synthesis of H₂O₂ has attracted considerable attention due to its mild operating conditions, environmental friendliness, and feasibility for on‐site production. The main electrochemical pathways for H₂O₂ synthesis include the two‐electron oxygen reduction reaction (2e‐ORR) [8] and the 2e‐WOR, as shown in Equations (1) and (2) [9]. From a thermodynamic perspective, the energy barrier for H₂O₂ synthesis via 2e‐ORR is much lower than that of the 2e‐WOR process. Nevertheless, the ORR involves a gas–liquid–solid three‐phase reaction, requiring the use of gas diffusion electrodes and continuous O₂ supply, which complicates operation. In contrast, the anodic 2e‐WOR uses water as the sole reactant without the need for gas involvement, offering a more promising route. The water oxidation reaction (WOR) on the anode involves three competing electron transfer pathways, yielding hydroxyl radicals (1e⁻, E ⁰ = 2.38 V), hydrogen peroxide (2e⁻, E ⁰ = 1.76 V), and oxygen (4e⁻, E ⁰ = 1.23 V), respectively [10]. Among them, the four‑electron oxygen evolution reaction (OER) is thermodynamically most favorable, severely limiting the selectivity and yield of H₂O₂. In this context, Park and colleagues [11] performed density functional theory (DFT) calculations and established that the activity and selectivity of catalysts are governed by the adsorption free energies (ΔG) of key intermediates (OH*, O*, and OOH*) on the surface, as shown in Equations (3) and (4); high selectivity toward H₂O₂ requires ΔG _OH* between 1.6–2.4 eV and ΔG _O* > 3.5 eV, with a theoretical optimum of 1.76 eV. And they identified CaSnO₃ as a highly promising electrocatalyst for the 2e‐WOR. This material exhibits a theoretical overpotential as low as 40–50 mV and achieves a Faradaic efficiency of up to 76%, demonstrating excellent overall catalytic performance. Furthermore, studies have shown that surface defects, exposure of specific crystal facets, electronic structure, and interfacial properties play decisive roles in the catalytic performance of such materials. For instance, Zhang et al. [12] successfully embedded CaSnO₃ into electrospun carbon fiber membranes, effectively tuning its electronic structure and O_V concentration, which significantly enhanced the 2e‐WOR performance of the catalyst. Their DFT calculations revealed that O_V increase the adsorption free energy of O* and OOH* intermediates, suppressing the competing 4e‐WOR pathway and thus enhancing 2e‐WOR selectivity. Although Park et al. first demonstrated the feasibility of CaSnO₃ as a 2e‐WOR catalyst, Zhang et al. significantly boosted the production rate through carbon fiber composite strategy with introduced oxygen vacancies (O_V), the former is limited by insufficient active sites and poor conductivity, while the latter relies on complex composite fabrication with limited regulation of the intrinsic electronic structure of CaSnO₃. Therefore, developing a green, mild, and precise method to tailor the surface structure and defect states of CaSnO₃ is of great significance for further enhancing its 2e‐WOR performance.

$$O_2+2H^{+}+2e^{-}\to H_2{O}_2\left(E^0=0.67Vvs.RHE\right)$$ (1)

$$2H_{2}O\to H_2{O}_2+2H^{+}+2e^{-}\left(E^0=1.76Vvs.RHE\right)$$ (2)

$$H_{2}O\to O{H}^{\ast }+H^{+}+e^{-}$$ (3)

$$2O{H}^{\ast }\to H_2{O}_2$$ (4)

SC CO₂ as a green, efficient, and physico‐chemically tunable medium, has demonstrated unique advantages in recent years for the preparation and modification of nanomaterials. It combines the high density of a liquid with the low viscosity and high diffusion coefficient of a gas, allowing effective penetration into micropores or interlayers of nanomaterials and enabling mild regulation of their surface, lattice, and even electronic structures [13, 14, 15]. By leveraging the unique physicochemical properties of SC CO₂, we successfully modified the internal chemical environment of CaSnO₃, enabling it to exhibit room‐temperature ferromagnetism without doping with magnetic elements [16]. Furthermore, previous studies have demonstrated that SC CO₂ can effectively convert crystalline oxides into amorphous structures characterized by abundant O_V, atomic disorder, and tunable plasmonic properties [17]. These amorphous nanomaterials exhibit enhanced surface adsorption, a higher density of defect sites, and flexible electronic structures, which collectively facilitate CO₂ activation, stabilize reaction intermediates, and modulate charge transfer, thereby offering significant advantages for CO₂ electroreduction [18]. More importantly, a synergistic effect exists between the amorphous region and O_V. The amorphous structure promotes the stabilization and exposure of defects, while O_V further enhance the electronic tunability and density of active sites of the amorphous material.

Therefore, in this study, a regulation strategy using SC CO₂ was employed to systematically investigate how different treatment conditions affect the crystal structure, microscopic morphology, surface defect states, and electronic structure of CaSnO₃. The aim is to elucidate the mechanism by which SC CO₂ modulation enhances the electrocatalytic H₂O₂ production performance of CaSnO₃. Our results reveal that SC CO₂ treatment induces surface amorphization and modulates the O_V concentration in CaSnO₃, thereby optimizing its surface‐active sites. Compared with previously reported approaches, our SC CO₂ treatment enables precise, pressure‑tunable control over both the degree of amorphization and O_V concentration in a single, green step. Consequently, the catalytic activity and stability of CaSnO₃ for the 2e‐WOR are further improved while maintaining high selectivity. This study provides new design insights and experimental evidence for the development of high ‐ performance and low ‐ cost electrocatalysts for H₂O₂ production.

2. Results and Discussion

The structural evolution of CaSnO₃ electrocatalysts prepared under different SC CO₂ pressures was characterized using XRD. As shown in Figure 1a, the diffraction peaks of all CaSnO₃ samples correspond well to the orthorhombic perovskite structure with the space group Pbnm, consistent with the standard card (PDF#77‐1797) [19]. Comparing the XRD patterns of CaSnO₃ before and after SC CO₂ treatment, the pristine CaSnO₃ exhibits sharp diffraction peaks with small full width at half maximum (FWHM), indicating its high crystallinity and long‐range ordered structure. However, after SC CO₂ treatment, the (111) peak at 2θ = 21° exhibits the pronounced amorphization features, characterized by significantly reduced peak intensity, substantial FWHM broadening [20]. This phenomenon is attributed to the unique physicochemical properties of SC CO₂. Its high permeability [21] enables it to penetrate the lattice or grain boundaries of CaSnO₃, where, under high pressure, it interacts with the framework to disrupt Sn─O bonds. It disrupts the periodic arrangement of SnO₆ octahedra, leading to partial collapse of the long‐range order and pronounced amorphization presented in the XRD patterns. Notably, magnified views of the (210) and (004) peaks (Figure 1b,c) reveal systematic low‐angle shifts after treatment. These shifts indicate an increase in interplanar spacing, providing evidence of tensile strain that is consistent with the lattice expansion observed via TEM [22]. This shift can be attributed to two primary factors. First, the introduction of abundant oxygen vacancies weakens the Coulombic interactions between adjacent cations, thereby inducing local lattice relaxation and structural expansion [23]. Second, the high permeability of SC CO₂ facilitates the release of internal stress within distorted SnO₆ octahedra, which also contributes to the systematic shift of the diffraction peaks.

FIGURE 1.

(a) XRD patterns of different CaSnO₃ samples. (b), (c) Enlarged views of the (210) and (004) diffraction peaks. (d) Raman spectra of different CaSnO₃ samples. (e) FTIR spectra of different CaSnO₃ samples.

Raman was employed to investigate the microstructural and molecular vibrational characteristics of CaSnO₃ samples subjected to SC CO₂ treatment at various pressures (Figure 1d). According to group theory, bulk orthorhombic CaSnO₃ with the Pbnm space group is expected to exhibit 24 Raman‐active vibrational modes, represented as Γraman = 7A_g + 5B_1g + 7B_2g + 5B_3g [24]. Three common vibrational bands were observed across all samples: the band near 174 cm⁻¹ is assigned to the B_2g mode, associated with the rotational motion of SnO₆ octahedra; the bands near 270 cm⁻¹ (A_g) and 351 cm−¹ (B_1g) arise primarily from the relative displacement vibrations of Ca and O atoms [25]. The presence of these modes confirms that the fundamental perovskite framework is retained in all samples. However, after SC CO₂ treatment, the characteristic Raman bands at 420, 578, and 697 cm⁻¹ were no longer detectable. The band at 420 cm⁻¹ corresponds to the B_2g mode, attributed to the bending and stretching vibrations of Sn‐O bonds. Meanwhile, the bands near 578 cm⁻¹ (A_g) and 697 cm⁻¹ (B_1g) are closely associated with the distortion vibrations of SnO₆ octahedra. These modes are particularly sensitive to changes in lattice ordering and therefore undergo vibrational relaxation and disappear more readily during amorphization [26, 27].

In contrast, the infrared spectra of the samples showed no significant differences after treatment, as shown in Figure 1e. All spectra exhibited characteristic peaks, including the H─O─H bending vibration of adsorbed water at 1634 cm⁻¹, the C─O stretching vibration of surface carbonate species at 1447 cm⁻¹, and the Sn─O bond stretching vibration at 651 cm⁻¹. These observations further confirm that the CaSnO₃ perovskite framework remains intact following SC CO₂ treatment.

To obtain information on the microstructure and morphology of CaSnO₃ after SC CO₂ treatment, the samples were characterized by transmission electron microscopy (TEM). In Figure 2b, the contrast difference was observed, confirming the presence of thin CaSnO₃ nanosheets [28]. High‐resolution TEM (HR‐TEM) was employed to characterize the atomic arrangement, as shown in Figure 2c. The lattice spacings of the pristine CaSnO₃ sample were measured to be 0.194 and 0.253 nm, which correspond well to the (004) and (210) crystal planes, respectively, as referenced from the standard PDF card. After SC CO₂ treatment, the CaSnO₃ sample exhibited exposure of the (111) crystal plane, accompanied by a slight increase in interplanar spacing [29]. For the sample treated at 16 MPa, the lattice spacing was determined to be 0.367 nm, increasing from the 0.362 nm of 14 MPa of CO₂‐treated CaSnO₃, indicating the increasing lattice tensile strain under this condition. However, when the SC CO₂ pressure further increased to 18 MPa, it can be observed the decreasing lattice spacing of 0.359 nm. This phenomenon may be closely related to localized amorphization and the formation of lattice defects induced by the SC CO₂ treatment. The interfacial mismatch between the amorphous and crystalline phases can generate local stress, leading to lattice distortion [30]. Furthermore, the generation of oxygen vacancies can disrupt the charge balance within the lattice, enhancing electrostatic repulsion between neighboring cations and thereby exacerbating lattice expansion [31], which can be presented in the following XPS characterization. As shown in Figures S1 and S2, distinct amorphous regions can be observed in the HR‐TEM and SEM image of the sample after SC CO₂ treatment. FFT analysis of the marked regions (Figure S1) shows diffuse rings, further corroborating the amorphous nature of the surface layer. The amorphization is consistently evidenced by XRD and Raman (Figure 1a–d).

FIGURE 2.

Lattice structure of bulk CaSnO₃ and treated CaSnO₃ under different SC CO₂ pressures. (a) bulk sample, (b) sample treated at 16 MPa. (c)–(f) HRTEM images: (c) bulk sample, (d) 14 MPa, (e) 16 MPa, and (f) 18 MPa.

Using XPS and EPR characterizations, the evolution of surface chemical states and defects in CaSnO₃ samples before and after SC CO₂ treatment was systematically investigated. Figure 3a shows that, compared to the bulk material, the binding energies of the Ca 2p_1/2 and Ca 2p_3/2 peaks of the samples treated with SC CO₂ shift to higher binding energy by 0.36 eV. This indicates a decrease in the electron cloud density around Ca atoms, primarily due to the introduction of O_V, which disrupts the lattice charge balance. To maintain local electroneutrality, the electron cloud density around adjacent Ca²⁺ cations redistributes, enhancing the binding ability of Ca atoms to outer electrons [32]. Additionally, surface amorphization induced by SC CO₂ alters the coordination environment of Ca, reducing its coordination number and thereby increasing the effective positive charge on Ca, which results in a higher binding energy.

FIGURE 3.

XPS and EPR characterizations of samples treated under different SC CO₂ pressures and the bulk CaSnO₃. (a) XPS spectra of Ca 2p; (b) XPS spectra of Sn 3d, with the relative content of Sn³⁺ indicated; (c) XPS spectra of O 1s, with the relative content of O_V indicated; (d) XPS survey spectra; (e) EPR spectra, with the main g‐values marked.

Figure 3b presents the peak‐fitting results of the Sn 3d core level. The Sn 3d_3/2 and Sn 3d_5/2 peaks of the bulk material are symmetric and exhibit a single peak shape, attributed solely to Sn⁴⁺. After SC CO₂ treatment, the Sn 3d peak can be resolved into two components, a main peak at a higher binding energy corresponding to Sn⁴⁺ and an additional peak at a lower binding energy corresponding to Sn³⁺ [33]. This indicates that SC CO₂ treatment induces the partial reduction of Sn⁴⁺ to Sn³⁺, thereby forming Sn³⁺ defects. Notably, the relative content of Sn³⁺ in samples treated under different pressures exhibits a nonlinear variation, which arises from the charge compensation mechanism induced by O_V.

As shown in Figure 3c, the O 1s spectrum can be deconvoluted into three characteristic peaks, corresponding to O_L (529.4 eV), O_V (531.1 eV), and O_A (533.2 eV) [34, 35]. The relative content of O_V also exhibits a nonlinear variation under different SC CO₂ treatment pressures, increasing from 37% in the bulk material to 49% and then to 54%, subsequently decreasing to 45%. This trend is highly consistent with the evolution of the relative Sn³⁺ content and can be attributed to the high permeability and strong solvation ability of SC CO₂. Under SC CO₂ pressure, CO₂ molecules penetrate the CaSnO₃ lattice and disrupt the Sn─O bonds, thereby generating O_V defects. The resulting charge imbalance increases electrostatic repulsion between neighboring cations, leading to local lattice expansion [36, 37], as evidenced by the increased interplanar spacing observed in HR‐TEM. Thus, higher O_V content correlates with more pronounced lattice expansion. The formation of O_V is a pressure‐driven kinetic process. At a pressure of 16 MPa, the permeability and reactivity of SC CO₂ reach an optimal balance, yielding the highest vacancy concentration. However, when the pressure is further increased to 18 MPa, two competing effects become significant: the external pressure is so high that it kinetically suppresses further release of oxygen from the lattice, and the high pressure also provides sufficient energy for vacancies to migrate, leading to vacancy–vacancy or vacancy–interstitial recombination. Such a pressure‑facilitated vacancy migration and recombination scenario is thermodynamically reasonable, as higher external pressure reduces the activation barrier for defect migration while favoring a more condensed lattice state. Additionally, the excess electrons released upon O_V formation are captured by neighboring cations, reducing Sn⁴⁺ to Sn³⁺. This finding is corroborated by Figure 3b, and together these observations constitute a defect‐coupled system induced by SC CO₂ treatment.

XPS survey spectra reveal that all samples exhibit only the characteristic photoelectron and Auger peaks of the CaSnO₃ matrix, with no peaks from other elements detected, as shown in Figure 3d [38]. Moreover, no significant overall shift or splitting of the main peaks is observed in all samples, reflecting the high purity of the CaSnO₃ samples and confirming that the SC CO₂ treatment process introduces no foreign impurities. To investigate the effects of SC CO₂ treatment on the defect states and local electronic structure of CaSnO₃ samples, EPR spectroscopic analysis is conducted on the samples. After SC CO₂ treatment, the EPR spectra exhibited characteristic resonance signals attributed to O_V (g = 2.004) [39] and Sn³⁺ (g = 1.976), as shown in Figure 3e. Both O_V and Sn³⁺ signals show the same pressure‑dependent trend: strongest at 16 MPa, weaker at 14 MPa, and decreased at 18 MPa, consistent with the O_V concentrations quantified by XPS. This directly demonstrates that SC CO₂ pressure actively controls defect generation and annihilation in CaSnO₃. This confirms that the SC CO₂ treatment not only introduced O_V but also induced a valence state reduction of neighboring Sn ions through a charge compensation mechanism.

Figure 4 presents the electrochemical performance of CaSnO₃ samples treated under different SC CO₂ pressures in 0.2 M KHCO₃ electrolyte. As shown in Figure 4a, the bulk material exhibits low current density and high overpotential, indicating poor 2e‐WOR catalytic activity. SC CO₂ treatment positively shifts the onset potential and markedly increases the current density. Among the samples, CaSnO₃ treated at 16 MPa of SC CO₂ shows the best intrinsic catalytic activity, achieving the highest current density of 80.89 mA cm⁻² at 3.5 V versus RHE. Figure 4b reveals that the 16 MPa sample has a Tafel slope of 45.1 mV dec⁻¹, significantly lower than those of the 14 MPa (65.9 mV dec⁻¹), 18 MPa (72.6 mV dec⁻¹), and bulk (89.2 mV dec⁻¹) samples, indicating superior kinetic performance. To investigate the influence of SC CO₂ treatment on the interfacial kinetic behavior of the CaSnO₃ working electrode, electrochemical impedance spectroscopy (EIS) was conducted. As shown in Figure 4c, the bulk material exhibits the largest charge transfer resistance, indicating the most severe hindrance to charge transfer at the electrode/electrolyte interface. After SC CO₂ treatment, the charge transfer resistance of all samples decreases to varying extents. The sample treated at 16 MPa exhibits the smallest charge transfer resistance, with a notably contracted semicircle diameter, suggesting the most facile interfacial charge transfer, followed by the 14 MPa sample and then the 18 MPa sample. This result is consistent with the UV–vis spectra and Tauc plots of the different samples presented in Figures S3 and S4, where the absorption edges of the samples exhibit varying degrees of redshift after SC CO₂ treatment.

FIGURE 4.

Characterization of electrocatalytic H₂O₂ synthesis performance depending on the as‐prepared samples treated under different SC CO₂ pressures. (a) LSV curve. (b) Tafel plots; (c) EIS spectra; (d) Variation of H₂O₂ production rate with applied potential; (e) Variation of FE for H₂O₂ production with applied potential; (f) Cumulative H₂O₂ production over time at a constant potential of 2.9 V versus RHE; (g) i–t curve of the 16 MPa sample at 2.9 V versus RHE; (h) Schematic diagram of CaSnO₃ surface amorphization and O_V defects induced by SC CO₂.

Figure 4d–f present the performance of CaSnO₃ samples treated under different SC CO₂ pressures for electrocatalytic 2e‐WOR toward H₂O₂ production. As shown in Figure 4d, the H₂O₂ production rates of the samples treated with SC CO₂ are 2 to 10 times higher than the bulk material over the applied potential range of 2.3‐3.3 V versus RHE. In particular, the sample treated at 16 MPa exhibits the optimal H₂O₂ production rate at 2.9 V versus RHE, reaching 26.6 µmol cm⁻² min⁻¹. Figure 4e shows the variation of Faradaic efficiency (FE) of the 2e‐WOR pathway as a function of applied potential. The CaSnO₃ treated with SC CO₂ exhibits much higher FE than the bulk material, following the same trend as the H₂O₂ production rate and reaching a maximum of 82%. Figure 4f shows the cumulative H₂O₂ production over time for different samples at a constant potential of 2.9 V versus RHE. During 300 min of electrolysis, the 16 MPa sample yields 3524 µmol of H₂O₂, significantly higher than the 14 MPa (2618 µmol) and 18 MPa (2114 µmol), and approximately eight times higher than the bulk material at 454 µmol. Table S1 compares the H₂O₂ production rate and FE achieved in this work with those of other electrocatalysts reported in recent years [40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50]. To evaluate long‑term stability and durability at a constant potential, chronoamperometric tests (i‑‐t) were conducted as shown in Figures 4g and S5. The 16 MPa sample, which exhibited the highest H₂O₂ production rate and best selectivity, has an initial current density of 60 mA cm⁻². After a brief decay, the current density stabilizes at 57 mA cm⁻². The stable 24 h chronoamperometric performance also confirms no gradual CO₂ release during electrolysis. To further evaluate the electrochemically active surface area (ECSA) of the samples, we measured the electrochemical double‑layer capacitance (C _dl) in the non‑faradaic region (0.38–0.48 V vs. RHE) at various scan rates (Figure S6). The 16 MPa sample exhibits the highest C _dl value (9.23 mF cm⁻²), indicating that the optimal SC CO₂ treatment provides the largest number of accessible active sites. This trend is fully consistent with the observed catalytic performance. As shown in Figure S7, the electrolyte containing H₂O₂ completely degrades methylene blue within 12 h, with the solution turning from blue to transparent, indicating that the prepared H₂O₂ possesses strong oxidizing ability.

The significant improvement in the electrocatalytic performance of CaSnO₃ can be attributed to the synergistic effect of surface amorphization and O_V defects induced by SC CO₂, as schematically illustrated in Figure 4h. Our group's previous work established the mechanistic framework for SC CO₂‑induced amorphization and defect formation. Ge et al. [51] revealed two distinct mechanisms depending on pressure: at lower pressure, 0.5 eV activation energy corresponds to fracture of metal–oxygen bonds and formation of oxygen vacancies; at higher pressure, 1.5 eV activation energy corresponds to shear stress‑induced atomic rearrangement. Our experimental data on CaSnO₃ are fully consistent with this framework. On the one hand, a moderate amorphous structure provides more unsaturated coordination sites, forming fast ion diffusion channels and accelerating interfacial charge transfer. On the other hand, O_V serve as surface active centers, offering abundant reaction sites [52], and the accompanying reduction of Sn⁴⁺ to Sn³⁺ modifies the local electron density, thereby lowering the reaction overpotential. O_V play a more direct role in enhancing intrinsic activity, while surface amorphization mainly contributes to charge transfer and stability. Both effects are controlled by SC CO₂ pressure, with optimal balance achieved at 16 MPa. At the optimal pressure of 16 MPa, the sample achieves the most suitable degree of amorphization and O_V concentration, resulting in the lowest onset potential, the highest current density, and the smallest Tafel slope. Furthermore, the amorphous layer possesses flexible structural relaxation characteristics that effectively maintain structural integrity [53]. And O_V improve the conductivity of the metal oxide, facilitate charge transfer, and mitigate electrode damage caused by charge accumulation, thus enhancing the activity retention during long‐term electrolysis [54].

3. Conclusion

In summary, SC CO₂ treatment induces partial surface amorphization and the formation of O_V alongside Sn³⁺ defects in orthorhombic CaSnO₃. This structural evolution exposes more unsaturated coordination sites while optimizing the local electronic structure, collectively enhancing the intrinsic catalytic activity and reaction selectivity of CaSnO₃ toward the 2e‐WOR pathway. Furthermore, the amorphous layer provides structural buffering capacity, thereby improving long‐term operational stability. The optimal sample at a pressure of 16 MPa achieves a H₂O₂ production rate of 26.6 µmol cm⁻² min⁻¹, a Faradaic efficiency of 82%, with a cumulative yield over 300 min approximately eight times that of the bulk material and stable operation for 24 h. This study demonstrates that SC CO₂ treatment offers a new paradigm for designing high ‐ performance 2e‐WOR electrocatalysts and holds significant promise for advancing green energy conversion and low‐carbon chemical technologies.

Author Contributions

Lei Xu: data curation, writing – review and editing, writing – original draft, and formal analysis. Ruisi Tao: writing – original draft, writing – review and editing. Qun Xu: writing – review and editing, conceptualization, and funding acquisition. Buxing Han: funding acquisition.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File: anie73890‐Sup‐0001‐SuppMat.docx.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.