Design of Hierarchical Structured Catalysts: SnO2-Modified TiO2 Nanotube Arrays Enabling Ultra-Low Overpotential Acidic Oxygen Evolution Reaction

Design of Hierarchical Structured Catalysts: SnO2-Modified TiO2 Nanotube Arrays Enabling Ultra-Low Overpotential Acidic Oxygen Evolution Reaction | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Design of Hierarchical Structured Catalysts: SnO2-Modified TiO2 Nanotube Arrays Enabling Ultra-Low Overpotential Acidic Oxygen Evolution Reaction Qingchen Lu, Xiaoyu Huang, Yaowen Zhang, Dayong Fan, Faming Han, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6261430/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract The construction of the strong oxid-support interaction (SOSI) between the support and the active component is crucial for regulating the atomic conTuration and electronic structure of the catalyst. In this study, the electrocatalytic oxygen evolution (OER) performance of IrO x in acidic electrolyte was significantly improved by constructing titanium dioxide nanotube array (TNT) and SnO 2 double intermediate layer. The overpotential of TNT/SnO 2 /IrO x at the current density of 10 mA cm -2 is 220 mV, which is 69 mV and 93 mV lower than that of directly loaded TNT/IrO x (289 mV) and TNT/IrO 2 (313 mV), respectively. In addition, the introduction of SnO 2 significantly improved the stability of the catalyst, and after 100 h static chronopotentiometry (CP) test at the current density of 10 mA cm -2 , the potential change was only 18 mV, much lower than that of TNT/IrO 2 (175 mV) and TNT/IrO x (50 mV). Through in-depth surface morphology and structure analysis, it is found that IrO x is anchored on the SnO 2 meslayer and uniformly dispersed. At the same time, TNT array has strong interaction with IrO x , and the addition of the intermediate layer SnO 2 can effectively stabilize Ir from being reduced. The results showed that the synergistic effect of SnO 2 and TNT significantly enhanced the catalytic activity of IrO x . In summary, this study successfully developed an efficient and stable acidic OER catalyst through multistage interface engineering design, providing a new solution for the industrial application of low iridium supported catalysts. IrOx mesosphere OER TNT SnO2 Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1 Introduction Carbon-based fossil fuels have long served as the primary global source of electrical energy. However, the combustion of fossil fuels causes severe environmental issues such as ecological destruction, air pollution, and global warming. Consequently, green energy production methods including solar, tidal, wind, and hydroelectric power have emerged and developed. Nevertheless, the utilization of these renewable energy sources faces spatial and temporal constraints, exhibits significant instability, and struggles to integrate converted electricity into national grids. Storing electricity generated from renewable sources through water electrolysis in high-energy-density hydrogen chemical bonds therefore holds great promise. The hydrogen produced via this method is termed "green hydrogen", which fuel cells can efficiently reconvert into electricity, ultimately establishing a zero-carbon energy circulation system[ 1 , 2 ]. The oxygen evolution reaction (OER), a core process in water electrolysis for hydrogen production, suffers from kinetic sluggishness in its four-electron transfer mechanism, which imposes an overpotential (η > 300 mV) and reduces system energy efficiency by over 30%. Commercial proton exchange membrane water electrolyzer (PEMWE) widely adopt iridium-based catalysts like IrO 2 , primarily because these materials demonstrate high catalytic activity, corrosion resistance, and exceptional electronic conductivity. However, the high cost (180 $ g − 1 ), scarcity (crustal abundance ~ 0.001 ppm), and uneven global distribution of iridium resources critically constrain their large-scale application[ 3 ]. These limitations severely hinder the commercialization of the technology, and improving energy efficiency while reducing system costs becomes imperative to enable widespread adoption of hydrogen production. Research confirms that iridium loading and cost primarily constrain the economic viability of PEMWE systems[ 4 , 5 ]. To address this challenge, three main strategies exist: the first focuses on developing non-precious metal alternatives to replace noble iridium, such as cobalt-based oxides[ 6 , 7 ]. Hao et al.[ 8 ] synthesized trace fluorine-doped Co 3 O 4 nanoneedles via a facile solvothermal and pyrolysis method, achieved a current density of 10 mA cm − 2 at an overpotential of just 350 mV, and demonstrated stable operation for 80 h. Li et al.[ 9 ] synthesized a carbon-coated CeO 2 /Co 3 O 4 hetero structured catalyst (C@CeO 2 /Co 3 O 4 ) through coprecipitation and pyrolysis methods, achieved a current density of 10 mA cm − 2 at an overpotential of 425 mV, and demonstrated stable operation for 50 h. Other examples include manganese-based oxides[ 10 ], Ghadge et al.[ 11 ] developed Cu 1.5 Mn 1.5 O 4 catalysts through ball milling followed by calcination and achieved an overpotential of 330 mV; Li et al.[ 12 ] synthesized γ-MnO 2 through a thermal decomposition method, demonstrated an overpotential of 420 mV in 1 M H 2 SO 4 and maintained stable operation for 8000 h in a pH = 2 electrolyte. The second strategy reduces iridium content in electrocatalysts by doping them with non-precious metals[ 13 , 14 ]. Liang et al.[ 15 ] synthesized SrTi 0.67 Ir 0.33 O 3 through a polymer complex method, achieved an overpotential of 247 mV in 0.1 M HClO 4 , and demonstrated excellent long-term stability at current densities of 10 mA cm − 2 and 30 mA cm − 2 ; Lee et al.[ 16 ] synthesized an Ir-Fe bimetallic oxide catalyst (IFG) supported on reduced graphene oxide (rGO) via ultrasonic spray pyrolysis (USP), achieved an onset overpotential of 260 mV in 0.1 M HClO 4 , and demonstrated 86% activity retention after 5,000 potential cycles. Hu et al.[ 17 ] synthesized an Ir-Co bimetallic oxide catalyst (Ir 0.7 Co 0.3 O x ) through thermal decomposition and cobalt leaching methods, and achieved an oxygen evolution reaction (OER) onset overpotential of 260 mV; Yi et al.[ 18 ] synthesized IrTiO x catalysts via a modified solvothermal method, achieved an overpotential of 296 mV, and demonstrated stable operation for 100 h. Researchers can fabricate highly ordered IrO x nanostructured films and disperse precious metals on inert substrates with high surface areas[ 19 – 21 ]. Most studies synthesize powder catalysts, and the high surface area of inert powder substrates necessitates relatively high noble metal loadings. Current optimization strategies employ photodeposition methods to deposit IrO x layers approximately 2 nm thick onto TiO 2 particles while controlling TiO 2 particle size around 5 µm to minimize iridium consumption. Even with these optimizations, the process still consumes 300 µg cm − 2 of iridium[ 22 ]. Thethird strategy synthesizes supported catalysts by engineering strong metal/support oxide interactions (SMSI/SOSI)[ 23 – 25 ]. Zheng et al.[ 26 ] engineered strong oxide-support interactions (SOSI) between IrO 2 and V 2 O 5 , which not only refined IrO 2 grain clusters to approximately 1 nm but also endowed the catalyst with a unique distorted IrO 2 configuration. This structural innovation enables significant enhancement in catalytic performance for the universal oxygen evolution reaction (OER) across a wide pH range. SnO 2 serves as a typical n-type semiconductor material and possesses excellent electron transport capabilities. Researchers have extensively studied SnO 2 as a support material in energy conversion technologies such as lithium-ion batteries[ 27 ], perovskite solar cells[ 28 , 29 ], and CO 2 reduction[ 30 ]. SnO 2 exhibits redox and Lewis acid-base properties due to its multivalent states, enabling strong interactions with foreign active species. Additionally, SnO 2 facilitates hydrolysis kinetics and supplies protons during electrochemical processes, which play crucial roles in surface catalytic reactions[ 31 ]. Furthermore, TiO 2 nanotube arrays integrate a rutile-type barrier layer with anatase-type tube walls, forming a heterojunction structure that exhibits enhanced conductivity compared to pure TiO 2 [ 32 ]. The vertically aligned anatase-phase tube walls integrate a highly conductive active layer on their surface, establishing conductive pathways between conductive and insulating materials[ 33 , 34 ]. Todoroki et al.[ 35 ] introduced a SnO 2 interlayer between RuO 2 and Nb-doped rutile TiO 2 , which stabilized the interface between RuO 2 and the TiO 2 substrate during the oxygen evolution reaction (OER). Pure rutile TiO 2 inherently acts as an n-type semiconductor and facilitates the formation of low-resistance interfaces with iridium oxides. This study fabricated a TNT/SnO 2 /IrO x catalyst through the following steps: First, we roughened the Ti foil surface by etching thin films followed by anodization to grow TiO 2 nanotube arrays (TNT). Next, we deposited a loosely porous SnO 2 2D interlayer framework via a facile impregnation method to disperse IrO x nanoparticles, while leveraging TNT to enhance the adhesion between the SnO 2 /IrO x nanocomposite and the Ti substrate. The SOSI-induced IrO x nanoclusters uniformly embedded within the SnO 2 porous network achieved a ultralow noble metal loading of 80 µg cm − 2 . As an extension, we directly loaded SnO 2 onto highly porous Ti felt substrates before depositing IrO x . Electrochemical impedance spectroscopy revealed that SnO 2 dramatically enhanced the conductivity of Ti felt, further reducing the Ir loading to 40 µg cm − 2 while maintaining prolonged stability under 0.1 A cm − 2 in three distinct pH electrolytes. This advancement holds significant implications for developing high-performance diffusion layers in proton exchange membrane water electrolyer (PEMWE). 2 Experimental 2.1 Materials and equipment Experimental Chemicals: Ti sheet, Ti felt, C 2 H 2 O 4 , C 2 H 5 OH, SnCl 4 ·5H 2 O, NaOH, DI water, NH 4 F, C 2 H 6 O 2 , C 3 H 6 O, IrCl 3 ·3H 2 O, Na 2 SO 4 , KOH, H 2 SO 4 . Experimental Equipment: Analytical balance (BSA124S, Sartorius, Germany); Muffle furnace (IKA-T25); Saisi Instrument Co, Ltd, Suzhou; Electrochemical workstation (CHI 760E, Beijing Bohui Innovation Technology Co, Ltd.); DC power supply (MDF-U3386S) Platinum electrode; (Ag/AgCl) reference electrode 2.2 Preparation of TNT/SnO 2 /IrO x catalyst We prepared a titanium sheet measuring 20×5×0.2 mm by sequentially grinding it with coarse and fine sandpaper to remove the surface oxide layer, revealing a metallic luster. We then ultrasonically cleaned the Ti sheet in acetone, ethanol, and water for 30 min each to remove surface oils. After rinsing with water, we immersed the Ti sheet in a 10 wt% oxalic acid solution at 95 ℃ and stirred for 3 h to etch the surface, resulting in a rough, gray, non-metallic finish. We stored the etched Ti sheet in ethanol for later use. Using a stainless-steel plate as the cathode and the pretreated Ti sheet as the anode, we prepared a precursor solution by dissolving 0.18 g of ammonium fluoride in 2.5 ml of water, followed by adding 50 ml of ethylene glycol. We maintained an electrode distance of 4 cm and applied a voltage of 60 V for 10 min to fabricate titanium dioxide nanotube arrays (TNT) via anodic oxidation using a DC power supply. We then annealed the TNT precursor in a muffle furnace at a heating rate of 2 ℃ min − 1 to 500 ℃ and held it for 2 h to obtain the TNT arrays. Next, we prepared a uniform suspension by adding 50 µl of 0.5 mol L − 1 SnCl 4 ·5H 2 O ethanol solution and 100 µl of 1 mol L − 1 NaOH solution into 2.5 ml of deionized water, following the reaction: SnCl 4 + 4NaOH → 4NaCl + SnO 2 ·2H 2 O. We repeatedly immersed the TNT, preheated to 350 ℃, into this solution and sintered it at 350 ℃ to stabilize the structure. After washing away surface chlorides with deionized water, we annealed the sample at 450 ℃ for 4 h to obtain a stable porous TNT/SnO 2 heterostructure. We prepared a 7 mM mL − 1 ethanol solution of IrCl 3 ·3H 2 O for later use. We heated the TNT/SnO 2 heterostructure in a muffle furnace to 350 ℃ and drop-coated 40 µl of the 7 mmol mL − 1 IrCl 3 ·3H 2 O ethanol solution onto it, ensuring an Ir loading of 80 µg cm − 2 . We then annealed the sample in the muffle furnace at a heating rate of 2 ℃ min − 1 to 350 ℃ and held it for 3 h to obtain the TNT/SnO 2 /IrO x catalyst. A schematic diagram of the preparation process is shown in Fig. 1 . 2.3 Characterizations We performed OER performance tests using the CHI 760E electrochemical workstation from Shanghai Chenhua Instrument Co, Ltd. We analyzed the crystal structure of thin-film samples using a grazing-incidence X-ray diffraction (XRD) method with the X'Pert3 Powder multifunctional X-ray diffractometer (Cu target, λ = 1.54056 Å) from PANalytical B.V, Netherlands. We characterized the surface morphology and microstructure of the materials using a Hitachi SU5000 thermal field-emission scanning electron microscope (SEM) and analyzed the chemical composition and content of specific regions using the energy-dispersive X-ray spectroscopy (EDS) system attached to the SEM. We employed a JEOL JEM-2100F field-emission transmission electron microscope (TEM) to characterize the microstructure of the materials. For TEM testing, we dispersed the samples in ethanol via ultrasonication and then drop-cast them onto copper grids coated with porous carbon films. We used a Thermo Scientific ESCALAB 250Xi X-ray photoelectron spectrometer (XPS) to characterize the surface chemical states of the materials. We measured and calculated the concentration of corresponding ions in the electrolyte after stability tests using an Agilent 725-ES full-spectrum direct-reading inductively coupled plasma optical emission spectrometer (ICP-OES). We calculated the specific surface area from low-pressure adsorption data using the Brunauer-Emmet-Teller (BET) model and determined the pore size distribution of two-dimensional porous materials using the Barrett-Joyner-Halenda (BJH) method. We collected Raman spectra using a Renishaw inVia confocal Raman microscope with a 514.5 nm laser as the excitation source and compared the peak positions with reference samples. We conducted H 2 temperature-programmed reduction (H 2 -TPR) experiments on an AutoChem II 2920 instrument with a heating rate of 10 ℃ min − 1 . 3 Results and discussions 3.1 Structural characterization of catalysts As shown in Fig. 2 a-b (details in Fig. S1 ), we prepared TNT tubes with a diameter of approximately 0.1 µm, and uneven surfaces caused by etching were visible around them. Subsequently, we heated the TNT to 350 ℃ and quickly immersed it into the impregnation solution. After maintaining the temperature for 2 h, we washed away the surface chlorides with deionized water and then annealed the sample at 450 ℃ for 4 h to obtain TNT arrays loaded with a porous SnO 2 structure, as shown in Fig. 2 c-d (details in Fig. S2a-h). Through elemental mapping (Fig. S2i1-i3), we observed that the SnO 2 loading on the TNT was relatively uniform. Next, we drop-coated an ethanol solution of IrCl 3 onto the porous structure. We noted that the grayish-white SnO 2 thin layer was uniformly covered by the brownish-yellow IrCl 3 ethanol solution, indicating that Ir 3+ were easily loaded into the porous structure. After annealing at 350 ℃ for 4 h, the catalyst color changed from brown to black. Using SEM, we observed typical cracks caused by thermal decomposition, as shown in Fig. 2 e (details in Fig. S3). Elemental mapping (Fig. 2 e1-e4) revealed the uniformity of these cracks. We further annealed the sample at 450 ℃ and performed XRD analysis (Fig. 3 a; to minimize the influence of TNT, we reduced the anodization time). We found that after treatment at 350 ℃, two peaks appeared at 27.98 ° and 34.66 °, but after treatment at 450 ℃, these peaks became sharper, and a new peak emerged at 53.93 ℃, indicating that amorphous IrO x transformed into more crystalline IrO 2 at 450 ℃. We conducted XRD analysis on TNT/SnO 2 /IrO x , TNT/IrO x , and Ti/SnO 2 (Fig. 3 b) and observed that the peaks of SnO 2 and IrO x mainly appeared between 25 °and 35 °. Comparing the peaks near 27.5 ° and 33.5 ° for the three samples, we found that after loading IrO x into the porous structure, the peaks of IrO x and SnO 2 overlapped. Additionally, no additional peaks appeared after the combination of IrO x and SnO 2 , suggesting that no new compounds formed between IrCl 3 and SnO 2 . Through SEM and TEM observations (Fig. S3l and Fig. 2 f), we noted that TNT/SnO 2 /IrO x exhibited similar cluster structures with a size of 25 nm. Figure 2 f-h displays the high-resolution transmission electron microscopy (HRTEM) images of TNT/SnO 2 /IrO x . The sample exhibits clear lattice fringes with spacings of 0.154 nm and 0.228 nm, corresponding to the (110) and (200) crystal planes of IrO 2 , respectively. Additionally, spacings of 0.152 nm and 0.186 nm correspond to the (110) and (101) crystal planes of SnO 2 , respectively, which aligns with the XRD analysis results. Through nitrogen adsorption-desorption isotherm tests on TNT/SnO 2 /IrO x and TNT/SnO 2 (Fig. S4a and S4b), we observed that TNT/SnO 2 adsorbs a larger amount of N 2 at the same relative pressure. This indicates that the SnO 2 interlayer possesses a loose and porous structure, with an average pore size of 6.59 nm (65.911 Å). In contrast, after drop-casting IrCl 3 onto TNT/SnO 2 , Ir(III) ions infiltrated this porous structure. Combined with the pore size distribution analysis, we found that after IrCl 3 drop-casting and calcination, the number of pores in the 25–50 nm range significantly decreased in TNT/SnO 2 /IrO x , and the average pore size reduced to 3.89 nm (38.943 Å). Meanwhile, the specific surface areas of the two materials were 11.12 m 2 g − 1 and 7.43 m 2 g − 1 , respectively. This is because Ir 3+ ions, after calcination, embedded into the porous SnO 2 structure as nanoclusters. Comparing the adsorption-desorption curves of the two materials, we noted that TNT/SnO 2 , with its larger pore size, exhibited a rapid initial increase followed by a slower trend, while TNT/SnO 2 /IrO x , with its larger pores filled by Ir nanoclusters and forming more small pores, showed a slower initial increase followed by a rapid trend. The higher specific surface area helps increase the number of active sites, thereby positively influencing the catalytic performance. This tight integration also significantly refined the IrO x particles, as shown in Fig. S3l. Furthermore, the elemental mapping of TNT/SnO 2 /IrO x (Fig. 2 e) clearly demonstrates the uniform distribution of Ir, Sn, and O. In the Raman spectroscopy tests (Fig. 3 c), we observed that all peaks of TNT (cyan) became broader compared to TNT/IrO x (red). For TNT/SnO 2 (green), due to the porous structure of SnO 2 , its peaks showed no significant change relative to TNT. Comparing Ti/SnO 2 /IrO x (blue) and TNT/SnO 2 /IrO x , we identified that the peaks of SnO 2 and IrO x mainly appeared between 500–700 cm − 1 . Comparing TNT/SnO 2 /IrO x (black) and TNT/SnO 2 (green), We found that the peaks at 520 cm − 1 and 640 cm − 1 shifted rightward by approximately 20 cm − 1 . This is attributed to the overlapping peaks of SnO 2 and IrO x , which is consistent with the XRD analysis results. Additionally, the sharp peak of TNT at 143.56 cm − 1 became broader after directly loading IrO x , indicating the formation of a dense IrO x structure on the surface. However, after loading SnO 2 , the peak remained sharp, and it became broader again after further loading IrO x . This is because the porous SnO 2 interlayer allowed the rays to reach the TNT surface. To further investigate the structure of the catalysts, we conducted X-ray photoelectron spectroscopy (XPS) and EDS analyses on TNT/SnO 2 /IrO x , TNT/IrO x , and Ti/IrO x (Fig. 3 e-h, Fig. S5, and Fig. S6). In the typical Ir 4f spectrum of Ti/IrO x , we assigned the peaks near 61.48 eV and 64.38 eV primarily to Ir 4f 7/2 and Ir 4f 5/2 , respectively, followed by three satellite peaks[ 36 , 37 ]. For SnO 2 /IrO x and IrOx bonded with TNT, we observed the 4f 7/2 and 4f 5/2 peak positions at 62.28 eV and 65.18 eV, respectively, which shifted 0.8 eV to the left compared to IrO x directly bonded with Ti. In the O 1s spectra, we noted a gradual rightward shift in the main peak positions from TNT/SnO 2 (531.3 eV) to TNT/IrO x (530.7 eV) and TNT/SnO 2 /IrO x (530.5 eV). These findings collectively indicate that SnO 2 forms a stable active layer with IrO x and exhibits strong interactions with the TNT substrate. Additionally, we performed H 2 temperature-programmed reduction (H 2 -TPR) tests on the catalysts TNT/IrO x , TNT/SnO 2 , and TNT/SnO 2 /IrO x , as shown in Fig. 3 d. In the H 2 -TPR profiles, comparing TNT/IrOx (blue) and TNT/SnO 2 /IrO x (black), we identified the peak at 672.3 ℃ as the reduction peak of SnO 2 , while the peak at 715.8 ℃ corresponds to the reduction of TNT. This is due to the presence of a rutile-phase barrier layer in TNT itself (Fig. S1 f). We found that IrO x directly loaded on TNT exhibits a higher reduction temperature and a broader reduction range compared to IrO x loaded onto SnO 2 and then onto TNT, primarily because the SnO 2 interlayer weakens the direct interaction between the rutile-phase barrier layer and IrO x . Furthermore, after loading IrO x onto TNT/SnO 2 , we observed the formation of a dense structure, resulting in a single hydrogen consumption reduction peak. The peak corresponding to Ti/TNT disappeared, and the main peak broadened and shifted to the right, with a reduction temperature significantly higher than that of commercial IrO 2 (210 ℃)[ 38 , 39 ]. Additionally, the reduction temperature was also higher than that of IrO x combined with V 2 O 5 , which exhibits a reduction temperature of 310 ℃[ 26 ]. This indicates that IrO x loaded on TNT/SnO 2 is more difficult to reduce. Therefore, IrO x exhibits a more stable oxidation state, which helps stabilize high valence states to promote the oxygen evolution reaction (OER), reduce the risk of catalyst deactivation (by preventing reduction to Ir 3+ ), optimize electron transfer efficiency, lower the reaction overpotential, and simultaneously suppress side reactions (such as catalyst corrosion or dissolution). 3.2 Catalytic activity of OER First, we conducted a systematic comparative study on the catalytic performance of TNT/IrO x , TNT/IrO 2 , Ti/SnO 2 /IrO x , and TNT/SnO 2 /IrO x . We evaluated the OER performance of these catalysts in a typical three-electrode setup. The experiments were carried out in a N 2 -saturated 0.5 M H 2 SO 4 solution. Prior to this, we optimized the preparation process of TNT/SnO 2 /IrO x and found that impregnating SnO 2 six times was the optimal number to load 80 µg Ir cm − 2 , achieving the best OER activity. Excessive or insufficient impregnation negatively affected its OER performance (as shown in Fig. S7). We recorded the linear sweep voltammetry (LSV) curves of the catalysts, as shown in Fig. 4 a, and measured the overpotential at a current density of 10 mA cm − 2 . The results revealed that TNT/SnO 2 /IrO x (black, 220 mV) exhibited a lower overpotential compared to Ti/SnO 2 /IrO x (blue, 237 mV), TNT/IrO x (green, 289 mV), and TNT/IrO 2 (red, 313 mV), indicating superior thermodynamic activity. Figure 4 b compares the Tafel slopes of the four catalysts. The Tafel slopes for TNT/IrO x , Ti/SnO 2 /IrO x , and TNT/IrO 2 were 140.76 mV dec − 1 , 86.02 mV dec − 1 , and 107.47 mV dec − 1 , respectively, while TNT/SnO 2 /IrO x showed a significantly lower slope of 77.76 mV dec − 1 , demonstrating better kinetic activity. Figure 4 c displays the impedance comparison of the four catalysts at a current density of 10 mA cm- 2 . The impedances for TNT/IrO x , Ti/SnO 2 /IrO x , and TNT/IrO 2 were 18.65 Ω, 17.97 Ω, and 4.43 Ω, respectively, while TNT/SnO 2 /IrO x exhibited a much lower impedance of 1.78 Ω, indicating faster electron transfer rates. Figure 4 d presents the equivalent circuit simulation of the TNT/SnO 2 /IrO x catalyst in 0.5 M H 2 SO 4 . Figure 4 e shows the double-layer capacitance of the four catalysts at scan rates ranging from 20 to 200 mV s − 1 . TNT/SnO 2 /IrO x had the highest slope, suggesting the largest number of active sites per unit area (calculated data from Fig. S8). Figure 4 f (details in Table. S9) compares the activity of TNT/SnO 2 /IrO x with recently reported acidic OER electrocatalysts. The results show that, despite a higher Tafel slope, its overpotential outperforms the others. We can reduce the Tafel slope by optimizing testing methods, such as increasing the testing temperature or coating on super-wetting substrates[ 40 ]. We used bar charts to visually compare the performance differences among the catalysts, as shown in Fig. 4 g. The yellow bars (left) represent the overpotentials of the catalysts at a current density of 10 mA cm − 2 , while the green bars (right) represent the current densities at an overpotential of 370 mV. The current densities for TNT/IrO x , Ti/SnO 2 /IrO x , and TNT/IrO 2 were 21.96 mA cm − 2 , 103.72 mA cm − 2 , and 24.16 mA cm − 2 , respectively, while TNT/SnO 2 /IrO x achieved a significantly higher current density of 152.36 mA cm − 2 . Figure 4 h compares the mass activities of the catalysts at an overpotential of 370 mV. The mass activities for TNT/IrO x , Ti/SnO 2 /IrO x , and TNT/IrO 2 were 274.55 A g Ir −1 , 1296.50 A g Ir −1 , and 301.95 A g Ir −1 , respectively, while TNT/SnO 2 /IrO x exhibited a much higher mass activity of 1904.50 A g Ir −1 . Combining these results with Fig. 5 a, we can more intuitively observe the advantages of TNT/SnO 2 /IrO x . It is noteworthy that we observed the TNT/SnO 2 /IrO x catalyst to exhibit an exceptionally low OER overpotential of 220 mV at 10 mA cm − 2 in 0.5 M H 2 SO 4 solution (Fig. 3 a), with a Tafel slope of 77.76 mV dec − 1 (Fig. 3 b), significantly lower than that of the commercially available Ti felt/IrO 2 catalyst (overpotential of 250 mV, Fig. S10f). Additionally, we found that the acidic OER catalytic activity of this catalyst surpasses that of most recently reported catalysts. As an extension of our research, we prepared a sample by directly impregnating Ti felt with SnO 2 followed by loading IrO x (as shown in Fig. S11). Since SnO 2 is an amphoteric oxide capable of demonstrating considerable activity in solutions of different pH levels, we tested its OER performance in 0.5 M H 2 SO 4 , 1 M KOH, and 0.5 M Na 2 SO 4 solutions. As illustrated in Fig. S10, given that Ti felt inherently outperforms Ti sheets, we reduced the Ir content to 40 µg cm − 2 for comparison with the commercial Ti felt/IrO 2 , as shown in Fig. S10f-h. As anticipated, the overpotential was 218 mV in 0.5 M H 2 SO 4 , 275 mV in 1 M KOH, and, due to sluggish intrinsic kinetics, a poorer performance with an overpotential of 540 mV in 0.5 M Na 2 SO 4 solution. We further confirmed that this catalyst maintains stability for at least 20 h at a high current density of 0.1 A cm − 2 in 0.5 M H 2 SO 4 , 1 M KOH, and 0.5 M Na 2 SO 4 solutions. Stability is one of the important criteria to evaluate the performance of electrocatalysis. In this study, the electrochemical stability of TNT/IrO x , TNT/IrO 2 and TNT/SnO 2 /IrO x catalysts was systematically evaluated using (CP). Figure 5 a shows the potential variation trend of the three catalysts during CP test. In the initial 50 h CP test, TNT/IrO 2 showed a significant increase in potential, while TNT/IrO x showed a large fluctuation in potential because IrO x was more soluble than IrO 2 . It is worth noting that after the introduction of the SnO 2 intermediate layer, the overpotential of TNT/SnO 2 /IrO x catalyst was significantly reduced, and the phenomenon of TNT surface shedding was effectively inhibited (compare Fig. S12), and the dissolution degree of IrO x was also significantly reduced. Specifically, the TNT/SnO 2 /IrO x potential change was only 18 mV during 100 h of CP testing. To further evaluate the stability of TNT/SnO 2 /IrO x , we performed long-term CP tests at current densities of 30 mA cm − 2 and 50 mA cm − 2 , respectively (Fig. 5 b). The results showed that the catalyst exhibited excellent stability with a potential change of 26 mV at 30 mA cm − 2 at 200 h and 33 mV at 50 mA cm − 2 at 100 h. By ICP-OES analysis of the amount of Ir dissolved in the electrolyte, it was found that the loss of Ir after 100 h 10 mA cm − 2 test was 2.2%, after 200 h 30 mA cm − 2 test was 5.6%, and after 100 h 50 mA cm − 2 test was 8.6%. We analyzed the microstructure of TNT/SnO 2 /IrO x in detail to investigate the mechanism behind the enhancement of its electrochemical properties and structural stability. Fig. S13 shows the SEM images after 40 h CP test (a-d) at 10 mA cm − 2 current density and after 200 h CP test (e) at 30 mA cm − 2 current density. By comparing the Mapping images (Fig. 5 e, g), HRTEM images (Fig. 5 f-h), EDS spectra (Fig. S14) and XPS images (Fig. 5 c and Fig. S15) of the catalyst before and after CP, it was found in Fig. 5 c that Ir 4+ peak at 62.28eV dominated after surface reconstruction of Ir ions. A weak peak centered on Ir 3+ at 65.18 eV (A Ir 4+ :A Ir 3+ =5.801) showed higher activity than the initial peak (A Ir 4+ :A Ir 3+ =1.047). At the same time, combined with HRTEM image comparison, it can be found that Ir ions accumulate after CP (from point-like clusters to continuous large areas). It is worth noting that despite the migration of Ir particles after CP, the catalyst maintained good stability combined with chronopotentiometric and ICP-OES results, which was significantly better than the catalyst without SnO 2 loading. By comparing the CP curves of TNT/IrO x and TNT/IrO 2 , we can find that although TNT/IrO x exhibits a lower oxygen evolution potential, it demonstrates poor stability. This instability primarily results from the higher activity of IrO x compared to IrO 2 , which causes surface reconstruction and subsequently leads to the shedding of TNT. The inherent stability of Ir 4+ in rutile IrO 2 prevents surface remodeling induced by water oxidation[ 41 ]. The addition of the loose SnO 2 framework stabilizes and refines the IrO x particle binding to the framework. In order to observe the connection between IrO x and TNT in a more in-depth and intuitive way, the nanotubes were directly grown and then the catalyst was prepared, and finally peeled off to observe the connection state between them. As shown in Fig. S16, it can be observed that there is also an ultra-thin layer of SnO 2 between the composite material of IrO x and SnO 2 and TNT, which not only effectively stabilizes the structure of TNT due to its high specific surface area and excellent corrosion resistance, but also ensures the firm combination of IrO x and SnO 2 with TNT. At the same time, XRD tests of TNT/SnO 2 /IrO x , TNT/IrO x and TNT/SnO 2 show that the position of diffraction peaks after the combination of IrO x and SnO 2 is superimposed. Figure 2 f-g shows that SnO 2 mainly exists (110) and (101) crystal planes. Many studies have shown that the surface of SnO 2 (110) is a metastable surface, which can be used as an active site for the activation of O 2 molecules. The adsorption of O 2 molecules by van der Waals force after hydroxylation on the crystal surface will increase the electrical conductivity of the crystal surface[ 42 – 44 ]. At the same time, the most active (110) crystal face of IrO 2 can be found by TEM, which shows the highest activity in OER due to its surface structure and electronic properties. Moreover, the surface energy of the (110) crystal plane is low, which is conducive to the adsorption and desorption of oxygen, thus improving the catalytic efficiency of OER[ 45 – 47 ]. There was almost no change in the position of Sn 3d before and after CP (Fig. 5 d), which also Eroved the stability of IrO x after reconstruction to a certain extent. Based on the synergistic effect of these factors, TNT/SnO 2 /IrO x has good activity and stability. 4 Conclusions In summary, a simple method has been developed to synthesize highly efficient thin film TNT/SnO 2 /IrO x catalyst. Different from the traditional powder loading strategy, this study proposes a three-dimensional nanostructured support design: TNT prepared by anodic oxidation is used as a conductive skeleton, and a multistage heterostructure is constructed through the SnO 2 intermediate layer. Through XRD, XPS and morphology analysis, this design optimizes the electronic structure of IrO x through the SOSI effect of TNT on SnO 2 and IrO x composites. Meanwhile, SnO 2 serves as an intermediate layer to refine IrO x particles to enhance their catalytic activity and stability, while using proton conduction properties to promote efficient water decomposition in interfacial mass transfer process. Combined with H 2 -TPR tests, it was found that the TNT/SnO 2 /IrO x catalyst was difficult to be reduced, and stable IrO x was one of the key factors for efficiently catalyzing OER reactions. Therefore, this study provided a new idea for developing low noble metal loading, efficient and stable acidic OER catalysts, and demonstrated the important role of multistage interface engineering in electrocatalysis. Abbreviations SMSI/SOSI Strong metal/oxid-support interaction OER Oxygen evolution reaction CP Chronopotentiometry TNT Titanium dioxide nanotube array PEMWE Proton exchange membrane water electrolyzer XRD X-ray diffraction SEM Scanning electron microscope EDS Energy-dispersive X-ray spectroscopy TEM Transmission electron microscope XPS X-ray photoelectron spectrometer ICP-OES Inductively coupled plasma optical emission spectrometer BET Brunauer-Emmet-Teller BJH Barrett-Joyner-Halenda H 2 -TPR H 2 temperature-programmed reduction LSV linear sweep voltammetry Declarations Ethics and Consent to Participate Not applicable. Consent for Publication Not applicable. Competing Interest No competing interests. Author Contributions Syntheses, characterizations, data analyses, manuscript writing and activity tests by Q.Lu, X.Huang, Y.Zhang; Work led by D.Fan, F.Han, C.Sundaram, H.Lu, Y.Liu; Manuscript validation by all. Funding This work was supported by Guangxi Science and Technology Development Program (AA24263043,AD22035102), National Natural Science Foundation of China (22165005，22262010). Availability of Data and Materials Data is provided within the manuscript or supplementary information files Acknowledgements This work was supported by Guangxi Science and Technology Development Program (AA24263043,AD22035102), National Natural Science Foundation of China (22165005，22262010). References Hwang J, Rao RR, Giordano L, Katayama Y, Yu Y, Shao-Horn Y (2017) Perovskites in catalysis and electrocatalysis. Sci 358:751–756 Xu ZJ, Wang X (2020) Electrocatalysis: A Core Technique for a Sustainable Future. Chem Eur J 26:3897–3897 Minke C, Suermann M, Bensmann B, Hanke-Rauschenbach R (2021) Is iridium demand a potential bottleneck in the realization of large-scale PEM water electrolysis. 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Supplementary Files supportinginformation.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 11 Apr, 2025 Reviews received at journal 08 Apr, 2025 Reviewers agreed at journal 29 Mar, 2025 Reviewers invited by journal 29 Mar, 2025 Editor assigned by journal 28 Mar, 2025 Submission checks completed at journal 28 Mar, 2025 First submitted to journal 19 Mar, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6261430","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":441698257,"identity":"46b91b95-486d-4d26-a247-2fb0045bdafe","order_by":0,"name":"Qingchen Lu","email":"","orcid":"","institution":"Guilin University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Qingchen","middleName":"","lastName":"Lu","suffix":""},{"id":441698258,"identity":"a306de4b-fe3c-4b8b-b5a8-e5f49afb9d6f","order_by":1,"name":"Xiaoyu Huang","email":"","orcid":"","institution":"Guilin University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Xiaoyu","middleName":"","lastName":"Huang","suffix":""},{"id":441698261,"identity":"dfdbc145-1a41-43ac-a821-e83e750d8bb8","order_by":2,"name":"Yaowen Zhang","email":"","orcid":"","institution":"Guilin University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Yaowen","middleName":"","lastName":"Zhang","suffix":""},{"id":441698263,"identity":"27023981-d6ff-4179-b635-862c3452cf53","order_by":3,"name":"Dayong Fan","email":"","orcid":"","institution":"Guilin University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Dayong","middleName":"","lastName":"Fan","suffix":""},{"id":441698266,"identity":"de370aac-6b09-47a2-b99c-cc7b23b05d6d","order_by":4,"name":"Faming Han","email":"","orcid":"","institution":"Guilin University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Faming","middleName":"","lastName":"Han","suffix":""},{"id":441698269,"identity":"cb22db19-c2d2-44ed-b5e9-c9999a0985bb","order_by":5,"name":"Chandrasekaran Sundaram","email":"","orcid":"","institution":"Guilin University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Chandrasekaran","middleName":"","lastName":"Sundaram","suffix":""},{"id":441698270,"identity":"5d07ad79-cc9d-412b-bd15-86aac7f44cdd","order_by":6,"name":"Huidan Lu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxUlEQVRIiWNgGAWjYBACPgkGhgM8IAZ7Y+PDD8RoYYNpYeM53GwsQawWBrAWifQ2AR6itEj3GB54U3PHrk3yYRuDBIOdnG4DIS0yZwwOzjn2LLlNOrHtQQFDsrHZAYIOyzE4zMN2OJlNOrHdQILhQOI24rT8A2qRPNgmwUO0Ft62w3ZsEoxEa0krODi373ACG08iMJANiPALv0Ty5g9vvh2252c//vDhhwo7OYJaYCCxAUwZEKkcBOxJUDsKRsEoGAUjDQAAc0k/hFB1LZEAAAAASUVORK5CYII=","orcid":"","institution":"Guilin University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Huidan","middleName":"","lastName":"Lu","suffix":""},{"id":441698275,"identity":"db14db14-5459-44ba-9ff0-b3687155064a","order_by":7,"name":"Yongping Liu","email":"","orcid":"","institution":"Guilin University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Yongping","middleName":"","lastName":"Liu","suffix":""}],"badges":[],"createdAt":"2025-03-19 12:08:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6261430/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6261430/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":80890501,"identity":"08e75d74-6be2-4529-8d19-5fa13b4d0d10","added_by":"auto","created_at":"2025-04-18 10:04:38","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":628851,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic image of the preparation process for the TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e electrocatalyst.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6261430/v1/3e26a84dacc808ec52087b93.jpeg"},{"id":80890309,"identity":"256fba92-75a1-4e0f-9593-b2b3272ca393","added_by":"auto","created_at":"2025-04-18 09:56:38","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":3196863,"visible":true,"origin":"","legend":"\u003cp\u003eMorphology characterization of the catalysts. \u003cstrong\u003ea-b)\u003c/strong\u003e SEM images of TNT; \u003cstrong\u003ec-d)\u003c/strong\u003e SEM images of TNT/SnO\u003csub\u003e2\u003c/sub\u003e; \u003cstrong\u003ee)\u003c/strong\u003e SEM image and corresponding elemental mapping of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e; \u003cstrong\u003ef)\u003c/strong\u003e TEM image of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e; \u003cstrong\u003eg-h)\u003c/strong\u003e HRTEM images of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6261430/v1/5e377c2683b908231057a4f2.png"},{"id":80890307,"identity":"3741213b-a082-4937-9f32-c630b7efd024","added_by":"auto","created_at":"2025-04-18 09:56:38","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":587749,"visible":true,"origin":"","legend":"\u003cp\u003eStructural characterization of the catalysts. \u003cstrong\u003ea)\u003c/strong\u003e XRD patterns of TNT/IrO\u003csub\u003e2\u003c/sub\u003e and TNT/IrO\u003csub\u003ex\u003c/sub\u003e; \u003cstrong\u003eb)\u003c/strong\u003e XRD patterns of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/IrO\u003csub\u003ex\u003c/sub\u003e and Ti/SnO\u003csub\u003e2\u003c/sub\u003e; \u003cstrong\u003ec)\u003c/strong\u003e Raman spectra of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/SnO\u003csub\u003e2\u003c/sub\u003e, Ti/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e and TNT; \u003cstrong\u003ed)\u003c/strong\u003e H₂-TPR profiles of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/IrO\u003csub\u003ex\u003c/sub\u003e and TNT/SnO\u003csub\u003e2\u003c/sub\u003e; \u003cstrong\u003ee)\u003c/strong\u003e XPS survey spectra of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/SnO\u003csub\u003e2\u003c/sub\u003e, and Ti/IrO\u003csub\u003ex\u003c/sub\u003e; \u003cstrong\u003ef)\u003c/strong\u003e Ir 4f spectra of Ti/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/IrO\u003csub\u003ex\u003c/sub\u003e and TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e; \u003cstrong\u003eg)\u003c/strong\u003e O 1s spectra of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/IrO\u003csub\u003ex\u003c/sub\u003e and TNT/SnO\u003csub\u003e2\u003c/sub\u003e; \u003cstrong\u003eh)\u003c/strong\u003e Sn 3d spectra of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e and TNT/IrO\u003csub\u003ex\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6261430/v1/f9a54ad84c19c282a2e9edd1.png"},{"id":80890323,"identity":"8ea12afe-addb-49e0-a1b9-557e1de90cf7","added_by":"auto","created_at":"2025-04-18 09:56:39","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":435266,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of OER activity for catalysts (Ir loading with 80 μg cm\u003csup\u003e-2\u003c/sup\u003e). \u003cstrong\u003ea)\u003c/strong\u003e Steady-state polarization curves recorded at a low scan rate of 1 mV s\u003csup\u003e-1\u003c/sup\u003e; \u003cstrong\u003eb)\u003c/strong\u003e Tafel plots of different electrocatalysts in 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e; \u003cstrong\u003ec)\u003c/strong\u003e Electrochemical impedance spectroscopy (EIS) spectra of various electrocatalysts in 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e; \u003cstrong\u003ed)\u003c/strong\u003e Equivalent circuit model for simulation; \u003cstrong\u003ee)\u003c/strong\u003e Double-layer capacitance measurements of electrocatalysts at scan rates ranging from 20 to 200 mV s\u003csup\u003e-1\u003c/sup\u003e; \u003cstrong\u003ef)\u003c/strong\u003e Activity comparison of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e with recently reported acidic OER electrocatalysts; \u003cstrong\u003eg)\u003c/strong\u003e Overpotentials at 10 mA cm\u003csup\u003e-2\u003c/sup\u003e and corresponding current densities at 370 mV overpotential for different catalysts; \u003cstrong\u003eh)\u003c/strong\u003e Mass activities of catalysts at a fixed overpotential of 370 mV.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6261430/v1/ad492332b4535903188adf99.png"},{"id":80890311,"identity":"8fce3f34-e5d5-4d57-a922-ac35444eef8e","added_by":"auto","created_at":"2025-04-18 09:56:38","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1364464,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea)\u003c/strong\u003e Chronopotentiometry (CP) profiles of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/IrO\u003csub\u003e2\u003c/sub\u003e and TNT/IrO\u003csub\u003ex\u003c/sub\u003e at current density of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e in 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e; \u003cstrong\u003eb)\u003c/strong\u003e CP profiles of the TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e catalyst at 10, 30 and 50 mA cm\u003csup\u003e-2\u003c/sup\u003e; \u003cstrong\u003ec, d)\u003c/strong\u003e Ir 4f and Sn 3d XPS spectra of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e before and after CP testing; \u003cstrong\u003ee)\u003c/strong\u003e Elemental mapping images of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e before CP; \u003cstrong\u003ef)\u003c/strong\u003e TEM image of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e before CP; \u003cstrong\u003eg)\u003c/strong\u003e Elemental mapping images of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e after CP; \u003cstrong\u003eh) \u003c/strong\u003eTEM image of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e after CP.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6261430/v1/f02b5b3aaea7c2b399be077b.png"},{"id":80891280,"identity":"f5b760af-6f42-4d9c-b4e0-32391826793e","added_by":"auto","created_at":"2025-04-18 10:12:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7166056,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6261430/v1/adae0b34-ed86-4176-826b-ddf6f45abd34.pdf"},{"id":80890503,"identity":"c094275b-8165-47b5-b6b2-19f8db4acf49","added_by":"auto","created_at":"2025-04-18 10:04:39","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":10838089,"visible":true,"origin":"","legend":"","description":"","filename":"supportinginformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-6261430/v1/2ea80c6f6b65e52343509ee4.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Design of Hierarchical Structured Catalysts: SnO2-Modified TiO2 Nanotube Arrays Enabling Ultra-Low Overpotential Acidic Oxygen Evolution Reaction","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eCarbon-based fossil fuels have long served as the primary global source of electrical energy. However, the combustion of fossil fuels causes severe environmental issues such as ecological destruction, air pollution, and global warming. Consequently, green energy production methods including solar, tidal, wind, and hydroelectric power have emerged and developed. Nevertheless, the utilization of these renewable energy sources faces spatial and temporal constraints, exhibits significant instability, and struggles to integrate converted electricity into national grids. Storing electricity generated from renewable sources through water electrolysis in high-energy-density hydrogen chemical bonds therefore holds great promise. The hydrogen produced via this method is termed \"green hydrogen\", which fuel cells can efficiently reconvert into electricity, ultimately establishing a zero-carbon energy circulation system[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe oxygen evolution reaction (OER), a core process in water electrolysis for hydrogen production, suffers from kinetic sluggishness in its four-electron transfer mechanism, which imposes an overpotential (η\u0026thinsp;\u0026gt;\u0026thinsp;300 mV) and reduces system energy efficiency by over 30%. Commercial proton exchange membrane water electrolyzer (PEMWE) widely adopt iridium-based catalysts like IrO\u003csub\u003e2\u003c/sub\u003e, primarily because these materials demonstrate high catalytic activity, corrosion resistance, and exceptional electronic conductivity. However, the high cost (180 \u003cspan\u003e$\u003c/span\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), scarcity (crustal abundance\u0026thinsp;~\u0026thinsp;0.001 ppm), and uneven global distribution of iridium resources critically constrain their large-scale application[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. These limitations severely hinder the commercialization of the technology, and improving energy efficiency while reducing system costs becomes imperative to enable widespread adoption of hydrogen production. Research confirms that iridium loading and cost primarily constrain the economic viability of PEMWE systems[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo address this challenge, three main strategies exist: the first focuses on developing non-precious metal alternatives to replace noble iridium, such as cobalt-based oxides[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Hao et al.[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] synthesized trace fluorine-doped Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoneedles via a facile solvothermal and pyrolysis method, achieved a current density of 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at an overpotential of just 350 mV, and demonstrated stable operation for 80 h. Li et al.[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] synthesized a carbon-coated CeO\u003csub\u003e2\u003c/sub\u003e/Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e hetero structured catalyst (C@CeO\u003csub\u003e2\u003c/sub\u003e/Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) through coprecipitation and pyrolysis methods, achieved a current density of 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at an overpotential of 425 mV, and demonstrated stable operation for 50 h. Other examples include manganese-based oxides[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], Ghadge et al.[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] developed Cu\u003csub\u003e1.5\u003c/sub\u003eMn\u003csub\u003e1.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e catalysts through ball milling followed by calcination and achieved an overpotential of 330 mV; Li et al.[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] synthesized γ-MnO\u003csub\u003e2\u003c/sub\u003e through a thermal decomposition method, demonstrated an overpotential of 420 mV in 1 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and maintained stable operation for 8000 h in a pH\u0026thinsp;=\u0026thinsp;2 electrolyte.\u003c/p\u003e \u003cp\u003eThe second strategy reduces iridium content in electrocatalysts by doping them with non-precious metals[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Liang et al.[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] synthesized SrTi\u003csub\u003e0.67\u003c/sub\u003eIr\u003csub\u003e0.33\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e through a polymer complex method, achieved an overpotential of 247 mV in 0.1 M HClO\u003csub\u003e4\u003c/sub\u003e, and demonstrated excellent long-term stability at current densities of 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 30 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e; Lee et al.[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] synthesized an Ir-Fe bimetallic oxide catalyst (IFG) supported on reduced graphene oxide (rGO) via ultrasonic spray pyrolysis (USP), achieved an onset overpotential of 260 mV in 0.1 M HClO\u003csub\u003e4\u003c/sub\u003e, and demonstrated 86% activity retention after 5,000 potential cycles. Hu et al.[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] synthesized an Ir-Co bimetallic oxide catalyst (Ir\u003csub\u003e0.7\u003c/sub\u003eCo\u003csub\u003e0.3\u003c/sub\u003eO\u003csub\u003ex\u003c/sub\u003e) through thermal decomposition and cobalt leaching methods, and achieved an oxygen evolution reaction (OER) onset overpotential of 260 mV; Yi et al.[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] synthesized IrTiO\u003csub\u003ex\u003c/sub\u003e catalysts via a modified solvothermal method, achieved an overpotential of 296 mV, and demonstrated stable operation for 100 h. Researchers can fabricate highly ordered IrO\u003csub\u003ex\u003c/sub\u003e nanostructured films and disperse precious metals on inert substrates with high surface areas[\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Most studies synthesize powder catalysts, and the high surface area of inert powder substrates necessitates relatively high noble metal loadings. Current optimization strategies employ photodeposition methods to deposit IrO\u003csub\u003ex\u003c/sub\u003e layers approximately 2 nm thick onto TiO\u003csub\u003e2\u003c/sub\u003e particles while controlling TiO\u003csub\u003e2\u003c/sub\u003e particle size around 5 \u0026micro;m to minimize iridium consumption. Even with these optimizations, the process still consumes 300 \u0026micro;g cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e of iridium[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThethird strategy synthesizes supported catalysts by engineering strong metal/support oxide interactions (SMSI/SOSI)[\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Zheng et al.[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] engineered strong oxide-support interactions (SOSI) between IrO\u003csub\u003e2\u003c/sub\u003e and V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, which not only refined IrO\u003csub\u003e2\u003c/sub\u003e grain clusters to approximately 1 nm but also endowed the catalyst with a unique distorted IrO\u003csub\u003e2\u003c/sub\u003e configuration. This structural innovation enables significant enhancement in catalytic performance for the universal oxygen evolution reaction (OER) across a wide pH range. SnO\u003csub\u003e2\u003c/sub\u003e serves as a typical n-type semiconductor material and possesses excellent electron transport capabilities. Researchers have extensively studied SnO\u003csub\u003e2\u003c/sub\u003e as a support material in energy conversion technologies such as lithium-ion batteries[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], perovskite solar cells[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e], and CO\u003csub\u003e2\u003c/sub\u003e reduction[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. SnO\u003csub\u003e2\u003c/sub\u003e exhibits redox and Lewis acid-base properties due to its multivalent states, enabling strong interactions with foreign active species. Additionally, SnO\u003csub\u003e2\u003c/sub\u003e facilitates hydrolysis kinetics and supplies protons during electrochemical processes, which play crucial roles in surface catalytic reactions[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Furthermore, TiO\u003csub\u003e2\u003c/sub\u003e nanotube arrays integrate a rutile-type barrier layer with anatase-type tube walls, forming a heterojunction structure that exhibits enhanced conductivity compared to pure TiO\u003csub\u003e2\u003c/sub\u003e[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The vertically aligned anatase-phase tube walls integrate a highly conductive active layer on their surface, establishing conductive pathways between conductive and insulating materials[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Todoroki et al.[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e] introduced a SnO\u003csub\u003e2\u003c/sub\u003e interlayer between RuO\u003csub\u003e2\u003c/sub\u003e and Nb-doped rutile TiO\u003csub\u003e2\u003c/sub\u003e, which stabilized the interface between RuO\u003csub\u003e2\u003c/sub\u003e and the TiO\u003csub\u003e2\u003c/sub\u003e substrate during the oxygen evolution reaction (OER). Pure rutile TiO\u003csub\u003e2\u003c/sub\u003e inherently acts as an n-type semiconductor and facilitates the formation of low-resistance interfaces with iridium oxides.\u003c/p\u003e \u003cp\u003eThis study fabricated a TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e catalyst through the following steps: First, we roughened the Ti foil surface by etching thin films followed by anodization to grow TiO\u003csub\u003e2\u003c/sub\u003e nanotube arrays (TNT). Next, we deposited a loosely porous SnO\u003csub\u003e2\u003c/sub\u003e 2D interlayer framework via a facile impregnation method to disperse IrO\u003csub\u003ex\u003c/sub\u003e nanoparticles, while leveraging TNT to enhance the adhesion between the SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e nanocomposite and the Ti substrate. The SOSI-induced IrO\u003csub\u003ex\u003c/sub\u003e nanoclusters uniformly embedded within the SnO\u003csub\u003e2\u003c/sub\u003e porous network achieved a ultralow noble metal loading of 80 \u0026micro;g cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. As an extension, we directly loaded SnO\u003csub\u003e2\u003c/sub\u003e onto highly porous Ti felt substrates before depositing IrO\u003csub\u003ex\u003c/sub\u003e. Electrochemical impedance spectroscopy revealed that SnO\u003csub\u003e2\u003c/sub\u003e dramatically enhanced the conductivity of Ti felt, further reducing the Ir loading to 40 \u0026micro;g cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e while maintaining prolonged stability under 0.1 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in three distinct pH electrolytes. This advancement holds significant implications for developing high-performance diffusion layers in proton exchange membrane water electrolyer (PEMWE).\u003c/p\u003e "},{"header":"2 Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials and equipment\u003c/h2\u003e \u003cp\u003eExperimental Chemicals: Ti sheet, Ti felt, C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eOH, SnCl\u003csub\u003e4\u003c/sub\u003e\u0026middot;5H\u003csub\u003e2\u003c/sub\u003eO, NaOH, DI water, NH\u003csub\u003e4\u003c/sub\u003eF, C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eO, IrCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO, Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, KOH, H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eExperimental Equipment: Analytical balance (BSA124S, Sartorius, Germany); Muffle furnace (IKA-T25); Saisi Instrument Co, Ltd, Suzhou; Electrochemical workstation (CHI 760E, Beijing Bohui Innovation Technology Co, Ltd.); DC power supply (MDF-U3386S) Platinum electrode; (Ag/AgCl) reference electrode\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e catalyst\u003c/h2\u003e \u003cp\u003eWe prepared a titanium sheet measuring 20\u0026times;5\u0026times;0.2 mm by sequentially grinding it with coarse and fine sandpaper to remove the surface oxide layer, revealing a metallic luster. We then ultrasonically cleaned the Ti sheet in acetone, ethanol, and water for 30 min each to remove surface oils. After rinsing with water, we immersed the Ti sheet in a 10 wt% oxalic acid solution at 95 ℃ and stirred for 3 h to etch the surface, resulting in a rough, gray, non-metallic finish. We stored the etched Ti sheet in ethanol for later use. Using a stainless-steel plate as the cathode and the pretreated Ti sheet as the anode, we prepared a precursor solution by dissolving 0.18 g of ammonium fluoride in 2.5 ml of water, followed by adding 50 ml of ethylene glycol. We maintained an electrode distance of 4 cm and applied a voltage of 60 V for 10 min to fabricate titanium dioxide nanotube arrays (TNT) via anodic oxidation using a DC power supply. We then annealed the TNT precursor in a muffle furnace at a heating rate of 2 ℃ min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 500 ℃ and held it for 2 h to obtain the TNT arrays. Next, we prepared a uniform suspension by adding 50 \u0026micro;l of 0.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e SnCl\u003csub\u003e4\u003c/sub\u003e\u0026middot;5H\u003csub\u003e2\u003c/sub\u003eO ethanol solution and 100 \u0026micro;l of 1 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e NaOH solution into 2.5 ml of deionized water, following the reaction: SnCl\u003csub\u003e4\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;4NaOH \u0026rarr; 4NaCl\u0026thinsp;+\u0026thinsp;SnO\u003csub\u003e2\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO. We repeatedly immersed the TNT, preheated to 350 ℃, into this solution and sintered it at 350 ℃ to stabilize the structure. After washing away surface chlorides with deionized water, we annealed the sample at 450 ℃ for 4 h to obtain a stable porous TNT/SnO\u003csub\u003e2\u003c/sub\u003e heterostructure. We prepared a 7 mM mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e ethanol solution of IrCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO for later use. We heated the TNT/SnO\u003csub\u003e2\u003c/sub\u003e heterostructure in a muffle furnace to 350 ℃ and drop-coated 40 \u0026micro;l of the 7 mmol mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e IrCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;3H\u003csub\u003e2\u003c/sub\u003eO ethanol solution onto it, ensuring an Ir loading of 80 \u0026micro;g cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. We then annealed the sample in the muffle furnace at a heating rate of 2 ℃ min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 350 ℃ and held it for 3 h to obtain the TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e catalyst. A schematic diagram of the preparation process is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Characterizations\u003c/h2\u003e \u003cp\u003eWe performed OER performance tests using the CHI 760E electrochemical workstation from Shanghai Chenhua Instrument Co, Ltd. We analyzed the crystal structure of thin-film samples using a grazing-incidence X-ray diffraction (XRD) method with the X'Pert3 Powder multifunctional X-ray diffractometer (Cu target, λ\u0026thinsp;=\u0026thinsp;1.54056 \u0026Aring;) from PANalytical B.V, Netherlands. We characterized the surface morphology and microstructure of the materials using a Hitachi SU5000 thermal field-emission scanning electron microscope (SEM) and analyzed the chemical composition and content of specific regions using the energy-dispersive X-ray spectroscopy (EDS) system attached to the SEM. We employed a JEOL JEM-2100F field-emission transmission electron microscope (TEM) to characterize the microstructure of the materials. For TEM testing, we dispersed the samples in ethanol via ultrasonication and then drop-cast them onto copper grids coated with porous carbon films. We used a Thermo Scientific ESCALAB 250Xi X-ray photoelectron spectrometer (XPS) to characterize the surface chemical states of the materials. We measured and calculated the concentration of corresponding ions in the electrolyte after stability tests using an Agilent 725-ES full-spectrum direct-reading inductively coupled plasma optical emission spectrometer (ICP-OES). We calculated the specific surface area from low-pressure adsorption data using the Brunauer-Emmet-Teller (BET) model and determined the pore size distribution of two-dimensional porous materials using the Barrett-Joyner-Halenda (BJH) method. We collected Raman spectra using a Renishaw inVia confocal Raman microscope with a 514.5 nm laser as the excitation source and compared the peak positions with reference samples. We conducted H\u003csub\u003e2\u003c/sub\u003e temperature-programmed reduction (H\u003csub\u003e2\u003c/sub\u003e-TPR) experiments on an AutoChem II 2920 instrument with a heating rate of 10 ℃ min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and discussions","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Structural characterization of catalysts\u003c/h2\u003e\n \u003cp\u003eAs shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea-b (details in Fig. \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e), we prepared TNT tubes with a diameter of approximately 0.1 \u0026micro;m, and uneven surfaces caused by etching were visible around them. Subsequently, we heated the TNT to 350 ℃ and quickly immersed it into the impregnation solution. After maintaining the temperature for 2 h, we washed away the surface chlorides with deionized water and then annealed the sample at 450 ℃ for 4 h to obtain TNT arrays loaded with a porous SnO\u003csub\u003e2\u003c/sub\u003e structure, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec-d (details in Fig. S2a-h). Through elemental mapping (Fig. S2i1-i3), we observed that the SnO\u003csub\u003e2\u003c/sub\u003e loading on the TNT was relatively uniform. Next, we drop-coated an ethanol solution of IrCl\u003csub\u003e3\u003c/sub\u003e onto the porous structure. We noted that the grayish-white SnO\u003csub\u003e2\u003c/sub\u003e thin layer was uniformly covered by the brownish-yellow IrCl\u003csub\u003e3\u003c/sub\u003e ethanol solution, indicating that Ir\u003csup\u003e3+\u003c/sup\u003e were easily loaded into the porous structure. After annealing at 350 ℃ for 4 h, the catalyst color changed from brown to black. Using SEM, we observed typical cracks caused by thermal decomposition, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ee (details in Fig. S3). Elemental mapping (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ee1-e4) revealed the uniformity of these cracks. We further annealed the sample at 450 ℃ and performed XRD analysis (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea; to minimize the influence of TNT, we reduced the anodization time). We found that after treatment at 350 ℃, two peaks appeared at 27.98 \u0026deg; and 34.66 \u0026deg;, but after treatment at 450 ℃, these peaks became sharper, and a new peak emerged at 53.93 ℃, indicating that amorphous IrO\u003csub\u003ex\u003c/sub\u003e transformed into more crystalline IrO\u003csub\u003e2\u003c/sub\u003e at 450 ℃. We conducted XRD analysis on TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/IrO\u003csub\u003ex\u003c/sub\u003e, and Ti/SnO\u003csub\u003e2\u003c/sub\u003e (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb) and observed that the peaks of SnO\u003csub\u003e2\u003c/sub\u003e and IrO\u003csub\u003ex\u003c/sub\u003e mainly appeared between 25 \u0026deg;and 35 \u0026deg;. Comparing the peaks near 27.5 \u0026deg; and 33.5 \u0026deg; for the three samples, we found that after loading IrO\u003csub\u003ex\u003c/sub\u003e into the porous structure, the peaks of IrO\u003csub\u003ex\u003c/sub\u003e and SnO\u003csub\u003e2\u003c/sub\u003e overlapped. Additionally, no additional peaks appeared after the combination of IrO\u003csub\u003ex\u003c/sub\u003e and SnO\u003csub\u003e2\u003c/sub\u003e, suggesting that no new compounds formed between IrCl\u003csub\u003e3\u003c/sub\u003e and SnO\u003csub\u003e2\u003c/sub\u003e. Through SEM and TEM observations (Fig. S3l and Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ef), we noted that TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e exhibited similar cluster structures with a size of 25 nm.\u003c/p\u003e\n \u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ef-h displays the high-resolution transmission electron microscopy (HRTEM) images of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e. The sample exhibits clear lattice fringes with spacings of 0.154 nm and 0.228 nm, corresponding to the (110) and (200) crystal planes of IrO\u003csub\u003e2\u003c/sub\u003e, respectively. Additionally, spacings of 0.152 nm and 0.186 nm correspond to the (110) and (101) crystal planes of SnO\u003csub\u003e2\u003c/sub\u003e, respectively, which aligns with the XRD analysis results. Through nitrogen adsorption-desorption isotherm tests on TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e and TNT/SnO\u003csub\u003e2\u003c/sub\u003e (Fig. S4a and S4b), we observed that TNT/SnO\u003csub\u003e2\u003c/sub\u003e adsorbs a larger amount of N\u003csub\u003e2\u003c/sub\u003e at the same relative pressure. This indicates that the SnO\u003csub\u003e2\u003c/sub\u003e interlayer possesses a loose and porous structure, with an average pore size of 6.59 nm (65.911 \u0026Aring;). In contrast, after drop-casting IrCl\u003csub\u003e3\u003c/sub\u003e onto TNT/SnO\u003csub\u003e2\u003c/sub\u003e, Ir(III) ions infiltrated this porous structure. Combined with the pore size distribution analysis, we found that after IrCl\u003csub\u003e3\u003c/sub\u003e drop-casting and calcination, the number of pores in the 25\u0026ndash;50 nm range significantly decreased in TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, and the average pore size reduced to 3.89 nm (38.943 \u0026Aring;). Meanwhile, the specific surface areas of the two materials were 11.12 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 7.43 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. This is because Ir\u003csup\u003e3+\u003c/sup\u003e ions, after calcination, embedded into the porous SnO\u003csub\u003e2\u003c/sub\u003e structure as nanoclusters. Comparing the adsorption-desorption curves of the two materials, we noted that TNT/SnO\u003csub\u003e2\u003c/sub\u003e, with its larger pore size, exhibited a rapid initial increase followed by a slower trend, while TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, with its larger pores filled by Ir nanoclusters and forming more small pores, showed a slower initial increase followed by a rapid trend. The higher specific surface area helps increase the number of active sites, thereby positively influencing the catalytic performance. This tight integration also significantly refined the IrO\u003csub\u003ex\u003c/sub\u003e particles, as shown in Fig. S3l. Furthermore, the elemental mapping of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ee) clearly demonstrates the uniform distribution of Ir, Sn, and O. In the Raman spectroscopy tests (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec), we observed that all peaks of TNT (cyan) became broader compared to TNT/IrO\u003csub\u003ex\u003c/sub\u003e (red). For TNT/SnO\u003csub\u003e2\u003c/sub\u003e (green), due to the porous structure of SnO\u003csub\u003e2\u003c/sub\u003e, its peaks showed no significant change relative to TNT. Comparing Ti/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e (blue) and TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, we identified that the peaks of SnO\u003csub\u003e2\u003c/sub\u003e and IrO\u003csub\u003ex\u003c/sub\u003e mainly appeared between 500\u0026ndash;700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Comparing TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e (black) and TNT/SnO\u003csub\u003e2\u003c/sub\u003e (green),\u003c/p\u003e\n \u003cp\u003eWe found that the peaks at 520 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 640 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e shifted rightward by approximately 20 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. This is attributed to the overlapping peaks of SnO\u003csub\u003e2\u003c/sub\u003e and IrO\u003csub\u003ex\u003c/sub\u003e, which is consistent with the XRD analysis results. Additionally, the sharp peak of TNT at 143.56 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e became broader after directly loading IrO\u003csub\u003ex\u003c/sub\u003e, indicating the formation of a dense IrO\u003csub\u003ex\u003c/sub\u003e structure on the surface. However, after loading SnO\u003csub\u003e2\u003c/sub\u003e, the peak remained sharp, and it became broader again after further loading IrO\u003csub\u003ex\u003c/sub\u003e. This is because the porous SnO\u003csub\u003e2\u003c/sub\u003e interlayer allowed the rays to reach the TNT surface.\u003c/p\u003e\n \u003cp\u003eTo further investigate the structure of the catalysts, we conducted X-ray photoelectron spectroscopy (XPS) and EDS analyses on TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/IrO\u003csub\u003ex\u003c/sub\u003e, and Ti/IrO\u003csub\u003ex\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ee-h, Fig. S5, and Fig. S6). In the typical Ir 4f spectrum of Ti/IrO\u003csub\u003ex\u003c/sub\u003e, we assigned the peaks near 61.48 eV and 64.38 eV primarily to Ir 4f\u003csub\u003e7/2\u003c/sub\u003e and Ir 4f\u003csub\u003e5/2\u003c/sub\u003e, respectively, followed by three satellite peaks[\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]. For SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e and IrOx bonded with TNT, we observed the 4f\u003csub\u003e7/2\u003c/sub\u003e and 4f\u003csub\u003e5/2\u003c/sub\u003e peak positions at 62.28 eV and 65.18 eV, respectively, which shifted 0.8 eV to the left compared to IrO\u003csub\u003ex\u003c/sub\u003e directly bonded with Ti. In the O 1s spectra, we noted a gradual rightward shift in the main peak positions from TNT/SnO\u003csub\u003e2\u003c/sub\u003e (531.3 eV) to TNT/IrO\u003csub\u003ex\u003c/sub\u003e (530.7 eV) and TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e (530.5 eV). These findings collectively indicate that SnO\u003csub\u003e2\u003c/sub\u003e forms a stable active layer with IrO\u003csub\u003ex\u003c/sub\u003e and exhibits strong interactions with the TNT substrate. Additionally, we performed H\u003csub\u003e2\u003c/sub\u003e temperature-programmed reduction (H\u003csub\u003e2\u003c/sub\u003e-TPR) tests on the catalysts TNT/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/SnO\u003csub\u003e2\u003c/sub\u003e, and TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed. In the H\u003csub\u003e2\u003c/sub\u003e-TPR profiles, comparing TNT/IrOx (blue) and TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e (black), we identified the peak at 672.3 ℃ as the reduction peak of SnO\u003csub\u003e2\u003c/sub\u003e, while the peak at 715.8 ℃ corresponds to the reduction of TNT. This is due to the presence of a rutile-phase barrier layer in TNT itself (Fig. \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003ef). We found that IrO\u003csub\u003ex\u003c/sub\u003e directly loaded on TNT exhibits a higher reduction temperature and a broader reduction range compared to IrO\u003csub\u003ex\u003c/sub\u003e loaded onto SnO\u003csub\u003e2\u003c/sub\u003e and then onto TNT, primarily because the SnO\u003csub\u003e2\u003c/sub\u003e interlayer weakens the direct interaction between the rutile-phase barrier layer and IrO\u003csub\u003ex\u003c/sub\u003e. Furthermore, after loading IrO\u003csub\u003ex\u003c/sub\u003e onto TNT/SnO\u003csub\u003e2\u003c/sub\u003e, we observed the formation of a dense structure, resulting in a single hydrogen consumption reduction peak. The peak corresponding to Ti/TNT disappeared, and the main peak broadened and shifted to the right, with a reduction temperature significantly higher than that of commercial IrO\u003csub\u003e2\u003c/sub\u003e (210 ℃)[\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e]. Additionally, the reduction temperature was also higher than that of IrO\u003csub\u003ex\u003c/sub\u003e combined with V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, which exhibits a reduction temperature of 310 ℃[\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. This indicates that IrO\u003csub\u003ex\u003c/sub\u003e loaded on TNT/SnO\u003csub\u003e2\u003c/sub\u003e is more difficult to reduce. Therefore, IrO\u003csub\u003ex\u003c/sub\u003e exhibits a more stable oxidation state, which helps stabilize high valence states to promote the oxygen evolution reaction (OER), reduce the risk of catalyst deactivation (by preventing reduction to Ir\u003csup\u003e3+\u003c/sup\u003e), optimize electron transfer efficiency, lower the reaction overpotential, and simultaneously suppress side reactions (such as catalyst corrosion or dissolution).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Catalytic activity of OER\u003c/h2\u003e\n \u003cp\u003eFirst, we conducted a systematic comparative study on the catalytic performance of TNT/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/IrO\u003csub\u003e2\u003c/sub\u003e, Ti/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, and TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e. We evaluated the OER performance of these catalysts in a typical three-electrode setup. The experiments were carried out in a N\u003csub\u003e2\u003c/sub\u003e-saturated 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solution. Prior to this, we optimized the preparation process of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e and found that impregnating SnO\u003csub\u003e2\u003c/sub\u003e six times was the optimal number to load 80 \u0026micro;g Ir cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, achieving the best OER activity. Excessive or insufficient impregnation negatively affected its OER performance (as shown in Fig. S7). We recorded the linear sweep voltammetry (LSV) curves of the catalysts, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea, and measured the overpotential at a current density of 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The results revealed that TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e (black, 220 mV) exhibited a lower overpotential compared to Ti/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e (blue, 237 mV), TNT/IrO\u003csub\u003ex\u003c/sub\u003e (green, 289 mV), and TNT/IrO\u003csub\u003e2\u003c/sub\u003e (red, 313 mV), indicating superior thermodynamic activity. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb compares the Tafel slopes of the four catalysts. The Tafel slopes for TNT/IrO\u003csub\u003ex\u003c/sub\u003e, Ti/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, and TNT/IrO\u003csub\u003e2\u003c/sub\u003e were 140.76 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 86.02 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 107.47 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively, while TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e showed a significantly lower slope of 77.76 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, demonstrating better kinetic activity. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec displays the impedance comparison of the four catalysts at a current density of 10 mA cm-\u003csup\u003e2\u003c/sup\u003e. The impedances for TNT/IrO\u003csub\u003ex\u003c/sub\u003e, Ti/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, and TNT/IrO\u003csub\u003e2\u003c/sub\u003e were 18.65 Ω, 17.97 Ω, and 4.43 Ω, respectively, while TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e exhibited a much lower impedance of 1.78 Ω, indicating faster electron transfer rates. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed presents the equivalent circuit simulation of the TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e catalyst in 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee shows the double-layer capacitance of the four catalysts at scan rates ranging from 20 to 200 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e had the highest slope, suggesting the largest number of active sites per unit area (calculated data from Fig. S8). Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ef (details in Table. S9) compares the activity of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e with recently reported acidic OER electrocatalysts. The results show that, despite a higher Tafel slope, its overpotential outperforms the others. We can reduce the Tafel slope by optimizing testing methods, such as increasing the testing temperature or coating on super-wetting substrates[\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]. We used bar charts to visually compare the performance differences among the catalysts, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eg. The yellow bars (left) represent the overpotentials of the catalysts at a current density of 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, while the green bars (right) represent the current densities at an overpotential of 370 mV. The current densities for TNT/IrO\u003csub\u003ex\u003c/sub\u003e, Ti/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, and TNT/IrO\u003csub\u003e2\u003c/sub\u003e were 21.96 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, 103.72 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, and 24.16 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively, while TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e achieved a significantly higher current density of 152.36 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eh compares the mass activities of the catalysts at an overpotential of 370 mV. The mass activities for TNT/IrO\u003csub\u003ex\u003c/sub\u003e, Ti/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, and TNT/IrO\u003csub\u003e2\u003c/sub\u003e were 274.55 A g\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e, 1296.50 A g\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e, and 301.95 A g\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively, while TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e exhibited a much higher mass activity of 1904.50 A g\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e. Combining these results with Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea, we can more intuitively observe the advantages of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e.\u003c/p\u003e\n \u003cp\u003eIt is noteworthy that we observed the TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e catalyst to exhibit an exceptionally low OER overpotential of 220 mV at 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solution (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea), with a Tafel slope of 77.76 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb), significantly lower than that of the commercially available Ti felt/IrO\u003csub\u003e2\u003c/sub\u003e catalyst (overpotential of 250 mV, Fig. S10f). Additionally, we found that the acidic OER catalytic activity of this catalyst surpasses that of most recently reported catalysts. As an extension of our research, we prepared a sample by directly impregnating Ti felt with SnO\u003csub\u003e2\u003c/sub\u003e followed by loading IrO\u003csub\u003ex\u003c/sub\u003e (as shown in Fig. S11). Since SnO\u003csub\u003e2\u003c/sub\u003e is an amphoteric oxide capable of demonstrating considerable activity in solutions of different pH levels, we tested its OER performance in 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, 1 M KOH, and 0.5 M Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solutions. As illustrated in Fig. S10, given that Ti felt inherently outperforms Ti sheets, we reduced the Ir content to 40 \u0026micro;g cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for comparison with the commercial Ti felt/IrO\u003csub\u003e2\u003c/sub\u003e, as shown in Fig. S10f-h. As anticipated, the overpotential was 218 mV in 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, 275 mV in 1 M KOH, and, due to sluggish intrinsic kinetics, a poorer performance with an overpotential of 540 mV in 0.5 M Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solution. We further confirmed that this catalyst maintains stability for at least 20 h at a high current density of 0.1 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, 1 M KOH, and 0.5 M Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solutions.\u003c/p\u003e\n \u003cp\u003eStability is one of the important criteria to evaluate the performance of electrocatalysis. In this study, the electrochemical stability of TNT/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/IrO\u003csub\u003e2\u003c/sub\u003e and TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e catalysts was systematically evaluated using (CP). Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea shows the potential variation trend of the three catalysts during CP test. In the initial 50 h CP test, TNT/IrO\u003csub\u003e2\u003c/sub\u003e showed a significant increase in potential, while TNT/IrO\u003csub\u003ex\u003c/sub\u003e showed a large fluctuation in potential because IrO\u003csub\u003ex\u003c/sub\u003e was more soluble than IrO\u003csub\u003e2\u003c/sub\u003e. It is worth noting that after the introduction of the SnO\u003csub\u003e2\u003c/sub\u003e intermediate layer, the overpotential of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e catalyst was significantly reduced, and the phenomenon of TNT surface shedding was effectively inhibited (compare Fig. S12), and the dissolution degree of IrO\u003csub\u003ex\u003c/sub\u003e was also significantly reduced. Specifically, the TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e potential change was only 18 mV during 100 h of CP testing. To further evaluate the stability of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, we performed long-term CP tests at current densities of 30 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 50 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb). The results showed that the catalyst exhibited excellent stability with a potential change of 26 mV at 30 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at 200 h and 33 mV at 50 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at 100 h. By ICP-OES analysis of the amount of Ir dissolved in the electrolyte, it was found that the loss of Ir after 100 h 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e test was 2.2%, after 200 h 30 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e test was 5.6%, and after 100 h 50 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e test was 8.6%.\u003c/p\u003e\n \u003cp\u003eWe analyzed the microstructure of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e in detail to investigate the mechanism behind the enhancement of its electrochemical properties and structural stability. Fig. S13 shows the SEM images after 40 h CP test (a-d) at 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e current density and after 200 h CP test (e) at 30 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e current density. By comparing the Mapping images (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ee, g), HRTEM images (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ef-h), EDS spectra (Fig. S14) and XPS images (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ec and Fig. S15) of the catalyst before and after CP, it was found in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ec that Ir\u003csup\u003e4+\u003c/sup\u003e peak at 62.28eV dominated after surface reconstruction of Ir ions. A weak peak centered on Ir\u003csup\u003e3+\u003c/sup\u003e at 65.18 eV (A\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e4+\u003c/sup\u003e:A\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e3+\u003c/sup\u003e=5.801) showed higher activity than the initial peak (A\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e4+\u003c/sup\u003e:A\u003csub\u003eIr\u003c/sub\u003e\u003csup\u003e3+\u003c/sup\u003e=1.047). At the same time, combined with HRTEM image comparison, it can be found that Ir ions accumulate after CP (from point-like clusters to continuous large areas). It is worth noting that despite the migration of Ir particles after CP, the catalyst maintained good stability combined with chronopotentiometric and ICP-OES results, which was significantly better than the catalyst without SnO\u003csub\u003e2\u003c/sub\u003e loading.\u003c/p\u003e\n \u003cp\u003eBy comparing the CP curves of TNT/IrO\u003csub\u003ex\u003c/sub\u003e and TNT/IrO\u003csub\u003e2\u003c/sub\u003e, we can find that although TNT/IrO\u003csub\u003ex\u003c/sub\u003e exhibits a lower oxygen evolution potential, it demonstrates poor stability. This instability primarily results from the higher activity of IrO\u003csub\u003ex\u003c/sub\u003e compared to IrO\u003csub\u003e2\u003c/sub\u003e, which causes surface reconstruction and subsequently leads to the shedding of TNT. The inherent stability of Ir\u003csup\u003e4+\u003c/sup\u003e in rutile IrO\u003csub\u003e2\u003c/sub\u003e prevents surface remodeling induced by water oxidation[\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e]. The addition of the loose SnO\u003csub\u003e2\u003c/sub\u003e framework stabilizes and refines the IrO\u003csub\u003ex\u003c/sub\u003e particle binding to the framework. In order to observe the connection between IrO\u003csub\u003ex\u003c/sub\u003e and TNT in a more in-depth and intuitive way, the nanotubes were directly grown and then the catalyst was prepared, and finally peeled off to observe the connection state between them. As shown in Fig. S16, it can be observed that there is also an ultra-thin layer of SnO\u003csub\u003e2\u003c/sub\u003e between the composite material of IrO\u003csub\u003ex\u003c/sub\u003e and SnO\u003csub\u003e2\u003c/sub\u003e and TNT, which not only effectively stabilizes the structure of TNT due to its high specific surface area and excellent corrosion resistance, but also ensures the firm combination of IrO\u003csub\u003ex\u003c/sub\u003e and SnO\u003csub\u003e2\u003c/sub\u003e with TNT. At the same time, XRD tests of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e, TNT/IrO\u003csub\u003ex\u003c/sub\u003e and TNT/SnO\u003csub\u003e2\u003c/sub\u003e show that the position of diffraction peaks after the combination of IrO\u003csub\u003ex\u003c/sub\u003e and SnO\u003csub\u003e2\u003c/sub\u003e is superimposed. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ef-g shows that SnO\u003csub\u003e2\u003c/sub\u003e mainly exists (110) and (101) crystal planes. Many studies have shown that the surface of SnO\u003csub\u003e2\u003c/sub\u003e (110) is a metastable surface, which can be used as an active site for the activation of O\u003csub\u003e2\u003c/sub\u003e molecules. The adsorption of O\u003csub\u003e2\u003c/sub\u003e molecules by van der Waals force after hydroxylation on the crystal surface will increase the electrical conductivity of the crystal surface[\u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e]. At the same time, the most active (110) crystal face of IrO\u003csub\u003e2\u003c/sub\u003e can be found by TEM, which shows the highest activity in OER due to its surface structure and electronic properties. Moreover, the surface energy of the (110) crystal plane is low, which is conducive to the adsorption and desorption of oxygen, thus improving the catalytic efficiency of OER[\u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e]. There was almost no change in the position of Sn 3d before and after CP (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ed), which also Eroved the stability of IrO\u003csub\u003ex\u003c/sub\u003e after reconstruction to a certain extent. Based on the synergistic effect of these factors, TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e has good activity and stability.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eIn summary, a simple method has been developed to synthesize highly efficient thin film TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e catalyst. Different from the traditional powder loading strategy, this study proposes a three-dimensional nanostructured support design: TNT prepared by anodic oxidation is used as a conductive skeleton, and a multistage heterostructure is constructed through the SnO\u003csub\u003e2\u003c/sub\u003e intermediate layer. Through XRD, XPS and morphology analysis, this design optimizes the electronic structure of IrO\u003csub\u003ex\u003c/sub\u003e through the SOSI effect of TNT on SnO\u003csub\u003e2\u003c/sub\u003e and IrO\u003csub\u003ex\u003c/sub\u003e composites. Meanwhile, SnO\u003csub\u003e2\u003c/sub\u003e serves as an intermediate layer to refine IrO\u003csub\u003ex\u003c/sub\u003e particles to enhance their catalytic activity and stability, while using proton conduction properties to promote efficient water decomposition in interfacial mass transfer process. Combined with H\u003csub\u003e2\u003c/sub\u003e-TPR tests, it was found that the TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e catalyst was difficult to be reduced, and stable IrO\u003csub\u003ex\u003c/sub\u003e was one of the key factors for efficiently catalyzing OER reactions. Therefore, this study provided a new idea for developing low noble metal loading, efficient and stable acidic OER catalysts, and demonstrated the important role of multistage interface engineering in electrocatalysis.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003e\u003cstrong\u003eSMSI/SOSI\u003c/strong\u003e\u0026nbsp; \u0026nbsp;Strong metal/oxid-support interaction\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOER\u003c/strong\u003e\u0026nbsp; \u0026nbsp;Oxygen evolution reaction\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCP\u003c/strong\u003e\u0026nbsp; \u0026nbsp;Chronopotentiometry\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTNT\u003c/strong\u003e\u0026nbsp; \u0026nbsp; Titanium dioxide nanotube array\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePEMWE\u003c/strong\u003e\u0026nbsp; \u0026nbsp;Proton exchange membrane water electrolyzer\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eXRD\u003c/strong\u003e\u0026nbsp; \u0026nbsp;X-ray diffraction\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSEM\u0026nbsp;\u003c/strong\u003e\u0026nbsp; Scanning electron microscope\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEDS\u003c/strong\u003e\u0026nbsp; \u0026nbsp;Energy-dispersive X-ray spectroscopy\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTEM\u003c/strong\u003e\u0026nbsp; \u0026nbsp;Transmission electron microscope \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eXPS\u003c/strong\u003e\u0026nbsp; \u0026nbsp;X-ray photoelectron spectrometer\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eICP-OES\u0026nbsp;\u003c/strong\u003eInductively coupled plasma optical emission spectrometer\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eBET\u003c/strong\u003e\u0026nbsp; \u0026nbsp;Brunauer-Emmet-Teller\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eBJH\u003c/strong\u003e\u0026nbsp; \u0026nbsp;Barrett-Joyner-Halenda\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eH\u003csub\u003e2\u003c/sub\u003e-TPR\u003c/strong\u003e\u0026nbsp; \u0026nbsp;H\u003csub\u003e2\u003c/sub\u003e temperature-programmed reduction\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLSV\u003c/strong\u003e\u0026nbsp; \u0026nbsp;linear sweep voltammetry\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics and Consent to Participate\u0026nbsp;\u003c/strong\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for Publication\u0026nbsp;\u003c/strong\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interest\u003c/strong\u003e No competing interests.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u0026nbsp;\u003c/strong\u003eSyntheses, characterizations, data analyses, manuscript writing and activity tests by Q.Lu, X.Huang, Y.Zhang; Work led by D.Fan, F.Han, C.Sundaram, H.Lu, Y.Liu; Manuscript validation by all.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003eThis work was supported by Guangxi Science and Technology Development Program \u0026nbsp;(AA24263043,AD22035102), National Natural Science Foundation of China (22165005，22262010).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of Data and Materials\u0026nbsp;\u003c/strong\u003eData is provided within the manuscript or supplementary information files\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u0026nbsp;\u003c/strong\u003eThis work was supported by Guangxi Science and Technology Development Program \u0026nbsp;(AA24263043,AD22035102), National Natural Science Foundation of China (22165005，22262010).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHwang J, Rao RR, Giordano L, Katayama Y, Yu Y, Shao-Horn Y (2017) Perovskites in catalysis and electrocatalysis. 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J Am Chem Soc 146:11719\u0026ndash;11725\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"catalysis-letters","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Catalysis Letters](https://link.springer.com/journal/10562)","snPcode":"10562","submissionUrl":"https://submission.springernature.com/new-submission/10562/3","title":"Catalysis Letters","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"IrOx, mesosphere, OER, TNT, SnO2","lastPublishedDoi":"10.21203/rs.3.rs-6261430/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6261430/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe construction of the strong oxid-support interaction (SOSI) between the support and the active component is crucial for regulating the atomic conTuration and electronic structure of the catalyst. In this study, the electrocatalytic oxygen evolution (OER) performance of IrO\u003csub\u003ex\u003c/sub\u003e in acidic electrolyte was significantly improved by constructing titanium dioxide nanotube array (TNT) and SnO\u003csub\u003e2\u003c/sub\u003e double intermediate layer. The overpotential of TNT/SnO\u003csub\u003e2\u003c/sub\u003e/IrO\u003csub\u003ex\u003c/sub\u003e at the current density of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e is 220 mV, which is 69 mV and 93 mV lower than that of directly loaded TNT/IrO\u003csub\u003ex\u003c/sub\u003e (289 mV) and TNT/IrO\u003csub\u003e2\u003c/sub\u003e (313 mV), respectively. In addition, the introduction of SnO\u003csub\u003e2\u003c/sub\u003e significantly improved the stability of the catalyst, and after 100 h static chronopotentiometry (CP) test at the current density of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e, the potential change was only 18 mV, much lower than that of TNT/IrO\u003csub\u003e2\u003c/sub\u003e (175 mV) and TNT/IrO\u003csub\u003ex\u003c/sub\u003e (50 mV). Through in-depth surface morphology and structure analysis, it is found that IrO\u003csub\u003ex\u003c/sub\u003e is anchored on the SnO\u003csub\u003e2\u003c/sub\u003e meslayer and uniformly dispersed. At the same time, TNT array has strong interaction with IrO\u003csub\u003ex\u003c/sub\u003e, and the addition of the intermediate layer SnO\u003csub\u003e2\u003c/sub\u003e can effectively stabilize Ir from being reduced. The results showed that the synergistic effect of SnO\u003csub\u003e2\u003c/sub\u003e and TNT significantly enhanced the catalytic activity of IrO\u003csub\u003ex\u003c/sub\u003e. In summary, this study successfully developed an efficient and stable acidic OER catalyst through multistage interface engineering design, providing a new solution for the industrial application of low iridium supported catalysts.\u003c/p\u003e","manuscriptTitle":"Design of Hierarchical Structured Catalysts: SnO2-Modified TiO2 Nanotube Arrays Enabling Ultra-Low Overpotential Acidic Oxygen Evolution Reaction","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-18 09:56:34","doi":"10.21203/rs.3.rs-6261430/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-04-11T13:04:05+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-08T06:52:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"122178063228370615649569588083039552849","date":"2025-03-29T23:01:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-29T18:32:26+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-29T02:40:00+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-29T02:39:06+00:00","index":"","fulltext":""},{"type":"submitted","content":"Catalysis Letters","date":"2025-03-19T12:05:04+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"catalysis-letters","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Catalysis Letters](https://link.springer.com/journal/10562)","snPcode":"10562","submissionUrl":"https://submission.springernature.com/new-submission/10562/3","title":"Catalysis Letters","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"5ad39b9f-7687-44e9-aa89-d53518d2051e","owner":[],"postedDate":"April 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-04-24T11:38:37+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-18 09:56:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6261430","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6261430","identity":"rs-6261430","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}