Sol-Gel Preparation and Acidic Oxygen Evolution Performance of IrO_x Catalysts AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY24090003

Chinese Library Classification Number:TQ426.83

Citation Information:

Climate change，environmental pollution，and the depletion of fossil fuel reserves urgently call for the development of clean and renewable energy sources. Hydrogen is considered one of the most promising energy carriers due to its high energy density，abundance，and zero-pollution combustion. Water electrolysis，which splits water （H₂O） into hydrogen （H₂） and oxygen （O₂） via the oxygen evolution reaction （OER） and hydrogen evolution reaction （HER） driven by electrical energy，represents the cleanest hydrogen production technology. Among various electrolysis technologies，proton exchange membrane （PEM） water electrolysis stands out as a key green hydrogen production method due to its low ohmic loss，fast response，and high hydrogen purity. However，the strongly acidic environment of PEM membrane，further intensified locally by the anodic OER，necessitates that OER catalysts possess both high activity and exceptional corrosion resistance. Iridium oxide （IrO_x） is currently one of the most stable OER catalysts under acidic conditions. Nevertheless，the catalytic performance of IrO_x is highly dependent on its synthesis method and processing conditions，prompting extensive research into optimizing its preparation. Sol-gel method is widely employed for nanomaterial synthesis due to its simplicity，versatility，and scalability. In this approach，inorganic salts or metal alkoxides are used as precursors to form a homogeneous sol，which subsequently evolves into a three-dimensional gel network through hydrolysis，condensation，or other chemical transformations. The gel can then be converted into the desired nanomaterial via post-treatments such as calcination or heat treatment. By precisely controlling the sol composition，gelation conditions，and post-treatment parameters，the morphology，structure，and properties of the final product can be finely tuned. Moreover，the highly dispersed nature of the gel network often enables the formation of ultrasmall nanoparticles. In this study，the influence of various organic complexing agents （citric acid，glucose，and others） on the structural characteristics and acidic OER performance of IrO_x nanoparticles synthesized via sol-gel method was systematically investigated. The morphology，crystal structure，and surface composition of the as-prepared electrocatalysts were characterized by scanning electron microscopy （SEM），X-ray diffraction （XRD），and transmission electron microscopy （TEM）. XRD analysis confirmed that the as-synthesized IrO_x catalysts exhibited diffraction patterns consistent with standard IrO₂，while SEM and TEM revealed nanoscale particle sizes with poorly defined lattice fringes，indicating low crystallinity. Electrochemical evaluations，including polarization curves，Tafel plots，Bode plots，electrochemical impedance spectroscopy （EIS），and electrochemical active surface area （ECSA） measurements，were conducted to assess OER performance. Notably，IrO_x nanoparticles synthesized with citric acid as the complexing agent （denoted IrO_x-CA） required an overpotential of only 266 mV to achieve a current density of 10 mA·cm^-2，significantly outperforming commercial iridium oxide and many Ir-based catalysts reported in the literature. Tafel slope of IrO_x-CA was 92 mV·dec^-1，markedly lower than that of commercial IrO₂ （109 mV·dec^-1）. EIS measurements showed that IrO_x-CA exhibited the smallest semicircle diameter in Nyquist plots and the smallest phase angle in Bode plots，indicating the lowest charge transfer resistance and fastest electrode kinetics. Furthermore，ECSA analysis revealed that IrO_x-CA possessed the largest electrochemically active surface area，corresponding to the highest density of exposed active sites，consistent with its superior morphological characteristics and catalytic activity. To evaluate the practical applicability of IrO_x-CA in PEM water electrolysis，membrane electrode assemblies （MEAs） were fabricated using IrO_x-CA as the anode catalyst and commercial Pt/C as the cathode catalyst. The assembled PEM electrolyzer demonstrated excellent durability，maintaining stable operation for 290 h at a current density of 50 mA·cm^-2 without significant voltage degradation，underscoring the outstanding stability of IrO_x-CA under realistic operating conditions. In summary，this work systematically elucidated the role of different organic complexing agents in modulating the acidic OER performance of IrO_x nanoparticles synthesized via sol-gel method. Among the complexing agents studied，citric acid yielded IrO_x-CA with the largest electrochemical active area，the highest catalytic activity，and exceptional long-term stability. These findings provided valuable insights into the rational design and development of high-performance IrO_x-based electrocatalysts for acidic OER，contributing to the advancement of efficient and durable PEM water electrolysis technologies.