Medium-temperature (up to 200°C) polymer membrane water (steam) electrolyzers are attractive due to improved thermodynamics and kinetics, and reduced specific electric energy consumption for electrolytic gas generation. Moreover, applications of alternative polymer membranes (such as acid-doped polybenzimidazoles) less sensitive to the presence of the impurities in water (in contrast to Nafion® and its analogs) significantly simplify the water treatment system.
The aim of this study is to develop electrocatalytic layers with high and stable proton and electron conductivity and mass transfer efficiency under conditions of strong electric/thermal/chemical fields for medium-temperature polymer membrane water electrolysis. The most severe conditions are associated with anodes, in which active oxygen and oxygen radicals are generated at increased temperatures and low pH values. Both mathematical modeling and experimental techniques have been applied to create a three-dimensional stable conducting network of pores, electrolytes, and supported catalytically active nanoparticles. The results show that IrO2 supported with Ta2O5 or TaC could be potentially used as catalysts for anode of medium-temperature electrolyzers with polybenzimidazole-based membranes doped with H3PO4. In particular, even a few % of Ta2O5 improves IrO2 activity and stability towards the oxygen evolution reaction, as well as reducing noble metal loading. It was shown that the optimum catalyst structure and composition depend on the applied synthesis method (chemical or physical). Electrocatalytic layers with a component concentration gradient are recommended. Numerical calculations have shown that in the anode electrocatalytic layer, the main reaction zone is shifted towards the gas diffusion electrode. Hence, during the formation of the catalyst layer, it is recommended to increase the concentration of the catalyst across the catalyst layer thickness (from the membrane towards the gas diffusion electrode). For the cathode, the use of carbon-supported Pt nanoparticles with a reverse concentration gradient is recommended.
The research was supported by RSF (project No. 25-29-00545).
