In polymer electrolyte water electrolysis (PEWE) oxygen evolution reaction (OER) kinetics are a major efficiency limitation. At least with thin membranes, the anode kinetic overvoltage is the main voltage loss. The reaction mechanism for IrO₂ in the most stable surface (110) configuration in acid environment was investigated by DFT calculation in literature and postulated according to reactions R1 to R4 [1]. The concept of gas feed electrolysis enables the identification of the rate determining step in the OER mechanism by using the additional freedom of water concentration variation. Therefore the activity of water was varied between 0.6 to 0.95 at 80°C. The determined reaction order is compared to proposed reaction mechanisms in literature.

The used materials were validated by determination of the IrO₂ activity as function of the loading. CCMs were prepared by automated spray coating process using IrO₂/TiO₂ catalyst. The loadings were varied from 1mg/cm² to 3mg/cm². In analogy to liquid PEWE, the CCMs were tested in cell configuration by using commercial Ti sinter based porous transport layers. The loading trends of exchange current densities estimated from Tafel fitting were compared to specific capacity determined by cyclic voltammetry at 1.0V. The linear dependence of specific capacity with loading exemplifies a constant roughness factor as shown in Figure 1. The catalyst layer utilization doesn’t show any impact on loading/catalyst layer thickness.

Reference

[1] J. Rossmeisl, Z.W. Qu, H. Zhu, G.J. Kroes, J.K. Nørskov, Electrolysis of water on oxide surfaces, J. Electroanal. Chem., 607 (2007) 83-89.