Significant reduction of the precious metal catalyst loading is one of the key challenges for the commercialization of proton-exchange membrane water electrolyzers. In this work we combine IrOx nanofibers with a conventional nanoparticle-based IrOx anode catalyst layer. With this hybrid design we can reduce the iridium loading by more than 80% while maintaining performance. In spite of an ultralow overall catalyst loading of 0.2 mgIr/cm2, a cell with a hybrid layer shows similar performance compared to a state-of-the-art cell with a catalyst loading of 1.2 mgIr/cm2 and clearly outperforms identically loaded reference cells with pure IrOx nanoparticle and pure nanofiber anodes. The improved performance is attributed to a combination of good electric contact and high porosity of the IrOx nanofibers with high surface area of the IrOx nanoparticles. Besides the improved performance, the hybrid layer also shows better stability in a potential cycling and a 150 h constant current test compared to an identically loaded nanoparticle reference.

Partial substitution of the Nafion binder with PEDOT:PSS resulted in higher efficiency of proton exchange membrane water electrolyzers thanks to the improved in-plane electrical conductivity in the electrode.

Optimizing the catalyst layer of polymer electrolyte membrane fuel cells and water electrolyzers requires a good understanding of its properties. The in-plane electrical resistance of the catalyst layer is a key property, which impacts the overall cell performance. In this work, we present a simple method to measure the in-plane electrical resistance of catalyst layers under various conditions based on the transfer length method. The applicability of the method was demonstrated on four examples: 1) Placing the compact setup in a climate chamber, showed that reducing the relative humidity from 95 % to 40 % yields a reduction of the resistivity of 15 % in a fuel cell cathode catalyst layer; 2) graphitizing CNovel™ carbon support reduces the resistivity by 98 % in a fuel cell cathode catalyst layer; 3) adding an electrically conductive polymer as electrode binder lowers the in-plane resistivity of a water electrolyzer anode by 50 %; 4) adding IrO2-nanofibers to a low-loaded IrO2-nanoparticle anode lowers its resistivity by 60 %. The broad range of applications in this work confirms the versatility of the setup enabling widespread application. The method hence contributes to an improved deconvolution of different loss mechanisms including electrical in-plane resistivity.