Crossover breakdown analysis: Impact of mass and charge transport processes on H2 crossover in PEM water electrolysis

This work investigates hydrogen crossover in proton exchange membrane (PEM) water electrolysis, emphasizing the influence of the cathode catalyst layer (CCL). A 1D model coupling mass and charge transport processes is proposed and validated against various literature data. It enables a breakdown of different contributions to crossover. The theoretical diffusion through the membrane at zero current density therefore serves as the baseline. Convection induced by electro-osmotic drag reduces the net crossover. Two other phenomena increase crossover with current density: first, the transfer of dissolved H 2 from production site into CCL pores, causing supersaturation within the ionomer and second, the transport of H 2 through the CCL pores, increasing local gas pressure. The first mechanism predominates but weakens with increasing CCL thickness, while the second intensifies. These phenomena are analyzed for different CCLs. This investigation contributes to a deeper understanding of crossover phenomena and aids in optimizing CCLs.