Impact of Multiphase Mass and Energy Transport Processes on Water Electrolysis in Polymer Electrolyte Membrane Cells

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Due to the continuous increase of renewable energy in the energy distribution system, the increase of surplus electrical energy supply is foreseeable. In this context, water electrolysis is a key technology able to convert electrical energy into hydrogen which can be used as energy storage medium or can be fed into the value chains of the chemical industries. Besides conventional alkaline water electrolysis, a water electrolysis technology based on a Polymer Electrolyte Membrane (PEM) is discussed since several years, which is the focus of this grant proposal. The particular advantages of PEM water electrolysis are higher attainable current densities, higher voltage efficiency, and higher load flexibility. Current disadvantages include far lower technical maturity, shorter life time, and higher specific costs compared to alkaline water electrolysis. The main reason for the higher costs of PEM electrolysis cells is, apart from expensive materials used in these cells, the far too small dimension of the single cells from which large-scale PEM electrolysis stacks should be built in the future. The prerequisite for the further increase of the cell area is the comprehensive understanding of the two-phase mass and energy transport phenomena taking place in PEM electrolysers. Controlling these transport phenomena is of paramount importance for optimal process operation and optimal design of the electrolysis cells. Thus, the aim of the here proposed project is to analyze and quantify the impact of two-phase mass and energy transport phenomena on the performance of PEM electrolysis cells. The work plan comprises (1) the experimental characterization and the model-based description of the local transport phenomena in the porous current collectors, the catalytic layers and the polymer electrolyte membrane, (2) the experimental characterization of the transport phenomena occurring in the anode flow channels of the electrolysis cell, and (3) the investigation of the coupling of transport processes taking place in the channel and in the membrane-electrode assembly, as well as their impact on the operational behavior of the cell as a whole.