Unraveling the impact of compression on the performance of porous transport layers in water Electrolyzers

This work systematically investigates the impact of compression on the properties of the porous transport layer (PTL) of polymer electrolyte membrane (PEM) water electrolyzers. We elucidate changes in morphology, topology, transport properties, gas transport, and electrochemical performance during compression. First, a stochastic reconstruction method and compression model are deployed to reconstruct a digital PTL and adjust different ratios of compression. Pore-scale modeling (PSM) and Lattice Boltzmann modeling (LBM) are then adopted to solve for the electrical and thermal conductivity of the PTLs and the oxygen removal within PTLs filled with water. Lastly, the computed PTL-related parameters are used to quantify the impact of compression on the electrochemical performance of the electrolyzer. The results show that the compression leads to flatter contact surfaces of the PTL material with the catalyst layer. And, better interfacial contact for the oxygen evolution reaction is generated under compression. Both a lower porosity and a more compact structure due to compression enhance the electrical and thermal conductivity. The sluggish oxygen transport within the compressed PTL is partially offset by the shorter propagation pathways and more favorable oxygen concentration distribution. The electrochemical simulation reveals that a moderate compression is advantageous for electrolyzer operation and an overpotential reduction of 186 mV can be obtained by compressing the PTL thickness by up to 30 %. These results emphasize the potential for improving interfacial contact and mass transport through compression, offering a pathway to enhance performance and durability in large-scale PEM electrolyzers. The findings from this study provide valuable insights into the optimization and application of PTLs, i.e., PTLs should be designed to ensure adequate interfacial contacts and effective pore networks, which can guide the design of more efficient electrolyzers for industrial applications.