Comprehensive\nAnalysis of the Gradient Porous Transport\nLayer for the Proton-Exchange Membrane Electrolyzer

A reasonable\nporous transport layer (PTL) is crucial to decreasing\nthe mass-transfer loss in proton-exchange membrane water electrolyzers\n(PEMWEs). In this study, it was experimentally demonstrated that the\ngradient porosity PTL is beneficial in improving the performance of\nelectrolyzers. The research comprehensively investigates the impact\nof gradient porosity PTL structures on the performance of the PEMWE,\nconsidering mass transfer and interfacial contact. It offers insights\ninto the two-phase (oxygen–water) flow transport mechanisms\nwithin the PTLs using a 2D numerical model based on the actual PTL\ngeometry. At the microscopic level, it analyzes how the interfacial\ncontact impacts proton and electron transport mechanisms, affecting\nnot only the contact resistance but also the number of effective catalytic\nsites for the oxygen evolution reaction. Experimental results demonstrate\nthat the cis-gradient porosity PTL leads to a performance enhancement\nof 9.3% at 2.2 A/cm<sup>2</sup>. Numerical simulations reveal that\nthe drivers of oxygen transport include the surface tension of the\nfibers and the pressure drop influenced by the local PTL porosity.\nFurther analysis indicates that the lower oxygen saturation in the\nbottom region of the PTL with cis-gradient porosity favors a lower\noxygen coverage area in the catalyst layers (CL) since the narrower\npore space and higher capillary pressure increase the number of water\nflow paths into the CL. Overall, this study provides valuable insights\nfor designing high-performance PTLs for use in electrolyzers.