The critical role of the anode porous transport layer/catalyst layer interface of polymer electrolyte membrane water electrolyzers: A parametric analysis

Abstract

Reducing the dependency of proton exchange membrane water electrolyzers (PEMWE) on precious metals, such as iridium (Ir), is necessary to develop a widespread green hydrogen system. This challenge requires a careful design of the interface between the anode porous transport layer (PTL) and the catalyst layer (CL). A comprehensive numerical analysis of relevant parameters that govern the behavior of the anode PTL/CL interface is presented. Calculations are also combined with an experimental characterization of the thickness and electrical conductivity of an unsupported CL as a function of Ir loading. The results show that the in-plane electrical resistance at the anode PTL/CL interface plays a critical role in cell performance. Reaching an acceptable electrical resistance at low Ir loading (𝐿Ir ≃ 0.1 mgIr , cm−2) can be accomplished through the incorporation of a micrometer-sized microporous layer (MPL) onto the PTL or the preparation of bimodal CLs with a secondary conductive phase. Further reduction of the Ir loading to the ultra-low regime (𝐿Ir ≲ 0.1 mgIr , cm−2) may require the use of nanometer-sized MPLs with unsupported CLs or micrometer-sized MPLs with bimodal CLs. Furthermore, the decline of the volume reactive area at ultra-low Ir loading needs a maximization of the exchange current density and the specific electrochemical surface area, and a decrease of the catalyst oxygen coverage factor in the anode CL.