Probing current density distribution over a catalyst layer at the micrometer scale in a water electrolyzer

Abstract

A better understanding of current density distribution, i.e. the true electrochemical reaction behavior, in electrochemical energy devices has long been desired. However, it is considered very challenging to comprehensively observe the current density within real PEMWE devices at the micrometer scale as the components are densely assembled by metal plates. Thus, an ex situ method for micron-level current density detection is proposed in this study, where the highly active but unstable characteristic of RuO₂ in the oxygen evolution reaction (OER) in acidic media was fully utilized. Compared to the average current density at the macrometer scale, the detection of current density at the micrometer scale can provide more valuable insights for the rational design of low iridium loading membrane electrodes. Our study showed that the border area of the PTL/CL interface exhibited the highest current density under any working condition. The untouched area exhibited the lowest current density because of poor conditions, which can be attributed to the combined effects of conductivity and mass transfer. Besides, an experimentally validated numerical model was also proposed, and the simulation results indicated that porosity was the most critical factor affecting the performance of PEMWE, and the optimized porosity was about 0.3. The new insights into the localized current density derived from this method open a new avenue for optimization of the performance and cost reduction of PEMWE.