Multi-scale revealing how real catalyst layer interfaces dominate the local oxygen transport resistance in ultra-low...

In view of a catalyst layer (CL) with low-Pt causing higher local transport resistance of O₂ (R_local), we propose a multi-study methodology that combines CO poisoning, the limiting current density method, and electrochemical impedance spectroscopy to reveal how real CL interfaces dominate R_local. Experimental results indicate that the ionomer is not evenly distributed on the catalyst surface, and the uniformity of ionomer distribution does not show a positive correlation with the ionomer content. When the ionomer coverage on the supported catalyst surface is below 20 %, the ECSA is only 10 m²·g^-1, and the ionomer coverage on the supported catalyst surface reaches 60 %, the ECSA is close to 40 m²·g^-1. The ECSA has a positive correlation with ionomer coverage. Because the ECSA is measured by CO poisoning, it can be inferred that the platinum contacted with ionomer can generate effective active sites. Furthermore, a more uniform distribution of ionomer can create additional proton transport channels and reduce the distance for oxygen transport from the catalyst layer bulk to the active sites. A higher ECSA and a shorter distance for oxygen transport will reduce the R_local, leading to better performance.