Electrochemical method to quantitate gas transport resistance at immediate vicinity of catalyst surface in polymer electrolyte fuel cells

Abstract

Reduction in the gas transport resistance in the immediate vicinity of the interface between the catalyst metal and the ionomer thin film is one of the primary challenges in achieving high-performance polymer electrolyte fuel cells with a low use of precious metals. In this study, a new electrochemical method was developed to evaluate the transport resistance separately from any other resistances in a porous electrode using only a single target sample. The transport resistance lying on the catalyst surface was evaluated from its inversely proportional dependence on the active surface area, which is controlled by an adsorbate that deactivates the catalyst surface; moreover, its coverage is quantifiable and controllable. After the coverage control, the limiting current technique provides the transport resistance of a catalyst layer. As a demonstration, an oxygen transport resistance lying on a Pt-surface in a Pt/C catalyst layer was investigated using CO as an adsorbate. The resistance lying on the Pt-surface was successfully evaluated from the CO-coverage dependence of the catalyst layer resistance. In particular for the reactant gas of oxygen, CO is not suitable for blocking the adsorbate over 40 °C, and another candidate that does not interfere with O2 is required.