Enhanced Oxygen Reduction Reaction Activity and Stability of the Ptco/C Catalysts with Pt-Enriched Surface Layer: An Investigation of the Effect on Acid-Leaching During the De-Alloying Process

Abstract

One of the key issues hinders large-scale commercial application of the proton exchange membrane fuel cells is the unsatisfactory performance of the Pt cathodic electrocatalysts for oxygen reduction reaction (ORR). The generally accepted solution is to alloy Pt with transitional metals at high temperatures. These catalysts are commonly prepared through high temperature annealing followed by de-alloying in acidic electrolytes. This work focuses on the effects of acid de-alloying on the structure of the Pt2Co/C catalysts and correlates with their activity and stability for ORR. It is found that the overall performance of the Pt2Co/C is greatly affected by the acid treatment temperatures (40, 60 and 80°C). When the Pt2Co/C is treated at 40°C in HNO3, the Pt2Co/C-40 displays the highest activity and stability, which is double-confirmed both by half-cell (rotating disk electrode) and single cell (membrane electrode assembly) evaluations. The catalyst treated under this condition reveals an alloyed structure with 3-4 Pt atomic layers and an optimal particle size of 4.8 nm. Meanwhile, the performance enhancement is possibly also aided by the introduced N-sources during synthesis. This synthesis offers an easier and scalable manner to produce Pt-alloyed catalyst with enhanced activity and stability.

Keywords: Oxygen reduction reaction, Acid treatment, De-alloying, Pt2Co/C