Pt-WxC nano-composites as an efficient electrochemical catalyst for oxygen reduction reaction

Abstract

WxC and Pt-WxC (x=1 or 2) nano-catalysts supported on carbon black were synthesized using a simple co-impregnation and thermal reduction method. An enhanced performance in the electro-reduction of oxygen in an alkaline media is achieved when Pt is incorporated into the WxC catalyst. In the presence of WxC, Pt loading in carbon-supported Pt-WxC catalysts can be reduced to as low as 5% while the oxygen reduction reaction (ORR) performance of the Pt-WxC catalyst remains comparable to that of a commercially available 20% Pt/C catalyst. This indicates that the Pt-WxC composite material is more cost-efficient in ORR than the conventional Pt catalysts since WC is three orders of magnitude less expensive than Pt. WxC alone is not an excellent ORR catalyst, but its addition can greatly enhance the ORR activity of Pt where it serves as an electronic promoter by preventing Pt from oxidation and modifying Pt d-band structure via charge flow from W2C to Pt which is confirmed by XPS and UPS. It is found by XRD and TEM characterizations that WxC may play a role as a structural promoter by preventing agglomeration of Pt particles. On the other hand, Pt is found to promote the formation of WxC during the synthesis and also to stabilize the WxC during ORR. The findings on the synergistic effects of this hybrid material are important in assisting the future design of more efficient and durable ORR catalysts. © 2012 Elsevier Ltd.