Exploring Fuel Cell Cathode Materials with Ab Initio High Throughput Calculations

One of the most critical problems hampering development of proton exchange membrane fuel cells (PEMFC) is finding cost effective and stable catalysts to promote the oxygen reduction reaction (ORR) at relevant temperatures, voltages and pH environment. According to the Sabatier principle, ORR activity is controlled by oxygen binding to the surface which has to be not too weak ( to split O2 molecules) and not too strong ( to allow easy desorption of hydroxyl and water products). For this purpose Platinum is found to be the most effective elemental material, albeit its surface binds oxygen a little stronger than would be optimal. Recently, some Pt alloys (most notably Pt3Co) were reported to have ORR activity superior to that of pure Pt. Our own measurements of catalytic activity on rotating disk electrodes (RDE) show similar improvement of Pd3Co with respect to pure Pd. It has been suggested that this enhancement is mostly due to the chemical modification of the host surface by the subsurface base atoms. In this paper we argue that another perhaps more important factor controlling surface activity is mechanical surface strain in this case induced by alloying. We apply high throughput calculation methodology and the plane wave density functional theory (implemented in Materials Studio and CASTEP) to simultaneously assess surface stability of Pt3Co and Pd3Co alloys and their catalytic activity with respect to ORR.