Alloyed Pt–Zn Oxygen Reduction Catalysts for Proton Exchange Membrane Fuel Cells
Samuel Dull, Olga Vinogradova, Shicheng Xu, David M. Koshy, Per Erik Vullum, Jan Torgersen, Sebastian Kirsch, Venkatasubramanian Viswanathan, Thomas F. Jaramillo, Fritz B. Prinz
Abstract
Better oxygen reduction catalysts are needed to appreciably increase the efficiency of proton exchange membrane fuel cells. In this work, high-activity Pt–Zn alloy catalysts were prepared using two distinct synthetic approaches. The first─where Zn was introduced to Pt nanoparticles via atomic layer deposition─led to a 30% increase in Pt-mass-normalized fuel cell activity. Density functional theory calculations elucidated the origin of this enhancement and motivated the preparation of an alloy with increased Zn content. To this end, a fabrication technique leveraging Zn electroplating was employed to prototype a second Pt–Zn alloy with a rotating disk electrode (RDE). The higher-dosed structure (∼19 at. % Zn) delivered exemplary activity (MA = ∼3 A/mgPt), but the synthetic approach was not amenable to membrane electrode assembly (MEA) fabrication. An Arrhenius analysis was carried out to project the hypothetical catalytic enhancement under fuel cell operating conditions. This exercise introduced a discussion on the reduced activity observed in MEAs relative to the benchtop RDE setups used more ubiquitously for catalyst evaluation.