Combinatorial Studies of Palladium-Based Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells.

Hydrogen fuel cells have emerged as promising, potentially renewable energy-based, energy conversion technologies for powering electric vehicles. However, the sluggish oxygen reduction reaction (ORR) at the cathode has remained a longstanding challenge and requires the design of nonplatinum electrocatalysts with high activity and, ideally, low cost. Here, we present a combinatorial study of Pd-Cu thin-film electrodes with well-defined composition and structures, prepared by magnetron sputtering, as a fast method for assessing the ORR activity of binary alloys. This represents a facile catalyst screening method, using replaceable glassy carbon disk electrodes, which enables the rapid and reliable evaluation of ORR activity using standard rotating disk electrode (RDE) measurements. Among nine Pd-Cu alloys, Pd50Cu50 was identified as the most promising composition for the ORR and employed as a target for nanoparticle synthesis. The PdCu nanoparticles, supported on carbon, achieved a mass-specific and surface-specific activity, 3 and 2.5 times, respectively, as high as Pd/C in 1 M KOH. PdCu/C further exhibited an impressive durability with only 3 and 13 mV negative shifts in the half-wave potential after 20000 and 100000 potential cycles, respectively. The combinatorial approach guiding the nanoparticle synthesis, described herein, provides an optimized high-throughput screening method for other binary or ternary alloys as fuel cell electrocatalysts.