Platinum–Cobalt Alloy Nanosheets Derived from Cobalt-Substituted Platinum Oxide Nanosheets for Oxygen Reduction Electrocatalysts

The sluggish kinetics of the oxygen reduction reaction limit the overall efficiency of polymer electrolyte fuel cells, hindering the widespread deployment of fuel cell vehicles and residential fuel cells. While PtCo alloy nanoparticles supported on carbon have been applied to practical fuel cells, Pt-based electrocatalysts with higher activity and enhanced durability remain essential to meet cost and resource targets. This study presents the first synthesis of metallic PtCo alloys with an atomically thin metallic nanosheet structure, exhibiting superior surface area, specific activity, and mass activity, as well as durability compared to conventional nanoparticle counterparts. The metallic PtCo alloy nanosheets are synthesized via thermal reduction of exfoliated cobalt-substituted platinum oxide monolayer nanosheets, which are also reported here for the first time. The Co-substituted platinum oxide nanosheets, as well as the reduced metallic nanosheets, were thoroughly characterized using a combination of diffraction, scattering, spectroscopy, and microscopy techniques, all of which confirmed the successful synthesis of PtCo alloy nanosheets with varying Co compositions. Carbon-supported PtCo alloy nanosheets were evaluated for the oxygen reduction reaction in an acidic electrolyte. The highest performance was obtained with a PtCo alloy nanosheet with 12 at.% Co (i.e., Pt 0.88 Co 0.12 ) with mass activity 1.4, 1.7, and 2.0 times higher than nondoped Pt nanosheets, PtCo nanoparticles, and Pt nanoparticles, respectively. Furthermore, the alloy nanosheets demonstrated superior durability, with negligible loss of Co after accelerated stress tests, highlighting the advantage of using a nanosheet morphology over that of nanoparticles. The enhanced performance is discussed on the basis of the high surface area of the atomically thin nanosheets combined with the higher specific activity due to the nanosheet morphology and electronic effects induced by Co alloying.