Extended-Surface Thin-Film Platinum Electrocatalysts with Tunable Nanostructured Morphologies

Abstract

Reducing platinum group metal (PGM) loadings in fuel cells and electrolyzers is paramount for cost reductions and getting hydrogen to scale to help decarbonize the global economy. Conventional PGM nanoparticle-based ink-cast electrocatalysts lose performance at high current densities owing to mass transport resistances that arise due to the use of ionomer binders. Herein, we report the development of binder-free extended-surface thin-film platinum electrocatalysts with tunable nanoscale morphology and periodic spacing. The electrocatalysts are prepared by sputtering various loadings of platinum on Al2O3 nanostructures templated from self-assembled block copolymer (BCP) thin films on glassy carbon substrates. Testing for oxygen reduction on a rotating disk electrode setup with ultralow PGM loadings (5.8 μgPt cm-2) demonstrates electrocatalyst performance that rivals commercial platinum electrocatalysts in terms of mass activity (380 mA mgPt-1 at 0.9 V vs RHE) while surpassing commercial catalysts in terms of stability (mass activity loss: 11-13% after 20,000 potential cycles). Moreover, catalyst performance probed as a function of nanoscale feature size and morphology reveals an inverse correlation between feature size and electroactivity, as well as the superiority of cylindrical morphologies over lamellae, presenting BCP templating as a fabrication pathway toward stable, tunable catalyst geometries.