Unraveling the Crystal Facet and Support Effects on the Oxygen Evolution Activity of Cobalt Oxide Using Single Nanoparticle Electrocatalysis

Abstract

Transition metal oxide catalysts have recently gained special interest in alkaline water electrolysis due to their relatively high abundancy and high catalytic activity. However, their catalytic performance has typically been evaluated based on measurements at composite electrodes, that is by immobilizing a large number of these nanoparticles together with inactive binders and additives on a current collector/support and measuring only their integral activity. In such studies, it is challenging to deconvolute the catalyst intrinsic properties from matrix effects. For example, the measured catalytic trends can be influenced by blocking of catalyst active sites by the additives or by non-optimal iR compensation or by different porosity within the composite, impeding a direct comparison of nanocatalysts.[1] Alternatively, single-particle electrocatalysis by the “nano impact” approach has been applied to assess the intrinsic activity of nanoparticles (NPs) at the individual particle level.[2] Exploiting this method, we demonstrate how the catalyst’s crystal facet/shape influences the OER activity by comparing the activity of cubes and spheres of Co3O4.[3] In contrast to the tentative differences in OER activity recorded on ensembles, the single particle studies unambiguously reveal that Co3O4 cubes are more active than spheres when both NPs have otherwise identical parameters. We also can link our experimental data to theory data obtained from DTU+U calculations. Furthermore, we investigate catalyst-support effects and show the higher activity of Pt support than carbon.[4]. This approach enables the identification of highly active facets to guide shape-selective syntheses of improved metal oxide nanocatalysts for water oxidation.