Size-Dependent Activity Trends in Combination with In Situ X-ray Absorption Spectroscopy Reveal Insights into Cobalt Oxide Catalyzed Bifunctional Oxygen Electrocatalysis
18th Topical Meeting of the International Society of Electrochemistry
Abstract
Bifunctional oxygen electrocatalysts play a vital role in important energy conversion and storage devices. Cost-effective, abundant, and active Co-based materials have emerged as promising bifunctional electrocatalysts, for which identifying catalytically active structures under reaction conditions and unraveling the structure–activity relationships are of critical importance. We investigated the sizedependent (3–10 nm) structure and catalytic activity of bifunctional cobalt oxide nanoparticle (CoOx NP) catalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). In situ X-ray absorption spectroscopy (XAS) revealed that the majority of NPs during OER and ORR was composed of the Co3O4 phase regardless of their particle sizes. The OER activity increased with decreasing NP size, which correlated to the enhanced oxidation state and larger surface area in smaller NPs, whereas the ORR activity was independent of NP size, revealing the auxiliary role of CoOx on the CoOx/CNTs for the reduction or disproportionation of peroxide rather than the direct reduction of oxygen. These particle sizedependent catalytic activities in conjunction with the in situ XAS results can provide critical insights into the CoOx-catalyzed bifunctional oxygen electrode reactions.