(Invited) Designing Electrocatalysts for Controlling Selectivity of Oxygen Reduction Reaction

Abstract

The oxygen reduction reaction (ORR) is arguably one of the most important electrochemical reactions affecting the efficiency of energy conversion devices such as fuel cells [1] and metal-air batteries [2]. Oxygen (O2) can be reduced in two ORR pathways are possible: the four-electron (4 e–) pathway to generate water (H2O) by complete reduction and the two-electron (2 e–) pathway to hydrogen peroxide (H2O2) involving partial O2 reduction [3,4]. Although the 2 e– pathway ORR has been regarded as an adverse side reaction that impedes the efficient 4 e– pathway, it has recently garnered a surge of interest as a means of the electrochemical production of H2O2.In this presentation, we present a catalyst design strategy for controlling catalytic selectivity of ORR. We have developed a general synthetic strategy that can produce atomically dispersed precious metal catalysts of Os, Ru, Rh, Ir, and Pt, which served as model catalysts for unravelling catalytic activity and selectivity trends for the ORR [5]. The atomically dispersed precious metal catalysts generally showed higher selectivity for H2O2 production, due to their isolated geometry, than their nanoparticle counterparts for the ORR. Among the atomically dispersed catalysts, the H2O2 selectivity was changed by the types of metals, with atomically dispersed Pt catalyst showing the highest selectivity. A combination of experimental results and density functional theory calculations revealed that the selectivity trend of atomically dispersed catalysts could be correlated to the binding energy difference between *OOH and *O species. In terms of 2 e− ORR activity, the atomically dispersed Rh catalyst showed the best activity. We also present our recent results on the design of carbon-based and non-precious metal catalysts for the selective 2 e– ORR for H2O2 production [6,7].