Design and Mechanistic Understanding of Earth-Abundant Metal Chalcogenide Electrocatalysts for Selective Electrosynthesis of Hydrogen Peroxide

Abstract

Hydrogen peroxide (H2O2) is a versatile and green oxidant with a variety of distributed applications such as environmental remediation, disinfection, and household sanitation, but its centralized chemical production via the anthraquinone process poses significant cost, energy, and safety concerns. Decentralized electrosynthesis using renewable electricity to selectively reduce O2 to H2O2 via the two-electron oxygen reduction reaction (2e- ORR) could better satisfy end-user demands on-site, yet robust, earth-abundant catalysts that are active and selective in acidic (or neutral) solutions are lacking. Here we present our recent joint efforts combining theory and experiments to establish rational design rules for selective and stable acidic 2e- ORR electrocatalysts based on earth-abundant metal chalcogenide compounds. We first showed that pyrite-type cobalt disulfide (CoS2) selectively catalyzes the acidic 2e- ORR at low overpotentials due to the spatial separation of active metal sites by anions, which kinetically suppresses the scission of O-O bond in OOH* adsorbate and the undesired 4e- ORR. We further established both pyrite- and marcasite-type cobalt diselenide (CoSe2) polymorphs as more stable and leaching-resistant acidic 2e- ORR catalysts because of the much weaker binding of O* adsorbate to Se sites. This stability allows for the bulk accumulation of practically useful 547 ppm H2O2 and the effective electro-Fenton degradation of organic pollutant for on-site environmental remediation. Building on the new mechanistic understanding, our ongoing developments and future perspectives of earth-abundant metal compound-based 2e- ORR electrocatalysts will also be discussed.