Electrocatalytic Production of H₂O₂ by Selective Oxygen Reduction Using Earth-Abundant Cobalt Pyrite (CoS₂)

Abstract

Decentralized on-site production of hydrogen peroxide (H2O2) relies on efficient, robust, and inexpensive electrocatalysts for the selective two-electron (2e–) oxygen reduction reaction (ORR). Here, we combine computations and experiments to demonstrate that cobalt pyrite (CoS2), an earth-abundant transition-metal compound, is both active and selective toward 2e– ORR in the acidic solution. CoS2 nanomaterials drop-casted on the rotating ring-disk electrode (RRDE) showed selective and efficient H2O2 formation in 0.05 M H2SO4 at high catalyst loadings, with their operational stability evaluated by structural and surface analyses. CoS2 nanowires directly grown on the high-surface-area carbon fiber paper electrode boosted the overall performance of bulk ORR electrolysis and the H2O2 product was chemically quantified to yield a ∼70% H2O2 selectivity at 0.5 V vs reversible hydrogen electrode (RHE), in good agreement with the RRDE results. Computations suggested the modest binding of OOH* adsorbate on the single Co site of CoS2 and the kinetically disfavored O–O bond scission due to the lack of active site ensembles in the crystal structure, consistent with the experimentally observed activity and selectivity. CoS2 also catalyzes 2e– ORR with less activity and selectivity in the noncorrosive neutral solution. This work opens up the exploration of diverse earth-abundant transition-metal compounds in search of highly active and selective electrocatalysts for efficient H2O2 production.