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

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 similar to 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.