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

Abstract

Decentralized on-site production of hydrogen peroxide (H 2 O 2 ) 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 (CoS 2 ), an earth-abundant transition-metal compound, is both active and selective toward 2e – ORR in the acidic solution. CoS 2 nanomaterials drop-casted on the rotating ring-disk electrode (RRDE) showed selective and efficient H 2 O 2 formation in 0.05 M H 2 SO 4 at high catalyst loadings, with their operational stability evaluated by structural and surface analyses. CoS 2 nanowires directly grown on the high-surface-area carbon fiber paper electrode boosted the overall performance of bulk ORR electrolysis and the H 2 O 2 product was chemically quantified to yield a ∼70% H 2 O 2 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 CoS 2 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. CoS 2 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 H 2 O 2 production.