Hydrogen Evolution in Neutral Media by Differential Intermediate Binding at Charge‐Modulated Sites of a Bimetallic Alloy Electrocatalyst

The energy barrier to dissociate neutral water has been lowered by the differential binding of H* and OH* on the charge-modulated metal centers of amorphous Co₈₅Mo₁₅ sheets supported on Ni-foam, resulting in an ultralow overpotential of 50±9 mV vs. the reversible hydrogen electrode at a current density of −10 mA cm⁻².

Abstract

The energy barrier to dissociate neutral water has been lowered by the differential intermediate binding on the charge-modulated metal centers of Co₈₅Mo₁₅ sheets supported on Ni-foam (NF), where the overpotential for hydrogen evolution reaction (HER) in 1 M phosphate buffer solution (PBS) is only 50±9 mV at −10 mA cm⁻². It has a turnover frequency (TOF) of 0.18 s⁻¹, mass activity of 13.2 A g⁻¹ at −200 mV vs. reversible hydrogen electrode (RHE), and produces 16 ml H₂ h⁻¹ at −300 mV vs. RHE, more than double that of 20 % Pt/C. The Mo^δ+ and Co^δ− sites adsorb OH*, and H*, respectively, and the electron injection from Co to H−O−H cleaves the O−H bond to form the Mo−OH* intermediate. Operando spectral analyses indicate a weak H-bonded network for facilitating the H₂O*/OH* transport, and a potential-induced reversal of the charge density from Co to the more electronegative Mo, because of the electron withdrawing Co−H* and Mo−OH* species. Co₈₅Mo₁₅/NF can also drive the complete electrolysis of neutral water at only 1.73 V (10 mA cm⁻²). In alkaline, and acidic media, it demonstrates a Pt-like HER activity, accomplishing −1000 mA cm⁻² at overpotentials of 161±7, and 175±22 mV, respectively.

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