Hydrogen Evolution in Neutral Media by Differential Intermediate Binding at Charge-Modulated Sites of a Bimetallic...

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.