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 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 1M 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 Mod+ and Cod‐ 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.