Surface Reconstruction of An Integrated CoO‐Co2Mo3O8 Electrode Enabling Efficient Ampere‐Level Hydrogen Evolution in Alkaline Water or Seawater

To accelerate the water dissociation in the Volmer step and alleviate the destruction of bubbles to the physical structure of catalysts during the alkaline hydrogen evolution, an integrated electrode of cobalt oxide and cobalt-molybdenum oxide grown on Ni foam, named CoO-Co₂Mo₃O₈, is designed. This integrated electrode enhances the catalyst-substrate interaction confirmed by a micro-indentation tester, and thus hinders the destruction of the physical structure of catalysts caused by bubbles. Electrochemical testing shows the occurrence of a surface reconstruction of the integrated electrode, and CoO is transformed into Co(OH)₂, denoted as Co(OH)₂-Co₂Mo₃O₈. Theoretical calculations determine that Co(OH)₂-Co₂Mo₃O₈ has significantly low activation barrier for water dissociation and presents easy hydroxide desorption, which accelerate the catalytic reaction. Electrochemical experiments show that Co(OH)₂-Co₂Mo₃O₈ exhibits outstanding activity, reaching current density values of -100 and -1000 mA cm^-2 with overpotentials only 57.8 and 195.8 mV, respectively. Furthermore, it demonstrates excellent stability at -500 and -1000 mA cm^-2 for 200 h. Combined with the previously reported anode, the two-electrode system also provides the stable operation from 100 to 1000 mA cm^-2 for 600 h in alkaline solution, and over 200 h at 500 and 1000 mA cm^-2 in alkaline seawater.