Highly Active NiO-Ni(OH)2-Cr2O3/Ni Hydrogen Evolution Electrocatalyst through Synergistic Reaction Kinetics.

High activity catalyst for hydrogen evolution reaction (HER) plays a key role in converting renewable electricity to storable hydrogen fuel. Great effort has been devoted to search for noble metal free catalysts to make electrolysis viable for practical applications. Here, we report a non-precious metal oxide/metal catalyst with high intrinsic activity comparable to Pt/C. The electrocatalyst consisting of NiO, Ni(OH)2, Cr2O3, and Ni metal exhibits a low overpotential of 27, 103, and 153 mV at current density of 10, 100, and 200 mA cm-2, respectively, in a 1.0 M NaOH electrolyte. The activity is much higher than that of NiOx/Ni or Cr2O3 alone, showing the synergistic effect of NiOx/Ni and Cr2O3 on catalyzing HER. Density functional theory calculation shows that NiO and Cr2O3 on Ni surface lower the disassociation energy barrier for breaking H-OH bond, while Ni(OH)2 and Cr2O3 create preferred sites on Ni surface with near-zero H* adsorption free energy to promote H* to gaseous H2 evolution. These synergistic effects of multiple-oxides/metal composition enhance the disassociation of H-OH and the evolution of H* to gaseous H2, thus achieving high activity and demonstrating a promising composition design for noble metal free catalyst.