Local Surface Modulation Activates Metal Oxide Electrocatalyst for Hydrogen Evolution: Synthesis, Characterization, and DFT Study of Novel Black ZnO

Modulation of atomic surface constitution has been previously reported to effectively activate inert metal oxides for electrocatalytic hydrogen evolution reaction (HER). This work follows on this seemingly untrodden path whereby, via utilization of first-principles DFT calculations and the accepted HER activity description (vertical bar Delta G(H*)vertical bar), the polar (002) surface of commercially abundant ZnO shows a clear preference toward HER activity compared to other facets. Further, a robust and systematic screening of viable surface modulators was performed, through which it was determined that surface oxygen vacancies atop (002) ZnO yield a phenomenal reduction in vertical bar Delta G(H*)vertical bar (namely, 36 meV) toward the ideal zero value. This shows promise for industrial realization as an alternative to Pt and transition-metal chalcogenides. The viability of production was ensured through the rational faceted growth of (002) ZnO followed by a physicochemical reduction technique. This resulted in a novel "black" ZnO material with universal pH stability. Electrochemical measurements showed that to achieve a current density of 10 mA cm(-2), black ZnO requires an overpotential of 220 mV, compared to 440 mV of its pristine counterpart in acidic (0.5 M H2SO4) electrolyte. It is this work's foresight that appropriate and facile structural modifications may be applied to the myriad of available transition-metal oxides as a way to ameliorate the pressure on environmentally poignant hydrogen generation methods for an array of industrial uses.