A Dynamic Active Site for OER Catalysis at Nickel-Vanadium-Phosphide Depends on V Surface Position and Fe in Alkaline

Enhancing the rate of the oxygen evolution reaction (OER) by doping Ni-based electrocatalysts with guest metals other than Fe (V in this work) and the stability of the metal site should be assessed independent of Fe traces and in relation to the guest metal activity in solution. We examined OER catalysis and its sustainability at vanadium-doped nickel phosphide (NiP-V) independent of the role of Fe traces in alkaline. V was included in NiP by codeposition at cathodic bias (termed V_bulk) or postdeposition during the phosphide-to-hydroxide surface transformation at anodic bias in alkaline spiked with VCl₃ (termed V_surface). Doping with V_surface strongly promoted OER and reduced the Tafel slope in KOH purified of Fe traces (Fe-free KOH), indicating a V_surface-path lowering of overpotentials independent of and different from the mechanism via Fe surface sites at NiOH. A similar effect was not observed with V_bulk inclusion. Sustaining catalysis via V_surface-sites required maintaining a sufficiently high activity of V in solution. The prominent role of V_surface sites and the dependence of stability on solution condition are reminiscent of the behavior of Fe surface sites in NiOH. This work points to a trend of behavior of active site dynamics at Ni-based OER catalysts in alkaline and presents a question and insight on how to stabilize the guest-metal site at the solid-liquid interface.