Vertical Alignment of Fe-Doped <i>β</i>‑Ni Oxyhydroxides for Highly Active and Stable Oxygen Evolution Reaction

Abstract

The layered transition metal oxyhydroxides have received increasing interest owing to the efficient energy conversion performance and material stability during oxygen evolution reaction (OER). In particular, Fe-doped Ni oxyhydroxides (NiOOH) have shown the record-high OER performance in alkaline media among various catalysts. Theoretically, under-coordinated facets including Ni4+, exposed at the edges of NiOOH, were predicted to perform highly active OER. Therefore, here we suggest a rational catalyst design that exposes NiOOH edges with Fe-doping, which could improve dramatically the OER performance. This unique structure was successfully prepared by electro-anodization process of Fe‑doped Ni octahedral nanocrystals. After anodization, metallic surface of the nanocrystal was transformed to vertically aligned β‑Fe/NiOOH layers with exposed Ni4+ edge sites. Electrochemical OER and anion exchange membrane based single-cell tests recorded the overpotential of 210 mV at a current density of 10 mA cm−2GEO and stable operation for 5 days, respectively. In-situ/operando studies revealed that the cycle of Ni oxidation state between +2 and +4 assisted by Fe dopant is the key engine that greatly accelerates OER kinetics, and that the aligned β‑Fe/NiOOH layers on Ni octahedra are stable under harsh OER conditions.