Vertical-crystalline Fe-doped β-Ni oxyhydroxides for highly active and stable oxygen evolution reaction

Abstract

<h2>Summary</h2> The layered transition metal oxyhydroxides have received increasing interest owing to the efficient energy conversion performance and material stability during the oxygen evolution reaction (OER). In particular, Fe-doped NiOOH has shown record-high OER performance in alkaline media among various catalysts. Theoretically, undercoordinated facets including Ni⁴⁺, exposed at the edges of NiOOH, were predicted to perform highly active OER. Therefore, here we suggest a rational catalyst design, a vertical-crystalline β-Fe/NiOOH layer built on faceted Fe/Ni nanocrystals, which exposes Ni⁴⁺ sites and could improve the OER performance dramatically. Electrochemical OER tests recorded the overpotential of 210 mV at a current density of 10 mA cm⁻²_GEO and stable operation for 5 days. <i>In situ/operando</i> and density functional theory studies revealed that the Ni valence cycle between +2 and +4 assisted by Fe dopant is the key engine that greatly accelerates OER kinetics and that the vertical-crystalline β-Fe/NiOOH layers on Ni octahedra are stable under harsh OER conditions.