Dischargeable nickel matrix charges iron species for oxygen evolution electrocatalysis

•MOxHy (M = Ni, Fe, and NiFe) film electrocatalyst fabricated on carbon substrate.•NiFeOxHy film exhibits excellent alkaline OER activity.•Operando XAS reveals the highly oxidized Fe which is active site in NiFeOxHy.•UPS confirms the electron transferring effect from FeOxHy to NiOxHy. Nickel-iron (oxy)hydroxide (NiFeOxHy) is a state-of-the-art non-precious electrocatalyst for oxygen evolution reaction (OER) in alkaline media. However, the origin of the synergy between Ni and Fe remains unclear. Here, operando X-ray absorption and ultraviolet photoelectron spectroscopy were used to prove the charging-discharging behavior of Ni and Fe when they are adjacent. Fe oxidation and Ni reduction were simultaneously observed during electrocatalytic OER in NiFeOxHy compared to unary metal (oxy)hydroxide. The higher Fermi level of FeOxHy compared to NiOxHy enables charge transfer from Fe to Ni domain near the boundaries. From the experimental results, the combination of Ni and Fe results in superior oxygen-evolving activity by exposing high valent Fe coupled with a dischargeable Ni matrix. [Display omitted]