Modulating the oxidation states in nickel–iron layered double hydroxides by natural cooling for enhanced oxygen evolution activity

Regulating surface oxidation state and understanding how it governs the reactivity and durability of electrocatalysts is a key problem for designing promising OER electrocatalysts. Here, a “natural cooling” method is reported for tuning the oxidation state of NiFe LDH. The optimal NiFe LDH electrocatalyst exhibits enhanced OER activity, such as low overpotential (231 mV at 20 mA cm−2), high TOFs (0.008–0.029 s−1 at 250–280 mV) and superior stability at high current densities (100 and 220 mA cm−2). XPS, Raman, and electrochemical analyses and theoretical calculations reveal that the Ni and Fe ions with higher oxidation state can greatly enhance OER activity. Our work shows that the oxidation states of active sites play a key role in promoting the OER activity of NiFe LDHs. As a non-composited strategy, the “natural-cooling” method can be employed to guide the designing of top electrocatalysts with favorable surface oxidation states.