Mesoporous Single Crystals with Fe‐Rich Skin for Ultralow Overpotential in Oxygen Evolution Catalysis

Abstract The oxygen evolution reaction (OER) is a key reaction in water splitting and metal–air batteries, and transition metal hydroxides have demonstrated the most electrocatalytic efficiency. Making the hydroxides thinner for more surface commonly fails to increase the active site number, because the real active sites are the edges. Up to now, the overpotentials of most state‐of‐the‐art OER electrocatalysts at a current density of 10 mA cm⁻² (η₁₀) are still larger than 200 mV. Herein, a novel design of mesoporous single crystal (MSC) with an Fe‐rich skin to boost the OER is shown. The edges around the mesopores provide lots of real active sites and the Fe modification on these sites further improves the intrinsic activity. As a result, an ultralow η₁₀ of 185 mV is achieved, and the turnover frequency based on Fe atoms is as high as 16.9 s⁻¹ at an overpotential of 350 mV. Moreover, the catalyst has an excellent catalytic stability, indicated by a negligible current drop after 10 000 cyclic voltammetry cycles. The catalyst enables Zn–air batteries to run stably over 270 h with a low charge voltage of 1.89 V. This work shows that MSC materials can provide new opportunities for the design of electrocatalysts.