Unveiling the active sites of ultrathin Co-Fe layered double hydroxides for the oxygen evolution reaction

Two-dimensional layered double hydroxides (LDHs) have been identified as promising electrocatalysts for the oxygen evolution reaction (OER); however, the simple and effective synthesis of high-quality LDHs remains extremely challenging and the active sites have not been clarified. Herein, we report a facile solution-reaction method for preparing an ultrathin (thickness < 2 nm) nonprecious CoFe-based LDH. Co1Fe0.2 LDH delivers a current density of 10 mA cm−2 and a high turnover frequency of 0.082 s−1 per total 3d metal atoms at a low overpotential of 256 mV. Its mass activity is 277.9 A g−1 at an overpotential of 300 mV for the OER. Kinetic studies reveal the Co site as the main active center for the OER. The doped Fe lowers the reaction barrier by accelerating the charge-transfer process. Theoretical calculations reveal that the surface Co sites adjacent to Fe atoms are the active centers for the OER and the subsurface Fe dopants excessively weaken the OH* adsorption, thus increasing the energy barrier of the rate-determining step. This study can guide the rational design of high-performance CoFe-based LDHs for water splitting.