Introducing oxygen vacancies to NiFe LDH through electrochemical reduction to promote the oxygen evolution reaction

The transition metal hydroxide NiFe LDH is a promising oxygen evolution reaction (OER) catalyst. Surface engineering, such as the introduction of oxygen vacancies into NiFe LDH, has been reported to further improve the OER performance; however, searching a facile approach remains an issue. In this work, we report a novel and efficient electrochemical reduction method for in situ introduction of oxygen vacancies into NiFe LDH laminates by applying a constant negative voltage. The results show that the reduced NiFe LDH (denoted as r-NiFe LDH) exhibits enhanced OER performance versus its counterpart NiFe due to the increase of oxygen vacancy density, the electrochemically active surface area, wetting ability, and the significant electron transfer rate. In 1 M KOH, the r-NiFe LDH shows a high current density of 110 mA cm^-2 at 1.60 V (vs. RHE), which is 2.8 times the current density of NiFe LDH (40 mA cm^-2), as well as the long-term stability of 100 h. This electroreduction method is also applicable to other LDH materials loaded by different current substrates or synthesized by various methods, demonstrating its universality for the enhancement of the OER activity of LDH electrocatalysts.