Influence of Co, Cu, Ni, Zn, and Ga on the iron-based trimetallic layered double hydroxides for water oxidation.

In this work, we synthesized five novel iron-based trimetallic layered double hydroxides (LDHs) by the urea-assisted co-precipitation method for the electrocatalytic water oxidation reaction (WOR). In particular, the synthesized electrocatalysts were labeled CoCuFe-LDH, ZnNiFe-LDH, ZnCoFe-LDH, ZnCuFe-LDH, and CoGaFe-LDH. The electrocatalysts were thoroughly characterized by means of Ultraviolet-visible spectroscopy (UV-Vis), N adsorption/desorption, and X-ray photoelectron spectroscopy (XPS). We analyzed the changes in the electronic structures, changes in the surface area, and the oxygen vacancies, respectively. X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the materials had the hydrotalcite-like structure typical of LDHs. Electrochemical results indicated that the best electrocatalyst was the CoGaFe-LDH achieving an overpotential of 369.9 mV at 10 mA cm and a Tafel slope of 64.8 mV dec in alkaline conditions (KOH 1 M). Additionally, this material displayed a charge transfer resistance ( ) of 30.1 Ω cm. Electrochemical measurements indicated that the materials containing Zn exhibit low kinetics; whilst materials with Co or Ga yield the best performances. The catalytic activity of the CoGaFe-LDH can be attributed to the decrease of the caused by electronic effects due to the addition of the Ga, lowering the thermodynamic barriers and thus enhancing the electron transfer. This work opens the door for a new approach to design efficient multimetallic catalysts based on the transition metals for WOR.