Influence of Co2+, Cu2+, Ni2+, Zn2+, and Ga3+ on the iron-based trimetallic layered double hydroxides for water oxidation

Abstract

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), N2 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−2 and a Tafel slope of 64.8 mV dec−1 in alkaline conditions (KOH 1 M). Additionally, this material displayed a charge transfer resistance (Rct) of 30.1 Ω cm2. Electrochemical measurements indicated that the materials containing Zn2+ exhibit low kinetics; whilst materials with Co2+ or Ga3+ yield the best performances. The catalytic activity of the CoGaFe-LDH can be attributed to the decrease of the Rct caused by electronic effects due to the addition of the Ga3+, 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.