Influence of Co(2+), Cu(2+), Ni(2+), Zn(2+), and Ga(3+) 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(2) 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 (R(ct)) of 30.1 Ω cm(2). Electrochemical measurements indicated that the materials containing Zn(2+) exhibit low kinetics; whilst materials with Co(2+) or Ga(3+) yield the best performances. The catalytic activity of the CoGaFe-LDH can be attributed to the decrease of the R(ct) caused by electronic effects due to the addition of the Ga(3+), 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.