Divalent site doping of NiFe-layered double hydroxide anode catalysts for enhanced anion-exchange membrane water electrolysis

Abstract

Nickel-iron layered double hydroxide (NiFe-LDH) catalysts exhibit excellent activity for the oxygen evolution reaction (OER) in alkaline media. Doping different metal cations in the divalent (Ni²⁺) sites of NiFe-LDH catalysts has been shown to enhance OER activity, though the enhancement mechanism remains unclear. Herein, we synthesized a series of MNiFe-LDH catalysts on Ni foams by partial substitution of Ni²⁺ for various divalent transition metals (M = Mn²⁺, Co²⁺, Cu²⁺, or Zn²⁺). A CoNiFe-LDH electrocatalyst outperformed both NiFe-LDH and the other MNiFe-LDH catalysts during OER in 1.0 M KOH, delivering a very low overpotential of 191 mV at a current density of 10 mA cm⁻² and achieving a high current density of 1 A cm⁻² at 1.90 V as the anode catalyst in an anion-exchange membrane water electrolyser (AEMWE) single cell. Density functional theory (DFT) calculations indicate that the introduction of Co²⁺ can significantly reduce the adsorption strength of the *OH intermediate on (015) facets of “working NiFe-LDH-based catalysts”, thereby reducing the theoretical overpotential for enhanced OER activity. Furthermore, the CoNiFe-LDH electrocatalyst showed excellent stability during OER at high current densities. Divalent-site doping therefore offers a simple and efficient strategy for enhancing the performance of NiFe-LDH-based catalysts for OER and AEMWEs.