W-promoted OER kinetics of bimetallic hydroxide: an experimental analysis via operando EIS and temperature-dependent study†

Abstract

Developing a cost-effective and highly efficient electrocatalyst to improve the oxygen evolution reaction (OER) remains a significant challenge in water splitting. A thorough understanding of the reaction kinetics and the physical, chemical, and electronic properties of the materials is crucial for meticulously designing efficient catalysts. In this work, we improve these properties of NiCo-LDH via W doping for enhanced OER performance under alkaline conditions. The doping of W is carefully optimized in the LDH lattice to obtain the best OER efficiency. The optimized W_2.4-NiCo-LDH exhibits a high TOF value of 0.0723 s⁻¹, which is 31 times more than that of the pristine material and the high faradaic efficiency value of 92.63% at 1.62 V potential indicates excellent selectivity of the material. Furthermore, the long-term stable nature for 100 hours at 1.52 V potential indicates its robustness. The reaction kinetics study via operando electrochemical impedance spectroscopy (EIS) reveals significantly improved OER kinetics of NiCo-LDH after W doping. Furthermore, the activation energy evaluations at different potentials show the requirement of less energy input in W_2.4-NiCo-LDH to catalyse the OER efficiently. The activation energy of W_2.4-NiCo-LDH (3.25 kJ mol⁻¹) is reduced to one-third of that of pristine NiCo-LDH (9.39 kJ mol⁻¹) at 1.8 V potential, suggesting the impact of W doping. Furthermore, the introduction of W into the lattice enhances the electronic conductivity of the material, resulting in excellent overall catalytic performance. This work offers a high valence cation doping approach coupled with an understanding of reaction kinetics for the design of an efficient catalyst for the OER.