Structural Transformations in Nickel-Doped Lanthanum-Based Electrocatalyst for Enhanced Oxygen Evolution Reaction
来源：ACS Publications
Metal oxides are among the most promising electrocatalysts for the oxygen evolution reaction (OER). However, metal oxides often exhibit poor conductivity and electron transfer, limiting efficient charge transfer. Tuning the population of the d-orbital near the Fermi level and inducing porosity at the electrode–electrolyte interface can alter the charge transfer kinetics. This can also be achieved via doping with a conductive metal such as nickel (Ni) as it effectively tunes the electronic conductivity of lanthanum (La) coordinated complex and offers lattice stability by lowering the formation energy of La2O(CO3)2. However, the precise addition of dopants for tuning the interfacial charge transfer properties and structural transformation of nanomaterials is poorly understood. Understanding and optimizing the surface and intrinsic properties are two integral parameters for developing an efficient electrocatalyst. Therefore, this work focuses on tuning and stabilizing the structure by lowering the lattice formation energy. Thick and broad petals developed at lower doping transformed into thin and sharp petals upon increasing the number of dopants. This transformation indicates that the optimal concentration facilitates greater electron redistribution and increased active site density. In addition, the transformation of smooth surface petals of Ni0.028LaOHCO3 to porous surface Ni0.028La2O(CO3)2 microflowers by calcination exhibits superior OER activity, exhibiting an overpotential of 309 mV at a current density of 10 mA cm–2 in alkaline conditions. This enhanced activity is attributed to enhanced ion diffusion and charge transfer kinetics. This work establishes a clear correlation between doping and the optimum molar concentration of Ni content for a stable lattice structure of La. Additionally, it explores the design and structural construction of electrocatalysts by doping and calcination processes to provide insights into the structural and chemical aspects that drive the OER efficiency.
In this work, Ni-doped La2O(CO3)2 microflowers were developed through a simple coprecipitation method at ambient temperature. By precisely controlling the ratio of Ni and La precursors, we achieved tunable structural and morphological characteristics of the resulting microflowers. The transformation from nanorods to microflowers occurred through self-assembly driven by the strong interactions between urea and metal ions, facilitated by hydrogen bonding. Increasing the Ni concentration led to the formation of thinner and sharper petals, enhancing ion diffusivity and contributing to the highly enhanced O2 evolution performance. Nevertheless, excessive Ni doping inhibits catalytic activity due to the agglomeration at the surface and lattice concentration, which hinders the mobility of the electrocatalysts. Upon calcination of the microflowers, the induced porosity improved electron transfer, resulting in a significant improvement in the overall electrochemical performance compared with bare La2O(CO3)2. The optimized electrocatalyst, calcined Ni0.028La2O(CO3)2 microflowers demonstrated excellent OER activity, requiring an overpotential of 309 mV to achieve a current density of 10 mA cm–2 in a 0.1 M KOH solution.