Constructing a composite catalyst containing amorphous nickel hydroxide and crystalline lanthanum carbonate hydroxide for urea electrolysis

Abstract

Urea oxidation reaction (UOR) is considered a promising alternative to the anodic oxygen evolution reaction (OER) with slow kinetics in water electrolysis due to its lower theoretical potential (0.37 V) compared with that of the OER (1.23 V). To design an efficient catalyst for UOR-coupled water electrolysis, in this work, a novel amorphous nickel hydroxide/lanthanum carbonate hydroxide composite catalyst (Ni(OH)₂/La₂(CO₃)₂(OH)₂) with a unique cactus-like morphology was grown on a nickel foam (NF) via a one-step hydrothermal strategy. Ni(OH)₂/La₂(CO₃)₂(OH)₂/NF exhibited a unique cactus-like morphology with 3D hierarchical heterostructures, which could expose more active sites and generate a large number of oxygen vacancies. The electron transfer from Ni to La and the synergistic effect of the amorphous/crystalline interface regulated the surface chemical environment of the catalyst, resulting in its enhanced electrocatalytic performance in the anodic UOR and cathodic HER. Therefore, the assembled two-electrode system for urea-assisted water electrolysis only required a cell voltage of 1.42 V to achieve a current density of 10 mA cm⁻², which was significantly superior to that of overall water electrolysis. This work provides a new idea for exploring metal carbonate hydroxides with high activity as stable electrocatalysts for water splitting and other organic electro-oxidation reactions.