Interface engineering in Ni(OH)₂/NiOOH heterojunction to enhance energy-efficient hydrogen production via urea...

Electrochemical urea electrolysis has merged as a promising alternative to conventional water splitting methods for hydrogen fuel production due to its cost-effectiveness and superior energy efficiency. The utilization of heterostructures has been proposed as a viable strategy to improve the efficiency of the urea oxidation reaction (UOR) by augmenting the quantity of active sites and optimizing the electronic structure. In this study, a Ni(OH)₂/NiOOH heterojunction, referred to as H-Ni, was synthesized via a straightforward hydrothermal synthesis method. The notable performance of H-Ni in UOR is ascribed to the synergistic interaction between Ni(OH)₂ and NiOOH, which constitute the principal components of the catalyst. Density functional theory (DFT) calculations reveal that the H-Ni composite is capable of modulating the d-band center, thereby enhancing the adsorption and desorption of reaction intermediates and decreasing the Gibbs free energy (ΔG) associated with the rate-determining step (RDS) of the UOR. Experimental results from catalytic performance tests indicate that the H-Ni-140 catalyst attains a current density of 10 mA·cm^-2 in a 1.0 M KOH electrolyte containing 0.33 M urea at a relatively low potential of 1.341 V versus reversible hydrogen electrode (RHE), thereby highlighting its superior electrocatalytic performance. Furthermore, the catalyst requires only a cell voltage of 1.78 V to achieve a current density of 100 mA·cm^-2, which is approximately 120 mV lower than that required for water electrolysis. This work presents a straightforward methodology for the cost-effective development of heterojunction catalysts.