Synergistic engineering of heterostructure and oxygen vacancy in cobalt hydroxide/aluminum oxyhydroxide as bifunctional electrocatalysts for urea-assisted hydrogen production.

Designing inexpensive, high-efficiency and durable bifunctional catalysts for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) is an encouraging tactic to produce hydrogen with reduced energy expenditure. Herein, oxygen vacancy-rich cobalt hydroxide/aluminum oxyhydroxide heterostructure on nickel foam (denoted as Co(OH)₂/AlOOH/NF-100) has been fabricated using one step hydrothermal process. Theoretical calculation and experimental results indicate the electrons transfer from Co(OH)₂ to highly active AlOOH results in the interfacial charge redistribution and optimization of electronic structure. Abundant oxygen vacancies in the heterostructure could improve the conductivity and simultaneously serve as the active sites for catalytic reaction. Consequently, the optimal Co(OH)₂/AlOOH/NF-100 demonstrates excellent electrocatalytic performance for HER (62.9 mV@10 mA cm^-2) and UOR (1.36 V@10 mA cm^-2) due to the synergy between heterointerface and oxygen vacancies. Additionally, the in situ electrochemical impedance spectrum (EIS) for UOR suggests that the heterostructured catalyst exhibits rapid reaction kinetics, mass transfer and current response. Importantly, the urea-assisted electrolysis composed of the Co(OH)₂/AlOOH/NF-100 manifests a low cell voltage (1.48 V @ 10 mA cm^-2) in 1 M KOH containing 0.5 M urea. This work presents a promising avenue to the development of HER/UOR bifunctional electrocatalysts.