Electronic and vacancy engineering of ruthenium doped hollow-structured NiO/CoO nanoreactors for low-barrier electrochemical urea-assisted energy-saving hydrogen production.

Discovering a valid approach to achieve a novel and efficient water splitting catalyst is essential for the development of hydrogen energy technology. Herein, unique hollow-structured ruthenium (Ru)-doped nickel-cobalt oxide (Ru-NiO/CoO/NF) nanocube arrays are fabricated as high-efficiency bifunctional electrocatalysts for hydrogen evolution reaction (HER)/urea oxidation reaction (UOR) through combined electronic and vacancy engineering. The structural characterization and experimental results indicate that the doping of Ru can not only effectively modulate the electronic structure of Ru-NiO/CoO/NF, but also increase the content of oxygen vacancies in the structure of Ru-NiO/CoO/NF to stabilize the existence of oxygen vacancies during the catalytic process. This can optimize the adsorption and desorption of the reactive intermediates on the surface of Ru-NiO/CoO/NF and dramatically accelerate the HER and UOR kinetics. As a result, the Ru-NiO/CoO/NF hollow structure nanocube arrays exhibit overpotentials of 21 and 60 mV for HER, as well as potentials of 1.36 and 1.42 V for UOR at 10 and 100 mA cm, respectively. Furthermore, the coupled HER and UOR system requires only 1.59 V of cell voltage to drive a current density of 100 mA cm, which is approximately 240 mV lower than conventional water electrolysis. This work provides a tremendous promise for the development of novel and high-activity electrocatalysts in future energy conversion applications.