An energy-efficient H2 production based on urea-aided water splitting enhanced by Ru induced in-situ speciation of NiO nanosheets on porous Ni

Abstract

Efficient hydrogen production by water electrolysis is primarily restrained by imperfect over-potential and poor reaction dynamics on oxygen evolution reaction (OER). Thermodynamically favourable urea oxidation reaction (UOR) is a class of promising routes for substituting sluggish OER and for coupling with cathodic hydrogen production because of smaller equilibrium potential (0.37 V) than that of OER (1.23 V). Herein, a versatile Ru-NiO/p-Ni catalyst was prepared through in-situ generating nickel hydroxide nanosheets on the surface of ordered porous Ni, then doping low Ru and annealing treatment. The optimized Ru-NiO/p-Ni displayed outstanding activity and stability towards hydrogen evolution reaction (HER), OER and UOR with potentials of −0.13 V, 1.57 V, and 1.39 V at 100 mA cm−2, respectively. Ru-NiO/p-Ni‖Ru-NiO/p-Ni can achieve 100 mA cm−2 in urea-aided water splitting at a voltage of only 1.58 V, which is prominently 170 mV smaller than the voltage of water electrolysis (1.75 V). The excellent electrocatalytic performance is owing to the outstanding inherent activity generated by cooperative effect of Ru and NiO, along with rich defect and active centre of Ru-NiO/p-Ni supplied by the large surface area of 3D porous structure. The formation of more rich Ni active species with a high valence through transport of electrons between Ru and Ni is favourable to promoting the dissociation of urea molecules, eventually improving UOR. Therefore, it can facilitate urea-aided water splitting, which provides a valuable strategy for constructing versatile catalysts for a cathodic energy-efficient hydrogen production coupled with other anodic oxidation reactions.