Accelerating catalytic reaction kinetics by coordination-unsaturated nickel sites in NiCo-LDH homojunction for urea-assisted water splitting

Developing green hydrogen production via urea-assisted water splitting is of great importance for mitigating energy crisis and environmental concerns. However, accelerating the sluggish anodic reaction kinetics yet remains challenging. Herein, self-supported nickel cobalt layered double hydroxides (NiCo-LDH) with unsaturated coordination nickel sites were prepared via regulating the crystallinity by an electrodeposition method. The NiCo-LDH-50 homojunction with an optimal amorphous/crystalline ratio exhibits rapid urea oxidation reaction (UOR) kinetics with a low Tafel slope of 10.9 mV dec −1 . It requires only 1.18/1.29 V versus reversible hydrogen electrode to reach 10/100 mA cm −2 during UOR. Structural characterizations and theoretical calculations reveal that a moderate ratio of amorphous/crystalline interface not only exposes more unsaturated coordination nickel sites and accelerates the electron transfer, but also lowers the energy barrier of Ni 3+ /Ni 2+ transformation and promotes a more reversible catalytic cycle, thus leading to excellent UOR performance. When employed as the anode in a two-electrode urea electrolyzer, 1.29 V is required to achieve 10 mA cm −2 with an excellent stability. This work provides an effective approach for designing high-performance electrocatalysts for sustainable development of the energy and environment field.