Rh-engineered ultrathin NiFe-LDH nanosheets enable highly-efficient overall water splitting and urea electrolysis

[Display omitted] •Ultrathin NiFeRh-LDH nanosheets with rich oxygen vacancies are successfully synthesized.•Ultralow overpotential for HER (η10 = 24 mV) and OER (η10 = 204 mV) are required.•The shift of d-band center endow the favorable intermediates adsorption for HER.•The overall water splitting and UOR performance of NiFe-LDH are greatly improved.•1.35 V is required for driving a urine-mediated electrolysis cell and can stably work for over 99 h. Water splitting is a green strategy for hydrogen generation but greatly hindered by the sluggish anodic oxygen evolution reaction (OER). Herein, ultrathin rhodium-doped nickel iron layered double hydroxide nanosheets are successfully synthesized, which exhibit outstanding hydrogen evolution reaction (HER) and OER performance, and advanced overall water splitting. More impressively, the remarkable mass activity of 960 mA mg1 at 1.55 V (1.7 times larger than NiFe-LDH) for urea electro-oxidation reaction (UOR) shows the great potential to surmount the sluggish OER for overall water splitting. A urine-mediated electrolysis cell is subsequently configured, delivering a current density of 10 mA cm-2 with a potential of 1.35 V, which is 105 mV lower than that of urea-free counterpart. The enhanced catalytic activity and cell performance are attributed to the introduction of Rh into NiFe-LDH matrix by changing the electronic structure, allowing optimization of the adsorbed species, as confirmed by experimental measurements and computational analyses.