Electron trapping agent triggers high valence active sites driving electrochemical urea-assisted hydrogen production

Urea oxidation reaction (UOR) is an ideal alternative to the traditional oxygen evolution reaction for hydrogen production in energy-saving water electrolysers. Ni³⁺ has been considered as the most active site in the UOR. However, due to the high oxidation energy barrier and strong oxidizability, it is difficult to obtain sufficient Ni³⁺ efficiently and steadily. Regarding this issue, we have synthesized a self-supporting electrode of V-doped Ni, Fe-based layered double hydroxides on a nickel foam substrate (V-NiFe-LDHs@NF), where the high-valence Ni³⁺ active species are formed and stabilized from the V-induced lattice distortion and electronic rearrangement. V-NiFe-LDHs@NF exhibits excellent UOR catalytic performances with only 1.253/1.372 V vs. RHE at the current density of 10/100 mA cm^-2, respectively. Structure-activity relationship studies demonstrate that the V as electron trapping agents can change the bond relationship between the key intermediate *CONH₂N and the active site by regulating the electron cloud density of the active center, thus avoiding the inactivation of the high valence active species due to migration, covering or reduction in complex environments. When it is directly used in urea-assisted hydrogen production, the cell voltage is only 1.432 V at 100 mA cm^-2, lower 308 mV than that of the traditional water electrolysis.