Abstract:In order to achieve high efficiency, low energy consumption and green hydrogen production, nickel and iron layered bimetallic hydroxide (NiFeLDHs@NF) nanosheet arrays were synthesized on foam nickel substrate by solvothermal method as selfsupporting electrodes. Structurally, the NiFeLDHs nanosheet array grows vertically on the porous nickel foam substrate, which provides a directional electron transport channel and avoids the masking effect of the adhesive on the active sites. At the same time, the ultrathin properties of nanosheets not only provide a larger specific surface area, enhance the coordination unsaturation of surface atoms, bring higher surface energy and reactivity, but also shorten the mass transfer path which is beneficial to the rapid diffusion of reactants and timely desorption of products, and improves the rate and efficiency of catalytic reaction. The results show that NiFeLDHs@NF exhibits excellent electrocatalytic performance of urea oxidation reaction (UOR). A high current density of 50 mA·cm-2 can be reached at a potential of only 146 V(vs. RHE). Compared with oxygen evolution reaction, the potential decreased greatly by 140 mV. Moreover, NiFeLDHs@NF shows the robust stability within 24 h. Theoretical calculation shows that the Bader charge of Ni site in NiFeLDHs is -125 e, indicating that Ni site is more likely to lose electrons and form NiOOH active species with high valence Ni3+. Ni3+ has strong adsorption to urea and is the real active site of UOR, which is beneficial to the rapid development of UOR and the stable progress of subsequent deprotonation. In addition, the conversion process of the intermediates from *CONH2N to *CONHN on Ni3+ sites is the reaction determination step of the whole UOR, with an energy of only 248 eV. It can be seen that the UOR is easy to occur on NiFeLDHs@NF and the reaction rate is fast. It provides a new idea for the application of layered bimetallic hydroxides in the field of hydrogen production coupled with the urea electrooxidation.
