Nickel Nanoflowers with Controllable Cation Vacancy for Enhanced Electrochemical Nitrogen Reduction.

The key to the design of electrochemical nitrogen reduction (NRR) catalysts is that the reaction sites can not only activate the N≡N bond but also have high catalytic selectivity. Vacancy engineering is an effective way to modulate active sites, and cation vacancies are considered to have enormous potential in tuning catalytic selectivity. However, research on NRR activity is still at an early stage due to the difficulty in preparation and precise regulation. Here, we provided an adjusted method of cation vacancy through topotactic transformation, which combines solvothermal reduction with etching via lattice confinement effect to accomplish precursor reduction and vacancy construction while maintaining consistent material morphologies. Based on the topotactic transformation, NiAl-LDH precursor was reduced to Ni metal nanoflower, while Al is simultaneously etched by alkali, thus the precise tunability of the cation vacancy can be achieved by adjusting the Al content in the LDH. The Ni nanoflower achieved excellent stability and high ammonia yield by adjusting the vacancy concentration. In addition, the insight into the selectivity and intrinsic activity of cation vacancies on NRR process has been revealed. For the reaction selectivity, the cation vacancy is beneficial to activate N≡N but not conducive to the HER process. For the intrinsic NRR activity, the generation of cation vacancies can also significantly reduce the energy barrier of NRR process and accelerate the reaction kinetics.