Delicate Tuning of the Ni/Co Ratio in Bimetal Layered Double Hydroxides for Efficient N2 Electroreduction

Electroreduction of N-2 to NH3 at ambient conditions using renewable electricity is promising, but developing efficient electrocatalysts is still challenging due to the inertness of N equivalent to N bonds. Layer double hydroxides (LDHs) composed of first-row transition metals with empty d-orbitals are theoretically promising for N-2 electroreduction (NRR) but rarely reported. Herein, hollow NiCo-LDH nanocages with different Ni/Co ratios were prepared, and their electronic structures and atomic arrangements were critical. The synergetic mechanisms of Ni and Co ions were revealed, and the optimized catalytic sites were proposed. Besides, in-situ Raman spectroscopy and N-15(2) isotopic labeling studies were applied to detect reaction intermediates and confirm the origin of NH3. As a result, high NH3 yield of 52.8 mu g h(-1) mg(cat)(-1) and faradaic efficiency of 11.5 % were obtained at -0.7 V, which are top-ranking among Co/Ni-based NRR electrocatalysts. This work elucidates the structure-activity relationship between LDHs and NRR and is instructive for rational design of LDH-based electrocatalysts.

Automated summary

In this study, hollow NiCo-LDH nanocages were successfully prepared and their relationship between structure and electrocatalytic performance was investigated. By revealing the synergetic mechanisms of Ni and Co ions and proposing optimized catalytic sites, high NH3 yield and faradaic efficiency in N-2 electroreduction were achieved.