Application And Research Of Non-noble Metal-based Catalysts In Electrocatalytic Reduction Of Nitrogen

Nitrogen cycle is a fundamental process highly related with the global living organisms and human activities.Currently,the artificial nitrogen fixation primarily relies on the Haber-Bosch technology,which consumed～2%of anthropogenic energy and emits over 300 million tons of CO₂ annually for N₂ dissociation and high-purity hydrogen production.Electrochemical nitrogen reduction reaction（NRR）provides a promising alternative for the synthesis of ammonia（NH₃）under ambient conditions.Electrocatalyst is an important part of it.Non-noble metal based catalysts have been widely studied because of their advantages of low price and high catalytic efficiency,in which the empty d orbitals of transition metals（Ni,Cu,Fe,etc.）in the d-zone can accept the lone pair electrons of N₂,and the p orbitals of metals（Bi,Sn,etc.）in the P-zone can effectively activate N₂ molecules,so the catalysts based on these metallic elements become promising electrocatalysts.However,competitive hydrogen evolution reactions（HER）and weak binding ability of key intermediates result in low catalytic activity and selectivity of NRR.Here,we prepare high-performance NRR catalysts by regulating oxygen content of different metal oxides or doping to inhibit HER and strengthen the binding of key intermediates.The specific research content is as follows:（1）A simple preparation method of oxide-derived Bi-based catalyst（OD-Bi）,which can be inherited from in-situ reduction ofβ-Bi₂O₃,was designed.The as-synthesized OD-Bi catalyst exhibits superior electroreduction of N₂and CO₂performance using both pure gases and flue gas as feedstocks.A high NH₃ FE of 18.53%and yield rate of 11.5μg h^-1 mg_cat.^-1are obtained at-0.1 V vs.RHE for pure N₂reduction.And the outstanding performances are well preserved in simulated flue gas（15%CO₂ concentration balanced by N₂ and trace amounts of O₂ and SO₂）,the maximum formate FE of 97.3%at-0.5 V vs.RHE and wide potential range of 700 m V with FEs above 90%are achieved within a flow cell reactor.The in-situ Raman spectroscopy detect reveals key intermediates of*N₂H_x（x=1-5）and*OCHO during N₂-to-NH₃ and CO₂-to-formate processes,respectively.DFT calculations further demonstrate that the oxygen species coordinated on OD-Bi surface can significantly favor the formation of*NNH and*OCHO intermediates and suppress the competing HER,thus leading to the high selectivity of NRR and CO₂RR.（2）A hydroxide-derived Ni Cu O_x with controlled Ni doping ratio was designed as an electrocatalyst to promote NRR.The metal atoms in the catalyst are evenly mixed by ultrasonic method.The synergistic effect of Cu and Ni makes Ni Cu O_x have higher activity and stability in thermodynamics and kinetics than the single Cu O and Ni O catalyst.After the addition of Ni in Cu O lattice,the synergistic effect of Cu and Ni changes the electron distribution of the catalyst.The adsorption and hydrogenation of nitrogen at the active site were promoted,and the process of nitrogen fixation was promoted.As a result,Ni Cu O_x The catalyst achieves 11.778μg h^-1 mg_cat.^-1and the best selectivity is 19.28%at low voltage.And ¹⁵N₂ isotope-labeling tests confirmed that the N element in ammonia came from nitrogen.