Ni/Cu Transition Metal Catalysts For Electrocatalytic CO₂/NO₃^- Reduction Coupling And Urea Oxidation

Electrocatalytic conversions of small molecules,such as CO₂ and NO₃^-reduction,urea synthesis and urea oxidation,are effective strategies to alleviate energy and environment crises,it not only reduces energy consumption and CO₂emissions,but also enables the synthesis of high value-added chemicals.The development of efficient and cost-effective transition metal electrocatalysts for small molecule conversion reactions is of great importance for academic research and practical application.In this thesis,a series of Ni/Cu transition metal catalysts have been developed and their performance in electrocatalytic CO₂ reduction to CO,electroreduction of NO₃^-to ammonia,electrocatalytic urea synthesis and oxidation has been investigated,and the conformational relationships between catalyst structure and performance and catalytic reaction mechanisms have been explored.Details of the studies are given below.1.In this work,we have developed an exceptionally active Ni-nanoparticle catalyst（Se Ni-p@NC）for potential industrial-scale CO₂ reduction via creating pyridinic N-Ni-Se electron donator-acceptor motifs at the interface between Ni NPs and nitrogenated carbon layer.More impressively,an industrial-level current density up to 350 m A cm^-2 with high CO selectivity(FE_CO of 97%)has been achieved.Mechanism studies reveal that pyridinic N-Ni-Se motifs induce electron localization effect,and consequently intensifies the interaction between Ni and N-C motifs,and uplifts the d-band center of surface Ni towards the Fermi level.The pyridine N species also facilitate the adsorption and activation of CO₂ and the stable adsorption of*COOH intermediates,endowing the Se Ni-p@NC with enhanced activity and stability.2.In this work,we have designed and synthesized a Cu-oxalate catalyst with an anti-reductive Cu-O structure,which exhibited good performance in electrocatalytic NITRR synthesis of ammonia as well as Urea synthesis.An industrial-level current density up to 229 m A cm^-2 with high NH₃ selectivity(FE_CO of 97%,-0.6 V vs.RHE)in NITRR and high Urea selectivity(FE_CO of 71%,-0.3 V vs.RHE)in Urea synthesis has been achieved.XPS characterisation showed that a stable Cu-O structure was maintained in the Cu-oxalate catalyst after the electrocatalytic reaction.The results of in-situ Raman spectroscopy show that the presence of the Cu-O structure significantly improves the selectivity of ammonia and urea.XRD characterisation showed significant tensile strain in the Cu singlet lattice produced by the electroreduction of the Cu-oxalate catalyst,which increased the electrochemically active surface area of the catalyst and the mass transfer rate of the reactants,facilitating the C-N coupling reaction and thus improving the selectivity of urea synthesis.3.NiSe@NF heterostructured catalysts were prepared by reconstructing the nickel foam surface through a Se doping-electrooxidation reaction.Ni Se@NF exhibited high urea electrooxidation（UOR）performance,in an electrolyte containing 1 M KOH and 0.33 M urea,an oxidation current density of 100 m A cm^-2can be obtained at a lower potential of 1.38 V vs.RHE.Structural characterisation of the catalysts showed that Ni Se@NF induces lattice compression strain on Ni through Se oxidation bias in the UOR,resulting in the generation of a large number of highly reactive Ni sites by reconfigurating the catalyst surface.In-situ Raman spectroscopy and EIS studies confirm the involvement of the highly reactive intermediate Ni OOH produced during the reaction in the urea oxidation reaction,following the indirect urea oxidation mechanism.During the UOR process,the doped-Se induces the formation of highly oxidised Ni,which leads to the generation of oxygen vacancies on the catalyst surface through the contraction of the nickel lattice,thus allowing Ni Se@NF to exhibit excellent catalytic activity.