Construction Of Ni-Based Multiscale Catalysts By Electrospinning And Its Electrochemical CO₂ Reduction Performance

The preparation of high value-added CO by electrochemical CO₂ reduction reaction（CO₂RR）is an effective method to realize the efficient conversion of carbon resources and achieve the target of“carbon peaking and carbon neutrality”.In expensive and abundant Ni-based materials show promising application prospects in CO₂RR.However,due to the strong binding ability between Ni and*CO intermediate,traditional Ni-containing catalysts suffer from low current density,poor product selectivity,and high overpotential toward CO production in CO₂RR,which significantly restricts the practical applications of Ni-based catalysts in CO₂RR field.Literature findings have shown that breaking the linear scaling relationship between the adsorption energy of*COOH and*CO intermediates is vital to achieve efficient CO₂RR to CO reaction.High-efficiency catalysts should simultaneously enhance the stability of*COOH intermediate and accelerate the desorption of*CO intermediate.It is well known that regulating the catalyst electronic structure can effectively balance the binding strength of the two key reaction intermediates on the catalyst.On this basis,the thesis is oriented towards regulating the electronic structure of metal Ni.A series of multi-scale and high-efficiency Ni-based CO₂RR catalysts for CO production are efficiently prepared by various regulation strategies,where the electrospun carbon nanofibers（CNFs）serve as reactor.Meanwhile,the relationship between CO product selectivity and catalyst structure was investigated as well as its catalytic mechanism.The main research contents of this thesis are as follows:（1）In order to achieve efficient regulation of the electronic structure of metallic Ni,the confined-effect from CNFs is employed to in situ construct Au Ni homogeneous solid solution alloy with positively charged Ni active sites.Aberration corrected-scanning transmission electron microscopy（AC-STEM）and X-ray diffraction（XRD）results confirm the successful preparation of Au Ni homogeneous solid solution alloy,and X-ray absorption fine structure（XAFS）analysis prove the positively charged Ni sites in Au Ni alloy in which an extensive electron transfer exists between high electronegativity Au element and low electronegativity Ni element.The CO₂RR performance of Au Ni alloy can be adjusted by the electronic structure regulation in Au Ni alloy.When the element ratios of Au and Ni are equal,the Au Ni alloy exhibits the optimal CO selectivity,the Faradaic efficiency of CO(FE_CO)reaches 92%at-0.98V versus reversible hydrogen electrode（vs.RHE）.Theoretical investigation shows that the alloying strategy of Au and Ni can positively shift the d-band center of the catalyst,lowering the activation energy barrier of CO₂ molecules and the binding energy of*CO intermediate.（2）In addition to the metal combination effect,the strain effect plays a crucial role in regulating the electronic structure of the alloy.Aiming at the complexity and difficulty of precisely controlling the strain effect of alloy,a thermodynamically driven strategy to regulate the strain of Ni-based alloys is reported,which can control the binding energy of CO₂RR intermediates on alloy catalysts.Utilizing the confinement effect of CNFs,Ni-based alloy nanoparticles with stress-strain effect have been successfully prepared,including s-Pd Ni,s-Ag Ni,and s-Au Ni.Molecular dynamics simulations（MDs）initially reveal that the strain effect in Pd Ni alloy（s-Pd Ni）is closely related to the preparation temperature.The thermal driving energy generated by high temperature can regulate the average bond length between heterogeneous metal atoms,thereby realizing the regulation of lattice strain.AC-STEM,XRD,and XAFS characterizations confirm the temperature gradient-induced strain relaxation in Pd Ni alloy.The optimized FE_CO of s-Pd Ni with a tensile strain of 2.3%can be up to 96.6%at-0.88V vs.RHE,which is higher than that of s-Pd Ni with a tensile strain of 3.2%,FE_CO=71.9%at-0.98 V vs.RHE.Besides,theoretical calculations reveal that strain relaxation can effectively regulate the surface electronic structure of Pd Ni alloy,leading to optimizing the formation energy barrier of*COOH and*CO intermediates,thus,endowing the outstanding performance toward CO production,which can also be proved by in situ spectroscopic characterizations.（3）Compared with Ni-based alloy NPs,the high atom utilization and unique electronic structure of Ni single atom catalysts（SACs）can efficiently enhance the CO₂RR activity and CO product selectivity.To suppress the sintering behavior of Ni NPs and realize the efficient preparation of Ni SAs.A competitively atoms trapping strategy is proposed to construct Ni atomical catalysts.Initially,the Ni NPs and VC NPs are in situ formed by using nitrogen-doped carbon nanofibers（NCNFs）as a carrier.The transformation of Ni NPs to Ni SAs in NCNFs can be achieved by gradient-temperature.The migration and trapping of Ni SAs from NCNFs to VC NPs surface can be realized by regulating the diffusion path of Ni SAs in NCNFs carrier,forming a unique Ni _SA-VC structure.Theoretical calculations demonstrate that VC NPs substrate own stronger adsorption capability and higher thermodynamic stability toward Ni SAs than that of NCNFs substrate,which facilitates the formation of Ni _SA-VC structure.XAFS results reveal that the integration of Ni SAs and VC NPs can effectively tune the coordination environment of Ni SAs.The VC-trapped Ni SAs can optimize its CO₂RR reaction pathway and exhibits outstanding CO product selectivity,the optimal FE_CO reaches 99.2%at-0.98 V vs.RHE.（4）In view of the single active site of Ni SACs,to enrich the active sites of Ni SACs and precisely regulate its coordination environment,an interatomic electronegativity compensation strategy is proposed based on Cu atom（1.90）and Ni atom（1.91）with analogous electronegativity,which is guided by the electronegativity of metal atoms.Using CNFs with nitrogen-rich sites as a reaction template,the Cu Ni dual single atom（DSA）anchored on CNFs（Cu Ni-DSA/CNFs）is realized by utilizing the high-temperature gas-phase migration strategy of Cu and Ni precursor metal salts.AC-STEM characterizations confirm the successful anchor in CNFs surface.XAFS results reveal the interatomic interaction between Cu and Ni atoms in Cu Ni-DSA sites.The obtained Cu Ni-DSA/CNFs show an outstanding CO product selectivity(FE_CO>90%)across a wide potential range from-0.78 to-1.18 V vs.RHE.Theoretical calculations demonstrate that the interatomic electronegativity compensation can optimize the binding strength of*COOH intermediate and facilitate the CO₂RR kinetics.