Design And Electrochemical Performance Of Zn-Based Catalysts For CO₂ Reduction

Electrocatalytic reduction of CO₂（CO₂RR）into high value-added chemicals has a broad application prospect,which could effectively solve the problem of carbon emission and alleviate the greenhouse effect.Among these possible products,CO has attracted extensive attention as an important industrial feedstock with high energy value and wide application.However,the CO₂RR still suffers from high overpotential,low selectivity,and poor long-term stability due to the high thermodynamic stability of CO₂and inevitable competing hydrogen evolution reactions.Although precious metal-based catalysts（e.g.Au,Pd and Ag）have been verified as the most efficient electrocatalysts for CO₂RR because of good catalytic activity and high CO selectivity,the high cost of these materials severely hindered their large-scale practical applications.Therefore,it is crucial to develop high performance non-precious metal catalysts for CO₂RR.Numerous studies have found that non-precious metal zinc（Zn）and its compounds could effectively catalyze the reduction of CO₂ to CO.However,Zn-based materials feature a limited number of active sites and low reaction rates,and the adsorption of reaction intermediate*COOH on Zn species was very weak due to the electron-rich characteristics of metal Zn,resulting in catalytic performance of Zn-based materials is far inferior to that of precious metal catalysts.Based on this,in this thesis,high performance Zn-based catalysts were designed and synthesized from Zn element,mainly by designing nanoporous structures and constructing heterostructure to fully expose the active site or enhance the formation process of key reaction intermediates.The main research contents are as follows:Firstly,a hierarchical porous Zn catalyst（HP-Zn）was designed and synthesized using the gas bubble-assisted method,with an abundant mesoporous structure and high specific surface area.The HP-Zn catalyst exhibited good catalytic activity and CO selectivity with a maximal FE_CO of 91.3%and high j _CO of-9.1 m A·cm^-2 at-1.1 V vs.RHE,and excellent long-term durability after an 8 h continuous electrolysis,demonstrating the advantages of the porous structure.This work provides a new idea for the synthesis of other types of porous materials.However,the HP-Zn catalyst still suffers from high overpotential and poor stability,and the catalytic performance needs to be further improved.After that,an accordion-like layered carbon catalyst with Ni₄N/Ni₃ZnC_0.7heterostructure was successfully prepared by a simple high-temperature pyrolysis and solid-state grinding strategy.The optimized Ni₄N/Ni₃ZnC_0.7electrocatalyst exhibited a a large CO partial current density(-14.6 m A·cm^-2)and high FE_CO（92.3%）at-0.8 V vs.RHE,together with a long-term stability about 30 h.A Zn-CO₂ battery was further assembled with Ni₄N/Ni₃ZnC_0.7 catalyst as the cathode,which showed a high power density of 0.85 m W·cm^-2.Density functional theoretical calculations also confirmed that Ni₄N/Ni₃ZnC_0.7 heterostructure is conducive to the formation of*COOH and charge transfer,and improve the catalytic activity and selectivity.