Tuning The Reaction Path For CO₂ Electroreduction Reaction Based On The Precisely Controlled Electrocatalysts

Electrocatalytic CO₂reduction reaction（CO₂RR）driven by renewable electricity to produce high value-added chemicals can not only alleviate the greenhouse effect,but also provide a feasible way for national carbon neutral strategy.However,the scale-up of CO₂RR technology is severely hindered by the limited selectivity towards targets products at present.Consequently,it is of particular importance to construct remarkable electrocatalysts,to understand the structure-performance correlation and regulate the reaction path.To this end,herein indium single-atom catalysts（SACs）with defined active sites and porous copper oxide nanosheet catalysts with adjustable nanopore structure,were precisely synthesized,so as to regulate the reaction path and reveal the in-depth catalytic mechanism.The main research contents of this thesis are as follows:（1）Tuning CO₂RR reaction path by coordination environment of indium single-atom catalysts.The coordinately unsaturated metal centers in single-atom catalysts（SACs）have unique affinity to reaction intermediates,and tuning the coordination structure of the active center can be an effective strategy to optimize the catalytic activity and reaction pathway.In this chapter,the coordination environments of indium single-atom catalysts（In SACs）were tuned by controlling the annealing temperature,enabling precise control of product selectivity.The CO₂RR tests show that the In SACs-800 and In₂O₃nanoparticles with In as the active center are favorable for formate production,while the In SACs-1000 catalyst with the carbon center near to indium,as active site,prefers CO production with the Faradaic efficiency of 97%at-0.6 V vs RHE.Notably,In SACs-1000 catalyst also show high stability towards CO formation,with durability over 60 h at 0.4 A while maintaining selectivity of 90%.Density functional theory（DFT）calculations and poisoning experiments show that the indium center in the In SACs is active for CO₂ conversion to formate,while carbon atoms adjacent to indium prefer the CO₂ to CO pathway.The idea on shift of active sites in this research offered new insights to understanding the excellent catalytic selectivity of SACs.（2）Controllable synthesis of porous copper oxide nanosheet catalysts and regulation of CO₂RR reaction pathwayDeveloping copper-based CO₂RR catalysts with high activity,selectivity and stability relies on exploring the precise synthesis,structure-activity relationship and electrocatalytic mechanism.In this chapter,porous Cu O nanosheet（p-Cu O NSs）catalysts with different nanopore sizes were designed by controlling the annealing time,and the impacts of pore size on competition between ethylene（C₂H₄）and ethanol（C₂H₅OH）,was investigated.It is experimentally discovered that with the increase of pore size,the selectivity of C₂H₅OH first increases and then decreases,with highest Faradaic efficiency of 44.1±1%at pore size 12.5 nm（p-Cu O-12.5 nm）.Remarkably,the partial current density of C₂H₅OH reaches high as 500 m A cm^-2,exceeding all state-of-the-art Cu-based catalysts to date.The systematic researches showed that ethanol selectivity can be significantly enhanced by increasing the OH^-concentration,of while the electrochemical measurements confirmed the highest^*OH coverage on the p-Cu O-12.5 nm catalyst owning to its strongest OH^-affinity.Moreover,DFT calculations show that the^*CHCOH intermediate tends to be converted to^*CCH under the condition of low^*OH coverage,which is favorable for the formation of C₂H₄.In contrast,high^*OH coverage benefits to create the electrostatic interaction between surface OH dipole and carbonyl dipole of hydrocarbon intermediates,thereby promoting the formation of^*CHCHOH and effectively improving the selectivity of C₂H₅OH.