Construction And Properties Of Cu-based CO₂ Electroreduction Catalyst Based On Surface Reconstruction

Electrocatalytic carbon dioxide reduction（CO₂RR）produces more valuable chemicals,which is not only an effective measure to mitigate the greenhouse effect,but also can convert renewable energy into chemical energy and improve energy efficiency.However,the CO₂RR kinetics is slow and it often accompanies by complex side reactions such as hydrogen evolution.Therefore,the development of high-performance catalysts has become a research hotspot of electrocatalytic CO₂ reduction.Cu-based catalysts are widely used to electrocatalyze CO₂RR to produce ethylene,methanol,methane and other products with high added value.However,surface reconfiguration is easy to occur during the CO₂RR process,resulting in changes on crystal phase and valence state,etc,resulting in poor stability and selectivity of copper-based catalysts in the CO₂RR.Therefore,controlling the surface reconfiguration of copper-based catalysts to improve the selectivity of products and catalyst stability has attracted extensive attention.In this paper,aiming at the dynamic factors limiting the activity of electroreduction CO₂ of copper-based catalyst,a series of synthetic strategies including electrodeposition,hydrothermal,electrospinning,etching etc,are used to regulate the interaction between metal and carrier,control the surface reconstruction process,and improve the catalytic activity of electroreduction CO₂through defect engineering,reaction-induced surface species reconstruction and synergistical effect of multiple composite.Specific research contents are as follows:（1）Preparation of Cu@Cu-x catalyst and its performance in electroreducing CO₂ to H₂/CO.A series of Cu@Cu-x catalysts are prepared by controlling deposition time via the traditional electrical deposition copper foams approach.During the electroreduction process,the copper particles grow into sea urchin-like structures in situ.Electrocatalytic CO₂RR performance of the catalyst was evaluated in the 1 mol·L^-1 KOH solution.The results show that Cu@Cu-1 indicated the best catalytic performance with the current density of 114.4 m A·cm^-2,a smallest Tafel slope of 185 m V·dec^-1,the fastest reaction kinetics and the largest electrochemical active area compared to those of Cu@Cu-x（x=1,2,3,4）.Under the overpotential of-0.977 V vs.RHE,Faraday efficiency（FE）of electrocatalytic CO₂ reduction to syngas is 89%,while maintains a good cyclic stability.With the increase of copper deposition time,Cu@Cu-x the activity of the catalyst decreases and then increases in a concave curve.At low overpotential,high current density can effectively regulate the composition of H₂/CO（0.3:1～1:1）.The Cu（111）surface and the high index Cu（200）and Cu（220）have lower binding energy of*CO,which is conducive to the desorption of*CO and can promote the formation of CO products.（2）Preparation of x-Cu O/Ce O₂ catalysts and the performance investigation on electrocatalytic CO₂ reduction to C₂H₄.A series of x-Cu O/Ce O₂ catalysts were synthesized by adjusting Cu/Ce ratio via two-step hydrothermal reaction.Adjusting the ratio of Cu/Ce cand effectively coordinate the interaction of metal and carrier in the catalyst.In the electroreduction process,copper nanoparticles grow into nanobeams in situ,which is conducive to the exposure of active sites.The easy capture of electrons by Ce O₂ can reduce Ce⁴⁺to Ce³⁺,and the reduction of Cu O to low-price copper by O vacancy.Cu₂O（211）and Cu（111）can promote the C-C coupling,which significantly enhances the C-C coupling and improves the selectivity of C₂H₄.The results show that 40-Cu O/Ce O₂exhibited the best electrochemical performance with the current density of 67.51 m A·cm^-2,the polarization curve corresponds to the minimum Tafel value(12.33 m V·dec^-1),and the maximum electrochemical active area of 11.8 m F·cm^-2;Under the overpotential of-1.27 V vs.RHE,the Faraday efficiency（FE）of 40-Cu O/Ce O₂-electrocatalyzed CO₂reduction to C₂H₄ is 55.3%.The 40-Cu O/Ce O₂ catalyst still maintains a good stability after consecutive run for 12 h.Note that the content of Cu O affects the adsorption performance of CO₂RR intermediates.With the increase of Cu O content,the adsorption configuration of*CO is adjusted from easy hydrogenation to CH₄ to easy coupling to C₂H₄.（3）Preparation of Cu-Ce-O_x-B catalyst and its performance in electrocatalytic CO₂ reduction to CH₄.A series of high conductive Cu-Ce-O_x-B electrocatalysts were synthesized by adjusting the Cu/Ce ratio through multiple-step electrospinning,calcination and etching.The phase composition,elemental valence,morphology and electrochemical properties of the catalyst were analyzed,and the selectivity and product distribution of Cu-Ce-O_x-B electrocatalytic CO₂ reduction were investigated.The results show that the Cu valence in Cu-Ce-O_x-B still preserves at+2,and the electrocatalytic performance of Cu-Ce-O_x-4 catalyst is the best,having the maximum current density of 237.1 m A·cm^-2.Under the overpotential of-1.0 V vs.RHE,the FE of Cu-Ce-O_x-4 electrocatalytic CO₂reduction to CH₄ is 53.6%,while Cu-Ce-O_x-4 catalyst shows a high stability after consecutive run for 6 h.In addition,the study reveals that Cu²⁺can increase the adsorption property of*CO,inhibit*CO dimerization and reduce the selectivity of C₂ products,and thereby improving the catalytic performance and selectivity of CH₄.