Design Of Ag,Sn-based Catalysts And Study Their Electrochemical CO₂ Reduction Performance

Using the electricity originated from renewable resources(such as solar,wind,tidal,etc.)to convert the incremental amount of CO₂ in the environment into chemicals with added value can not only contribute to the mitigation of the greenhouse effect,but more importantly,can realize the carbon cycle in nature,which is an effective way to achieve the goal of global carbon neutrality.However,the electrochemical reduction of CO₂(CO₂RR)is limited by high reaction overpotential,slow reaction kinetic process,uncontrollable hydrogen evolution side reaction,and lower stability due to the inertness of CO₂ molecular structure.Therefore,design electrocatalyst with high selectivity and stability is the foundation for achieving the industrialization of CO₂RR.In this paper,a series of highly active CO₂RR catalysts were prepared by adjusting the oxidation state of the catalyst,designing the single-atom dispersed catalyst,regulating the metal-carrier interaction,and constructing porous materials with high active sites.These strategies can effectively promote the activation of CO₂,inhibited the hydrogen evolution reaction(HER),and improved the catalytic stability.The concrete research contents are shown as follows:Oxide-derived silver-based electrocatalysts have been prove could enhance the performance of CO₂RR by improving the binding capacity of intermediates.However,the oxygen species are easy to vanish at reduction potential,resulting in low catalytic stability.Therefore,we designed an oxide-derived electrocatalyst Ag/g-C₃N₄,which is rich in stable oxygen species,by the thermal decomposition of silver oxide using g-C₃N₄ as support.When used as catalyst for CO₂RR,an overpotential 190 m V and a maximum CO Faraday efficiency(FE_CO)of 94.0%was achieved on Ag/g-C₃N₄,which is superior to the physically mixed sample(P-Ag/g-C₃N₄)and chemical reduced sample(C-Ag/g-C₃N₄).These oxygen species can exist even after 20 h stability test,which is the reason for the higher stability.In addition,the strong interaction between Ag NPs and g-C3N4 can alter the rate-determining step(RDS)of CO₂RR from the electron transfer to the proton transfer process,which is another reason for the high activity of Ag/g-C₃N₄.To further improve atomic availability,based on the above research,we prepared atomically dispersed silver catalyst(SAC-Ag/g-C₃N₄)using g-C₃N₄ as support by silver oxide thermal decomposition method.The dispersed silver atoms were anchored by the Ag-N bond,which is originated from the rich lone pair electron coordination of nitrogen atom on g-C₃N₄,to prevent the aggregation of the silver atom.When used as catalyst for CO₂RR,a maximum FE_CO of 93.7%correspond with a mass activity as high as320.5 m A mg^-1 could be obtained at-0.7 V vs.RHE in the H-type electrolytic cell,which is higher than most silver-based catalysts reported currently.Meanwhile,SAC-Ag/g-C₃N₄shows significantly higher stability than the silver nanoparticles sample during 20 h experiment,proving that SAC-Ag/g-C₃N₄ possesses high atomic availability,product selectivity as well as high durability.A simple strategy to modify the surface electronic state of Sn O₂ nanoparticles(NPs)rich in divalent Sn²⁺and Sn⁴⁺was developed by metal oxide-support interaction using g-C₃N₄ and reduced graphene oxide(r GO)as substrate.The interaction between Sn O₂and g-C₃N₄ enables the lone pair electrons on N atom transfer to the surface of Sn O₂nanoparticles,result in surface electron-rich electronic Sn⁴⁺@Sn²⁺core-shell structure like nanoparticles.Sn O₂/g-C₃N₄ exhibits a higher FE_C1 above 90%under a wide potential range from-0.86 to-1.36 V vs.RHE and reach its maximum value of 95.1%(including the FE of 76.2%for HCOOH and FE of 18.9%for CO)at-1.06 V,which is significantly higher than the Sn O₂/r GO sample.Besides,Sn O₂/g-C₃N₄ displayed stable durability of 70h efficient electrolysis without obvious activity attenuation at-1.06 V.Systematic experiment and characterization show that the catalytic performance of C₁product is positively correlated with the content of divalent Sn²⁺on the surface of Sn O₂.It is speculated that the core-shell electronic structure of Sn⁴⁺@Sn²⁺can well maintain the HER suppress role of Sn²⁺and the higher CO₂ activation ability of Sn⁴⁺.Based on the property that organic amine cations in metallic chalcogenide crystal materials can be removed at relatively mild temperature to form a porous structure,choline-templated layered selenidostannate,[(CH₃)₃N(CH₂)₂OH]₂[Sn₃Se₇]?H₂O(Ch-Sn₃Se₇),was used as precursor to convert into a series of P-Sn O₂ materials with tuned particle size under air atmosphere.P-Sn O₂ exhibits high FE_C1 beyond 90%(maximum value:94.5%)under a wide potential range from-0.96 to-1.26 V and excellent long-term stability(100 h)without decay.Detailed investigation of the long-term electrolysis revealed a gradual fragmentation of the pristine Sn O₂ nanoparticles along with a partial Sn O₂-Sn O-Sn self-reduction,which contributes to increased active sites that account for the highly selective and stable electrolysis process.