Surface Structure Regulation Of Metal/Metal Oxides And Their Application In Electrocatalytic CO₂ Reduction And Photocatalytic CH₄ Oxidation

At present,the global energy crisis and climate warming have brought great challenges to the sustainable development of human society.Converting CO₂ or CH₄（the main components of greenhouse gases）into high value-added fuels by designing high-efficiency photocatalysts and electrocatalysts is an important solution to the above challenges.The adsorption and activation of reactants,electron/energy transfer and other processes are important factors affecting the efficiency of the catalytic reaction,and they are closely related to the structural characteristics of the catalyst surface.Herein,we regulated the surface structure of metal/metal oxide catalysts by constructing single atomic sites or oxygen defects,exploring the structure-activity relationship in the catalytic reaction.The main contents of this paper are as follows:1.Design of BiCu single-atom alloy catalyst for efficient electroreduction of CO₂ to formate:To improve the current density and Faradaic efficiency of Bi-based catalysts in the electrocatalytic CO₂ reduction process,we introduced isolated Cu single atoms sites into the Bi lattice to obtain a BiCu single-atom alloy catalyst（BiCu-0.5）.The experimental results show that BiCu-0.5 can deliver an ultrahighformate partial current density(j_formate)of 434 m A cm^-2,with a formate Faradaic efficiency(FE_formate)of 96.5%at-0.55 V vs.RHE in a gas diffusion electrolyser（GDE）,while BiCu alloy catalyst containing Cu nanoclusters can only deliver a j_formate of 48.5 m A cm^-2 with a FE_formate of 37.3%under an identical condition.Mechanism investigations and and experimental results reveal that the isolated Cu atoms in BiCu-0.5 can dramatically decrease the energy barrier of water activation to*H（the Volmer step）,and at the same time inhibit the generation of H₂,thereby promoting the reaction of*H with CO₂ to form formate.This work provides a new strategy for designing efficient electrocatalytic catalysts for CO₂ reduction.2.Constructing oxygen-vacancy-rich surface disorder layer for selective photocatalytic CH₄ conversion:To improv the photocatalytic CH₄ conversion rate and selective without using noble-metal cocatalyst,we constructed a disordered layer with abundant oxygen vacancies on the surface of Ti O₂.（Photo）electrochemical and in situ Raman spectroscopic measurements reveal that an optimized oxygen-vacancy-rich surface disorder layer with a thickness of 1.37 nm can simultaneously promote the separation and migration of photogenerated charge carriers,and enhance the activation of O₂ and CH₄ to·OH and·CH₃ radicals,thereby synergistically boosting HCHO production in aerobic photocatalytic CH₄ conversion.Benefiting from the above advantages,the production rate of HCHO is up to 3.16 mmol g^-1 h^-1,and the selectivity is 81.2%,outperforming those of the reported photocatalytic systems.This work sheds light on the mechanism of O₂-participated photocatalytic CH₄ conversion on defective metal oxides,and expands the application of defect engineering in designing low-cost and efficient photocatalysts.3.Constructing surface defects that can modulate reactive oxygen species for selective photocatalytic CH₄ conversion:To achieve the goal of efficiently tuning photocatalytic CH₄ conversion to different kinds of oxygen-containing liquid-phase products,we constructed different kinds of oxygen defects on the surface of Ti O₂ by Na BH₄ reduction method,to manipulate the activation of O₂ into various reactive oxygen species.The results show that the main product of the photocatalytic CH₄oxidation by point-defect-modified Ti O₂（Point-Def-Ti O₂）is HCHO,and the production rate is 650.7μmol g^-1 h^-1,the selectivity is 68.1%,while the main product of the photocatalytic oxidation of CH₄ by pit-defect-modified Ti O₂（Pit-Def-Ti O₂）is CH₃OOH,and the production rate is 577.7μmol g^-1 h^-1,the selectivity is 63.6%.（Photo）electrochemical test show that the introduction of oxygen defect can promote the separation of photogenerated carriers and prolong the lifetime of the carriers.In addition,the in-situ Raman results of O₂ adsorption show that the Point-Def-Ti O₂ can promote the adsorption of O₂ in a Yeager-type（side-on）,forming Ti-OO-Ti intermediate,which is beneficial to the generation of·OH,while the Pit-Def-Ti O₂ can promote the adsorption of O₂ in a Pauling-type（end-on）,forming Ti-OOH intermediate,which is beneficial to the generation of·OOH.This study demonstrates that modulating the fine structure of surface defects can change the way of O₂ activation and modulate the species of reactive oxygen species,thereby achieving highly selective photocatalytic conversion of CH₄ to different products.