Boosting CO₂ Electroreduction To Multicarbon Products Via Tuning Of The Copper Surface Charge

Serious environmental problems have been caused by more and more CO₂ emissions into the air by the development of human society.We urgently need to develop CO₂ conversion and utilization technology.Electrochemical CO₂ reduction（ECR）produces valuable chemicals,which can not only reduce the amount of CO₂ in the atmosphere,but also effectively solve the problem of resource shortage.ECR reaction involves multiple electron-proton transfer to obtain a large number of products.*CO is usually recognized as a key intermediate,and the reaction paths of different products cross,resulting in extremely complex reaction mechanism.Electrocatalysts have an important effect on the electrochemical reduction of CO₂.Among many widely used heterogeneous catalysts,Cu can effectively reduce CO₂ into valuable products and chemicals.The adsorption and desorption of reaction intermediates such as*CO and*OCCO are crucial.The different properties of Cu-based catalysts can affect the reaction intermediates,thereby affecting the distribution of products.However,ECR still has many problems that restrict its further industrial application,such as low overall Faraday efficiency（FE）of the product,low selectivity of a single product,severe hydrogen evolution reaction（HER）,high overpotential,low current density,and poor stability of the catalysts.Therefore,it is necessary to design effective catalysts and innovative catalytic systems to solve these problems.In this paper,we adjust the selectivity of ECR products by adjusting the surface charge of Cu.The specific findings are as follows:（1）The surface charge of Cu in CuSiO₃@SiO₂ was tuned through different hydrogen（H₂）annealing temperatures,leading to selective conversion of CO₂ into C₂₊chemicals（C₂H₄,C₂H₅OH,n-C₃H₇OH）.The simultaneous presence of Cu⁺and Cu⁰ is beneficial to the formation of C₂₊products.Regulating different proportions of Cu⁺and Cu⁰ on the surface of SiO₂ can optimize this synergistic effect,and the Cu^δ+-O-Simaintains the stability of Cu⁺in an electrolytic environment.（2）Density functional theory（DFT）indicated that Cu catalysts with lower valence states can significantly reduce the intermediate energy barrier of*CO coupling,while their H₂ precipitation energy is higher.Therefore,we predicted that adjusting the surface Cu⁺content may affect the selectivity of C₂₊products.The catalyst obtained by H₂ reduction at 250℃ is labeled as Cu^δ+@SiO₂-250,which can be quantitatively analyzed by XPS,and the ratio of Cu⁰ to Cu⁺on its surface is 0.5.HAADF-STEM showed that part of the surface of Cu was in close contact with Cu₂O nanoparticles.²⁹SiMAS NMR showed the generation of Cu^δ+-O-Si.（3）In an H-type electrolytic cell,the catholyte is 0.1 M KHCO₃ and the anolyte is 0.1 M H₂SO₄.A C₂₊selectivity of about 53.1%was achieved over Cu^δ+@SiO₂-250.Subsequently,under the condition that both the anolyte and catholyte were Cs Br electrolyte,C₂₊FE can reach as high as 70%.It was worth noting that the FE of the C₂₊product was 10 times that of the C₁ product,with a C₂₊partial current density of 9 m A cm^-2,and a stable electrolysis of 12 hours.At the same time,when tested in a flow cell,there was still 52%C₂₊selectivity at a current density of 500 m A cm^-2.