Surface Modification And Synchrotron Radiation Characterization Of Cu-based CO Electro Reduction Catalysts

The increasing exploitation and utilization of non-renewable energy such as fossil energy has promoted the all-around development of social economy,science and technology.Whereas,at the same time,it has also brought two major crises of energy shortage and environmental pollution.The electrocatalytic CO reduction is driven by renewable electricity and aims to indirectly convert greenhouse gases into C2+carbon-containing fuels and high value-added chemicals through a two-step process.This provides a green and sustainable development platform for solving the energy and environmental crisis,and provides an ideal strategy for large-scale storage of intermittent electricity.Cu-based catalysts are widely used in the electrocatalytic CO reduction reaction due to their unique carbon-carbon coupling ability.In order to further improve the performance of the catalyst and further understand the mechanism of electrocatalytic CO reduction,a series of surface modified Cu-based catalysts with high efficiency which contribute to the formation of C2+products were successfully constructed.The structural properties of the catalysts and the reaction mechanism of CO reduction were systematically investigated by synchrotron radiation spectroscopy,density functional theory calculations and other research methods.More importantly,the vital influence of the regulation mechanism of the reaction intermediates on the electrocatalytic CO reduction performance was successfully elaborated in this dissertation.The main contents of this dissertation are as follows:1.The effect of amino modification on the electrocatalytic CO reduction performance of Cu-based catalysts was investigated.We obtained a surface amino-modified Cu@H2 catalyst by electrochemical in-situ reconstruction and evaluated its electrocatalytic CO reduction performance.The as-obtained Cu@NH2 catalyst showed a high selectivity to acetate with the highest Faradaic efficiency of 51.5%and the effective current density of acetate was around 150 mA cm-2.Synchrotron radiation spectra,kinetic isotope effect experiments and in-situ spectra corporately confirmed that the introduction of surface amino group can not only maintain the low oxidation state of Cu during the reduction process,but also promote the protonation process of*CO intermediate and enrich the*CHO intermediates.Combining with density functional theory calculations,the carbon-carbon coupling mechanism from stabilized*CHO intermediates through hydrogen bonding and promoted the coupling of*CO-*CHO to produce acetate was expounded.This study deepened the understanding of the mechanism of electrocatalytic CO to acetate,and provided a reference for designing efficient electrocatalysts by stabilizing reaction intermediates.2.The effect of surface porous structure of Cu-based catalyst on electrocatalytic CO reduction performance was investigated.By constructing a large number of nanoporous structures on the surface of Cu-based catalysts,we successfully obtained an efficient electrocatalytic catalyst for the conversion of CO to ethlyne with the highest ethylene Faradaic efficiency of 65.8%and the ethylene effective current density of 263.2 mA cm-2.The normalized ethylene partial current density to the electrochemical double-layer capacitance(Cal)of porous CuOx was 5.8 times that of the non-porous CuOx at 300 mA cm-2,indicating that the introduction of the porous structure improved the intrinsic activity of the catalyst.In-situ synchrotron radiation X-ray absorption spectra analyses showed that the active site in the electrocatalytic CO reduction process was metallic Cu,and the porous structure played a vital role in enriching the*CO intermediate,which promotes subsequent carbon-carbon coupling to produce ethylene by increasing the coverage of*CO on the catalyst surface.This study uncovered the reaction mechanism of electrocatalytic CO to ethylene,and provided a reference for designing efficient electrocatalysts by enriching reaction intermediates.3.The effect of surface Bi doping on the electrocatalytic CO reduction performance of Cu-based catalysts was investigated.On the basis of the porous CuOx,the hydrogenation ability of the catalysts was regulated by introducing different contents of Bi species,thereby further improving the performance of the catalysts.The electrochemical test results showed that the Bi species exhibited a stronger ability to activate water molecule.The results of electrochemical active surface area characterization showed that the introduction of an appropriate amount of Bi species effectively increased the active surface area of the catalyst,and further improved its ethylene selectivity.The work provided a reference for designing efficient electrocatalysts by regulating the hydrogenation ability of reaction intermediates,and provided new insights to further study the influence of doping metals on the product distribution of electrocatalytic CO reduction.