Preparation And Catalytic Performance Research On Metal/Graphene Catalyst Of Electrochemical Reduction Of CO₂

At present, the world-wide environmental issues, especially the greenhouse effect, attracts more and more attentions. Due to CO2 is the main greenhouse gas, the researchers have focused on the reduction and recycling utilization of CO2 for a long time. CO2 emission reduction and cyclic utilization conforms to the requirements of the harmonious development of human and nature. Besides, it is conducive to environmental protection and sustainable development of economy. In this experiment, the natural flake graphite could be oxidized to graphite oxide by improved Hummers method and metal/graphene catalysts for electrochemical reduction of CO2 were prepared by means of sodium borohydride reduction in a graphite oxide suspension, which were characterized by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) technologies. Besides, electrochemical performance tests of the catalysts were carried out by cyclic voltammetry (CV), chronoamperometry (I-t), electrochemical impedance spectroscopy (EIS) technologies.The characterization results of metal/graphene (Pd/graphene, Cu/graphene, Pd-Cu/graphene) with different qualities proportion of Pd and Cu prepared in this experiment showed that the characteristic peak of graphite oxide was disappeared, and the characteristic peaks of Pd and Cu could be observed after reduction by sodium sodium hydride. It indicated that the metal particles were successfully loaded on the surface of graphene. The metal particles loaded on the surface of graphene were distributed without reunion. Among them, 1%Pd/graphene catalysts with the metal particles size was 6.5±0.25 nm, 1%Cu/graphene catalysts with the metal particles size was 5.4±0.10 nm,1%:2%Pd-Cu/graphene catalyst with the metal particle size was 7.5±0.25 nm, which were all within the range of 8 nm. The thickness of 1%:2%Pd-Cu/graphene layer was 3.0-3.5 nm.The test results of electrochemical performance showed that 1%:2%Pd-Cu/graphene catalyst had the best catalytic effect in 0.5 mol/L KHCO3 solution saturated with CO2, which had a small peak potential and reduction current were-1.3 V (vs. Ag/AgCl) and-2.8 mA compared with other catalysts, respectively. Besides, through comparison of CV result of N2 solution (peak potential:-1.75 V, reduction current:-0.5 mA), the catalyst suppressed the reaction process of hydrogen effectively. In addition, it had the most stable effect on catalytic reduction of CO2. The EIS result further verified the results of cyclic voltammetry tests. The results showed that the surface charge of this catalyst with the best catalytic performance migrated fastest. CO2- intermediates played a key role in the electrochemical reduction of CO2. Additionally, HCO3- was involved in the reaction and promoted the reaction process. The presence of HCO3-was positive related to the reaction rate in the reaction.