(Keynote) Understanding Selective C-C Coupling Reaction on Cu Based Nanoparticle from Electrochemical CO_2 Reduction Reaction

摘要

Cu is one of the interesting CO_2 reduction reaction catalysts due to its unique capability to produce many of the hydrocarbon chemicals in addition to H_2, and the nanostructures of the Cu-based electrocatalyst significantly affect the product selectivity for C_(2+) over C_1 chemicals. Although material engineering strategies have aimed at the design of a selective C_(2+)-producing catalyst, the role of the fundamental descriptor allowing control of the desired pathway is not yet well-understood. In this context, reliable guidelines for highly selective reactions require understanding the catalyst material and the reaction pathways. Both of a H-cell and gas-diffusion-electrode (GDE) based gas-fed cells have shown the enhanced ethylene selectivity with Cu nanoparticles prepared by oxide forms. The fragmented Cu surfaces having high defects or grain boundaries are proposed as active sites for C-C coupling based on the material characterization. In addition, in-situ spectroscopy such as X-ray absorption spectroscopy, Raman spectroscopy, and infrared absorption spectroscopy can provide additional information of the catalyst and intermediate operando condition. We demonstrated that the sites showing high vibrational frequency of *CO on the fragmented Cu surface are the potential active sites for the fast dimerization of CO, and C-C coupling occurs exclusively by CO dimerization toward *OCCO, without the participation of *CHO which is an intermediate for CH_4 production. We propose that the reactions leading to formation of *CHO and *OCCO are non-competitive and kinetically independent, implying the selective C-C coupling is potentially controllable.