Mechanism study of reduction of CO2 into formic acid by in-situ hydrogen produced from water splitting with Zn: Zn/ZnO interface autocatalytic role

We have previously developed a new process of highly efficient conversion of CO2 and water into formic acid with metallic Zn without the addition of catalyst, however, its mechanism is not clear, particularly in the catalytic role of Zn/ZnO interface. Herein, the autocatalytic role of Zn/ZnO interface formed in situ during the reduction of CO2 into formic acid with Zn in water was studied by combining high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques and experimental data. The electron microscope results show that possible defects or dislocations formed on Zn/ZnO interface, in which plays a key role for ZnH- formation. Further XPS analyses indicate that oxygen vacancies on Zn/ZnO interface increased at short reaction times (less than 10 min). These analyses and experimental results suggest that a highly efficient and rapid conversion of CO2 and water into formic acid should involve an autocatalytic role of the Zn/ZnO interface formed in situ, particularly at the beginning of the reaction. (C) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.