| dc.description.abstract | The increasing concentration of CO2 in the atmosphere leads to global warming, which greatly changes the climate and the ecological balance of nature. Therefore, electrochemical CO2 reduction reaction (CO2RR) to produce highly value-added products is regarded as a prospective path toward carbon cycling. However, the challenges in electrochemical CO2RR are its competition to hydrogen evolution reaction (HER) and unsatisfied products selectivity. Therefore, the design and preparation of highly effective catalysts with low overpotential, high faradaic efficiency (FE), and high selectivity is key consideration for the development of CO2RR technology.
This research is divided into two parts. In the first part, the binary In-Sn catalysts with In/Sn atomic ratios of 3/1 and 1/1 have been prepared. In -Sn nanoparticles (NPs) are composed of In, In(OH)3 and few InSn4 with some surface In hydroxides and Sn oxides. The catalyst with surface In hydroxide not only effectively suppresses the HER to increase the CO2RR activity but also interacts with CO2 to form In-CO3- species which then is reduced to formate. Therefore, the InxSny NPs show outstanding performance with a HCOOH FE of 92.6 % and excellent durability for 10 h at -1.0 V.
In the second part, a series of Ag-Sn binary NPs was designed for CO2RR. Structural characterizations reveal that the existence of Ag, Ag3Sn and SnO2 with few surface Ag oxides and many surface SnOx. The surface SnOx is the major active site in the formation of formate. According to the electrochemical results, Ag catalyst exhibits high CO FE of 94.9 %, without any formate products while SnO2 shows the formate FE of 71.0 %. It is interesting to find that Ag4Sn particularly shows excellent catalytic CO2RR to formate, with maximum formate FE of 90.9 % and partial current density of -4.64 mA cm-2 at the overpotential of -1.0 V (vs.RHE). Moreover, the catalytic activity of Ag4Sn remains reasonably stable over a 10 h period of electrolysis, demonstrating its potential for electrochemical CO2RR to formate. Based on the above results, the transformation of product selectivity, the optimization of the HCOOH selectivity, activity and stability stem from the synergistic effect between metals and oxides in Ag-Sn during electrocatalysis. This research provides guidelines for the improvement of CO2RR selectivity by optimization of compositions and structures of Sn-based NPs. | en_US |