Synthesis, Characterization and Application of Anisotropic Cu Nanowires and Nanoparticles for the Electrocatalytic Reduction of CO2

Abstract

Two fundamental steps are needed to halt or at least slowdown climate change. One is the reduction of atmospheric carbon dioxide (CO2), and two is developing more efficient renewable energy storage solutions. The electrocatalytic reduction of CO2 toward fuels or valuable chemicals is a promising candidate to solve both problems. Copper (Cu) is a unique catalyst capable of the electrocatalytic conversion of CO2 into a variety of carbon products like methane (CH4), ethylene (C2H4), or formic acid (HCOOH). However, the low selectivity towards C2 and C2+ products and the low stability of the bulk Cu catalyst complicate the economic viability of the electrocatalytic reduction of CO2. The use of Cu nanostructures as a catalyst has been shown to enhance the selectivity and the faradaic efficiency (FE) of the electrocatalysis due to the increased catalyst’s surface area and the control of the exposed Cu facets. Exposure of the Cu (100) facets in the catalyst’s surface has been demonstrated to enhance the FE for C2 products, especially ethylene. During our research, we used a colloidal approach to synthesize Cu nanowires (NWs) with exposed (100) facets. However, a side nucleation of nanoparticles (NPs) was observed in all cases. Adjusting the synthesis parameters, we were able to control not only the length and thickness of the NWs but also the size and structure of the side nucleation. Little to no research has been done on the impact on selectivity and stability of combining different Cu nanocrystals, nanocrystals with different shape, size, and exposed facets. By controlling the concentration of ligands during the colloidal synthesis, we were able to produce three different Cu catalysts: NWs with a diameter of 30 nm and multi–shaped NPs, 30 nm NWs with nanopyramids and 40 nm NWs with multi–shaped NPs. After modifying the NP’s concentration of the three different catalysts and comparing its electrocatalytic performance, we were able to show the impact of the NPs over the selectivity of the NWs. It has been revealed that a high concentration of NPs, in the case of 30 nm NWs with multi–shaped NPs and 30 nm NWs with nanopyramids, increases the selectivity towards ethylene and the stability of the catalyst. This increment is due to the creation of CO* intermediate over the NPs´ surface and its transfer to the NWs for its reduction to ethylene. The results of this research are promising with a maximum selectity towards, however, there is a need for more research to understand the mechanism of this synergy and how to optimize it