Scientists are looking for new ways to break down CO2 molecules to make useful carbon-based fuels, chemicals, and other products. Researchers have developed a method to fine-tune a copper catalyst to produce complex hydrocarbons — known as C2-plus products — from CO 2. The catalyst can produce C2-plus compounds with up to 72% faradaic efficiency (a measure of how efficiently electrical energy is used to convert carbon dioxide into chemical reaction products). That’s far better than the reported efficiencies of other catalysts for C2-plus reactions. The preparation process can be scaled up to an industrial level fairly easily, which gives the new catalyst potential for use in large-scale CO2 recycling efforts.
There have been advances in recent years in developing copper catalysts that could make single carbon molecules but interest is increasing in reactions that can produce C2-plus products. Prior research showed evidence that halogenation of copper — a reaction that coats a copper surface with atoms of chlorine, bromine, or iodine in the presence of an electrical potential — could increase a catalyst’s selectivity of C2-plus products.
The team experimented with a variety of different halogenation methods, zeroing in on which halogen elements and which electrical potentials yielded catalysts with the best performance in CO2-to-C2-plus reactions. They found that the optimal preparations could yield faradaic efficiencies of between 70.7% and 72.6%.
The research helps to reveal the attributes that make a copper catalyst good for C2-plus products. The preparations with the highest efficiencies had a large number of surface defects — tiny cracks and crevices in the halogenated surface — that are critical for carbon-carbon coupling reactions. These defect sites appear to be key to the catalysts’ high selectivity toward ethylene, a C2-plus product that can be polymerized and used to make plastics.
Ultimately, such a catalyst will aid in large-scale recycling of CO2. The idea is to capture CO2 produced by industrial facilities like power plants, cement manufacturing, or directly from air and convert it into other useful carbon compounds. That requires an efficient catalyst that is easy to produce and regenerate and inexpensive enough to operate on an industrial scale. Although the team has worked with lab-scale catalysts for the experiments, the researchers believe a catalyst of virtually any size could be developed using the method.