Producing renewable fuels and other useful materials from carbon dioxide that has been pulled from the atmosphere has become one of the most important tasks for modern fuel research. The catalysts in use, which can perform this conversion, are usually made from expensive metals. Now, scientists at the Lawrence Berkeley National Laboratory have discovered an inexpensive and environmentally safe method to create a clean chemical system for producing renewable energy from carbon dioxide using oxide-derived copper.
The scientists have built on the results of previous studies which investigated the catalytic properties of copper (e.g. copper nanoparticles, copper oxide) and shown in a recent study (2018) that copper oxide nanoparticles as a catalyst can initiate processes with carbon and water to produce many useful products, such as ethanol. The surface of copper is rough at the micrometre scale. These rough areas are ideal for copper electrons to react with molecules in chemical reactions. The oxide-derived copper nanoparticle catalyst is responsible for the formation of new molecules through electron exchange. Some of the sites of copper oxide have specific shapes to efficiently transform CO2 into ethanol, ethylene, and propanol through electrochemical CO2 reduction (CO2R) in aqueous media. The catalyst used in this experiment was made up of tightly packed copper oxide spheres which fused and transformed into cube-like nanostructures during electrolysis.
Research on ethanol production with the help of copper nanoparticle catalysts is not new and has been conducted since the 1980s. At that time it was assumed that copper as a catalyst was not product-specific and could be used for making ethanol, ethylene, propanol, or some other carbon-based chemical, but the process would involve a lot of steps to separate residual chemicals before achieving the chemical end-product. In the following years, research, however, revealed that costly and energy-intense production can be avoided by using oxide-derived copper.
In 2015, scientific research was carried out on selective electroreduction of CO2 to C2 compounds on copper(I) oxide films. An interesting finding of this study is that the thickness of the deposited overlayers can influence the faradaic yields of ethanol.
In another study (2016) research was conducted on a nanostructured catalyst for the direct electrochemical conversion of CO2 to ethanol with high faradaic efficiency and high selectivity (84 %) which can operate in water and at an ambient temperature and pressure. The catalyst contained no noble metals, only copper nanoparticles on an N‐doped carbon nanospike film. The study suggests that the carbon nanospikes work in tandem to control the electrochemical reduction of a carbon monoxide dimer to alcohol.
In 2017, scientists designed a new catalyst for the direct transformation of carbon dioxide into multi-carbon fuels and alcohols using record-low inputs of energy. The catalyst consisted of an electrocatalyst made up of pure copper nanoparticles which provided the conditions necessary to convert carbon dioxide into ethylene, ethanol, and propanol.
One of the advantages of oxide-derived copper nanoparticle catalysts is that, in contrast to conventional copper electrodes which consist of individual nanoparticles sitting on top of each other, oxide-derived copper is made of copper nanocrystals that form a network with clear grain boundaries. Oxide-derived Cu (OD Cu) catalysts exhibit higher selectivity towards potentially valuable multi-carbon products (for example, ethanol and ethylene) with lower overpotential requirements. They also require only a small voltage to give good results.
Furthermore, using sun or wind energy to provide the energy needed to produce ethanol would make the process carbon neutral. The CO2 used for conversion into ethanol would be taken out of the atmosphere and then returned there during combustion. Thus, a closed loop and emission-free system could be created.
The scientists are confident that “putting these product-specific sites into a single catalyst could one day result in a very efficient and selective generation of chemical products.” They hope that this will mark the beginning of a new form of chemical manufacturing where solar cells could feed electrons to copper oxide catalysts to produce ethanol fuels, reduce CO2 emissions and create an environmentally safe system for the generation of chemical products.