The electrocatalytic conversion of CO2 using renewable energy could establish a climate-neutral, artificial carbon cycle. Excess energy produced by photovoltaics and wind energy could be stored through the electrocatalytic production of fuels from CO2. These could then be burned as needed. Conversion into liquid fuels would be advantageous because they have high energy density and are safe to store and transport. However, the electrocatalytic formation of products with two or more carbon atoms (C2+) is very challenging.
Now, researchers in China have developed a new electrocatalyst that yields ethanol, acetone, and n-butanol as major products with a total C2-4 faradaic efficiency of about 49 % at −0.8 V vs. reversible hydrogen electrode (RHE), which can be maintained for at least 3 months. A paper on the development is published in the journal Angewandte Chemie.
Credit: Angewandte Chemie
To make the electrocatalyst, the team from Foshan University (Foshan, Guangdong), the University of Science and Technology of China (Hefei, Anhui), and Xi’an Shiyou University (Xi’an, Shaanxi), led by Fei Hu, Tingting Kong, Jun Jiang, and Yujie Xiong, etched thin ribbons of a copper/titanium alloy with hydrofluoric acid to remove the titanium from the surface.
This results in the material a-CuTi@Cu, with a porous copper surface on an amorphous CuTi alloy. It has catalytically active copper centers with remarkably high activity, selectivity, and stability for the reduction of CO2 to C2+ products. In contrast, pure copper foil produces C1 products but hardly any C2+ products.
The reaction involves a multistep electron-transfer process via various intermediates. In the new electrocatalyst, the inactive titanium atoms below the surface actually play an important role; they increase the electron density of the Cu atoms on the surface. This stabilizes the adsorption of *CO, the key intermediate in the formation of multicarbon products, allows for high coverage of the surface with *CO, and lowers the energy barrier for di- and trimerization of the *CO as new carbon–carbon bonds are formed.
Hu, F., Yang, L., Jiang, Y., Duan, C., Wang, X., Zeng, L., Lv, X., Duan, D., Liu, Q., Kong, T., Jiang, J., Long, R. and Xiong, Y. (2021), “Ultrastable Cu Catalyst for CO2 Electroreduction to Multicarbon Liquid Fuels by Tuning C–C Coupling with CuTi Subsurface.” Angew. Chem. Int. Ed.. https://doi.org/10.1002/anie.202110303