Selective CO2 Electroreduction to Ethylene and Multicarbon Alcohols via Electrolyte-Driven Nanostructuring

Posting date on solidfuturism: March 7th 2024
Published date: Nov 11th 2019
Authors: Dunfeng Gao, Ilya Sinev, Fabian Scholten, Rosa M. Arán-Ais, Nuria J. Divins, Kristina Kvashnina, Janis Timoshenko, Beatriz Roldan Cuenya
DOI: https://doi.org/10.1002/ange.201910155
Abstract composer: Seyed Amirhosein Mirsadri

Many electrochemical researches today are interested in converting carbon dioxide into good products, which is called Carbon Capture. Many studies had shown that copper metal could be a suitable electrocatalyst for this type of reactions. Because it showed very good and stable faradaic efficiency and current density, but it was more selective for methane and two-carbon compounds such as ethylene. Among the researchers' studies, one thing is more interesting and that is nothing but the shape and structure of the electrode and electrocatalyst! Therefore, nanocomposites with different nanostructures can show different selectivity and efficiencies. In this paper, it has been tried to make electrocatalysts based on copper metal and halides (CuX) and carbonate and investigate their impact on efficiency and selectivity for ethylene and multi-carbon alcohols. The electrocatalysts included CuCl, CuBr, CuI and CuCO3. Therefore, the copper-halide and carbonate electrocatalysts were formed by electrochemical deposition (Electro deposition) on the electrode and placed in a 0.1 molar potassium hydrogen carbonate environment, which resulted in a high efficiency of eighty percent and a current density of 2.31 milliamps per square centimeter.

carbon capture
Fig.1 | SEM imagesof Cu_Cl, Cu_Br, Cu_I, and Cu_CO3 samples before and after 1 h of CO2RR at @ 1.0 V vs. RHEin a CO2-saturated 0.1m KHCO3 solution. The scale bars in the main images and insets are 1mm and 200 nm for the Cu_Cl sample(A,E),5 mm and 500 nm for Cu_Br(B,F),Cu_I(C,G),and Cu_CO3 samples (D,H).

When 1 hour of the reduction reaction of carbon dioxide to different compounds passed, the electron microscope images made the researchers aware of an interesting fact and that was that the surface of the electrocatalysts changed after 1 hour! And many of the halides had been removed from the surface of the electrode and this itself could affect the efficiency. Carbonates that had been completely removed and only holes remained on the surface of the pure copper electrode and halides also had a very hard surface, which showed that the electrocatalyst containing iodine was much harder than the electrocatalyst containing bromine by the double-layer capacity tests. X-ray fluorescence spectroscopy (HERFD-XANES) studies by the linear combination analysis (Linear combination analysis-LCA) method showed that after one hour of the reduction reaction, no copper oxide (Cu2O) was seen on the electrocatalysts of CuI and CuBr, but on the chloride electrocatalysts, 14% Cu2O and 3% CuO were formed, and also carbonates did not remain until 1 hour. XPS spectroscopy studies also showed that after 1 hour of the reduction reaction, copper iodide did not feel any change on its surface, but copper bromide experienced 65% Cu2O. Also, copper chloride remained 56% on the surface of the electrocatalyst and 31% of it was converted to Cu2O and 12% of it was converted to CuCl2. Although the surface of the carbonates was also converted to copper oxide and copper carbonate. Their selectivity and activity and efficiency were investigated by the chronoamperometry reaction and all the electrocatalysts showed higher efficiency than the polished copper electrode.

carbon capture
| Figure 2. Quasi insitu Cu AugerLMMXPS spectra of Cu_CO3,Cu_Br,and Cu_I before(A) and after(B) 1 h of CO2RR at @ 1.0 V vs. RHE in a CO2-saturated 0.1m KHCO3solution.Br 3p and I3dXPS spectra of the Cu_Br(C) and Cu_I(D) measured befor eand after CO2RR are also shown.

In normal mode and at -1 volt, iodide showed the highest current density, but when we normalize all the diagrams, they mostly show the same specific activity. The highest efficiency of converting carbon dioxide gas to multi-carbon alcohols and ethylene was at -0.9 volts with an efficiency of eighty percent for the copper iodide electrocatalyst. But when we apply more negative potentials, instead of reaching two-carbon or more than two-carbon compounds, we reach hydrogen gas, which itself is a reason for the limitations of mass transfer of carbon dioxide gas. In this paper, XPS, SEM, HERFD-XANES, and chronoamperometery devices were tested and showed a good efficiency compared to pure copper. For the halide electrocatalysts, a good current density stability was obtained in 22 hours, while the carbonate electrocatalyst experienced a 20% drop in current. In the iodide electrocatalyst, which had a low drop until 5 hours and then became constant, with the decrease of current, the production of ethylene changed to methane. This means that by reducing the production of ethylene, the reaction goes towards the production of methane. While the carbonate electrocatalyst selectively reacts towards methane.

carbon capture
| Figure 3. Total geometric current density (A), total Faradaic efficiency and geometric partial current density of (B) C2+products,and partial geometric current densities of C)C2H4,D)C2H5OH, E) n-C3H7OH,and F) CH4 as afunction of the applied potential after 1h of CO2RR in aCO2-saturated 0.1m KHCO3 solution.