The electrolysis of carbon dioxide (CO2) and carbon monoxide (CO) offers a way to convert emissions into multi-carbon products such as ethanol and ethylene. However, low energy and carbon efficiency limits current systems.
Now, researchers from the School of Applied Sciences and Engineering at the University of Toronto have developed a new catalyst design that could dramatically improve the feasibility of an electrochemical process.
In their work, the researchers focused on a variation of the process known as “cascading CO2 reduction“. In this process, CO2 is first dissolved in a liquid electrolyte and then passed through an electrolyzer, where it reacts with electrons to form carbon monoxide. The CO then passes through a second electrolyser, where it is converted into two-carbon products such as ethanol, often used as fuel, and ethylene, a precursor to many types of plastics and other consumer goods.
In the second stage, the team discovered inefficiencies that they believed could be overcome. The challenges were related to selectivity, which is the ability to maximize the production of target molecules while reducing the formation of unwanted side products.
One of the main problems is the poor selectivity under conditions of low reagent availability. This, in turn, leads to a trade-off between energy efficiency – that is, how efficiently we use electrons, which we pump into the system – and carbon efficiency, which is a measure how efficiently we use CO2 and CO
Adnan Ozden, postdoctoral researcher
Investigating the reasons for this shift, the team discovered that it was caused by the excessive accumulation of positively charged ions, called cations, on the surface of the catalyst, as well as the unwanted migration of negatively charged ions, called anions, away from the catalyst. catalyst surface.
To meet this challenge, they were inspired by the design of supercapacitors. They added a porous material, called a covalent organic framework, to the surface of the catalyst, allowing them to control the transport of cations and anions in the local reaction environment.
With this modification, we obtained a very porous and highly hydrophobic catalyst layer. In this design, the covalent organic framework interacts with the cations to limit their diffusion to the active sites. The covalent organic framework also confines locally produced anions due to its strong hydrophobicity.
Jun Li, lead author.
Using the new catalyst design, the team built an electrolyser that converts CO into two-carbon products with 95% carbon efficiencywhile maintaining a relatively high energy efficiency of 40%.
The technology still needs to be improved if it is to be commercially adapted. In testing, the prototype device maintained performance for more than 200 hours, but it will need to last even longer for industrial use.
Via New catalyst design could make better use of captured carbon, researchers say (utoronto.ca)
The references: Adnan Ozden, Jun Li, Sharath Kandambeth, Xiao-Yan Li, Shijie Liu, Osama Shekhah, Pengfei Ou, Y. Zou Finfrock, Ya-Kun Wang, Tartela Alkayyali, F. Pelayo García de Arquer, Vinayak S. Kale, Prashant M Bhatt, Alexander H. Ip, Mohamed Eddaoudi, Edward H. Sargent and David Sinton. Energy and carbon saving CO2/CO electrolysis into multi-carbon products by asymmetric ion migration-adsorption. Nature Energy, 2023; DOI: 10.1038/s41560-022-01188-2
