Industrial-scale CO2 electrolysis could potentially upgrade CO2 to valuable fuels and chemicals using intermittent wind or solar renewable energy. However, the advanced design for electrode architectures and cell structures is still a formidable challenge to achieve accelerated reaction rates (i.e. current density over 1 A/cm2) to minimize operating costs and large-scale economic cells (electrode size over 100 cm2) to minimize capital costs.
So far, after decades of effort, these research challenges seem to set an unbreakable boundary to the yield of desired products, which is the bottleneck of the commercialization of ambient CO2 electrolysis technology. It is well accepted that the major difficulties are the simultaneous improvements of reaction kinetics and reactants/electrons/products transfer at high current densities.
Outlined in a paper published today in the journal Nature Energy, a breakthrough is made by devising a gas-exsolution flow cell that harnesses the convection of aqueous CO2-saturated catholyte throughout the porous electrode and exploits in situ formed triple-phase interfaces (Figure 1).
This new type of flow cell devised by Professor Zhongwei Chen (http://chemeng.uwaterloo.ca/zchen/) and collaborators breaks through the present challenges and delivers a high current density with in-situ electrodeposited Ag cathode and commercial Ni foam anode. The first reported commercial size 100 cm2 cell achieves a superior and stable yield of CO for the unprecedented operation time. The 4×100 cm2 electrolyzer stack (Figure 2) is assembled with a CO yield of 90.6 ± 4.0 L/h. Such electrolyzer is successfully extended to in-situ electrodeposition of Cu for the production of two-carbon products.
Such electrolyzer simultaneously improves the transfer of CO2, electrons, protons, and products (CEPP) at high current densities by a ten-fold decrease of diffusion layer thickness and boosts the performance of electrocatalytic CO2 upgrade. CO2 supply is expedited by increased exsolution of gaseous CO2 from dissolved CO2 and bicarbonate because of local pressure decreases from the pore body to the pore throat according to Bernoulli’s principle in fluid dynamics. Additionally, Darcy’s law indicates that the increase of flow rate in flow-through configuration amplifies the effect of such localized pressure decreases.
Therefore, such CO2-exsolution architecture owns multiple merits:
- CO2 supply is expedited by increased exsolution of gaseous CO2 from dissolved CO2 and bicarbonate due to the effect of local pressure decreases.
- Simultaneous CEPP transfer is promoted with a ten-fold decrease of diffusion layer thickness.
- Such cell further enables thorough catalyst coating by in-situ electrodeposition with the forced convection of catalyst precursor, boosting reaction kinetics.
We believe that this work delivers an ultrahigh yield of CO2 electrolysis with the new type of gas exsolution-induced flow cell, opening up new opportunities to extend into other large-scale electrochemical conversion devices and bridging practical applications and fundamental research.
Dr. Zhongwei Chen’s collaborators at Waterloo included postdoctoral fellows Dr. Guobin Wen, Dr. Bohua Ren, and chemical engineering professors Dr. Aiping Yu and Dr. Jeff Gostick. Dr. Xin Wang and several researchers at the South China Normal University also contributed.
Dr. Zhongwei Chen's website: http://chemeng.uwaterloo.ca/zchen/
DOI: 10.1038/s41560-022-01130-6. (https://www.nature.com/articles/s41560-022-01130-6)