On October 6, 2022, Academicians Chen Zhongwei and Professor Yu Aiping of the University of Waterloo in Canada and Professor Wang Xin of South China Normal University collaborated to publish a new research result entitled “Continuous CO2 electrolysis using a CO2 exsolution-induced flow cell” in the journal Nature Energy.
This result proposes a new type of flow electrolysis cell for electrocatalytic CO2 catalytic conversion, using CO2-saturated all-liquid cathode liquid convection flow through the porous electrode, generating gas-liquid three-phase interface in situ, thinning the mass transfer boundary layer, and improving the transfer and transfer of carbon source, electrons, protons and products, achieving ultra-high product yield, building a bridge between commercial applications and basic research, and providing new ideas for the design of large-scale electrochemical conversion devices.
The corresponding authors of the paper are Academician Chen Zhongwei, Professor Yu Aiping and Professor Wang Xin; The first author is Dr. Wen Guobin and Dr. Ren Bohua. The communication units are the University of Waterloo and South China Normal University in Canada.
The rapid development of China’s economy and society needs sustained and green energy support. However, the main energy carriers currently relied on are still oil, natural gas, etc., resulting in a continuous increase in the concentration of carbon dioxide (CO2) in the atmosphere, making the frequent occurrence of environmental disasters and other problems more and more serious. Therefore, the recovery and conversion and utilization of CO2 urgently needs further research and development to form a sustainable artificial carbon cycle system that serves China’s “30-60 double carbon” goal.
Large-scale CO2 electrocatalytic reduction (CO2RR) upgrades CO2 conversion to high value-added carbon-based chemicals and fuels, while coupling intermittent wind or solar energy, enabling peak regulation and long-term storage of new energy. In recent years, electrocatalytic materials have made significant progress in catalyst activity and selectivity, however, innovative design of flow cell structures and electrode construction still faces great challenges. Because industrial-grade CO2RR electrolyzers need to improve both reaction kinetics and material/electron transfer at the same time, high current densities (> 1 A/cm2) are used to reduce operating costs and large-area electrodes (> 100 cm2) are used to reduce fixed investments. But until now, these research challenges seem to have set an unbreakable boundary for further improvement of product yields, becoming a bottleneck for commercialization.
Academician Chen Zhongwei, Professor Yu Aiping of the University of Waterloo in Canada and Professor Wang Xin of South China Normal University have made significant progress in the study of electrocatalytic flow cells, and they propose a new type of flow electrolysis cell in Nature Energy, which uses CO2-saturated all-liquid cathode liquid convection to pass through the porous electrode, generate CO2(g)-liquid-catalyst three-phase interface in situ, and reduce the thickness of the mass transfer boundary layer to less than 1.5 μm, so as to simultaneously enhance CO2, electrons (electrons) The transfer transfer of protons and products (CEPP transfer) realized the efficient and stable conversion of CO2 into CO in the flow electrolysis cell of 100 cm2 by using in situ electrodeposition of silver cathode and commercial foam nickel anode, and the commercial stack of 4×100 cm2 was amplified, and the CO yield reached 90.6 ± 4.0 L/h, and the gas in situ dissolved electrolysis cell was successfully extended to the copper-based cathode and the C2+ product was efficiently synthesized.
Figure 1: CEPP transfer transfer, different CO2RR electrolytic cells, and the concept of dynamic three-phase interface.
Because when the current density increases further, the reaction is limited by mass transfer, the ideal electrode structure needs to balance factors such as reactant feeding, reaction kinetics, and product discharge. Specifically, these processes rely heavily on the co-boost of CEPP transfer transfer, as CO2RR involves multiple coordinated proton-electron transfers (xCO2 + ne-+ nH+ = CxHyOz + mH2O). Therefore, it is critical to reduce the concentration gradients of various substances in the electrolyte flow boundary layer and local microenvironment (e.g., reactants: CO2 and H+, products: other CxHyOz substances such as CO, H2, and other ions HCO3-, OH- and alkali metal cations in the electrolyte, etc.).
Figure 2: Structure and mechanism of CO2 dissolution cell in situ.
The gas in situ dissolution process uses the Bernoulli principle in fluid dynamics, when the liquid phase electrolyte flows from the pore cavity to the porous throat, due to the decrease of the flow cross-sectional area, the flow rate increases, the local pressure is reduced, and the gaseous CO2 molecules are easy to dissolve from the molten CO2 and bicarbonate in the electrolyte, thereby providing sufficient CO2 supply at the reaction interface, in addition, the whole liquid phase feed ensures high ion conductivity and proton supply rate, and promotes the transfer of CEPP. At the same time, according to Darcy’s law, the increase in the flow rate of the electrolyte in the cathode further strengthens this change in local pressure and amplifies the in-situ dissolution phenomenon of the gas.
Figure 3: Performance comparison of gas-in-situ dissolution cells.
The research group assembled five types of electrolytic cells using Ag-based cathode catalysts, and by comparison, the gas in situ dissolution cell not only has a higher current density, but also has a wider potential window, indicating that it also strengthens the CEPP transfer transfer and reaction kinetics. In addition, this electrode structure prolongs the interface between the reactant and the catalyst, eliminates the stagnation region in the electrode structure, and gives full play to the intrinsic properties of the catalyst.
Figure 4: Gas solubilization concept extended to 4×100 cm2 stack and Cu-based catalyst to synthesize C2+ products.
The gas in situ dissolution concept also successfully assembled the stack, consisting of four modular units. The total current of the stack can reach 59.0 ± 2.6 A at a voltage of 14 V, and the CO yield is maintained at around 90 L/h for the first 120 minutes, providing an alternative method for large-scale industrial applications of CO2 recovery and conversion.
Overall, this research provides a new type of gas in situ dissolution cell with ultra-high yield, provides new ideas for the design of large-scale electrochemical conversion devices, and builds a bridge between commercial applications and basic research. (Source: Science Network)
Related Paper Information:https://doi.org/10.1038/s41560-022-01130-6