Large-Scale and Highly Selective Electrochemical CO2 to C2H4 Conversion Based on the Giner Water Management GDL

Abstract

C2H4 is a key building block in the chemical industry to produce a wide range of plastics, solvents, cosmetics, etc. On average, the production of 1 MMT of C2H4 generates 1.5 MMT of CO2, coming from fuel combustion, decoking, and utilities. Globally, C2H4 production by steam cracking is ranked as the second-largest contributor of energy consumption (2.8 EJ/year) and greenhouse gas emissions (300 MMT of CO2-e/year) in the chemical industry. Electrochemical CO2 reduction reaction (CO2RR) to produce C2H4 at ambient conditions, when coupled with renewable electricity, could reduce dependence on fossil fuels and decarbonize the chemical sector associated with C2H4 production. However, more efforts are needed to improve selectivity, productivity, and durability before the CO2 electrolyzer can be deployed commercially.State-of-the-art continuous CO2 electrolyzers utilize gas diffusion electrodes (GDEs) to achieve CO2-to-C2H4 conversion at industrially relevant current density. However, managing the flooding of liquid electrolytes into the porous structure of GDE remains a critical practical challenge for stable and efficient CO2 transport. To date, most CO2 electrolyzers used commercial gas diffusion layer (GDLs) designed for polymer electrolyte membrane fuel cells (PEMFC), which operate under different conditions than CO2RR. The conventional GDL is generally made of carbon paper coated with 5-30 wt.% of polytetrafluoroethylene (PTFE) to protect against flooding. These GDLs still lose hydrophobicity fast during CO2 electrolysis at highly negative potentials due to the electrowetting of carbon materials, salt precipitation, and chemical degradation. As a result, the electrolyte even penetrates the micropores of the GDL, blocking CO2 transport to catalyst sites.Giner has designed an innovative structure, the water management GDL (WM-GDL), providing a breakthrough solution for water management under the operational conditions of a CO2 electrolyzer. The WM-GDL has dedicated mass transport pathways for gas and electrolyte, which allows durable and efficient mass transport of both over long-term operation. The utilization of WM-GDL will assist in the scale-up of electrochemical CO2-to-C2H4 conversion. Currently, the state-of-the-art WM-GDL achieved 60% C2H4 selectivity at 500 mA cm-2 and 3 V in a 50 cm2 MEA electrolyzer. Larger-scale demonstration of the CO2-to-C2H4 conversion with high selectivity and durability will be carried out in stacks. Acknowledgment: The project is financially supported by the Department of Energy’s Office of EERE under the Grant DE-EE000942l