Electrochemical CO 2 conversion technologies: state-of-the-art and future perspectives

Electrochemical reduction of CO 2 to produce chemicals or fuels may contribute to the zero-emission goal of the chemical industry. Here, we report the state-of-the-art and future perspective of electrochemical CO 2 conversion processes to produce CO, syngas, formic acid and ethylene. We selected and explored six routes: low-temperature CO production, low-temperature formic acid production, low-temperature ethylene production, high-temperature CO production, high-temperature syngas production, and a tandem approach to produce ethylene. For these routes, we describe the current level of development, performance indicators, and costs. The state-of-the-art of the chlor-alkali process is included as an example of a commercially applied electrochemical process. We calculate the economic performance of the various pathways in terms of levelized production costs and we use a learning curve method to project costs up to 2050. The greenhouse gas performance for all routes is determined and compared to the current reference of production from fossil-based resources. We conclude that high-temperature solid-oxide electrolysis to produce CO and syngas is the most developed and closest to reaching break-even levelized production cost in comparison to the fossil reference. Low-temperature electrolysis processes are at a lower technology readiness level and still need a substantial reduction in investment costs and improvements in process efficiency to achieve break-even with incumbent technology. The most promising of the low-temperature processes is formic acid production. Electrochemical production of formic acid, CO, and syngas results or can soon result in substantial GHG savings compared to their fossil-based alternatives. The extent to which savings can be achieved depends merely on the carbon intensity of the local power grid, or more generally, the supplied electricity. Electrochemical CO 2 conversion to produce ethylene would require a very low emission factor of electricity (