Techno-economic Assessment of CO2 Electrolysis: How Interdependencies between Model Variables Propagate Across Different Modeling Scales.

The production of base chemicals by electrochemical conversion of captured CO2 has the potential to close the carbon cycle, thereby contributing to a future energy transition. With the feasibility of low-temperature electrochemical CO2 conversion demonstrated at lab scale, research is shifting toward optimizing electrolyser design and operation for industrial applications, with target values based on techno-economic analysis. However, current techno-economic analyses often neglect experimentally reported interdependencies of key performance variables such as the current density, the faradaic efficiency, and the conversion. Aiming to understand the impact of these interdependencies on the economic outlook, we develop a model capturing mass transfer effects over the channel length for an alkaline, membrane electrolyser. Coupling the channel scale with the higher level process scale and embedding this multiscale model in an economic framework allows us to analyze the economic trade-off between the performance variables. Our analysis shows that the derived target values for the performance variables strongly depend on the interdependencies described in the channel scale model. Our analysis also suggests that economically optimal current densities can be as low as half of the previously reported benchmarks. More generally, our work highlights the need to move toward multiscale models, especially in the field of CO2 electrolysis, to effectively elucidate current bottlenecks in the quest toward economically compelling system designs.

Electrochemical Reduction of CO2 in Tubular Flow Cells under Gas-Liquid Taylor Flow.

Electrochemical reduction of CO2 using renewable energy is a promising avenue for sustainable production of bulk chemicals. However, CO2 electrolysis in aqueous systems is severely limited by mass transfer, leading to low reactor performance insufficient for industrial application. This paper shows that structured reactors operated under gas-liquid Taylor flow can overcome these limitations and significantly improve the reactor performance. This is achieved by reducing the boundary layer for mass transfer to the thin liquid film between the CO2 bubbles and the electrode. This work aims to understand the relationship between process conditions, mass transfer, and reactor performance by developing an easy-to-use analytical model. We find that the film thickness and the volume ratio of CO2/electrolyte fed to the reactor significantly affect the current density and the faradaic efficiency. Additionally, we find industrially relevant performance when operating the reactor at an elevated pressure beyond 5 bar. We compare our predictions with numerical simulations based on the unit cell approach, showing good agreement for a large window of operating parameters, illustrating when the easy-to-use predictive expressions for the current density and faradaic efficiency can be applied.