Is electrochemical CO2 reduction the future technology for power-to-chemicals? An environmental comparison with H2-based pathways

Abstract

Power-to-chemical pathways are gaining attention as a promising approach to reduce greenhouse gas (GHG) emissions of the chemical industry. Most power-to-chemical pathways use water electrolysis and hydrogenation of carbon dioxide (H₂-based pathways). An emerging power-to-chemical technology is electrochemical CO₂ reduction (eCO₂R) that converts carbon dioxide (CO₂) and water (H₂O) directly into chemical products. An early assessment of the environmental potential of eCO₂R can accelerate the eCO₂R development toward more sustainable technology. So far, only a few environmental assessments have been conducted using fixed assumptions of eCO₂R operating parameters. To overcome this limitation and reflect all possibilities of future eCO₂R development, we design a parameter-dependent approach using a variable eCO₂R model. The considered eCO₂R model can produce carbon monoxide (CO), methanol, or ethylene. Together with the conversion of syngas (CO and hydrogen mixture) to methanol and with the methanol-to-olefins (MtO) conversion to ethylene, five different eCO₂R pathways to produce methanol and ethylene are possible. By applying our parameter-dependent approach, we determine the minimum development requirements for the eCO₂R pathways to achieve climate benefits over the H₂-based pathways. By comparing the obtained minimum development requirements to data from experimental studies, we evaluate potential development gaps. The direct eCO₂R to ethylene pathway shows a moderate development gap and could reduce GHG emissions over the H₂-based pathway by up to 44%. The eCO₂R via CO to methanol and eCO₂R via CO to ethylene pathways can already fulfill the minimum development requirements; however, the GHG reduction potential is limited to 12%. The direct eCO₂R to methanol pathway shows a significant development gap. Compared to the fossil fuel-based technologies, both the H₂-based and the eCO₂R pathways offer large climate benefits of up to 88% and up to 93%, respectively. The presented parameter-dependent assessment offers an in-depth understanding of the eCO₂R operating parameters and provides a valuable approach for future assessments of the emerging eCO₂R technology.