Controlling selectivity of CO2 electrolysis with back pressure

What is it about?

The electrochemical reduction reaction of CO2 (CO2RR) is a promising avenue towards the renewable energy-driven transformation of a greenhouse gas towards fuels and value-added chemicals. While copper is uniquely able to catalyse this reaction to longer carbon chains, CO2RR on Cu-based electrodes continues to face numerous challenges, including low selectivity towards desired products and poor stability. To unlock its potential for large-scale industrial implementation, research efforts in both industy and academia show great interest in tackling these challanges, primarily focusing on catalyst and electrode modifications, and thereby leaving a research gap in the effects of operation conditions. In this work, back pressure application in CO2 electrolyzers at industrially relavant current densities(200 mA cm-2) in order to drive membraneembedded catalyst selectivity towards C2+ products is introduced. The back pressure is shown to adjust CO2 availability at the electrode surface, with a high CO2 surface coverage achieved at ΔP = 130 mbar suppressing the competing hydrogen evolving reaction for 72 hours to the faradaic selectivity range of 15-25% and a doubling of stable ethylene production timescales from 36 to 72 h. The ratio of oxygenate productsto hydrocarbon products can be selectively controlled from 0.53 to 0.85 at a ΔP = 0 - 130 mbar range. Back pressure combined with low gas flow rates ensures a longer residence time in the catalyst layer and optimal CO*/H* coverage on the catalyst surface for ethylene, achieving faradaic efficiencies of 38.5% for ethylene and 60% for total C2+ products, representing an overall C2+ conversion effiency of 19.8%. The easily implementable back pressure operation mode presented in this study is proven to be a promising tool for product selectivity control in future upscaled Cu-based CO2 electrolysis cells.

Featured Image

Photo by Jasmin Sessler on Unsplash

Photo by Jasmin Sessler on Unsplash

Why is it important?

Applying a back pressure on the gas diffusion electrode is proven to be an effective tool to control the product distribution in a Cu-based CO2 electrolysis system.

Perspectives