The co-electrolysis of CO2–H2O to methane via a novel micro-tubular electrochemical reactor

Abstract

Efficient and direct conversion of CO₂ to hydrocarbons through electrolysis is a promising approach for energy storage and CO₂ utilization. In this study, high temperature co-electrolysis of H₂O–CO₂ and low temperature methanation processes are synergistically integrated in a micro-tubular reactor. The temperature gradient along the micro-tubular reactor provides favorable conditions for both the electrolysis and methanation reactions. Moreover, the micro-tubular reactor can provide high volumetric factor for both the electrolysis and methanation processes. When the cathode of the micro-tubular reactor is fed with a stream of 10.7% CO₂, 69.3% H₂ and 20.0% H₂O, an electrolysis current of −0.32 A improves CH₄ yield from 12.3% to 21.1% and CO₂ conversion rate from 64.9% to 87.7%, compared with the operation at open circuit voltage. Furthermore, the effects of the inlet gas composition in the cathode on the CO₂ conversion rate and the CH₄ yield are systematically investigated. Higher ratio of H : C in the inlet results in higher CO₂ conversion rate. Among all the cases studied, the highest CH₄ yield of 23.1% has been achieved when the inlet gas in the cathode is consisted of 21.3% CO₂, 58.7% H₂ and 20.0% H₂O with an electrolysis current of −0.32 A.