Productivity and Selectivity of Gas‐Phase CO 2 Electroreduction to Methane at Copper Nanoparticle‐Based Electrodes

In this study, copper nanoparticles are supported on porous carbon papers by airbrushing; they are then coupled with a Nafion 117 membrane to form working electrodes for the continuous production of methane through gas‐phase electroreduction of CO 2 in a filter‐press electrochemical cell. The methane production and Faradaic efficiency (FE) are evaluated and compared at different applied voltages (from −1.8 to −2.4 V vs. Ag/AgCl) and catalyst loadings (0.25, 0.5, 1, and 1.5 mg cm −2 ). The maximum methane production rate is achieved at −2 V and 0.5 mg cm −2 (4.4 μmol m −2  s −1 ) whereas the highest Faradaic efficiencies can be obtained at 1 mg cm −2 ( FE =10.1 %) and at −1.8 V ( FE =12.1 %). The role of the porous carbon support and the possibility of humidifying the CO 2 stream before it enters the cell are also tested. These results may provide a new understanding of the use of gas–liquid electrochemical membrane reactors for the direct conversion of CO 2 in the gas phase.