Copper Electrode Fabricated via Pulse Electrodeposition: Toward High Methane Selectivity and Activity for CO2 Electroreduction

Electrochemical reduction of CO2 (ERC) to methane has significant economic benefits and represents one promising solution for energy and environmental sustainability. However, traditional metal electrodes suffer from higher overpotentials, low activities, and poor selectivity. In this article, the pulse electrodeposition (P-ED) method is employed to prepare a copper electrode for ERC. The P-ED method can easily create Cu coatings on carbon paper with a much rougher surface and extended surface area, which is highly beneficial for improving their activity and selectivity. As a result, the prepared Cu electrodes exhibit high faradaic efficiency (of 85% at −2.8 V) and enhanced partial current density (jCH4 = 38 mA cm–2) for methane, which is by far the highest value ever reported at room temperature and ambient pressure. The enhanced activity is attributed to the extended reactive areas with rough morphology and loosened coating structure to ensure CO2 access the reaction sites located at the sublayers of the deposited Cu coatings. The prominent selectivity for CH4 is likely due to the presence of a stepped surface, which is formed by introduction of Cu (100) step into Cu (111) and Cu (220) terraces during the P-ED processes. The lower resistance to the one-electron transfer to CO2, which is a pre-equilibrium step prior to the rate-limiting nonelectrochemical step, is another positive factor to improve the ERC activity for CH4. Furthermore, we surprisingly find that the activity and selectivity of the Cu electrode can be easily recovered through continuous CO2 bubbling. This paper provides a facile method to prepare highly effective electrodes for electrochemical conversion of CO2.