Electroreduction of CO 2 to CH 4 without overpotential using Pt‐black catalysts: Enhancement of faradaic efficiency

Summary The use of metal electrocatalysts (Cu, Au, and Ag) is the mainstream in primary CO 2 reduction systems, but their large overpotential induces a decrease in energy conversion efficiency. Recently, it has been discovered that carbon‐supported Pt can make a game change to reduce CO 2 to CH 4 electrocatalytically without overpotential; however, its faradaic efficiency remains only 12.3% thus far. One approach is to investigate the role of carbon supports for improving the efficiency. In this study, improved CO 2 reduction was carried out by employing a Pt‐black electrocatalyst without a carbon support in a polymer electrolyte membrane electrolyzer cell. When supplying CO 2 diluted by Ar gas at CO 2 concentrations of 4‐7 vol.%, the efficient CH 4 generation was observed. The reason behind the improved production of CH 4 occurs by a Langmuir‐Hinshelwood mechanism associated with adsorbed CO (CO ads ) and H (H ads ) on the Pt electrocatalyst. Moreover, a high‐density CO ads environment (surface) can be created at the Pt‐black catalyst, achieving CH 4 generation with a faradaic efficiency of 23.2% at 0.18 V vs RHE. Therefore, this study succeeded in improving the faradaic efficiency of CH 4 production from CO 2 reduction without overpotential using a Pt‐black electrocatalyst.