Photoelectrochemical Reduction of Carbon Dioxide with a Copper Graphitic Carbon Nitride Photocathode

Research on the photoreduction of CO 2 often has been dominated by the use of sacrificial reducing agents. A pathway that avoids this problem would be the development of photocathodes for CO 2 reduction that could then be coupled to a photoanodic oxygen evolution reaction. Here, we present the use of copper‐substituted graphitic carbon nitride (Cu−CN) on a fluorinated tin oxide (FTO) electrode for the photoelectrochemical two‐electron reduction of CO 2 to CO as a major product (>95 %) and formic acid (<5 %). The results show that at a potential of −2.5 V versus Fc\Fc + the CO 2 reduction activity of Cu−CN on FTO electrode improves by 25 % upon illumination by visible light with a faradaic efficiency of nearly 100 %. Independently, X‐ray photoelectron spectroscopy conclusively shows a pronounced increase in the electrical conductivity of the Cu−CN upon white light illumination under vacuum and a contactless measuring configuration. This photo‐assisted charge mobility is shown to play a key role in the increased reactivity and faradaic efficiency for the reduction of CO 2 .