Regulation of functional groups on graphene quantum dots directs selective CO2 to CH4 conversion

A catalyst system with dedicated selectivity toward a single hydrocarbon or oxygenate product is essential to enable the industrial application of electrochemical conversion of CO₂ to high-value chemicals. Cu is the only known metal catalyst that can convert CO₂ to high-order hydrocarbons and oxygenates. However, the Cu-based catalysts suffer from diverse selectivity. Here, we report that the functionalized graphene quantum dots can direct CO₂ to CH₄ conversion with simultaneous high selectivity and production rate. The electron-donating groups facilitate the yield of CH₄ from CO₂ electro-reduction while electron-withdrawing groups suppress CO₂ electro-reduction. The yield of CH₄ on electron-donating group functionalized graphene quantum dots is positively correlated to the electron-donating ability and content of electron-donating group. The graphene quantum dots functionalized by either -OH or -NH₂ functional group could achieve Faradaic efficiency of 70.0% for CH₄ at -200 mA cm⁻² partial current density of CH₄. The superior yield of CH₄ on electron-donating group- over the electron-withdrawing group-functionalized graphene quantum dots possibly originates from the maintenance of higher charge density of potential active sites (neighboring C or N) and the interaction between the electron-donating group and key intermediates. This work provides insight into the design of active carbon catalysts at the molecular scale for the CO₂ electro-reduction.