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.