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 but suffers from diverse selectivity. Here, we report that functionalized graphene quantum dots (GQDs) can direct CO2-to-CH4 conversion with simultaneous high selectivity and production rate. Electron-donating groups (EDGs) facilitate CH4 formation from CO2 electro-reduction while electron-withdrawing groups (EWGs) suppress CO2 reduction. The CH4 yield on EDG-functionalized GQDs correlates positively with the electron-donating ability and content of the EDG. GQDs functionalized by either –OH or –NH2 achieve a Faradaic efficiency (FE) of 70.0% for CH4 at −200 mA cm−2 partial current density of CH4. Superior CH4 yield on EDG- over EWG-functionalized GQDs likely originates from maintaining higher charge density at neighboring C or N active sites and EDG–intermediate interactions. This work provides molecular-level insight for designing active carbon catalysts for CO2 electro-reduction.