Municipal sludge-derived carbon dots-decorated, N-doped hierarchical biocarbon for the electrochemical reduction of carbon dioxide

Uncontrolled emission of carbon dioxide (CO2) from various industries, which poses a severe threat to the environment and induces climate change, CO2 electroreduction is an advanced technology for converting waste CO2 and closing anthropogenic carbon cycle. However, developing novel, affordable and high-performance electrocatalysts for converting CO2 to value-added hydrocarbons remains highly challenging. Herein, a carbon dots-decorated, N-doped hierarchical biocarbon material is developed from municipal sludge, which can work as an effective and robust carbocatalyst for the electrochemical reduction of CO2. More importantly, such hierarchical biocarbon catalyzes the electrochemical conversion of CO2 to value-added organic products, including methane, methanol and ethanol, with excellent stability and total Faraday efficiency of 90.14% at about -0.71 V vs. RHE. Reasons for the carbocatalyst electroactivity toward efficient and selective production of ethanol is proposed to be the carbon dots and the doped N sites (especially pyridinic-N and pyrrolic-N), which is also validated by density functional theory calculations (DFT). A possible route for the electrochemical reduction of CO2 is also unraveled. This study is a significant step forward to the exploitation of biomass wastes for harvesting greenhouse gasses and electrochemical energy conversion.