Ultrahigh oxygen-doped carbon quantum dots for highly efficient H2O2 production via two-electron electrochemical oxygen reduction

Direct electrochemical two-electron oxygen reduction (2eORR) into H2O2 provides a promising alternative for on-site green H2O2 production to the predominant anthraquinone oxidation technology. Oxidized carbon materials have demonstrated their impressive 2eORR activity due to oxygenated functional groups beneficial to the H2O2 formation pathways. However, the 2eORR capability of O-doped carbon catalysts is hindered by the density of O-induced active sites due to the rather low O content (<15%). Herein, we reported a carbon quantum dot (CQD) catalyst with an ultrahigh O content (30.4 at%) fabricated by using glucose (C6H12O6) as the carbon source due to its high atomic ratio of oxygen-to-carbon. The O-rich CQD catalyst exhibits an excellent catalytic capability of H2O2 production with nearly 100% selectivity, exceeding all reported O-doped carbon catalysts. Besides, the CQD catalyst exhibits great potential in practical H2O2 production with a high yield of 10.06 mg cm(-2) h(-1) and Faraday efficiency of 97.7%, as well as good stability over 10 hours. Experimental and theoretical investigations confirm that the great majority of the C-O bonds are from the etheric groups in the CQD catalyst, and the carbon atoms of the C-O bonds are the most active sites for the 2eORR.