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 H ₂O ₂ provides a promising alternative for on-site green H ₂O ₂ production to the predominant anthraquinone oxidation technology. Oxidized carbon materials have demonstrated their impressive 2eORR activity due to oxygenated functional groups beneficial to the H ₂O ₂ 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 (C ₆H ₁₂O ₆) 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 H ₂O ₂ production with nearly 100% selectivity, exceeding all reported O-doped carbon catalysts. Besides, the CQD catalyst exhibits great potential in practical H ₂O ₂ 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.