A metal-free cascaded process for efficient H2O2 photoproduction using conjugated carbonyl sites

Carbon-based metal-free catalysts are promising green catalysts for photocatalysis and electrocatalysis due to their low cost and environmental friendliness. A key challenge in utilizing these catalysts is identifying their active sites, given their poor crystallinity and complex structures. Here we demonstrate the key structure of the double-bonded conjugated carbon group as a metal-free active site, enabling efficient O2 photoreduction to H2O2 through a cascaded water oxidation − O2 reduction process. Using ethylenediaminetetraacetic acid as a precursor, we synthesized various carbon-based photocatalysts and analyzed their structural evolution. Under the polymerization conditions of 260 °C to 400 °C, an N-ethyl-2-piperazinone-like structure was formed on the surface of the catalyst, resulting in high photocatalytic H2O2 photoproduction (2884.7 μmol g−1h−1) under visible light. A series of control experiments and theoretical calculations further confirm that the double-bond conjugated carbonyl structure is the key and universal feature of the active site of metal-free photocatalysts. Elucidating active sites and reaction pathways is an important goal for understanding catalytic reaction mechanisms. Here, the authors report the key role of conjugated carbonyl sites in carbon nitrides for photocatalytic H2O2 production.