Abstract
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 O(2) photoreduction to H(2)O(2) through a cascaded water oxidation - O(2) 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 H(2)O(2) photoproduction (2884.7 μmol g(-1)h(-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.