An Atomically Dispersed Mn-Photocatalyst for Generating Hydrogen Peroxide from Seawater via the Water Oxidation Reaction (WOR)

In this work, we have fabricated an aryl amino-substituted graphitic carbon nitride (g-C 3 N 4 ) catalyst with atomically dispersed Mn capable of generating hydrogen peroxide (H 2 O 2 ) directly from seawater. This new catalyst exhibited excellent reactivity, obtaining up to 2230 μM H 2 O 2 in 7 h from alkaline water and up to 1800 μM from seawater under identical conditions. More importantly, the catalyst was quickly recovered for subsequent reuse without appreciable loss in performance. Interestingly, unlike the usual two-electron oxygen reduction reaction pathway, the generation of H 2 O 2 was through a less common two-electron water oxidation reaction (WOR) process in which both the direct and indirect WOR processes occurred; namely, photoinduced h + directly oxidized H 2 O to H 2 O 2 via a one-step 2e – WOR, and photoinduced h + first oxidized a hydroxide (OH – ) ion to generate a hydroxy radical ( • OH), and H 2 O 2 was formed indirectly by the combination of two • OH. We have characterized the material, at the catalytic sites, at the atomic level using electron paramagnetic resonance, X-ray absorption near edge structure, extended X-ray absorption fine structure, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, magic-angle spinning solid-state NMR spectroscopy, and multiscale molecular modeling, combining classical reactive molecular dynamics simulations and quantum chemistry calculations.