Hydrogen peroxide synthesis on porous graphitic carbon nitride using water as a hydrogen source

Abstract

Using water as a hydrogen source is a promising strategy for alternative hydrogen peroxide (H₂O₂) synthesis. By a series of ab initio molecular dynamics (AIMD) simulations and reactive molecular dynamics (RxMD) calculations, fundamental details have been revealed regarding how liquid water interacts with oxygen on a metal-free carbon nitride catalyst, and the two-step reaction mechanism of H₂O₂ synthesis. Metal-free porous graphitic carbon nitride (g-C₅N₂) catalysts are also systematically screened by using a thermodynamics approach through the ab initio density functional theory (DFT) method. Key results include: (a) pristine g-C₅N₂ is most active to catalyze the H₂O/O₂ reaction and produce H₂O₂; (b) the adsorption and activation of water at unsaturated carbon sites of g-C₅N₂ are critical to initiate the H₂O/O₂ reaction, producing HOO* intermediates; (c) interfacial free water and adsorbed water at g-C₅N₂ form a synergetic proton transfer cluster to promote HOO* intermediates to form H₂O₂. To the best of our knowledge, this work presents long-needed theoretical details of direct H₂O₂ synthesis via the water/oxygen system, which can guide further optimization of carbon-based catalysts for oxygen reduction reactions.