Boosting the Quantum Efficiency of Ionic Carbon Nitrides in Photocatalytic H₂O₂ Evolution via Controllable n → π* Electronic Transition Activation

Abstract

<p>Hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) is a crucial chemical used in numerous industrial applications, yet its manufacturing relies on the energy-demanding anthraquinone process. Solar-driven synthesis of H<sub>2</sub>O<sub>2</sub> is gaining traction as a promising research area, providing a sustainable method for its production. Herein, a controllable activation of n → π* electronic transition is presented to boost the photocatalytic H<sub>2</sub>O<sub>2</sub> evolution in ionic carbon nitrides. This enhancement is achieved through the simultaneous introduction of structural distortions and defect sites (─C ≡ N groups and N vacancies) into the KPHI framework. The optimal catalyst (2%Ox-KPHI) reached an apparent quantum yield of 41% at 410 nm without the need for any cocatalysts, outperforming most previously reported carbon nitride-based photocatalysts. Extensive experimental characterizations and theoretical calculations confirm that a corrugated configuration and the presence of defects significantly broaden the light absorption profile, improve carrier separation and migration, promote O<sub>2</sub> adsorption, and lower the energy barriers for H<sub>2</sub>O<sub>2</sub> desorption. Transient absorption spectroscopy indicates that the enhanced photocatalytic performance of 2%Ox-KPHI is largely attributed to the preferential migration of electrons at defect sites over extended timescales, following the diffusion of geminate carriers across the PHI sheets.</p>