NH <sub>3</sub> ‐Guided Low‐Temperature Nanostructural Refinement Boosts Visible‐Light‐Driven H <sub>2</sub> O <sub>2</sub> Synthesis in Ionic Carbon Nitrides
Jaya Bharti, Jokotadeola Odutola, Zahra Hajiahmadi, Karlo Nolkemper, Zhihong Tian, Haijian Tong, V. V. Shvalagin, Thomas D. Kühne, Tero‐Petri Ruoko, Christian Mark Pelicano
Abstract
Abstract Solar‐driven oxygen reduction on ionic carbon nitride frameworks presents a compelling strategy for sustainable hydrogen peroxide (H 2 O 2 ) production. Herein, a nanostructural engineering strategy is presented to tailor the morphology and defect chemistry of potassium poly(heptazine imide) (KPHI), enabling extended solar coverage and enhance photocatalytic performance. By incorporating NH 4 Cl into a molten KCl/LiCl eutectic medium, simultaneous nanoscale fragmentation of KPHI crystals and controlled introduction of cyano (–C≡N) defects are achieved. These molecular modifications induce n → π* electronic transitions, facilitate efficient charge separation, and accelerate oxygen reduction reaction kinetics. The optimal catalyst reaches an apparent quantum yield (AQY) of 49% at 410 nm and 5% at 525 nm without the need for cocatalysts, among the highest values reported for metal‐free photocatalyst systems. Transient absorption spectroscopy confirms preferential photoexcited electron localization at –C≡N sites, highlighting their key role in enhancing the charge carrier dynamics. Crucially, autogenous NH 3 pressure is harnessed from NH 4 Cl decomposition to unlock a low‐temperature (500 °C) KPHI variant that delivers analogous performance to its counterpart produced at 600 °C, offering a more sustainable synthetic route. This study elucidates the structure‐activity relationship in ionic carbon nitrides and provides a generalizable approach for controlling their morphology and defect characteristics.