Ion-Regulated Charge Distribution in Potassium Poly(heptazine imides) for Efficient Seawater Photocatalysis

Abstract

Seawater offers a vast resource for photocatalytic H2 generation. Typical ions in seawater, such as Na+ and Cl–, are known to considerably enhance the activity of representative photocatalysts (e.g., polymeric carbon nitride and titanium dioxide). However, the underlying mechanism of this phenomenon remains ambiguous, and further performance improvement is highly sought after. Herein, we introduce a facile and controllable ion-exchange strategy to unveil the origin of this phenomenon using potassium poly(heptazine imides) (K-PHI), a type of polymeric carbon nitride (PCN) photocatalyst. Our findings reveal that the primary contributor behind the enhanced reaction activity is charge redistribution within the PHI framework, triggered by the substitution of intrinsic lattice potassium ions (K+) with hydrated potassium ions (Ka+q). This charge redistribution strengthens the interaction between the catalyst and dissolved ions, therefore promoting the reactivity in seawater. Moreover, this modulation results in a 28-fold increase in H2 evolution in KCl solution compared to KCl-free conditions, with an apparent quantum efficiency of 34.1% at 410 nm.