Mechanism insights for efficient photocatalytic seawater splitting in poly(heptazine imide): inhibited ion exudation and improved charge separation

Potassium poly(heptazine imide) (KPHI) has emerged as a highly promising photocatalyst for H₂ evolution via water splitting, particularly in seawater, where ions significantly enhance its activity. However, the mechanisms underlying this enhancement remain debated. This study elucidates that seawater ions can inhibit the exudation of K⁺ and further enter the framework of KPHI through ion exchange, enhancing the real-time separation and transfer of photogenerated electron–hole pairs. Comprehensive characterization reveals that charge separation efficiency depends on both ion type and concentration. Among them, K⁺ exhibits the best effect on the enhancement of photocatalytic H₂ evolution activity of PHI when the concentration is 0.2 M. Density Functional Theory (DFT) simulations show that the entry of alkali metal ions generates a greater electrostatic potential and electron transfer capacity. These findings clarify the ion-mediated enhancement of photocatalytic performance, providing critical insights for optimizing H₂ production from seawater splitting and advancing sustainable energy technologies.