Suppressing Nonradiative Recombination through Dielectric Screening of Defects in Crystalline Carbon Nitride for Enhanced Photocatalytic Activity

Abstract

Abundant defect-induced nonradiative recombination greatly reduces the charge separation efficiency in photocatalysts. Dielectric screening of defects has been proven to be an effective strategy to improve the charge separation efficiency; however, it has been rarely reported in photocatalysis. Here, a developed calcium poly(heptazine imide) (CaPHI) is utilized as a model photocatalyst to explore the dielectric screening of defects. Through embedding potassium ions in CaPHI, the dipole moment and polarity of the PHI structure are increased, thus enhancing the dielectric constant and enabling the dielectric screening of defects. In addition, compared to the original CaPHI, the optimized Ca/KPHI exhibits a 79.3% reduction in defect capture cross-section, and a decrease in the nonradiative recombination rate from 0.6224 to 0.1452 ns–1, thus achieving an apparent quantum efficiency of 51.4% for H2 production at 420 nm. This proposed dielectric screening strategy effectively addresses the issue of slow carrier transport and separation caused by defect-induced nonradiative recombination in photocatalysts.