Non-photochromic solar energy storage in carbon nitride surpassing blue radicals for hydrogen production

Potassium poly(heptazine imide) (KPHI) exhibiting the dual functionality of photon absorption and photoelectron storage for solar energy conversion is a new class of ionic two-dimensional (2D) carbon nitrides. Rather than forming blue radicals upon storing photoelectrons in the yellow crystalline KPHIs, here non-photochromic solar energy storage in the in-plane short-range-ordered KPHI is reported, which demonstrates superior photocatalytic and dark photocatalytic activities for hydrogen evolution. Density functional theory calculations confirm that the electron storage capacity of the short-range-ordered KPHI is higher than that of the crystalline one. Moreover, the molecular structure remains unchanged after electrons are stored, resulting in non-photochromic solar energy storage in short-range-ordered KPHI. In crystalline KPHI, the stored photoelectrons drive the change of potassium ion locations to form a blue radical. This work demonstrates that the photophysical properties of light-storing carbon nitrides are tunable by modifying the microstructure of KPHIs towards efficient solar energy storage and conversion.