Bottom‐Up Strategy to Enhance Long‐Range Order of Poly(Heptazine Imide) Nanorods for Efficient Photocatalytic CO2 Methanation

Poly(heptazine imide) (PHI), one of the crystalline or long‐range ordered allotropes of polymeric carbon nitride, is a promising polymeric photocatalyst; however, preparation of highly crystalline PHI remains a challenge. Herein, through a bottom‐up strategy involving repair of structural defects and increase of specific surface area of melon precursor, we prepared PHI nanorods with dramatically improved long‐range order. The resulting PHI exhibited a shift of product selectivity in CO2 photoreduction from CO to CH4 with a high methanation activity in contrast to the pristine PHI with relatively low long‐range order. The improvement of long‐range order for PHI remarkably enhanced the separation efficiency and transfer dynamics of photogenerated charges as well as the adsorption capacity for *CO intermediate. This study revealed the relationship between the precursor structure and PHI crystal growth in ionothermal synthesis, and also showcased the great potential of highly crystalline PHI in artificial photosynthesis.