Promoting Heptazine-Based\nGraphitic Carbon Nitride\nPhotocatalytic Overall Water Splitting by Effectively Assembling Double-Unit\nPolymers

Replacing the sole heptazine unit of graphitic carbon\nnitride (g-C<sub>3</sub>N<sub>4</sub>) with double-unit polymers (DHP)\nhas garnered\nwidespread attention for photocatalytic overall water splitting due\nto their suitable band alignment, well-photogenerated electron and\nhole separation, and abundant active sites. However, relying solely\non static type II band alignment of building blocks to assemble DHP\nis inadequate. Herein, we propose a comprehensive “static–dynamic”\nevaluation strategy for improving the assembly efficiency of DHP including\nunit selection, band alignment, catalytic site activity, photogenerated\nelectron and hole separation dynamics, carrier lifetime, and photocurrent.\nA group of DHP is constructed through electron-rich phenyl derivatives\nand electron-deficient heptazine. Among them, although these frontier\norbitals of units can form type II band alignment with each other,\nonly DHP1 and DHP7 achieve spatial separation of the photogenerated\nelectron and hole. Then, based on catalytic activity screening, DHP1\nexhibits remarkable bifunctional catalytic performance with a low\noverpotential of hydrogen (0.05 V) and oxygen (0.59 V). Through further\ndynamic evaluation, the photogenerated carrier lifetimes of DHP1 can\nreach up to 15 times compared to the pristine g-C<sub>3</sub>N<sub>4</sub>, owing to the dominant low-frequency phonon modes suppressing\nstrong electron–phonon coupling. Simultaneously, the photocurrent\ncan achieve 9 A/m<sup>2</sup>. The “static–dynamic”\nstrategy offers systematic evaluation for advancing photocatalytic\ndesign.