| Summary: | Adjusting the structure of g-C<sub>3</sub>N<sub>4</sub> to significantly enhance its photocatalytic activity has attracted considerable attention. Herein, a novel, sponge-like g-C<sub>3</sub>N<sub>4</sub> with a porous structure is prepared from the annealing of protonated melamine under N<sub>2</sub>/H<sub>2</sub> atmosphere (PH-CN). Compared to bulk g-C<sub>3</sub>N<sub>4</sub> via calcination of melamine under ambient atmosphere (B-CN), PH-CN displays thinner nanosheets and a higher surface area (150.1 m<sup>2</sup>/g), which is a benefit for shortening the diffusion distance of photoinduced carriers, providing more active sites, and finally favoring the enhancement of the photocatalytic activity. Moreover, it can be clearly observed from the UV-vis spectrum that PH-CN displays better performance for harvesting light compared to B-CN. Additionally, the PH-CN is prepared with a larger band gap of 2.88 eV with the Fermi level and conduction band potential increased and valence band potential decreased, which could promote the water redox reaction. The application experiment results show that the hydrogen evolution rate on PH-CN was nearly 10 times higher than that of B-CN, which was roughly 4104 μmol h<sup>−1</sup> g<sup>−1</sup>. The method shown in this work provides an effective approach to adjust the structure of g-C<sub>3</sub>N<sub>4</sub> with considerable photocatalytic hydrogen evolution activity.
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