| Summary: | Graphitic C<sub>3</sub>N<sub>4</sub>-based materials are promising for photocatalytic H<sub>2</sub> evolution applications, but they still suffer from low photocatalytic activity due to the insufficient light absorption, unfavorable structure and fast recombination of photogenerated charge. Herein, a novel anion–cation co-doped g-C<sub>3</sub>N<sub>4</sub> porous nanotube is successfully synthesized using a self-assembly impregnation-assisted polymerization method. Ni ions on the surface of the self-assembly nanorod precursor can not only cooperate with H<sub>3</sub>P gas from the thermal cracking of NaH<sub>2</sub>PO<sub>2</sub> as an anion–cation co-doping source, but, more importantly, suppress the shape-collapsing effect of the etching of H<sub>3</sub>P gas due to the strong coordinate bonding of Ni-P, which leads to a Ni and P co-doped g-C<sub>3</sub>N<sub>4</sub> porous nanotube (PNCNT). Ni and P co-doping can build a new intermediate state near the conduction band in the bandgap of the PNCNT, and the porous nanotube structure gives it a higher BET surface area and light reflection path, showing a synergistic ability to broaden the visible-light absorption, facilitate photogenerated charge separation and the light-electron excitation rate of g-C<sub>3</sub>N<sub>4</sub> and provide more reaction sites for photocatalytic H<sub>2</sub> evolution reaction. Therefore, as expected, the PNCNT exhibits an excellent photocatalytic H<sub>2</sub> evolution rate of 240.91 μmol·g<sup>−1</sup>·h<sup>−1</sup>, which is 30.5, 3.8 and 27.8 times as that of the pure g-C<sub>3</sub>N<sub>4</sub> nanotube (CNT), single Ni-doped g-C<sub>3</sub>N<sub>4</sub> nanotube (NCNT) and single P-doped g-C<sub>3</sub>N<sub>4</sub> nanotube (PCNT), respectively. Moreover, the PNCNT shows good stability and long-term photocatalytic H<sub>2</sub> production activity, which makes it a promising candidate for practical applications.
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