Porous nanostructured cationic conjugated polyelectrolyte/titanium dioxide nanosheet heterojunction for enhanced cocatalyst-free photocatalytic hydrogen evolution.

Modified TiO₂ photocatalysts face challenges dependence on cocatalysts, weak interfacial interactions, and poor wettability. This work presents an effective strategy by coupling donor-donor (D-D) type cationic conjugated polyelectrolyte poly[(9,9-bis(3'-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]dibromide (PFN-Br) with two-dimensional TiO₂ (2D-TiO₂) nanosheets to construct type-II heterojunctions rich in active sites. Under optimal conditions, the 2D-TiO₂/50 wt% PFN-Br (2D-Ti/PBr-50) heterojunction achieved a hydrogen evolution reaction of 2621.01 μmol g^-1 h^-1 without any cocatalyst-representing 21.86 times higher than that of pristine 2D-TiO₂ nanosheets. This significant enhancement is mainly attributed to the strong visible-light absorption capability of PFN-Br, well-matched band alignment with 2D-TiO₂ nanosheets, reinforced interfacial interactions via hydrogen bonding and electrostatic forces, the porous nanostructure of the 2D-Ti/PBr heterojunction, and good interfacial wettability due to the ionic side chains of PFN-Br. This study offers new insights into polyelectrolyte-assisted TiO₂ photocatalysts for cocatalyst-free applications.