Polymeric photocatalysts for water splitting have received extensive attention recently. However, most polymeric photocatalysts suffer from an unexceptional hydrogen/oxygen evolution rate, primarily originating from less understanding of the molecular design of conjugated polymers for photocatalysis. Herein, we show that facile substituent regulation on conjugated polymers can boost the hydrogen evolution efficiency. Conjugated polyelectrolytes with different substituent groups (−F, −CN) were designed and synthesized. Compared to the unmodified polymer, the −F and −CN modified polymers showed 2.9-and 12-times improvements in the hydrogen evolution rate (3 μmol h −1 vs 8.8 μmol h −1 vs 38.3 μmol h −1 ). Notably, −CN substituents in the polymer could reduce the exciton binding energy, induce closer packing and higher crystallinity, improve the charge transporting, and reduce the charge recombination. Moreover, higher efficient exciton generation and charge transfer efficiency to cocatalysts were observed in −CN modified polymers, indicating the great promise of using substituent regulation to achieve high-performance organic photocatalysts.

We report here a series of water–alcohol-soluble hyperbranched polyelectrolytes, which can be used as both cathode interfacial materials (CIMs) in polymer solar cells (PSCs) and organic photocatalysts for hydrogen or oxygen evolution. Hyperbranched polyelectrolytes (HD-Br, HN-Br, and HP-Br) are quaternization-polymerized from 1,3,5-tri­(pyridin-4-yl)­benzene and alkyl bromide terminated conjugated moieties, including diketopyrrolopyrrole (DPP), naphthalene diimide (NDI), and perylenediimide (PDI) moieties. These hyperbranched polyelectrolytes possess good water/alcohol solubility and a semiconductive property, which render them good candidates for applications in PSCs and photocatalysis. In PSCs, these hyperbranched polyelectrolytes could lower the work function of the metal electrode, facilitate electron collection, and improve the photovoltaic performance. In photocatalysis, these hyperbranched polyelectrolytes show good water dispersity and provide good interface contact between polyelectrolytes and water, resulting in efficient photocatalytic hydrogen or oxygen evolution.

Tetra-armed conjugated microporous polymers for gas adsorption and photocatalytic hydrogen evolution SCIENCE CHINA Chemistry 60, 1075 (2017); Theoretical investigation of loading Ni clusters on the α-Ga2O3 surfaces for photocatalytic hydrogen evolution