Novel conjugated organic polymers as candidates for visible-light-driven photocatalytic hydrogen production

Artificial photosynthesis aiming to capture and convert renewable solar energy into solar fuels (e.g., hydrogen, chemicals) provides a blueprint for sustainable and carbon-neutral world. In artificial photosynthesis, developing novel semiconductors for visible-light-driven photocatalytic water splitting is one of the most demanding challenges. Herein, we designed and explored two kinds of novel bipyridine-based covalent organic polymers, Bp-COP (2,2'-bipyridine-5,5'-diamine: Bp-NH2) and BpZn-COP (2,2'-bipyridine-5,5'-diamine Zn complex: BpZn), both of which exhibit excellent light-harvesting properties with absorption edges expanding to larger than 600 nm and have appropriate band structures for water splitting. Polymers Bp-COP and BpZn-COP are found to enable efficient photocatalytic hydrogen production under visible light irradiation with Pt as the proton reduction cocatalyst. Further assembling conjugated organic polymers with TiO2 as charge transferring mediate can remarkably boost their photocatalytic activities to more than 8 times (1333 vs. 162 mu mol g(-1) h(-1)), giving an apparent quantum efficiency (AQE) of over 2.5% at the input wavelength of 420 nm. This work not only presents a methodology for designing and synthesizing novel organic-based polymers, but also provides promising candidates for potential applications in solar energy conversion.