Polaron and bipolaron induced charge carrier transportation for enhanced photocatalytic H2 production

Abstract

Photocatalysis is one of the facile approaches for efficient solar energy conversion and storage. However, rapid charge carrier recombination considerably decreases solar to energy conversion efficiency. Herein, polaron and bipolaron rich polypyrrole (PPy) has been utilized as a solid support for effective photogenerated charge carrier separation. Simple oxidative polymerization using a high concentration of ammonium persulfate (APS) induces radical cation/bipolaron formation in PPy due to the cleavage of π-bonds as confirmed by electron paramagnetic resonance spectroscopy (EPR). The formation of radical cations led to an increase of the dielectric constant which retards the charge carrier recombination and thereby enhances the conductivity. Moreover, the polarons and bipolarons induced charge carrier separation in photocatalytic H₂ production was studied with the well-known g-C₃N₄ photocatalyst. It is worth mentioning that compared to bare g-C₃N₄, the PPy supported system showed a drastically enhanced photocatalytic H₂ production rate. A maximum H₂ production rate of 1851 μmoles per g is achieved, which is ∼51 times higher than that of the bare g-C₃N₄ catalyst due to efficient charge carrier separation assisted by radical cations/bipolarons. Thus, utilizing this simple polaron and bipolaron rich PPy solid support could be an effective strategy and alternative for using noble metal cocatalysts to enhance charge carrier separation.