Metal oxide nanocrystals embedded polypyrrole nanohybrid: Exploring role of interface in photocatalytic hydrogen generation

Abstract

Photocatalytic water splitting is considered as a sustainable way to produce hydrogen in the water−based energy cycle. Inorganic semiconductors, specifically metal oxides are extensively used as efficient photocatalysts, however, intrinsically poor charge-transfer and wide band gap with lower negative conduction band potential than the hydrogen evolution potential affect the water-splitting efficiency. In view of superior charge-transfer, and tunable energy levels, polymer-based nanohybrids (NHs) have been fabricated using polypyrrole (PPy) nanofibers with a series of transition metal oxides (MO) nanoparticles, namely TiO2, ZnO, CeO2, Fe2O3, NiO, and SnO2. A series of photoanodes have been tested for photoelectrochemical water splitting to elucidate the effect of interfacial charge transfer at the interfaces of NHs. The high photocurrent response of 44 μA cm−2 at 0.9 V vs. Ag/AgCl has been achieved for Fe2O3/PPy. While, ZnO/PPy NHs demonstrated a superior photocatalytic H2 generation rate of ∼162 mmol/g/h, which is ∼27 times higher than pure PPy. Based on energy level calculation, the charge transfer mechanism occurs through p−n junction in TiO2/PPy and SnO2/PPy NHs while the other NHs structures follow a Z−Scheme of charge transfer pathway. This finding opens an avenue for designing highly efficient polymer-metal oxide heterojunctions for water splitting and solar fuel applications.