Z-Scheme Heterostructures Using Band-Gap-Tunable ZnO by Metal Doping and Coupling with Polypyrrole for Enhanced Photocatalytic Water Splitting
Srabanti Ghosh, Pradip Sekhar Das, Dipendu Sarkar, S. Pal, Milan Kanti Naskar, Yatendra S. Chaudhary, Sunanda Dey, Chittaranjan Sinha
Abstract
Solar-to-hydrogen (H 2 ) conversion is one of the sustainable and renewable approaches to mitigate ever-increasing environmental pollution and the global energy crisis. Despite significant progress, the most critical aspect remains the design of highly efficient and stable photocatalysts. Although ZnO-based photocatalysts exhibit high catalytic activity, they suffer from the intrinsic drawback of the broadband gap with ultraviolet (UV) light absorption and are susceptible to oxidation. Herein, a strategy to extend light harvesting in the visible region by metal doping (M = Bi, Cu, and Al) of ZnO nanocrystals and their functionalization with polypyrrole (PPy) nanofibers to drive water-splitting efficiently has been presented. The interfacial band alignment and charge transport of nanohybrids reveal electron transfer from metal-doped ZnO to PPy through the Z-scheme mechanism. Impedance spectra indicate efficient charge separation of ZnO:Bi/PPy nanohybrids, which exhibit a 10-fold increase in photocurrent density for visible-light-driven water splitting and improved photostability compared to PPy. The ZnO:Bi/PPy nanohybrid shows a H 2 generation of 13.5 mmol/g/h, ∼9.6 times higher than PPy nanofibers (1.4 mmol/g/h). In contrast, the pure ZnO nanocrystal leads to the formation of a p–n ZnO/PPy junction with moderate catalytic efficiency. This study identifies a viable approach for developing high-performance conducting polymer-based nanohybrid photocatalysts for water splitting to produce green hydrogen.