Fe controlled charge-dynamics in ZnO for solar hydrogen generation

Abstract

An efficient photoanode of Fe doped ZnO was fabricated using an economic and simple spray pyrolysis technique. It exhibited 5-fold photocurrent enhancement as compared to an un-doped photoelectrode irradiated under simulated solar radiation (AM 1.5G). The photo-conversion efficiencies of the electrodes fabricated by variation in the dopant concentration in the range 10−4–10−1% of Fe have been estimated and compared. The doping enabled to control the charge dynamics in ZnO photoanode to yield enhanced photocurrent. The photo electrochemical hydrogen evolution under solar-photons from the doped photoanode was 17-times larger in magnitude i.e. ∼307 μmol/h, than un-doped film electrodes (18 μmol/h). The film exhibited wurtzite structure (Space Group – P 63mc) which did not show any structural lattice deformation after Fe doping of ≤10−1%. Optical studies revealed a red-shift in the band-gap, while a decrease in the absorption-coefficient, with the increase in Fe concentration. These photoanodes also displayed higher Incident-Photon-Current-Conversion efficiency (IPCE) in the 400–430 nm wavelength range. Electrochemical studies revealed n-type conductivity of these photoanodes. An anodic shift in the flat-band potential was observed with an increase in the Fe dopant concentration in the ZnO lattice. The result of the experimental study is illustrated in the form of schematic diagram which demonstrates the suitability of the doped system for solar hydrogen generation. Dopant induced improved optical absorption is mainly attributed to the enhancement in photo-response of these Fe doped ZnO films. The study indicates high potential of these ZnO films for solar energy applications especially with respect to their ability to work under solar radiation.