Improved photoelectrochemical water oxidation using wurtzite ZnO semiconductors synthesized through simple chemical bath reaction

• Chemical bath synthesis of ZnO nanoparticles at 185 °C using simple precursor salt.
• XRD analysis confirms hexagonal ‘wurtzite’ crystallites of average size of 25 ± 5 nm.
• Highest water oxidation current of 440 μAcm−2 even at low illumination of 35mWcm−2 with minimum applied external bias.
• Stable PEC activity with high photoconversion efficiencies like 35% IPCE, 65% APCE and better fill factor.
• High rate of photocatalytic decoloration of Rhodamin-B dye by ZnO nanoparticles.

In this paper we demonstrate, the drop-casting of chemically synthesized ZnO nanoparticles over ITO coated glass substrate to obtain the good-quality semiconductor thin film. UV-visible absorption spectrum of the ZnO film indicates the direct band gap energy of 3.21 eV. Scanning electron microscopy confirms the presence of small particles of ∼30 nm dimension whereas X-ray diffraction analysis indicates the presence of hexagonal wurtzite ZnO structure. Maximum photoelectrochemical water oxidation current of 440 μA cm−2 has been recorded even at a low overpotential of 0.25 V vs. Ag/AgCl reference electrode under minimum illumination of 35 mW cm−2, when tested in 0.1 M Na2SO4 solutions (pH7). The incident photon to current conversion efficiency (IPCE) and absorbed photon to current conversion efficiency (APCE) measurements reflect high photo-conversion efficiencies as 35% and 65%, respectively, when measured with the semiconductor. Photocatalytic activity of the ZnO semiconductors has been measured spectrophotometrically using aqueous Rhodamine-B solution under same Xe-light irradiation.

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