Development of Nanostructured Zn Ferrite Photoelectrode for Water Splitting and its Photoelectrochemical Properties

Abstract

One-dimensional zinc ferrite (ZnFe2O4) photoanode is fabricated on an F-doped tin oxide substrate at a low temperature by an all-solution method. To activate the material for photoelectrochemical water splitting, the hybrid microwave annealing (HMA) is applied with graphite powder as a susceptor. Thus, HMA treatment of ZnFe2O4 photoanode synthesized at 550oC increases the photocurrent density of water oxidation by 15 times. In contrast, the conventional thermal annealing at 800oC brings only 1.7-fold increase. The various physical characterizations and hole scavenger photo-oxidation experiments with H2O2 reveal that the post HMA treatment anneals the surface defect states and enhances the crystallinity. Hence HMA treatment is effective to suppress charge carrier recombination both on the surface and in the bulk of ZnFe2O4 to bring out its latent solar water splitting activity. Also, one-dimensional zinc ferrite (ZnFe2O4) nanorod photoanode was treated by thermal treatment under the hydrogen or vacuum atmosphere and improved the photoelectrochemical water oxidation activity up to 20 times. The various physical characterizations revealed that the oxygen vacancies were created by the treatments in the near surface region, which increased donor density and passivated the surface states. Hydrogen treatment was more effective and it was important to find optimum treatment conditions to take advantage of the positive role of oxygen vacancy as a source of electron donors and avoid its negative effect as electron trap sites.