Awakening Solar Water-Splitting Activity of ZnFe2O4 Nanorods by Hybrid Microwave Annealing

1D 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 550 degrees C increases the photocurrent density of water oxidation by 15 times. In contrast, the conventional thermal annealing at 800 degrees C brings only 1.7-fold increase. The various physical characterizations and hole scavenger photooxidation 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.