Preparation of BiVQ4-decorated ZnO nanorods for oxygen evolution using photo-electrocatalysis

The use of semiconductor heterojunction nanostructures to obtain hierarchical electrodes have been widely investigated, especially in the field of energy conversion and photoelectrocatalysis.1 Zinc oxide nanorod (ZnONR) is a suitable catalyst for photoelectrochemical water splitting applications, however it only absorbs UV radiation.1-2 On the other hand, bismuth vanadate (BiV04), exhibit high visible light absorptivity due to its small band gap energy (2.4 eV).1 ln this work, we have studied the role of the ITO and FTO bottom electrode on the self-assembled stability of BiV04-ZnO nanostructure architecture, and the effect of heat-treatment at 600 ºC for 1 h. To grow the ZnONR films, a two-step method based on the literature with minar modifications was used.2 BiV04 nanostructures were prepared through precursor mediated growth method and decorated on the surface of ZnONRs by using a colloidal BiV04 solution (previously ultrasonicated). The structural and chemical properties of the films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. Fig. 1 shows the morphologies of the obtained samples. lt can be seen that ZnONRs with 100-200 nm in diameter were successfully synthesized on both substrates. The BiVQ4 nanofibers are well dispersed on the surface, and penetrates completely between the rods, as shown in Fig. 18. According to the XRD analyses, BiVQ4 takes the monoclinic structure and ZnONR takes the wurtzite structure. However, for the calcined samples, we have observed a slight growth in the (002) plane by monitoring the Bragg peak intensity. As shown in Fig. 1, the current was directly generated from the designed photoanode as no current was detected when applying a linear sweep within a range from -0.5 to +1.0 V in the darkness. Compareci with pristine ZnONRs, the ZnONRs coated with BiVQ4 film shows higher photocurrent density under light illumination, which can be related to the increase of light absorption capability of ZnO. However, the ZnONR films grown in FTO substrate showed better photocurrent density stability than ZnONR/ITO electrodes. The heat-treated BiV04-ZnONR electrodes exhibit a lower response compareci with electrodes based on ZnONR films.