Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Au/Ga 2 O 3 /ZnO heterostructure nanorods arrays for effective photoelectrochemical water splitting Akram Abdalla a,b , Ibrahim Khan a , Manzar Sohail a,c , Ahsanulhaq Qurashi a, ⁎ a Center of Research Excellence in Nanotechnology, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia b School of Engineering, Department of Materials and Environmental Technology, TalTech University, Ehitajate tee 5, Tallinn 19086, Estonia c Department of Chemistry, School of Natural Sciences, National University of Science and Technology, H-12, Islamabad 44000, Pakistan ARTICLE INFO Keywords: Au/Ga 2 O 3 /ZnO Heterostructure Nanorods arrays Water splitting ABSTRACT Heterostructure semiconductors are considered as suitable candidates for solar-driven photo-electrochemical (PEC) water splitting due to their viable photoactive nature. Therefore, in this article, we have demonstrated the synthesis of Ga 2 O 3 /ZnO nanorods arrays (NRAs) by two-step physical vapor deposition (PVD) and wet chemistry method, directly on the glass and indium tin oxide (ITO) support. Morphological features, structural properties and chemical composition were investigated by scanning electron microscopy (FESEM), X-ray diffraction (XRD) spectroscopy and EDX, respectively. The optical properties through photoluminescence (PL) revealed that with increasing concentration of gallium content, reduction of visible peak of the PL spectrum is observed. Additionally, an ultra-thin nanofilm of gold nanoparticles (AuNPs) is also sputtered on the Ga 2 O 3 /ZnO NRAs to make Au/Ga 2 O 3 /ZnO heterostructures photoanodes. These photoanodes successfully split water under artificial solar light. Our results indicated the Au/Ga 2 O 3 /ZnO NRAs heterostructure photoanodes, which assimilates two different semiconductors with tunable band gaps can be realistically applied to photoelectrochemical applica- tions. 1. Introduction Zinc oxide (ZnO), is an important n-type semiconductor which can be grown into different morphologies under different reaction condi- tions. The unique optoelectronic characteristics of ZnO include tunable bandgap, thermodynamically suitable band positions for water splitting (especially water oxidation) and other multi-functional physical prop- erties (Djurišić and Leung, 2006; Xu and Wang, 2011). It has been utilized for in various optoelectronic devices, sensors and photovoltaics (Ahsanulhaq et al., 2012; Qurashi et al., 2015). However, the wide band gap i.e. 3.37 eV, of ZnO, limits its application in photoelectrochemical (PEC) applications. Therefore, it is important to engineer the bandgap of ZnO to suitable range. Various methods are adopted by researchers, among which the nanohybrid formation with suitable metal oxide is receiving great prominence. ZnO nanomaterials can be combined with a suitable band gap materials for respective applications. As reported, ZnO NRAs have been used for PEC water splitting, by sensitizing with quantum dots or via nitrogen doping or nanocomposite formation and have shown morphological flexibility in the form of various nanos- tructures (Chen et al., 2014; Hsu and Chen, 2012; Yang et al., 2009). In addition to their morphological advantages, ZnO photoanodes also have shown a better stability and ease of fabrication. Gallium oxide (Ga 2 O 3 ), is relatively less used for photocatalysis and like ZnO it is also n-type semiconductor having wide band gap. Besides photocatalysis, Ga 2 O 3 has been explored for various applications such as transparent conductors, gas sensors, power devices and phosphors (Gordon and Schaak, 2014a; Higashiwaki et al., 2016, 2012; Sharma and Sunkara, 2002). Nitrogen doping is a conventional approach to enhance the PEC performance of Ga 2 O 3 (Hou et al., 2016; Iqbal et al., 2016). To enhance the efficiency of wide bandgap Ga 2 O 3 the suitable approach is to prepare their heterostructures with suitable combina- tion. Shimura et al. reported the effect of zinc doped species on the PEC performance of gallium oxide for overall water splitting (Shimura and Yoshida, 2012). It was realized that doped Zn 2+ ions substantially enhanced the photocatalytic behavior of Ga 2 O 3 in the methane steam reforming reaction. Based on the available literature, the optoelectronic properties of ZnO and Ga 2 O 3 in a heterostructure always provide an efficient way for efficient charge transferring and hence the charge recombination suppression as well as enhanced PEC water splitting achieved. Recently, our group have successfully developed GaON/ZnO nanoarrays photoanodes over ITO substrates. This material showed excellent optoelectronic behavior and demonstrated a photocurrent https://doi.org/10.1016/j.solener.2019.01.065 Received 8 March 2018; Received in revised form 3 December 2018; Accepted 19 January 2019 ⁎ Corresponding author. E-mail address: ahsanulhaq06@gmail.com (A. Qurashi). Solar Energy 181 (2019) 333–338 0038-092X/ © 2019 Published by Elsevier Ltd on behalf of International Solar Energy Society. T