## 1 Introduction  
In recent years, the modern energy crisis has been one of the major problems that has concerned human beings in the 21 st century. Therefore, a recent flourish of studies have been inspired to develop environmental-friendly and renewable fuels [1]. Particularly, the use of photocatalytic water splitting for hydrogen production is an attractive strategy in the field of energy conversion with abundant solar energy, since the pioneering report of photoelectrochemical water splitting was published in 1972 [2]. Currently, a lot of photocatalysts, such as TiO\({}_{2}\)[3, 4, 5], WO\({}_{3}\)[6, 7], g-C\({}_{3}\)N\({}_{4}\)[8, 9, 10], ZnO [11, 12, 13], and metal complexes [14, 15, 16], have been employed for the photocatalytic water splitting reaction. However, it has been demonstrated that most of these photocatalysts with wide band gaps are only active under UV irradiation. Thus, it is vital to develop a highly active photocatalysts with a sufficiently narrower bandgap for efficient visible-light-driven hydrogen production.  
So far, nitride [17, 18] or metal oxynitrides [19, 20], absorbing visible light with a larger wavelength range, have been found to be capable of splitting water into hydrogen and oxygen under visible-light illumination. Among them, GaN:ZnO solid solution possesses a wurtzite-type structure with a d\({}^{10}\) typical electronic configuration, which has been actively investigated [21, 22]. It shows a narrower band gap, ranging from 2.4-2.8 eV [23, 24], which can be ascribed to the p-d repulsion in the valence band between Ga3d/Zn3d and N2p/O2p [25]. However, as for GaN:ZnO solid solution, due to the lack of H\({}_{2}\) evolution sites, it is necessary to employ a cocatalyst that plays a vital role in providing active sites and improving the charge separation for photocatalytic redox reactions [26; 27; 28]. Rh\({}_{2-y}\)Cr\({}_{y}\)O\({}_{3}\), as a traditional cocatalyst, has been found to be capable of promoting the realization of the photocatalytic water splitting [29; 30]. Therefore, high-efficiency GaN:ZnO solid solutions decorated with cocatalyst of Rh\({}_{2-y}\)Cr\({}_{y}\)O\({}_{3}\) were designed and prepared.  
Typically, GaN:ZnO is synthesized by nitriding the mixture of Ga\({}_{2}\)O\({}_{3}\) and ZnO under anhydrous NH\({}_{3}\) gas flow, and calcinating it for a relatively long reaction period to guarantee a successful formation of solid solution [21; 31; 32]. However, the as-prepared GaN:ZnO possesses a non-uniform elemental distribution of Zn and Ga after long-term nitriding [24; 33]. Herein, it is significant to develop a facile and versatile approach to prepare the GaN:ZnO solid solution with higher homogeneous particles. In recent years, electrospinning has been proven as a simple and widely used technology for the preparation of nanofiber materials with a larger specific surface area and better light harvesting ability [34; 35; 36]. The electro-spun nanofibers also show good recoverable character in comparison to nano-powders [37]. Furthermore, the problem of the elemental aggregation of GaN:ZnO solid solution can be efficiently eliminated by immobilizing the elements of Ga and Zn on polyacrylamide (PAN) during the electro-spun process [38].  
In this study, we present for the first time nanorod GaN:ZnO solid solutions prepared using an electrospinning method for photocatalytic H\({}_{2}\) production under visible-light irradiation. The phase microstructure and morphology of the nanorods prepared at different nitriding temperatures were determined. The optical properties were evaluated via UV-vis diffuse reflectance spectra (DRS), photoluminescence (PL), and an electrochemistry workstation. The photocatalytic efficiency of the samples was estimated by water-splitting H\({}_{2}\) production under visible-light irradiation. In addition, the photocatalytic mechanism of GaN:ZnO solid solution under visible-light irradiation was proposed.