## 1 Introduction  
Transition-metal oxide nanoparticles have been a subject of intense research due to unique optical, electrical, catalytic, spin and electronic properties [1; 2; 3]. It has been widely used in energy, sensor, sterilization and photocatalysis [4; 5; 6; 7], and is an extremely important part of the research of inorganic functional materials. In the study of transition-metal oxide nanomaterials, preparation technology has an important influence on the microstructure and macroscopic properties of nanomaterials. Up to now, a rich variety of methods, namely the template directed method, solvothermal or hydrothermal synthesizezer, self-assembly and vapor-phase approach [8; 9; 10; 11], have been proposed for fabricating transition-metal oxide nanoparticles. Over the past decades, significant progress has been achieved by the aforementioned methods. However, some intractable problems, such as long preparation cycles, high equipment requirements, low yield, and especially the problem of agglomeration [12; 13; 14; 15], are still great challenges to overcome. Therefore, it has become an urgent task for scientists to explore simple methods and equipment to prepare transition-metal oxide nanoparticles with uniform size, good dispersibility and high yield. One-dimensional metal oxide nanomaterials [16; 17], as the name implies, refer to materials containing metal oxide nanoparticles in one-dimensional nanostructures. Due to the spatial orientation of one-dimensional structures, nanoparticles can be uniformly dispersed along the axial direction of the nanomaterials, which can effectively be against the agglomeration of nanoparticles. Among the different strategies for producing one-dimensional metal oxide nanomaterials, electrospinning has proved a remarkably simple, straightforward and cost-effective process to obtain long continuous metal oxide nanofibers with a diameter ranging from submicrometre to nanometre scales [18; 19; 20; 21; 22]. To date, many groups have focused on designing one-dimensional transition-metal oxide nanofibers composed of nanoparticles. [PERSON] et al. successfully developed a simple strategy for the preparation of Fe\({}_{3}\)O\({}_{4}\)/N-C hybrid nanofibers as artificial peroxidase mimics combining electrospinning and pyrolysis processes, which have promising potential applications in biosensing, medical diagnostics and environmental monitoring [23]. [PERSON] et al. successfully synthesized aligned TiO\({}_{2}\) nanofibers (NFs) using an electrospinning technique with a two-piece Al collector. They demonstrated that, by controlling the needle-to-collector distance and applied voltage, well-aligned TiO\({}_{2}\) NFs with controllable diameters can be obtained [24]. [PERSON] et al. fabricated Co\({}_{3}\)O\({}_{4}\) nanoparticles (NPs) anchored on N-doped mesoporous carbon nanofibers (Co\({}_{3}\)O\({}_{4}\)/NMCF) by electrospinning combined with simple heat treatment. Because of its superior electrochemical performance, Co\({}_{3}\)O\({}_{4}\)/NMCF composite is a promising choice, serving as an efficient electrocatalyst for oxygen reduction reaction (ORR) [25]. Apparently, transition-metal oxide nanofibers are rich in types and structures, resulting in a variety of properties and applications. Therefore, systematic comparative studies on a series of transition-metal oxide nanofibers, including the composition, morphology and formation mechanism, can effectively analyze the relationship between structure and properties of nanomaterials. In addition, the synthesis of functional materials with expected structures can be controlled according to one's wishes, so as to achieve an excellent performance. Yet, to the best of our knowledge, few studies have been done on this aspect. In addition, it should be noted that the preparation process of one-dimensional transition-metal oxide nanofibers is linear nucleation and growth of nanocrystals in the one-dimensional direction.