# Electrospun Nanomaterials for Energy Applications: Recent Advances
## 1 Introduction  
Electrospinning is one of the most widely adopted techniques for the production of high aspect-ratio nanostructures featured by high porosity, great surface area-to-volume ratio, and cross-sectional diameters ranging from tens to hundreds of nanometers. It is a very simple, scalable, and cost-effective technique, particularly suitable for the manufacturing of fibrous nanomaterials on an industrial scale since the production process, involving two well distinct steps (namely, fibrous film deposition and subsequent thermal treatment, if any), can progress without any interruption.  
The wide variety of intriguing nanomaterials with outstanding physical and chemical properties that can be produced by electrospinning (natural and synthetic polymers, ceramic oxides, carbon and composite carbon-based fibers, and fibrous flexible membranes with hierarchical porosity) find application in a plethora of both well-assessed and emerging applications, spanning from healthcare and biomedical engineering (e.g., wound dressing, biological sensing, drug and therapeutic agent delivery, tissue regeneration, and engineering) to environmental protection and remediation (e.g., chemical and gas sensing, photocatalytic abatement of pollutants, water treatment), from energy harvesting, generation, and storage (e.g., solar cells, hydrogen production and storage, supercapacitors, batteries, and fuel cells) to electronics (e.g., field-effect transistors, diodes, photodetectors, and electrochromic devices) [1; 2; 3; 4; 5; 6; 7; 8; 9; 10].  
The huge number of potential applications in which electrospun nanomaterials (ENMs) can have significant impact hinders from exhaustively describing all of them in a single review. On the other hand, several excellent reviews illustrating the current status, challenges, and emergingdevelopment of nanofiber technology for specific application fields are already available in the literature (see f.i. [3; 4; 5; 6; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18]), just to cite a few of them).  
This paper deals with a specific theme--the energy-related applications of ENMs, which are increasingly gathering interest by the scientific community, as demonstrated by the impressive rate at which the number of published papers dealing with this subject is growing. Figure 1 displays the numbers relative to a single database. Among them, those concerning rechargeable alkali metal-ion batteries, supercapacitors, reactors for water desalination via capacitive deionization and for hydrogen production by photo-assisted water splitting (which presently represent the field on which the scientific interest of the author's research group is mainly focused), as well as redox flow batteries, metal-air batteries, nanogenerators for energy harvesting, and textiles for energy saving through personal thermal management are selected and discussed, trying to report aspects, which can attract the interest and stimulate the inventiveness of the readers to produce further remarkable advances not only in the presented application fields, but also in others.  
A brief description of the principle on which electrospinning is based and of the parameters to be tuned to control the physicochemical properties (size, morphology, texture, alignment, porosity, composition, etc.,) of the produced ENMs is first given. Aiming at facilitating the comprehension of the subject to readers experienced in different fields, each section begins with a very short introductive outline on the discussed application. Finally, the concluding section discusses the future prospects for the commercialization of ENM-related applications and their entrance in our daily life.