Nanofibers are defined as one-dimensional nanomaterials with diameters less than 1 µm (1000 nm), and an aspect ratio (length/ diameter) larger than 100:1. They are also named as superfine or ultrathin fibers in some literature [1, 2]. When the fibers are in the range of 100-1000 nm, they are also referred to as submicron fibers [3-5]. This intrinsic feature offers them drastically increased surfaceto-volume ratio and high aspect ratio. There are several methods to produce nanofibers, including phase separation [6], self-assembly [7, 8], template synthesis [9], melt-blowing [10], flash spinning [11], bicomponent spinning [12], and electrospinning [13, 14]. Nanofiber mats produced from electrospinning have a naturally formed porous structure with excellent pore interconnectivity, and the pores are in the range between tens of nanometers to a few micrometers. The open pore structure and high permeability to gas, along with the high surface area, make them ideal porous membranes. Compared with other one-dimensional nanostructures (e.g., nanotubes or nano-rods), continuous nanofibers are advantageous in terms of fabrication cost and the possibility of being integrated into other desired assembly in one step.