Electrospun Nanofibers for Applications in Energy Harvesting and Generation
Electrospun nanofibers have gained great research interest for decades as attractive nanomaterial for various applications due to their ultra-high specific surface area, flexibility in materials, and ease of fabrication. Furthermore, fine tuning of electrospinning or post-electrospinning process conditions can allow for precise control of morphology, composition, physical, electrical, and electrochemical properties to tailor the nanofibers for a specific application. In this work, the effect of various electrospinning-related conditions on properties of polyacrylonitrile (PAN)-derived nanofibers was elucidated by series of systematic variation of parameters called design of experiment (DOE). Analyses on the DOE revealed solution viscosity, mainly controlled by polymer concentration, was the predominant factor for nanofiber morphology, while the addition of composite materials such as multi-walled carbon nanotubes and zinc acetate also strongly affected the nanofiber dimensions.
To study the suitability of the PAN nanofibers with controlled properties for applications in energy harvesting and generation, piezoelectric and electrochemical properties of PAN-derived as-spun and heat-treated nanofibers were characterized. For the first time, size-dependent piezoelectric properties for PAN nanofibers was carefully investigated, which showed the voltage generated perpendicular to the direction of the fiber (V33) increased as a function of decreasing fiber dimensions, similar to more commonly studied piezoelectric polymers. Electroanalytical methods such as cyclic voltammetry, linear polarization and electrochemical impedance spectroscopy were employed to investigate the feasibility of various carbonaceous nanofibers as electrode material.
Enzymatic fuel cell was chosen as the device of interest for energy generation application in this work. In an attempt to utilize the naturally abundant yet complex cellulose as fuel, a multienzyme cascade complex in nature called cellulosome was biomimetically fabricated by site-specific immobilization of 5 enzymes on customized DNA scaffold for sequential hydrolysis of cellulose followed by catalytic oxidation of glucose for electricity generation. With successful demonstration of the synergistic effect of enzyme immobilization on DNA scaffold, similar system was functionalized onto an electrode for preliminary electrochemical studies, which exhibited great promise as multienzyme cascade-based bioanode for cellulolytic fuel cell.