Nanofibers for energy
The worlds growing demand for clean energy will require the development of new technologies and new materials. The high surface area to mass ratio of nanofibers, in addition to semiconductive behavior for certain types of oxide nanofibers, encourages the use of these materials in the fabrication of energy devices.
Nanofibers can be used in the following applications:
- Li-ion battery electrodes
- Battery separators
- Solar cells
- Fuel cells
The primary benefits of nanofibers in these applications are:
- High capacity and power
- High charging rates
- DSSC efficient in indirect sunlight
- High conversion efficiency
Lithium-ion batteries are the densest method of storing electrochemical energy. This is made possible by their high specific surface area and the permeability of the materials within the battery. Lithium-ion batteries have shown continuous performance enhancements when materials have incorporated new improvements in surface-area to volume ratios. Ternary oxide nanofibers using lithium titanate have demonstrated similar improvements and other improvements using nanofibers are expected. Improving the surface area and porosity of lithium-ion components allows for batteries that can be charged more quickly and which can hold their charge longer.
Nanofiber morphology makes electrospun materials an excellent choice for application as battery separator membranes. Battery separators keep the positive and negative electrodes apart to prevent electrical short circuits and allow rapid ionic flow needed to complete the circuit during the passage of current in an electrochemical cell. This enables construction of a battery with superior power density, which is able to keep its capacity even at high charging or discharging rates. Such a battery is able to keep its capacity even at charging or discharging rates above 2C with conventional electrode materials such as graphite and LiCoO2. This high rate battery performance is not possible with traditional polyolefin membranes.
Nanofiber materials can be integrated into dye sensitized solar cells (DSSC), which offer unique advantages in comparison to other types of solar cells. In addition to low cost, good transparency of the DSSC allows it to be used as a window on a building and it’s flexibility offers the potential to be laminated to almost any other material. This type of solar cell can be applied to any surface accessible to light, even indirect light with a very low intensity, expanding the opportunities to use solar energy.
Fuel cells as electrochemical conversion devices produce electricity continuously from fuel delivered by an external resource and an oxidant in the presence of an electrolyte. Direct Methanol Fuel Cells (DMFC) can become the best choice since it is inexpensive and the storage of methanol is quite easy. Catalysts remain the key component of fuel cells due to their high cost to manufacture. Although there have been years of effort developing effective catalysts, slow anode kinetics, poisoning of catalysts and stability problems associated with the chemical resistance of metal catalysts in the harsh environment of DMFC operating conditions are major barriers to overcome. New types of functional catalysts for a DMFC anode can be prepared by using direct electrospinning. The potential of graphite nanofiber supported metal (oxide) alloy catalysts as an electrode is promising. Traditional methods to prepare carbon nanostructures including vapor growth and plasma enhanced chemical vapor deposition, a complicated and expensive process.
