|Energy Harvesting Research at Stevens|
Ambient vibration energy harvesting
Vibration energy harvesting is an emerging field where one seeks to convert ambient vibrations to small but useful levels of electrical energy; for example, to power the individual nodes of a wireless sensor network with applications in areas such as Homeland Security (biohazard detection and monitoring) and National Infrastructure (Structural Health Monitoring of critical civil infrastructure such as bridges). As the power requirements for sensors and wireless communication continue to decrease, it has been proposed that vibration energy harvesting has the potential to provide a permanent, on-chip power source for powering wireless sensor nodes in the network. One way to scavenge energy from the environment is to use piezoelectric materials, which generate electrical charge when subject to mechanical stress. If one can create piezoelectric structures that are in resonance with the environmental frequency, the stresses induced in the piezoelectric structure upon vibration can be converted to electric energy. One challenge in this area is to develop a means to tune the energy harvesting device so that it's resonant frequency can be adjusted to match the frequency of the environmental vibration source. We have recently developed a semi-active, magnetically-based tuning mechanism. The article was recently highlighted as one of the most-accessed articles by that journal for the year 2008.
Distributed Production of Advanced Biofuels from Biomass Waste
We demonstrate a transformative technology which combines innovative reactor concepts with fundamental catalytic studies and catalyst development for the distributed production of biofuel from various forms of biomass waste.
Our approach comprises two key steps:
- thermochemical conversion of biomass by fast pyrolysis to pyrolysis oil, (PO), followed by
- upgrading of the PO to biofuel.
A number of approaches are currently being investigated for the upgrading of the PO including (i) hydrodeoxygenation, (ii) (hydro)cracking and (iii) autothermal reforming (ATR) of PO to synthesis gas ssssss(H2/CO mixture), followed by Fischer-Tropsch (F-T) conversion of synthesis gas to fuel.
The economic viability of biofuel production from lignocellulosic biomass can only be achieved in part through efficient distributed processing, because of the prohibitive transportation cost associated with centralized processing of low bulk density lignocellulose sourced from vast geographical areas. The new paradigm we envision, involves an on-site distributed production platform for biomass pyrolysis to PO. The PO from various producers within the same geographical region will then be transported using existing infrastructure to a gathering point where the PO will undergo ATR and subsequent F-T conversion to fuel.
A compelling and distinguishing attribute of our process is the flexibility of
- converting biomass of different compositions derived from multiple sources to PO and syngas and
- using this syngas to produce any transportation fuel: ethanol, gasoline, or diesel.
Petahertz Diode for Highly Efficient Solar Energy Harvesting
We are developing a highly efficient solar energy harvesting technology using nanoengineered diode structures with a petahertz cutoff frequency. The approach is to use a metal-insulator multilayer structure, enabling 1 Petahertz bandwidth with nanometer-scale point contacts which permit an extremely high-cutoff frequency from a diode. There is low photon energy absorption, unlike P-N junction-based solar cells. The benefits are a smaller, lighter and less costly device, with opportunities for new computing, sensing and actuation functions It can be integrated into flexible membranes for “smart skin” in UAVs and micro-autonomous vehicles.
Nanofluidic Energy Harvesting
When a solid surface contacts a liquid electrolyte, a thin electric double layer (EDL) is formed at the interface. Both the solid surface and the EDL carry electrical charges. In a nanofluidic channel, the density of free charge in the liquid electrolyte increases dramatically due to the overlapping EDLs. A forced flow of electrolyte through nanofluidic channels can therefore be used to establish streaming current and potential. This phenomenon, known as electrokinetic energy conversion, has been explored to generate electricity from liquid flow. However, one key challenge for its practical application is how to improve the energy conversion efficiency, which is currently ~3% or lower. We have been investigating various nano-engineered surfaces to improve the efficiency. One example is to use nano-textured superhydrophobic surfaces on the nanochannel walls. The superhydrophobic surfaces of the nanochannel will generate slip flow and greatly reduce the flow resistance in nanochannels. It has been theoretically predicted that such a slip surface has the potential to improve the energy conversion efficiency to 30-40%. If carried out successfully, the proposed work will enable efficient energy harvesting from various flow sources. A wide variety of systems can benefit from such technologies, both macroscopic systems where flows can be directed to nanochannels and directly in microfluidic devices.
Thermoelectric nanostructures for thermal energy scavenging
Perovskite La1-xSrxCoO3 is a very promising complex oxide thermoelectric material. It is expected that its thermoelectric figure of merit ZT will be significantly increased at nanoscale. We are developing cobalt-based nanostructures to convert thermal energy to electricity using integrated micro and nanofabrication methods. This project involves the fabrication of thermoelectric nanofibers; design and fabrication a MEMS scale tester for the measurements of the Seeback coefficient and characterization of thermal/electric properties, and the optimization of the performance of energy harvesting device, which can potentially be used as portable wireless energy source as well as large scale energy converter.
Dye Sensitized Solar cells
Dye sensitized solar cells (DSSCs) are promising photovoltaic devices as they offer advantages such as low cost and simple fabrication process while having potentially high energy conversion efficiency compared with silicon based solar cells. The key component of a typical DSSC is a sintered film of TiO2 nanoparticles which has a large surface area for the absorption of dyes. However, the electron transport in TiO2 nanoparticles in a DSSC rely on trap-limited diffusion process, in which photo-generated electrons repeatedly interact with a distribution of traps before they can reach the collecting electrode. It has been shown that this trap-limited process leads to a higher probability of charge–carrier recombination, which diminishes the device efficiency. In this project, we are exploring one dimensional nanostructure such as TiO2 nanofibers to improve electron transport and enhance efficiency of solar cells. Currently an open circuit voltage of 0.7 V and a short circuit current density of 1 mA /cm2 have been demonstrated.