One dimensional nanotubes and two dimensional nanonetworks, such as graphene, are able to reach thermal conductivities that exceed those of conventional materials by orders of magnitude. Controlling the rate and direction of energy release from these materials may lead to more efficient chemical energy conversion processes and devices. Thermopower waves (TPWs) are self-propagating chemical reactions of a fuel along the length of a thermally and electrically conductive conduit. The reaction wave creates a corresponding voltage pulse of high specific power that can potentially be used as a portable power source with extremely high power density. Quantum confined materials such as carbon nanotubes and graphene that have anisotropy in the transport properties are ideal for supporting such waves. This technology can be used to create electromagnetic pulses for intermittent but high load operations (such as emission of a modulated RF signal), thermopower wave propagation, energy storage, and metal-free alternative power sources with energy density commensurate with commercial lithium ion battery but a much higher power density.
Environmental energy scavenging can regenerate storage devices, but the maximum power capable remains insufficient for RF communications over practical distances. Therefore, there is a need to develop new types of power sources that provide peak power density for intermittent but high load operations, such as emission of a modulated RF signal or powering a fuse. This technology demonstrates encouraging power densities, surpassing the experimental values of micro lithium-ion batteries. As a result, the invention increases the power of "small volume" batteries that will be capable of generating sizable thermopower waves. Meanwhile, there is a pressing need to find alternatives to conventional batteries such as Li-ion, which contain toxic metals, present recycling difficulties due to harmful inorganic components, and rely on elements in finite global supply. Thermopower wave (TPW) devices, which convert chemical to electrical energy by means of self-propagating reaction waves guided along nanostructured thermal conduits, have the potential to address this demand.
This invention describes the generation of a high power electrical pulse from sub-mm3 devices. A carbon nanotube, a high aspect-ratio molecule with a large phonon thermal conductivity, is used to launch a thermopower wave along its length, which provides a useable power pulse from a sub-micron scale component. The invention is implemented with an annular coating of a reactive, high energy chemical around a carbon nanotube or nanowires, or by depositing a thin layer on a graphene sheet. Upon decomposition of the energetic chemical, its heat of reaction funnels into the thermal conduit where the thermal wave propagates much faster than the bulk reaction. The directed wave pushes an accompanying electron wave that generates sizeable thermopower for a device of its size. Thus, this invention leads to thermal conductivities that often exceed those of conventional materials by orders of magnitude.
- Can scale to the sub-mm3 size needed to power MEMS and "smart dust"
- Thermoelecric wave with peak specific power as much as 761.6 kW/kg (6008.3 μW/mm3)
- Chemical-to-electrical conversion efficiency of thermopower wave devices, in excess of 1%, with sustainable fuels such as sucrose and NaN3, can be achieved, and this produces energy densities on par with Li-ion batteries operating at 80% efficiency (0.2 MJ L-1 versus 0.8 MJ L-1)
- Reaction front velocity was 10 to 100 times faster than bulk trinitramine
- Can be applied to collections of nanotube/nanowires for scale up
- Present an environmentally friendly alternative (metal-free) to lithium ion batteries