Plasmons can fire up a radiolytic energy conversion in aqueous solution according to research from a team at the University of Missouri, Columbia, USA [Jae W. Kwon et al. (2014) Sci Rep 4, #5249; DOI: 10.1038/srep05249]
Until recently, the direct conversion of the energy inherent in radioactive decay involved the use of solid radioisotope materials. Essentially, beta particles can generate "electron-hole" pairs in a semiconductor material through loss of their kinetic energy to the system, although the process is not highly efficient in electricity generation.
Now, Jae Kwon's research group has demonstrated that beta radiation in solution generates a constant stream of free radicals - hydroxyl and hydroperoxyl radicals and free electrons - and which can be used to establish surface plasmons in metallic nanoporous structures on titanium dioxide coated with platinum. The narrow junction between the platinum layer and the nanoporous titania particle provides for a stable metal-semiconductor junction. Then, in turn, this energy can be tapped from the solution as an electric current, opening the way to an entirely novel kind of battery for use in a wide range of systems from spacecraft to electric vehicles and medical implants in which recharging of the more conventional form of battery is a significant limitation. The team points out that ionic solution has a low freezing point, which bodes well for winter driving and use in space.
"Betavoltaics, a battery technology that generates power from radiation, has been studied as an energy source since the 1950s,” explains Kwon. But, aside from something of an image problem associated with radioisotopes, “Controlled nuclear technologies are not inherently dangerous. We already have many commercial uses of nuclear technologies in our lives including fire detectors in bedrooms and emergency exit signs in buildings,” he explains.
The team points out that the inefficient generation of free radicals by sunlight in photovoltaic devices, such as dye-sensitized solar cells and photochemical cells. The limited bandwidth of visible light means very few radicals are ever generated in such devices making them inherently weak. In the team's novel betavoltaic device, the source is the radioactive element strontium-90, which boosts the available electrochemcial energy of the solution; the water acting as a buffer to the surface plasmons and absorbing their kinetic energy to generate large numbers of free radicals. Indeed, the team confirmed the greater efficacy of the device with the plasmonic platinum layer than that made without it.
"This finding reveals new mechanisms for power generation in radiolytic chemical cells. Our unique approach further paves the way for producing chemical cells with higher power density," the team concludes.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".