Clean Technology : Energy storage

Clean Technology Portfolios


“Green” Triboelectric Power Boards Turn Footsteps into Electricity and More

UW–Madison researchers have developed the first TENG device built entirely from biodegradable and green materials. The two active layers comprise cellulose nanofibrils (CNFs) or wood fibers chemically treated to alter their electron affinity. CNFs and wood fibers are ideal because they have high surface areas, can be functionalized with a variety of chemical groups and can be formed into flexible and optically transparent films.

Atmospheric Growth of Vertically Oriented Graphene

Researchers at the University of Wisconsin – Milwaukee have developed an atmospheric pressure based deposition method to produce vertically oriented graphene nanosheets, two-dimensional ‘graphitic’ platelets standing vertically on silicon, stainless steel and copper substrates. The resulting product shows increased surface area compared to traditional horizontally oriented graphene structures. Early data shows improved performance when compared to existing materials. Early research has shown the method to be amenable to continuous production.

Photovoltaic Capacitor for Direct Solar Energy Conversion and Storage

UW–Madison researchers have developed a two-electrode bio-inspired photovoltaic capacitor that can directly convert and store solar energy in a single structure. The device includes a transparent electrode and a second electrode disposed opposite from the transparent electrode. The structure features an electrolyte slurry containing semiconducting particles along with particles of low ionic diffusivity. This medium exhibits a combination of photovoltaic and ferroelectric properties. The slurry is sandwiched between the transparent electrode and a membrane of low ionic diffusivity adjacent to the negative electrode.

To harvest energy, incident photons excite the electrons within the semiconducting layer and holes in the electrode to generate electron-hole pairs via the photovoltaic effect of solar energy being absorbed. The electrons attract ions to the cathode electrode, creating a concentration gradient across the device. The device is charged using this process until a saturated electric potential difference is reached. The diffusion force of the ions and electric field are counter-balanced and maintain a stable electrical double layer across the two electrodes.

Improved Electrochemical Double-Layer Capacitor Using Organosilicon Electrolytes

UW-Madison researchers now have developed improved supercapacitors that use the novel organosilicon electrolytes in place of conventional liquid electrolytes, along with improved electrodes. These supercapacitors are safer than supercapacitors that use conventional electrolytes and are capable of stable operation at high voltages. They are useful in applications including electric and hybrid-electric vehicles, satellites, wind generators, photovoltaics, copy machines, household appliances, electric tools and electric power generation and distribution systems.

The organosilicon electrolytes can be produced as liquids or solids with high room temperature ionic conductivity. As liquids, they are stable and capable of withstanding voltages higher than any other known organic or aqueous electrolyte. As solids, they have excellent mechanical stability and great packaging versatility. In solid form they have somewhat lower ionic conductivity than liquid electrolytes, but their stability is higher, and they can be used for all-solid-state supercapacitor production. Both forms exhibit low volatility, flammability and toxicity.

The electrodes consist of a porous solid material having high surface area, such as carbon nanofibers or nanotubes, which allows ions to easily flow at high density from the electrode to the collector and vice versa. These electrodes exhibit increased accessibility of ions and better electrical contact with collectors as compared to conventional electrodes, increasing the response time of the supercapacitor to rapid changes in current. This is particularly important in automobiles, which require high instantaneous electrical current for functions such as acceleration.