Here is an excerpt of a story that appeared on May 11, 2013 at YaleScientific.org: Their title, “Electricity from Thin Air,” is misleading since the source of energy is solar and movement.
Energy exists all around us — in the motion of a heartbeat, the fluorescent light in an office building, and even the flow of blood cells through the body. These individual units of energy are relatively small, but they are numerous.
Dr. Zhong Lin Wang, Professor of Materials Science and Engineering at the Georgia Institute of Technology, has developed a way to harness this ambient energy. After months of work, Wang and his team have developed the very first hybrid cell, which is capable of harnessing both motion and sunlight. By tapping into multiple sources of readily available energy, the tiny cells have the potential to revolutionize the way we power our devices.
[...] Since Wang’s cell is small enough to work on the nanoscale, it can readily be incorporated into biomedical sensors, cellphones, and other small electronics. The cell’s hybrid design is an advantage as well: Solar energy alone produces high voltages but is unsuitable for devices used in the dark, while energy from ambient motion is more consistent but is available on a smaller scale. By combining these sources, Wang’s device can provide a highly reliable supply of electricity.
Wang developed the motion-harnessing component of the hybrid cell in 2006. These devices, called nanogenerators, can collect energy at the micro- and nanoscales of motion by relying on piezoelectricity, the production of a current from compression or strain. To construct a nanogenerator, Wang grew a vertical array of microscopic zinc oxide (ZnO) wires on a flat base. On top of this, he placed an electrode with multiple pointed peaks that give it a “zig-zag” appearance. When the ZnO nanowires are bent out of their ordered formation, they generate small electric charges due to piezoelectricity. They then touch the zig-zag edge of the electrode, which collects all the electricity to produce a current. Due to its sensitivity, a nanogenerator can capture even vibrations of very small magnitudes, which can then be harnessed to power an object such as a pacemaker. In fact, nearly a milliwatt of mechanical energy exists in each cubic centimeter of the ambient environment.
Many devices, however, cannot be sustainably powered by nanogenerators alone; solar cells generate a larger voltage more practical for use in bright environments. To miniaturize solar power capture, Wang made use of an existing technology called a dye-sensitized solar cell (DSSC). These cells are made by combining an anode with an electrolyte solution to form a semiconductor. First, a dye is applied to the anode to make it sensitive to light. When light strikes the dye, it releases electrons that flow through the anode toward the electrolyte solution, generating a current. Wang’s method employs the same principle on a miniaturized scale. Dye-coated ZnO nanowires serve as the anode, surrounded by the cell with a chamber of electrolytic fluid, forming a DSSC small enough to integrate with a nanogenerator.
After refining both technologies in collaboration with Dr. Xudong Wang of the University of Wisconsin-Madison, Wang has discovered a way to incorporate both nanogenerators and DSSCs into a device he terms a “hybrid cell.” The upper layer of the cell harvests light energy, and the nanogenerator below collects ambient motion. A single layer of silicon is sandwiched between the two and functions as an electrode for both devices, combining their energy into a single output. The two sources can be connected in parallel for higher currents and in series for higher voltages.
For balance of article, go to YaleScientific.org
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