Almost any liquid or moist object that has enough ions to be electrically conductive can serve as the electrolyte for a cell. As a novelty or science demonstration, it is possible to insert two electrodes made of different metals into a lemon, potato etc. and generate small amounts of electricity. "Two-potato clocks" are also widely available in hobby and toy stores; they consist of a pair of cells, each consisting of a potato (lemon, et cetera) with two electrodes inserted into it, wired in series to form a battery with enough voltage to power a digital clock. Homemade cells of this kind are of no real practical use, because they produce far less current-and cost far more per unit of energy generated-than commercial cells, due to the need for frequent replacement of the fruit or vegetable. In addition, one can make a voltaic pile from two coins (such as a nickel and a penny) and a piece of paper towel dipped in salt water. Such a pile would make very little voltage itself, but when many of them are stacked together in series, they can replace normal batteries for a short amount of time.
Lead acid cells can easily be manufactured at home, but a tedious charge/discharge cycle is needed to 'form' the plates. This is a process whereby lead sulfate forms on the plates, and during charge is converted to lead dioxide (positive plate) and pure lead (negative plate). Repeating this process results in a microscopically rough surface, with far greater surface area being exposed. This increases the current the cell can deliver.
Sony has developed a biologically friendly battery that generates electricity from sugar in a way that's similar to what's found in living organisms. The battery generates electricity through the use of enzymes that break down carbohydrates, which are essentially sugar.
Battery test cells have generated up to 50 milliwatts, or enough electricity to power music playback on a memory-type Walkman.
Sony has developed a biologically friendly battery that generates electricity from sugar in a way that's similar to what's found in living organisms. Battery test cells have generated up to 50 milliwatts, or enough electricity to power music playback on a memory-type Walkman. The battery generates electricity through the use of enzymes that break down carbohydrates, which is essentially sugar. Sony has increased battery output by efficiently immobilizing enzymes and the electronic conduction materials, while retaining enzyme activity at the anode, an electrode through which positive electric current flows into a polarized device.
Sony also developed a new structure for the cathode, which is an electrode through which positive current flows out of a polarized electrical device. The new structure efficiently supplies oxygen to the cathode while ensuring that appropriate water content is maintained to optimize enzyme activity and the flow of electricity.
The bio battery could evolve into an ecologically friendly device, because sugar is a naturally occurring energy source produced by plants through photosynthesis and can be found in most areas of the earth . In addition, Sony made the battery casing of vegetable-based plastic.
Such ecologically friendly batteries could help reduce the disposal problem with batteries used today. Many of the chemicals used in current batteries are toxic and environmentally destructive. Sony plans to continue its research into so-called "immobilization systems," electrode composition, and other technologies to increase power output and durability. Sony hopes to one day use the new technologies for practical applications.
In other recent ecologically friendly battery research, scientists at the Rensselaer Polytechnic Institute reported creating a paper-sized device that functions as a high-energy battery and a supercapacitor that can use human blood and sweat to recharge. The device is lightweight, thin, flexible, and geared toward future use for medical implants, transportation, and gadgets.
Batteries are practically essential devices but present a whole host of problems. Over time they can have trouble retaining a charge. Some stop working altogether. Others overheat or leak or even explode. They're also rigid and sometimes bulky. Then how about, instead of your standard AA or lithium-ion, a flexible, incredibly thin battery that could be powered by blood or sweat? Seems like an improvement, right?
RPI's battery is paper-thin, can be cut into a variety of shapes and runs on blood or sweat.
A group of scientists at Rensselaer Polytechnic Institute claims they've created just such a battery, one that uses the electrolytes naturally found in bodily fluids.
The battery is not only as thin as paper; it essentially is paper. At least 90 percent of the battery is made from cellulose, which makes up traditional paper and other paper products. Aligned carbon nanotubes make up the other 10 percent, give the paper its conductive abilities and also make it black. The nanotubes are imprinted in the very fabric of the paper, creating what's called a nanocomposite paper.
Using nanotechnology, the battery's small size, flexibility and replenishing electrolyte source -- that is, as long as you eat -- make it ideal for medical applications. When using the battery away from the human body, scientists soaked the paper in an ionic fluid (a salt in liquid form), which provides the electrolytes.
The battery's paper-like construction grants it significant flexibility. The RPI research team believes that the battery could, in the future, be printed in long sheets, which could then be cut into small, custom-shaped batteries. The nanocomposite paper can have holes poked in it or be cut into unusual shapes and continue to function. Several sheets could be lumped together to power medical implants, such as pacemakers, artificial hearts or advanced prosthetics. The battery would easily fit under the skin without causing any discomfort.
Because the ionic liquid used doesn't freeze or evaporate like water, the battery could be employed at a wide range of temperatures: from -100 degrees Fahrenheit up to 300 degrees Fahrenheit. Its temperature resistance and light weight mean that manufacturers of automobiles and airplanes -- both of which require light, durable materials -- may come calling.
The researchers behind the battery claim that their device is unique because it can act "as both a high-energy battery and a high-power supercapacitor". Supercapacitors allow for large, quick bursts of energy, potentially extending the technology's already wide range of applications.
Other Types of Bio-Batteries
It's not just researchers at the Rensselaer Polytechnique Institute who are working on bio-batteries. Many other corporations, universities and research foundations are competing to produce viable batteries that can be powered off of organic compounds, especially human fluids. Researchers consider sugar and human blood glucose potentially valuable sources of power because they occur naturally, are easily accessible and don't produce harmful emissions.
In 2003, Japanese researchers at Panasonic's Nanotechnology Research Laboratory announced that they were working on extracting power from blood glucose. At the time, they were using enzymes -- a frequent component of bio-batteries due to their catalytic properties -- to retrieve electrons from glucose. Two years later, a different Japanese research team, this one from Tohoku University, announced that they had succeeded in creating a small "biological fuel cell." Their cell could be used to power small medical devices, such as an implant to measure blood sugar levels in diabetics. Future versions of such technology could, like RPI's nanocomposite paper, be used to power an artificial heart with the blood that flows through and around it.
In August 2005, scientists in Singapore developed a battery that uses human urine as its fuel. Despite its potentially off-putting power source, the battery has a wide variety of applications. The researchers said that their device was the size of a credit card and could form the basis of inexpensive, disposable disease-testing kits. (Urine is already used to detect drugs and some diseases.) What makes the device particularly useful is that it integrated the battery and testing device into one disposable chip. Imagine a one-time use home-testing kit for diseases like cancer or hepatitis. One of the researchers involved in the project said that the battery could also be adapted to provide a brief charge to other electronic devices. A lost hiker might use one to power a cell phone for a short emergency call.
Some bio-batteries can extract energy from many forms of sugar, whether it's blood glucose or a soft drink.
Electronics giant Sony announced in August 2007 that it had also created a battery that derives energy from sugar. One demonstration showed the small battery extracting energy from a glucose solution. In another demonstration, the battery sipped on a sports drink for power.
If urine-powered or sports drink-sipping batteries were not strange enough, a South Korean research team may have produced one of the strangest of all bio-devices in September 2007. These scientists produced "crab-like microrobots" made out of genuine living tissue. They made the tiny robots by extracting tissue from neonatal rat hearts and growing it on miniscule 'E'-shaped skeletons. These heart cells then "pulsated" for more than 10 days, allowing the robots to move up to 50 meters. With the right refinements, these microrobots could be used to clear away blockages in arteries.
While many exciting announcements have been made in the field of bio-batteries, it may be some time before we see them replacing nickel-cadmium, lithium-ion or the several other types of traditional batteries. Even so, the small, flexible, long-lasting and environmentally friendly battery technologies discussed here show the great possibilities researchers see in bio-batteries, especially for the field of medicine. With that in mind, scientists seem to be exploring every possible option in bio-battery and fuel-cell technology: One research team even devised a fuel cell that ran off of gin and vodka.
Bio-battery runs on shots of vodka
An enzyme-catalysed battery has been created that could one day run cell phones and laptop computers on shots of vodka. The key to the device is a new polymer that protects the fragile enzymes used to break down the ethanol fuel, scientists told the American Chemical Society's annual meeting in New Orleans on Monday.
Enzyme-based batteries have the potential to be cheaper than fuel cells that rely on expensive platinum or ruthenium catalysts."Enzymes are inexpensive and catalytically very active."
Fuel cells work by converting into electricity the energy released when oxygen and hydrogen react to produce water. Pure hydrogen is an explosive gas and difficult to store, so fuel cells often use a chemical source. Ethanol is used in Minteer's cell, and the enzymes strip off the hydrogen. But the enzymes are sensitive to slight changes in pH and temperature and can rapidly degrade and become inactive. Until now no bio-battery had enzymes that lasted for more than a few days.
Specially tailored pores
The typical approach to solving this problem has been to immobilise the enzymes by attaching them to the fuel cell's electrodes, but they still tend to decay too quickly to be useful. Researchers in Missouri coated the electrodes with a polymer that has specially tailored pores. These maintain a neutral pH, while being small enough to trap the enzymes yet big enough to let the alcohol pass through.
"The enzymes have lasted over two months now and they are still functioning," she says. Thanks to the polymer, the new bio-batteries have power densities 32 times greater than those of other groups, the team claim.
Toshiba has just unveiled its first miniature fuel cell, which uses a metal catalyst and runs on methanol. Researchers says: "The main advantage of ethanol over methanol is that it is simply more readily available. We have actually run our cells off vodka and gin." Ethanol is also less toxic and, with the enzymes used in bio-batteries, more productive.
However, unlike the Toshiba prototype, the cell is still too large for portable use. The group is currently working to shrink the technology, perhaps by tweaking the polymer-enzyme matrix in order to increase its surface area further.
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