A bio-battery is an energy storing device that is powered by organic compounds, usually being glucose, such as the glucose in human blood. When enzymes in human bodies break down glucose, several electrons and protons are released. Therefore, by using enzymes to break down glucose, bio-batteries directly receive energy from glucose. These batteries then store this energy for later use. This concept is almost identical to how both plants and many animals obtain energy. Although the batteries are still being tested before being commercially sold, several research teams and engineers are working to further advance the development of these batteries.
Like any cell battery, bio-batteries contain an anode, cathode, separator and electrolyte with each component layered on top of another. Anodes and cathodes are the positive and negative areas on a battery that allow electrons to flow in and out. The anode is located at the top of the battery and the cathode is located at the bottom of the battery. Anodes allow electrons to flow in from outside the battery, whereas cathodes allow current to flow out from the battery.
Between the anode and the cathode lies the electrolyte which contains a separator. The main function of the separator is to keep the cathode and anode separated, to avoid electrical short circuits. This system as a whole, allows for a flow of protons (H+) and electrons (e-) which ultimately generates electricity.
Bio batteries are heavily based on the amount of glucose available. This glucose (sugar) can be provided from nearly anything, including soda, waste materials (such as old papers), or the glucose in living organisms. The decomposition of materials to glucose (if they are not already in the proper stage) is the main step in getting the cycle started. Materials can be converted into glucose through the process of enzymatic hydrolysis. Enzymatic hydrolysis is the process in which cellulose (an insoluble substance) is converted to glucose by the addition of enzymes. Once glucose is present, oxygen and other enzymes can act on it to further produce protons and electrons.
Similar to how human bodies convert food to energy using enzymes, bio-batteries use enzymes to convert glucose into energy. When glucose first enters the battery, it enters through the anode. In the anode the sugar is broken down, producing both electrons and protons.
Glucose → Gluconolactone + 2H+ + 2e−
These electrons and protons produced now play an important role in creating energy. They travel through the electrolyte, where the separator redirects electrons to go through the mediator to get to the cathode. On the other hand, protons are redirected to go through the separator to get to the cathode side of the battery.
The cathode then consists of an oxidation reduction reaction. This reaction uses the protons and electrons, with the addition of oxygen gas, to produce water.
O2 +4H+ + 4e− → 2H2O
There is a flow created from the anode to the cathode which is what generates the electricity in the bio-battery. The flow of electrons and protons in the system are what create this generation of electricity.
A significant advantage that bio-batteries have in comparison to other batteries is their ability to allow an instant recharge. In other words, through a constant supply of sugar, or glucose, bio batteries are able to continuously keep themselves charged without an external power supply. Bio batteries are also a source of non-flammable, and non-toxic fuel. This provides a clean alternative renewable power source.
Compared to conventional batteries, such as lithium batteries, bio-batteries are less likely to retain most of their energy. This causes a problem when it comes to long term usage and storage of energy for these batteries. However, researchers are continuing to develop the battery in order to make it a more practical replacement for current batteries and sources of energy.
Although biobatteries are not ready for commercial sale, several research teams and engineers are working to further advance the development of these batteries. Sony has created a bio battery that gives an output power of 50 mW (milliwatts). This output is enough to power approximately one MP3 player. In the coming years, Sony plans to take bio batteries to market, starting with toys and devices that require a small amount of energy. Several other research facilities, such as Stanford and Northeastern, are also in the process of researching and experimenting with bio batteries as an alternative source of energy. Since there is glucose in human blood, some research facilities are also looking towards the medical benefits of bio-batteries and their possible functions in human bodies. Although this has yet to be further tested, research continues on the subject surrounding both the material/device and medical usage of bio-batteries.
There has been a recent interest in using bacteria to generate and store electricity. In 2013, researchers found that E. coli is a good candidate for a living biobattery because its metabolism may sufficiently convert glucose into energy thus produce electricity. Through the combination of differing genes it is possible to optimise efficient electrical production of the organism. Bacterial bio-batteries have great potential in that they can generate electricity rather than just storing it and also that they may contain less toxic or corrosive substances than hydrochloric acid, and sulphuric acid.
Another bacteria of interest is a newly discovered bacterium, Shewanella oneidensis, dubbed "Electric Bacteria" which can reduce toxic manganese ions and turn them into food. In the process it also generates electrical current, and this current is carried along tiny wires made of bacterial appendages called bacterial nano-wires. This network of bacteria and interconected wires creates a vast bacterial biocircuit unlike anything previously known to science. Besides generating electricity it also has the ability to store electric charge, which makes it of special interest to create a bacterial biobattery which can be used for things such as charging a cellphone or computer.
Scientists showed that bacteria could load electrons onto and discharge electrons from microscopic particles of magnetite. Researchers had new experiments with purple bacteria, Rhodopseudomonas palustris, by controlling the amount of light the bacteria was exposed to. This bacteria was able to pull electrons from its surrounding environment. The team changed the light conditions. During the day-time, phototrophic iron-oxidizing bacteria were able to remove electrons from the magnetite discharging it. During the night-time, the bacteria were able to put electrons back onto the magnetite recharging it.  During this process, researchers found out that this magnetite could be used to clean up toxic metals. Magnetite can reduce the toxic form of chromium, chromium VI, to the less toxic chromium (III).
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