Geobacter Bacterial Battery
Geobacter is a genus of proteobacteria that uses what is called anaerobic respiration; this refers to the oxidation of molecules in the absence of oxygen in order to produce energy. Geobacter was found to be the first organism with the ability to oxidize organic compounds and metals including iron, radioactive metals, and petroleum compounds. The organism turns these metals and compounds into harmless carbon dioxide while using iron oxide or other available metals as an electron acceptor. The Geobacter metabolizes the material by creating "pili," columns the width of a 3-5 nanometers that act as conduits to pass electrons between the food material and the Geobacter. This manner of consumption has lead scientists to theorize that the Geobacter could act as a natural-Battery. In a recent BBC article Secretary of Energy Spencer Abraham said, "The genome of this tiny micro-organism may help us to address some of our most difficult cleanup problems and to generate power through biologically-based energy sources."
The Spinach Battery
Taking a cue from nature, scientists researching plant photosynthesis have developed a type of solar energy source that utilizes spinach. The process of photosynthesis is powered in part by a protein complex called Photosystem I (PSI). This protein complex converts sunlight into plant energy for growth, but also produces a tiny, but still measurable amount of electricity. Researchers used this knowledge and sandwiched this protein complex between layers of transparent conductive materials, creating a tiny energy producing cell. Although still in early development, it is certainly an interesting step in the direction of safer more easily renewable energy sources.
Researchers in Dallas, at the University of Texas have found a protein that they say has the ability to behave like a battery, capable of receiving, storing, and dispensing electrical charges. The protein called "Sprouty2" clumps into larger particles that are able to internally store electrical charges. Inside the clump, the bonds and the electrical state are protected by the cells immediate environment and cannot be discharged by normal biochemical methods; meaning the charge is protected until it meets the proper receptor, giving it great potential for further development into an efficient natural battery.
Fruit and Vegetable Batteries
While not feasible for powering anything beyond a light bulb or small radio, any fruit or vegetable that is acidic or contains electrolytes can be used as a sort of rudimentary battery. By inserting two different metallic objects, such as a copper coin and a galvanized nail, you are can create an electrochemical reaction which generates a small potential difference. By connecting many lemons, potatoes, apples etc. in series you can produce enough electricity to power larger objects. Below is an image of a 500lb potato battery that could power a small sound system. Pretty neat.
As one of the few animals on the planet with the ability to make, store, and discharge electricity, the electric eel is nature's oldest battery. Eighty percent of an Electric eel's body is taken up by three abdominal pairs of organs that produce electricity. The Sachs' organ, the Main and the Hunter Organs are three parts of the eel’s abdominal pairs of organs that produce electricity. The electric organs are made up of electrocytes. These electrocytes are stacked in a sequence, similarly to a dry cell battery. Each cell can store and discharge .15 volts. With 4,000 of these cells discharging at the same time, the shock can reach 600+ volts, easily enough to paralyze or kill a human with repeated shocks.
The Baghdad Battery
The earliest known man made batteries, known collectively as the "Baghdad Battery" were found in Khuyut Rabbou'a, a city near to present day Baghdad in Iraq in 1936. These artifacts are thought to be Parthian (between 250 BC and 224 AD) because the village where they were excavated was under Parthian rule at the time, but the actual age of these batteries is undetermined and a subject of contention among scholars.
The artifacts consist of tall terracotta jars containing a copper cylinder made of a rolled-up copper sheet, which houses a single iron rod. At the top, the iron rod is isolated from the copper by asphalt plugs or stoppers, and both rod and cylinder fit snugly inside the opening of the jar which bulges outward towards the middle (reverse hourglass shape). It is thought that that jar was filled with lemon juice, grape juice, or vinegar which acted as an acidic agent to jumpstart the electrochemical reaction with the two metals. In replicas made today (including an experiment on Mythbusters) it has been shown that the "Baghdad Battery" was capable of producing enough electricity to be used for electroplating or electrical stimulation.
The Virus Battery
As current energy consuming devices require portable energy for increasingly long periods of time, new technologies will be needed to move beyond what is provided by today's batteries. One of the most interesting and potentially promising technologies has been developed by MIT Researchers, through a combination of genetic design and directed evolution of Viruses. Materials science professor Yet-Ming Chiang and chemical engineering professor Paula Hammond, have engineered viruses that coat themselves in inorganic materials and arrange themselves in crystalline structures on a polymer sheet. They are then doped in gold to enhance connectivity, resulting in what looks like a sheet of cellophane. These virus assembled battery components can store three times as much energy as traditional materials by packing highly ordered materials into a very small space.
Just as with fruit and vegetable batteries, electrical current can be created by using two conducting plates located at different locations in the electropotential series, submerged (or in this case buried) in some sort of electrolyte. In an "Earth Battery" the electrolyte is the ground itself. One of the earliest examples of an earth battery was built by Alexander Bain in 1841. Bain was the one of the first people to construct an electromagnetic clock and to devise a unique system to run the mechanical device. Bain buried plates of zinc and copper in the ground about one meter apart and used the resulting voltage, of about one volt, to operate a clock.