Biofuel cells generate electricity through redox reactions using biological materials, mimicking natural processes used to produce energy. They consist of two sections divided by a permeable barrier, with one section oxidizing a carbohydrate and the other reducing it. There are two methods for extracting electrons from the enzyme at the anode: Direct Electron Transfer (DET) and mediated electron transfer (MET). Biofuel cells are non-polluting and use inexpensive and renewable raw materials, but are inefficient and low-powered. Ongoing research is investigating solutions, including the use of bacteria in microbial fuel cells. Biofuel cells have potential as an alternative energy source and in medical applications.
A biofuel cell is a device that uses biological materials to generate electricity directly through redox reactions. This contrasts with the conventional use of biofuels to generate electricity from the heat provided by the combustion of the material. The principle behind biofuel cell technology is to mimic various natural processes used to produce energy within living organisms. In some cases, bacteria may play a role in these fuel cells. As of 2011, biofuel cells show potential as an alternative energy source and in various medical and bioengineering applications.
Living organisms obtain energy from the oxidation of carbohydrates, which are generated by photosynthesis in plants and ingested as food by animals. Enzymes facilitate reactions, in which carbohydrates are converted into carbon dioxide and water by the removal of electrons, which are then stored in adenosine triphosphate (ATP) molecules. In a biofuel cell, electrons produced by the oxidation of organic molecules, usually carbohydrates, as in living organisms, are used to generate an electric current. The idea of using these biological processes to generate electricity has been around since the 1960s, but early attempts to build a practical, working biofuel cell have run into difficulties.
A biofuel cell will typically consist of a container divided into two sections by a permeable barrier. In one section, the oxidation of a carbohydrate, such as glucose, provides electrons. In the other section, a reduction reaction takes place, using these electrons. By connecting the two electrodes, a current can be created from the electrode in the oxidation section, the anode, to the electrode in the reduction section, the cathode.
One of the major practical problems hindering the development of biofuel cells has been finding an efficient way for the electrons released by carbohydrates to enter the anode. The electrons are initially stored in the oxidizing enzyme and, in the natural process, would be chemically transferred into ATP molecules. There are two possible methods for extracting electrons from the enzyme at the anode in a biofuel cell.
In the Direct Electron Transfer (DET) method, the enzyme must be bound to the anode. This can be done chemically or by other methods, such as building the anode from a network of carbon nanotubes onto which the enzyme is adsorbed. These methods result in reduced activity in the enzyme and subsequent loss of efficiency, but this is, at the time of writing, an area of ongoing research and improved techniques that may be developed.
The other method of electron transfer is known as mediated electron transfer (MET). This does not require the enzyme to be in contact with the anode; instead, the electrons are passed to another molecule with a lower redox potential, which then gives the electrons away to the anode. This compound, known as a mediator, must also have a higher redox potential than the anode. This extra step results in a loss of energy and therefore the fuel cell is less efficient in practice than it could be in theory.
Biofuel cells are an active research area and various possible solutions to these problems are being investigated. One possibility is the use of bacteria in microbial fuel cells. Iron-reducing bacteria living anaerobically show particular promise as they naturally reduce iron in its +3 oxidation state to its +2 oxidation state. The iron can then give up an electron at the anode, returning to its +3 state and acting as a natural mediator molecule by transferring electrons from the bacteria to the anode.
The main advantages of biofuel cells are that they are non-polluting, do not require expensive catalysts and use common, inexpensive and easily renewable raw materials. The main disadvantages of biofuel cells are their inefficiency and low power. As of 2011, however, there are hopes that these problems can be overcome, opening up a new range of possibilities. These include not only cheap, clean, renewable energy, but also the prospect of implanted biofuel cells, running on substances produced by the body, used to power medical devices such as pacemakers.
Protect your devices with Threat Protection by NordVPN
