Everyone who has watched his or her kids bounce around the house after feasting on Halloween treats knows that sugar is a powerful source of energy. "If only that energy could be harnessed and put to good use", you thought to yourself after trying to get your kids settled into bed on Halloween night. While it's not quite the same phenomena, a research team at Virginia Tech has developed a battery that runs on sugar, and also with extremely high energy density-perhaps even more than your kids. Their work was published in the recent issue of Nature Communications.
Sugars have always been excellent sources of energy, but converting that energy in a useful fashion outside of living systems is difficult. Biosystems use enzymes to break down the sugars into energy, and researchers have been trying to do the same thing for years with artificial enzyme pathways to create fuel cells. These fuel cells contain an enzyme mix to sequentially strip and release the electrons from the sugar.
Compared to traditional batteries, sugar batteries require relatively inexpensive enzymatic catalyst material (as opposed to precious metals in conventional batteries), and are kinder to the environment with their output (electricity and water) and their disposal (biodegradable, non-hazardous components). Disposal should be infrequent, since the batteries can be refilled with fresh sugar solution and re-used. Sugar-based fuel cells are not explosive or flammable like methanol or hydrogen fuel cells. With all these advantages, why haven't we seen these in use already?
The problem is that unlike your kids, these systems are notoriously inefficient at extracting energy from sugar, and finding the proper enzyme sequences and orientation is difficult. However, the Virginia Tech team seems to have succeeded. Their battery requires a mix of 13 enzymes and air to operate. Their conversion method produces a 0.8 milliwatt/cm power output, and an energy storage density value of 596 amp-hours/kilogram. This energy storage value gets everyone's attention, as it's approximately 10 times the energy density of a typical lithium-ion battery that is used in mobile devices.
The sugar used for this battery was maltodextrin, a relatively common and inexpensive material made from the partial hydrolysis of starch. The economics appear to be favorable for eventual large-scale production. However, there is still a lot of testing to do with respect to optimization, battery life, integration into devices, and reliability and repeatability of the enzyme process under various conditions. For example, how does the system handle temperature changes that any battery-powered device might experience?
Nevertheless, the research team believes that this style of sugar-powered fuel cell could be commercialized for use in electronic devices in as little as three years. Also, since these fuel cells should be compatible with biological systems, it makes sense that they could be used to power implant devices such as pacemakers. They could potentially run off of your body's own supply of glucose. Imagine that-a variant of the bioprocesses that make your kids bounce off the walls may finally be harnessed and put to good use, as every parent has dreamed of doing.