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Asugar battery is an emerging type ofbiobattery that is fueled bymaltodextrin and facilitated by theenzymatic catalysts.
The sugar battery generateselectric current by theoxidation of theglucose unit ofmaltodextrin. The oxidation of theorganic compound producescarbon dioxide and electrical current. 13 types ofenzymes are planted in the battery so that the reaction goes to completion and converts mostchemical energy intoelectrical energy. The experimental results have shown that the sugar battery of the same mass can store at least two times, up to ten timeselectrical energy than the traditionallithium-ion battery can. The sugar battery is expected to be the next general type of mobile electric power source and the possible power source forelectric cars. But the sugar battery'soutput voltage(0.5V) is lower than that of the lithium-ion battery (3.6 V), which causes itselectric power (the rate of electrical energy transfer) to be low.
Sony, a Japanese corporation, first published the theory of sugar battery in 2007. A research team led by Dr. Y.H. Percival Zhang atVirginia Tech provided the latest version of it in 2014.
Sony, a Japanese corporation, first published the theory of sugar battery in 2007. This type of sugar battery is air-breathing and utilizes the oxygen as theoxidizing agent. The battery achieved expected highenergy density and reasonable output voltage. Then the company shifted its researching direction in 2012 to thepaper battery, which uses paper as fuel. After 2013, Sony didn't release more information about their research project on thebiobattery.[1][2]
A research team led by Dr. Y.H. Percival Zhang atVirginia Tech started the project of the sugar battery in 2009. The team first focused on the connection with thehydrogen economy. In 2014, they published their research on the sugar battery that utilizes enzymes in oxidization. This type of sugar battery reached a highenergy density. The sugar battery was expected to be realized in an application in 3 years.[3][4]
In 2017, Dr. Y.H. Percival Zhang was arrested by theFBI (has been released in 2019). The federal government accused Dr. Zhang of over twenty counts[example needed]. Dr. Zhang then resigned from his position at Virginia Tech. Since then, Virginia Tech stopped publishing the result of the sugar battery study.
In 2019, Dr. Zhang was acquitted of 19 counts but found guilty of conspiring to commit federal grant fraud.[5]
Since 2014, Several Chinese universities, includingZhejiang University andTianjin University, started working on researches on the sugar battery.
Compared to the currently widely usedlithium-ion battery, the sugar battery has potential benefits in many aspects.
Compared to the traditional lithium-ion battery, sugar battery does not require toxic metals in manufacturing and releases only carbon dioxide gases. The production of the standard lithium-ion battery would require several metals, including but not limited tolead (Pb),Cadmium (Cd), andChromium (Cr). The leakage of these metals accumulates inside the vegetables and animals that humans depend on and finally reach humans.[6] Besides, overheating may cause the lithium-ion battery to release up to 100 types of harmful gases to the human body. In some instances, the rechargeable lithium-ion battery explodes to cause a physical casualty.
The primary fuel of the sugar battery,maltodextrin, can be enzymatically derived from any starch, such as corn and wheat.[7] Therefore, maltodextrin is renewable. In contrast, the primary constructing block of the lithium battery,lithium carbide, is an unrenewable compound that occurs naturally in the earth. To obtain it, manufacturers need to mine, extract, and purify.[8]
The products of oxidation reaction inside the sugar battery are mainly water, carbon dioxide, and recyclableadenosine triphosphate (ATP). Whereas the disposal of lithium batteries produces heavy metals that contaminate the soil. According to the field experiments, several vegetable species extract the heavy metals from soil and store concentrated metals inside. The carbon dioxide produced by the sugar battery does not contribute to the crisis ofgreenhouse gas, because the sugar battery uses bio-fuel that iscarbon-neutral. Since the production of the fuels involves thephotosynthesis of plants, which removes carbon dioxide from the atmosphere, the new greenhouse gas released is counted as a net-zerocarbon footprint.[9][10]
The completeoxidation reaction of unit glucose in 15%maltodextrin solution enables the sugar battery to have anenergy density of 596 Ah kg−1, which is over twice as high as that of the widely used lithium-ion battery(~270 Ah kg−1). In application, this means that the lifetime of the battery increases. Alternatively, the mass and volume of the battery reduce.[4]
As a newly invented idea, the sugar battery is not well developed yet. It has several drawbacks in the current state.
Though the output voltage of sugar battery (0.5 V) exceeds that of former enzymatic fuel batteries by the use of various enzymatic catalysts, it is still much lower than that of the commonly used lithium-ion battery (3.6 V).[3] That results in lowelectric power. In application, it means that the sugar battery takes more time to charge the appliance than the lithium-ion battery does.
The production of the fuel of the sugar battery and the reaction inside the sugar battery require water to complete. If the battery is going to be used widely around the world, it will undoubtedly lead to a requirement for a considerable amount of water. Under current conditions, the consequence will be further intensifying thewater scarcity.[11] Which is a weak argument against, because any type of farming or many other industrial process consume water in larger amounts.
The design of the sugar battery is based on the theory of theprimary cell. The main components of a sugar battery are ananode, acathode, amembrane, and a synthetic pathway. Theoxidation reaction happens in the anode side where the fuel,maltodextrin, is oxidized. Electrons are released from the fuel and go through the wire connected to the cathode, forming adirect electrical current. Electrical appliances are installed between anode and cathode so that the electrical current powers the appliance.[4]
Theredox reaction that produces the electrical current happens in the synthetic pathway, where 13enzymes, such asglucose 6-phosphate andphosphoglucomutase, act ascatalysts (the substance that is bothreactant andproduct). The fuel,maltodextrin, is divided frompolymer tomonomer and then oxidized into carbon dioxide andhydrogen ions during four reactions. The reactions involve the enzymatic catalysts, but since they act both as reactant and product, the amount of the enzymes does not decrease in the end so that they can keep facilitating the reaction. At the end of the reaction, Oneglucose unit and a certain amount of water can produce 24 electrons. The electrons then flow to thecathode through the wire, causing anelectrical current flowing from cathode to anode.[4][9]
The synthetic pathway is composed of 13enzymes to ensure theredox reaction goes into completion (that is, 24 electrons produced per glucose unit). By adding all thesecatalytic enzymes into the pathway, the overall chemical equation goes as:
Theoretically, onemaltodextrin's glucose unit (C6H10O5) generates 24 electrons, which makes the sugar battery's maximumcurrent density 35% higher than the maximum current density of a similar system based on 2dehydrogenases.[4] Practically, the researchers at Virginia Tech measures thefaraday efficiency (the percent of measured output against theoretical output) of the sugar battery's redox reaction. The outcome was 97.6±3.0% under oxygen-free conditions for the anode compartment, suggesting high efficiency in the electron transmission.[4]
Different from the natural pathway, which utilizes NADP (nicotinamide adenine dinucleotide phosphate)-dependent enzyme, the synthetic pathway makes use of the other cytosolic enzymes to mediate the reaction. As a result, the sugar battery does not depend on the use of complex organic chemicals (for example,adenosine triphosphate), which are expensive and unstable.[4][3]
The researchers developed the design of the sugar battery from the prototypedenzymatic fuel cells, which use enzymes ascatalysts in theredox reaction. Based on the design of regular enzymatic fuel cells, the sugar battery employs several methods to enlarge the effect produced by theenzymes so that the overall efficiency of the battery is improved.
The enzymes in sugar battery are no more fixed to theelectrode, nor entrapped in a limited space near the electrode. The enzymes in the sugar battery can move freely in a larger space and retain the enzymatic activity. To sustain high-speedmass transfer, the researchers immobilizedvitamin K3 to the electrode. The corresponding experiments suggest that the non-immobilization method helps the sugar battery to reach a higher and more stableenergy density level than the regular enzyme fuel cells withimmobilized enzymes. Hence, the energy density of the sugar battery increased so that the battery life extended.[4]
Thermoenzymes, enzymes with highthermostability, are used as the non-immobilized enzymes to ensure stability. In the sugar battery, the thermo enzymes are produced byEscherichia coli. Then the enzymes are purified through heat precipitation method and put into use.[9]
Theoxidation reaction inside the sugar battery happens in a synthetic catabolic pathway, which contains 13enzymes.[4] This pathway is constructed as air-breathing rather than closed so that the researchers ensure the air pressure inside the battery stable and the oxidation reaction goes into completion. The enzymes act ascatalysts so that the total amount of them remains the same. Therefore, the overall reaction consumes only the fuel and water while the enzymes recycle in the system. According to the lab experiments, the sugar battery reaches an electron-transmission efficiency of almost 24 electrons permonomerglucose, which is the basic unit of organic fuels. In comparison, the oxidation reaction in the prototypedenzymatic fuel cells could only generate 2 electrons per glucose unit, resulting in lowenergy density.[4]
