"Biofuel Cell" Could Replace Rechargeable Batteries

EMBARGOED FOR RELEASE: Monday, March 24, 10:30 a.m., Central Time

From scientists at Saint Louis University comes a gadget fit for a James Bond movie. Imagine 007 sauntering up to the bar, ordering his trademark martini (shaken, not stirred) and, before taking a sip, topping off his cell phone with a few drops of alcohol to recharge the battery.

Researchers have developed a new type of biofuel cell -- a battery that runs off of alcohol and enzymes -- that could replace the rechargeable batteries in everything from laptops to Palm Pilots. Instead of plugging into a fixed power outlet and waiting, these new batteries can be charged instantly with a few milliliters of alcohol. The new findings were presented today at the 225th national meeting of the American Chemical Society, the world's largest scientific society, in New Orleans.

Biofuel cells have been studied for nearly half a century, but the technology has not advanced to the point of practical use. Instead of using expensive metals to catalyze the power-producing reaction, these cells use enzymes -- molecules found in all living things that speed up the body's chemical processes.

"The only items consumed in a biofuel cell are the fuel and oxygen from the air," says Shelley Minteer, Ph.D., an assistant professor of chemistry at Saint Louis University who presented the research. "Given the proper environment, an enzyme should last for long periods of time. It is creating this environment in a fuel cell that researchers have struggled with for years," Minteer says.

Enzymes are extremely sensitive to changes in pH and temperature, and even slight departures from ideal conditions can lead to inactivation of the enzymes, producing a short supply of power.

The typical approach to overcoming this barrier has been to immobilize the enzymes by attaching them to the electrodes, but they still tend to decay too quickly to be useful. Minteer and her colleagues coated the electrodes with a polymer that has specially tailored micelles -- pores in which the enzymes find an ideal "micro-environment" to thrive. "The enzyme has everything it needs to function for a very long period of time instead of denaturing like it normally would," Minteer says. "Other biofuel cell studies have had lifetimes of a few days; our technique allows for enzyme activity over several weeks with no significant power decay. With proper optimization, these biofuel cells could last up to a month without recharging."

Most other biofuel cells have used methanol as a fuel, but the researchers chose ethanol because it supports more enzyme activity. Ethanol is abundant and cheap to make, relying on the well-established corn industry for its production. It is also far less volatile than hydrogen, which has seen a great deal of interest as a potential alternative fuel for automobiles.

Minteer and her colleagues are focusing on small-scale applications, with the preliminary fuel cells being no bigger than five square centimeters -- about the size of a postage stamp. "We've tested probably 30 to 50 of the ethanol cells," Minteer says. They have successfully run their cells with vodka, gin, white wine and flat beer ("The fuel cell didn't like the carbonation," Minteer says).

While consumer applications are still a few years off, "these results show the applicability of biofuel cell technology and help move the research from a purely academic endeavor to a more practical technology," Minteer says.

The paper on this research, ANYL 285, will be presented at 3:15 p.m., Thursday, March 27, at the Morial Convention Center, Room 384, during the symposium, "Microelectrochemical Systems and Arrays." It also will be featured in a press conference on Monday, March 24, at 9:00 a.m., at the Morial Convention Center, Room 280.

Shelley Minteer, Ph.D., is an assistant professor of chemistry in the Department of Chemistry at Saint Louis University.

-- Jason Gorss

#13466 Released 03/27/2003

Paper: ANYL 185Presenter: Shelley Minteer, Ph.D., assistant professor of chemistry, Saint Louis UniversityArrive: Saturday, March 22, NoonDepart: Friday, March 28, mid-morningStaying at: Wyndham Whitney

Names of others outside group who could discuss this area of research:

Harold Bright at the Office of Naval Research. He is the program manager for biofuel cells.

EMBARGOED FOR RELEASE: Monday, March 24, 10:30 a.m., Central TimeANYL 285 Development and characterization of microbioanodes for alcohol/oxygen biofuel cellsShelley D. Minteer, Nick L. Akers, Trisha J. Thomas, and Christine M. Moore, Department of Chemistry, Saint Louis University, 3501 Laclede Ave., St. Louis, MO 63103

Quaternary ammonium bromide salt-treated Nafion membranes provide an ideal environment for enzyme immobilization. Because these quaternary ammonium bromide salt-treated Nafion membranes retain the electrical properties of Nafion and increase the mass transport of ions and neutral species through the membrane, they are also ideal for modifying electrodes. Therefore, high current density microscale bioanodes are formed from poly(methylene green) (an electrocatalyst for NADH) modified electrodes that have been coated with a thin layer of tetrabutylammonium bromide salt-treated Nafion with dehydrogenase enzymes immobilized within the layer. Ethanol/O2 biofuel cells employing these bioanodes have yielded power densities of 1.16 mW/cm2 to 2.04 mW/cm2 depending on the ratio of alcohol dehydrogenase to aldehyde dehydrogenase in the polymer layer. Methanol/O2 biofuel cells employing these bioanodes have yielded power densities of 1.55 mW/cm2 and open circuit potentials of 0.71V.

EMBARGOED FOR RELEASE: Monday, March 24, 10:30 a.m., Central TimeANYL 285

Development and characterization of microbioanodes for alcohol/oxygen biofuel cells

* Briefly explain in lay language what you have done, why it is significant and its implications, particularly to the general public.

Batteries are typically divided into three categories: primary, secondary, and fuel cells. Primary batteries are disposable batteries and secondary batteries are rechargeable batteries. A fuel cell is a device that continuously changes the chemical energy of a fuel (such as hydrogen) and an oxidant directly into electrical energy (it is recharged by adding more fuel). The public might be most familiar with this technology in reference to electric vehicles powered by fuel cells. Most commonly, the fuel discussed in relation to automotive fuel cells is hydrogen and the oxidant is oxygen from air. Electricity is produced when electrons are stripped from the hydrogen fuel traveling through a proton exchange membrane in the cell. The resulting current is used to power the engine that runs the car giving off water vapor as emissions.

There are, however, problems associated with using hydrogen as the power source for fuel cells. Hydrogen is an extremely volatile substance which leads to major storage concerns. Additionally, there is a substantial cost and energy investment required to produce hydrogen in the quantities needed to facilitate a mass transport system. Fuel cells also rely on precious metals such as platinum to catalyze the complete electron transfer reaction. The use of precious metals further increases the expense associated with such technology.

* How new is this work and how does it differ from that of others who may be doing similar research?

The research at Saint Louis University is focused on producing a fuel cell that uses alcohol as the fuel source and biomolecules as the catalyst. There are several advantages to this approach. Choosing alcohol, specifically ethanol, as the fuel immediately reduces the cost of the technology. Liquid ethanol is produced from corn and there is already a well-established industry for its production. Furthermore, ethanol contains 34% more energy than is used to grow and harvest the corn and distill it into ethanol. This means that the amount of energy required to produce ethanol is less than the possible energy yield as a fuel. Ethanol is a flammable liquid, but it remains significantly less volatile than gasoline. This means that storage concerns are much less than those associated with hydrogen, and current gasoline storage protocols would transfer when using ethanol.

We at Saint Louis University are using enzymes in fuel cells in replace of precious metal catalyst. Enzymes are common molecules found in all living cells used to speed up the reactions that occur in a cell. Enzymes are not consumed in chemical reactions, and given the proper environment should theoretically last forever. The enzymes catalyze the oxidation of the alcohol at the electrode of the fuel cell.

Fuel cells that utilize biologic molecules in the electricity generating reactions are referred to as biofuel cells. Biofuel cells have been studied for nearly half a century, but have not advanced to practical use due to insufficient power outputs. The main cause for low energy production comes from the difficulty associated with using enzymes. Again, given the proper environment an enzyme should last indefinitely. It is creating this environment in a fuel cell that researchers have struggled with for years. Enzymes are very sensitive to changes in pH and temperature. Even slight departures from the optimal environment will lead to inactivation of the enzyme.

Additionally, most biofuel cell studies have been conducted with methanol rather than ethanol as the fuel source. We have chosen to use ethanol over methanol due to it being more abundant, cheaper to produce, and higher activity with the enzyme being used. Early biofuel cells contained enzymes in solution with the fuel and not in direct contact with the electrode. This resulted in low power densities and short lifetimes for the enzyme. Researchers progressed to immobilizing the enzyme at the electrode surface by various techniques which lead to a modest increase in power, but there was still a short lifetime associated with it. For practical applications of biofuel cell technology, these hurdles must still be overcome.

Our research has begun solving these problems by employing a unique enzyme immobilization technique utilizing a modified polymer membrane. We employ an ion exchange polymer that is frequently used for fuel cells, but we modify the polymer to ensure an ideal environment for immobilizing the enzyme. By modifying the polymer, its acidity is reduced to near neutral pHs and the pore structure of the membrane is increased to a size that will form pockets that are ideally sized to trap and hold enzymes while allowing small fuel molecules to transport through the membrane. These pockets or pores provide a stable environment for the enzyme, hindering inactivation. This polymer is then applied to the electrode in a fuel cell. Whereas other biofuel cell studies with immobilized enzymes have had lifetimes of a few days, our technique allows for enzyme activity over several weeks with no significant power decay.

Our biofuel cells utilizing this immobilization method have produced power densities of up to 32 times the power densities of the state-of-the-art biofuel cells of other groups. The development of high surface area electrodes will further increase the power output of biofuel cells. These results prove the applicability of biofuel cell technology and help move the research from a purely academic endeavor to a more practical technology.

The immediate future of biofuel cells is as a competitive, replacement for rechargeable batteries. The only consumed item in a biofuel cell is the fuel itself, and with proper optimization these biofuel cells could last up to a month without recharging. Recharging electronic devices will be incredibly simple too. Imagine instantly recharging your cell phone by simply adding a few milliliters of alcohol. Another advantage of using ethanol as a fuel (the vast majority of biofuel cell research has used methanol) is its widespread availability in everyday life. If your cell phone dies in the middle of a business power lunch, then order a shot of vodka and recharge it. Similarly, this technology can be applied to laptop batteries, PDA's, and any rechargeable power source. Consumer applications can be envisioned in the 5-10 year range as a conservative estimate, but quite probably sooner than that. Our group has already started to design functional prototypes for such electronic devices.

As can be seen, biofuel cells offer an attractive alternative to hydrogen/oxygen fuel cells. They are cheaper to operate due to lack of precious metals and existing mass production facilities for the alcohol fuel which is also less dangerous to transport. Our group has overcome the traditional problem of low power output from biofuel cells by immobilizing enzymes in modified polymers allowing for practical applications to be developed. Finally, biofuel cells using enzymes and ethanol represent possibilities for a more consumer friendly product that will have long life and ease of use.

Dr. Shelley Minteer andNick AkersSaint Louis UniversityDepartment of ChemistryMonsanto Hall3501 Laclede Ave.St. Louis, MO 63103-2010