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Impressive idea – self-sufficient fuel cells

The idea is already 30 years old, originally scorned at and which has now been rediscovered. Sven Kerzenmacher and Dr. Felix von Stetten, scientists at the Institute for Microsystems Technology at the University of Freiburg are working on a fuel cell that is able to supply implants like cardiac pacemakers with a self-sufficient energy source. The energy for the fuel cell is supplied by oxygen and glucose, two compounds that are abundant in body fluids.

Fuel cell that turns glucose and oxygen into energy (Photo: IMTEK)
Fuel cell that turns glucose and oxygen into energy (Photo: IMTEK) 
In the 1970s, Siemens scientists constructed a self-sufficient fuel cell that used glucose - which occurs naturally in the body - and oxygen for the production of energy. At that time, implants like cardiac pacemakers were operated with zinc-carbon batteries that needed to be replaced every three years. A fuel cell, which was able to produce energy independently, was therefore a research project with enormous future potential. Therefore, both Siemens and Monsanto were focussing on the development of what is known as a “biofuel cell”. The Siemens engineers made considerable progress and succeeded in implanting the fuel cell in animals. The cell remained functional for several months. Then lithium-iodine batteries entered the market and cardiac pacemakers and other implants were stable for five to ten years. It no longer seemed to make financial sense to further pursue the “biofuel cell” project.

New arguments for developing a fuel cell

“The situation has once again changed. Increasing numbers of people are supplied with implants, the patients concerned are often very young and life expectancy is increasing,” said Kerzenmacher, explaining the reasons for picking up research on glucose-consuming biofuel cells. Kerzenmacher is a doctoral student in von Stetten’s research group. He has already succeeded in constructing a functional fuel cell that is similar to the one previously made by the Siemens engineers in the 1970s. “Unfortunately, the assembly of the fuel cell was badly documented in the literature,” complains the engineer. “And colleagues who previously worked on such a fuel cell no longer remember the technical details.” Therefore, the scientists had to reinvent the fuel cell.

The glucose fuel cell does not rely on enzymes and microorganisms. Platinum serves as a catalyst. “A microbial fuel cell would of course generate more power but is clearly unsuitable for implantation,” explained the young scientist. “A fuel cell with an enzymatic catalyst has limited long-term stability and cannot be sterilised without causing the destruction of the enzymes themselves.”

Oxygen and glucose must be separated from each other

Fuel cell - Click on picture to enlarge.new window
Fuel cell - Click on picture to enlarge. Fuel cell - Click on picture to enlarge. 
A fuel cell using precious metal as catalyst functions according to the following principle: the cathode at which oxygen is reduced is located in the outer layer and is made of charcoal. This compartment is separated from the anode by a hydrogel membrane. Glucose is oxidised into gluconic acid using water. The released electrons pass through a wire to the site of power consumption and reduce the oxygen at the cathode. Oxygen and the protons produced during glucose oxidation form water.

The layer construction is necessary in order for the reaction to take place and separate oxygen and glucose from each other, both of which occur naturally in the body. The charcoal in the outer layers catches oxygen, and glucose diffuses through both this area and the hydrogel membrane, before reaching its final destination at the platinum catalyst. The difference in potential between the two electrodes guarantees a current flow.

Investigation of the materials’ biocompatibility and cytotoxicity

Kerzenmacher is now working with two graduate students who are assisting him in his investigations on the biocompatibility and cytotoxicity of materials used. The scientists also hope to clarify whether reaction products other than gluconic acid and water are generated and how the fuel cell behaves in a cell culture.
Three fuel cells produce the power required for the operation of a digital watch (Photo: IMTEK)
Three fuel cells produce the power required for the operation of a digital watch (Photo: IMTEK) 
In March 2006, the scientists will take on a project with Prof. Dirk Jansen and Prof. Bernd Spangenberg from the Offenburg University of Applied Sciences. The partners plan to develop an energy management system for the fuel cell. “The currently achieved voltage is too low, it only just reaches 300 to 500 millivolts. We need a voltage transducer that we can use to operate the electronics with 3.6 volts. In addition, we need to think about buffer storage options since the cardiac pacemaker does not require constant energy. It only requires energy in situations when it has to assist the heart,” explained Kerzenmacher. It is also planned to optimise the catalyst and test metals such as iridium and gold. The project involving the development and optimisation of glucose fuel cells is financed with funds from the Healthy Aims project of the EU.

kb – 20 Jan. 06

Further information on this article:

Sven Kerzenmacher

IMTEK

University of Freiburg

Goerges-Köhler-Allee 103
Germany

79110 Freiburg

Phone: +49 (0)761/203-7328

Fax: +49 (0)761/203-7322

E-mail: kerzenma@imtek.de

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02.02.2006

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