Electronic Design

Portables Eye Micro Fuel Cells To Replace Batteries

Once commercialized, micro fuel cells promise more backup "green power" at lower costs than competing battery technologies. Batteries, closing in on their performance limit, may fall short in the next generation of powerhungry cell phones, laptops, digital cameras, camcorders, PDAs, and military applications.

The task of recharging delineates batteries and micro fuel cells. Users can recharge batteries by supplying them with the appropriate voltage and current. However, users recharge micro fuel cells by refilling their reservoir or by removing the spent fuel cartridge and replacing it with a new one. Recharging a conventional battery can take hours, while replacing a fuel cartridge takes a few seconds.

High cost, complex design, and fuel problems have plagued the development of micro fuel cells, but solutions soon may come from a number of researchers. Frost & Sullivan examined the technologies moving toward commercialization in its recent study, "World Advances in Microfuel Cell Technologies."

The study points out the potential of micro fuel cells to deliver more energy per volume weight than conventional batteries. This should motivate designers to consider micro fuel cells for portable applications. The main challenge will be identifying the right technology and the configuration of fuel cells for portables.

TYPES OF CELLS
Borohydride fuel cells use sodium borohydride with a standard proton-exchange-membrane (PEM) stack. This technology requires micro pumps and strict control of the release of hydrogen to the fuel cell. Boron hydrides have large amounts of energy. But releasing energy from the boron hydrides is a problem, as direct combustion of these compounds doesn't provide favorable results. Some companies and research institutions have solved this problem, though.

Direct methanol fuel cells (DMFCs) employ methanol as a fuel to generate electricity. DMFCs use a polymer membrane as an electrolyte. Methanol is fed directly to the anode. The platinum catalyst strips hydrogen directly from methanol without the use of reformers. There are two types of DMFC technologies: active-based and passive-based. Notable players include Toshiba, Hitachi, Fujitsu, NEC Corp., MTI Microfuel Cells, Neah Power Systems, and Smart Fuel Cell AG.

Reformed methanol to hydrogen fuel cells (RHFCs) reform methanol to liberate hydrogen and feed into the fuel-cell stack to generate electricity. This technology uses a fuel processor and operates at 150°C. Key companies in this segment include Motorola Inc. and Casio Computer Co. Ltd.

Formic-acid fuel cells feed formic acid to the anode and oxygen to the cathode. Protons and electrons are formed at the anode, venting carbon dioxide as a byproduct. The protons pass through an electrolyte, and the electrons pass through an external circuit to the cathode, producing electricity. The protons and the electrons from the circuit react with oxygen to produce water as a byproduct at the cathode. Motorola has invested in Tekion Inc., which is working to commercialize this technology.

Bio-fuel cells (BFCs) are useful for powering implantable electrically operated medical devices, including pacemakers and insulin production generators. These devices require unlimited power, because replacing them would require surgery. BFCs extract the fuel from a living organism (for example, glucose from the blood stream) to generate electricity. The fuel cell would continue to function as long as the individual is alive.

BFCs use biocatalysts to convert chemical energy to electrical energy. The biocatalyzed oxidation of organic substances by oxygen or other oxidants generates electricity. Organic raw materials such as methanol, organic acids, or glucose can be used as substrates for the oxidation process. There are two types of biofuel cells: microbial-based and enzymatic bio-fuel-based. University spinoffs include Akermin Inc. and PowerZyme Inc.

MICRO FUEL-CELL APPLICATIONS
You can divide the micro fuel-cell market into three device categories: consumer portable, military portable, and industrial portable. Micro fuel-cell technologies such as direct methanol, borohydride, reformed hydrogen, and formic acid can find applications in all three markets. Applications such as drug-delivery systems, diagnostic tools, and human augmentation devices probably would employ biofuel cells.

Market factors (e.g., funding) play a vital role in the pace of commercialization. As these technologies evolve, they require R&D funding, whose sources represent an essential part of any emerging technology. These sources include government bodies, military associations, and venture capitalists.

Regulatory and safety standards also are important because they facilitate consumer use. Groups developing safety codes and standards include CSA ( Canadian Standards Association) America, Underwriters Laboratories Inc., the International Electrotechnical Commission (IEC), the U.N. Committee of Experts on the Transport of Dangerous Goods, and the International Civil Aviation Organization.

Three IEC working groups (WGs)—WG 8, 9, and 10—are examining micro fuel cells for portable electric devices. WG 10 includes Toshiba Corp., WG 8 involves Underwriters Laboratories, and Hitachi is in the mix with WG 9.

References: Frost & Sullivan's Technical Insights, World Advances in Microfuel Cell Technologies, 2005 MTI MicroFuel Cells Inc., www. mtimicrofuelcells.com

TAGS: Toshiba
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