Electronic Design

When Will Micro-Fuel Cells Replace Batteries?

Battery technology is reaching its performance limit and may not be able to cope with the next generation of power hungry cell phones, laptops, digital cameras, camrecorders, PDAs and military applications. To meet these future needs, portable fuel cells, called micro-fuel cells, have the potential for replacing conventional batteries.

Micro-fuel cell technologies face competition from advanced energy storages devices such as lithium ion batteries and nickel based batteries. However, micro-fuel cells, once commercialized, hold the promise for providing more back up 'green power' at lower cost than its competing battery technologies.

A major difference between batteries and micro-fuel cells is recharging. Batteries may be recharged by supplying them with the appropriate voltage and current. In contrast, you replenish a micro-fuel cell, by refilling its reservoir, or by removing the spent fuel cartridge and replacing it with a new one. Recharging a conventional battery may take hours, but once the commercial versions are available replacing a fuel cartridge should take a few seconds.

Although the development of these fuel cell technologies have suffered from high cost, complex design and fuel problems, many researchers are working on solutions. A recent Frost & Sullivan's Technical Insights study, World Advances in Microfuel Cell Technologies, examines the technologies moving toward commercialization.

The study points out the potential of micro-fuel cells to deliver more energy per volume weight than conventional batteries - a motivating factor to consider micro-fuel cells for portable applications. The main challenge will be to identify the right technology and the configuration of fuel cells for portable applications. Listed below are descriptions of the competing technologies.

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. US-based Millennium Cell, Materials & Energy Research Institute Tokyo Ltd (MERIT), Japan, Medis Technologies, USA and Protonex Corporation, USA are some of the important players in this segment.

Boron hydrides have large amounts of energy. However, releasing energy from the boron hydrides is a problem as direct combustion of these compounds does not give favorable results. Some companies and research institutions have found solutions to overcome this problem.

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 DMFC and passive-based DMFC. Some of the notable players include Toshiba, Hitachi, Fujitsu, NEC Corporation as well as 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. The notable players 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 electrolyte, and the electrons pass through an external circuit to the cathode, thereby producing electricity. The protons and the electrons from the circuit react with oxygen to produce water as a byproduct at the cathode. Tekion Inc is working on commercialization of this technology.

Bio-fuel Cells (BFCs) are useful as an energy source for powering implantable electrically-operated medical devices, including pacemakers and insulin production generators. These implanted devices require unlimited power as replacing them would require surgery. BFCs offer solutions by extracting the fuel (for example glucose from the blood stream) from a living organism, for generating electricity. The fuel cell would continue to function as long as the individual is alive.

BFC 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 oxidation process. There are two types of bio-fuel cells: microbial-based and enzymatic bio-fuel based.

Some of the university spin offs include Akermin Inc and PowerZyme Inc, USA.

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 the above three categories. Applications such as drug delivery systems, diagnostic tools and human augmentation devices probably would employ bio-fuel cells.

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

Regulatory and safety standards are another important area because these factors act as a channel that facilitates consumer use of these technologies. Some of the organizations involved in developing safety codes and standards include CSA (Canadian Standards Association) America, Underwriters Laboratories Inc, USA, International Electrotechnical Commission (IEC), Switzerland, UN Committee of Experts on the Transport of Dangerous Goods, and International Civil Aviation Organization.

There are currently three working groups (WG) WG 8, 9, and 10 on micro-fuel cells in IEC for portable electric devices. A convener of WG 10 includes Toshiba Corporation, Japan, WG8 from Underwriters Laboratories, USA and WG9 from Hitachi, Japan.

Reference

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


What are micro-fuel cells?

Fuel cells are electrochemical devices that convert chemical energy into electrical energy. The pressing need for green power and the demand for sustainable power back-up have motivated many companies to consider fuel cells. When fed with hydrogen derived from a renewable energy source, fuel cells emit zero or very low green-house emissions.

The micro-fuel cell introduces fuel into the cell's anode catalyst layer (Figure 1). A catalyst at the anode causes the fuel to react with water, producing protons, electrons and carbon dioxide. The membrane allows protons to pass through to the cathode's catalyst layer. Electrons take an alternate path and flow through the wires of the electronic device, providing electrical power. At the cathode catalyst layer, the protons and electrons recombine and react with oxygen to form water vapor and carbon dioxide as the only two byproducts.

MTI MicroFuel Cells Inc. (Albany, NY) has developed the Mobion™ system (Figure 2) that employs a proprietary process to control the supply of 100% methanol to the cell with uniform distribution across the cell. It achieves water flow within the cell from the cathode (air) side to the anode (fuel) side without the use of a pump.

This technology reduces parts count and the need for complex components, resulting in a smaller system. It is also scalable to a wide range of product options - from accessories to battery replacements - in both the commercial and military markets. A series of system prototypes have been developed showing size reductions and performance improvements, including operation on an increased concentration of 50% methanol.



TAGS: Toshiba
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