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MicroMagazine.com

Micro Fuel Cells for Portable Electronics

Realization of True Mobility with Long Operation Time Is on Horizon

by Bijan Moslehi

Bijan Moslehi, PhD, is chief technology officer and senior vice president, semiconductor technology research, for The Noblemen Group, a boutique investment banking, strategic advisory, and business development firm. Moslehi has 20 years' experience working in the semiconductor and semiconductor equipment industries. He can be reached at bmoslehi@noblemengroup.com.

Fuel cells were first developed nearly 170 years ago and have continued to evolve throughout the 20th and 21st centuries, with routine applications in space science and technology, such as the Apollo and Space Shuttle programs. In recent years, various industries have witnessed a renewed interest and extensive efforts in the development of fuel cells for power generation.

Fuel cells have applications in three major segments: residential/commercial stationary electrical power generation, automotive, and, more recently, portable electronic systems. Escalating energy prices drive the stationary power generation and automotive applications, together with the ever-growing concerns about pollution and its detrimental effects on health and global warming. The high demand for flexible mobility with extended duration of the operation of electronic devices, widespread use of wireless technologies, and growing power consumption needs of portable multifunctional consumer electronic systems have all fostered a rising interest in portable electronics applications.

Fuel cells have the potential to revolutionize many applications in these three segments and evolve into a massive market. For instance, they would enable realization of the promise of a true electric vehicle at a high overall efficiency and negligible or near-zero emissions. Technologies and products for the three main markets (stationary, automotive, and portable electronics) are available and, in many cases, pilot demonstration projects are under way or have been successfully conducted.

However, much work remains before their large-scale market adoption. The main tasks include reducing costs; improving durability (lifetime); resolving fuel system and operational safety and regulatory issues; and addressing the infrastructure requirements for the working fuel, especially if it is hydrogen. It appears that, over the next five years, many of these issues could be addressed for portable electronic applications. Therefore, micro fuel cells are seen as the leading wave of commercialization. This will likely be followed by small- and large-scale stationary applications. The phenomenal success of hybrid cars and difficult technical challenges may push out the more-complex automotive applications by at least another decade.

The focus of this issue’s column is the myriad applications of fuel cells in mobile electronics systems. The expected market size of portable fuel cells for 2006 is around $600 million, with the market projected to approach $2 billion after 2010.

Many portable consumer products could incorporate micro fuel cells, including PCs, camcorders, digital cameras, PDAs, music players, mobile phones, and printers. The military has a keen interest in fuel cells as replacements for the rechargeable batteries now used in field applications. Many large electronic companies and start-up firms in the United States, Canada, South Korea, Taiwan, Europe, and particularly Japan have been developing various types of fuel cells in the hope of commercializing them over the next five years. The players among established companies include Toshiba, NEC, Fujitsu, Matsushita, Panasonic, Canon, Sanyo, Casio, NTT, Sony, Hitachi, Motorola, LG Chem, and Samsung.

Similar to batteries, fuel cells are electrochemical energy-conversion systems. However, through catalytic reactions, they directly convert the chemical energy of oxygen and hydrogen or methanol, gasoline, methane, butane, and other hydrogen-containing fuels into electricity. In this process, fuel cells usually produce heat and water as by-products. Therefore, they are significantly cleaner and more environmentally friendly than conventional power sources. They can also be much more energy efficient. Unlike batteries, fuel cells do not need to be recharged or replaced. They only require periodic refilling or replacement of their fuel reservoir.

Typically, fuel cells include three main parts, which are sandwiched together. Their structure contains a porous anode and a porous cathode, separated by an ion-conducting membrane electrolyte or proton exchange membrane (PEM). One side of each anode and cathode electrode is coated with a catalyst (usually platinum). First, at the anode, the catalyst breaks the hydrogen of the fuel into electrons and hydrogen ions (protons). The anode repels the electrons, which move through the external electrical circuitry toward the cathode. The hydrogen ions (protons) diffuse through the intermediate membrane electrolyte toward the cathode. At the cathode, the hydrogen ions and the electrons from the external electrical circuitry catalytically combine with oxygen or another oxidant to produce water and heat. The continuous flow of electrons (and ions) leads to the generation of direct-current electricity. Several fuel cells stacked together can provide a higher voltage.

To avoid the challenges of relying on hydrogen as a fuel and its infrastructure difficulties, the industry has focused quite a bit on direct methanol fuel cell (DMFC) technology for portable electronics applications. In a DMFC, in the presence of a catalyst, methanol and water at the anode side form carbon dioxide, electrons, and protons. At the cathode, in a catalytic reaction, oxygen is mixed with the protons (which have diffused through the membrane electrolyte) and electrons (which have been conducted through the external circuit), and produce water and heat. Continuously, this water is either actively pumped or passively back-diffused through osmosis to the anode side for subsequent reaction with methanol and a repeat of the cycle.

Between 2007 and 2010, micro fuel cells are expected to enter a large-scale commercialization phase. However, in the interim, many issues remain to be solved and are being addressed through significant investments and massive efforts by many groups in industry, academia, and government. For instance, work is under way to standardize fuel cartridges. Also, regulations prohibit carrying fuel cells into a passenger aircraft. The International Electrotechnical Commission (IEC) has completed development of specifications for micro fuel-cell safety. The specs are in the process of being adopted by the international commercial aviation industry and corresponding governmental entities so that micro fuel cells will be allowed onboard passenger airplanes by early 2007. Therefore, January 2007 has emerged as the magic date for the start of the fuel-cell commercialization process.

Other issues include high costs, the challenges of miniaturization, and the need to further improve power density (W/ft3) and efficiency. The primary cost drivers are the expensive platinum-based catalysts and the membrane electrolyte. Researchers are investigating the replacement of these expensive materials with lower-cost components and the simplification of fuel cell structure and design. The use of MEMS technology, nanotechnology, and thin films in fuel cell fabrication are among the miniaturization approaches under investigation.

Current DMFC efficiencies hover around 20–30% and can possibly be increased to 40–50%. The maximum theoretical volumetric energy density of methanol is 4780 W-hr/L. This value for rechargeable batteries (such as NiMH, lithium-ion, and lithium-ion polymer) ranges from 200 to 310 W-hr/L. The U.S. Department of Energy has developed a set of micro fuel cell targets for 2010. This document calls for more than tripling both the specific power (W/kg) and power density (W/L) from 30 in 2006 to 100 in 2010. The energy density needs to double, going from 500 to 1000, and the lifetime must increase fivefold from 1000 to 5000 hours. Also, the cost has to be reduced from $5/W to $3/W.

Toshiba touts the smallest publicly known DMFC, which uses 99.5% methanol. It is a 22 (W) × 56 (L) × 4.5-mm (H) device, with a 2-ml (9.1 mm [H]) fuel tank , weighing about 8.5 g. It features a 100-mW output at 10 hours per millileter of fuel and is targeted for market entry next year.

Portable electronics applications power requirements range widely, from 1 to 3 W for lower-power systems up to 30 to 100 W for applications that require high power consumption. For example, PCs may require somewhere between 25 and 75 W. At times, the peak power is 10 times higher than the average power needs. An elegant design would address this issue by combining the fuel cell with a smaller version of the rechargeable Li-ion batteries, which could be much less than 25% of the normal size. Here, the fuel cell would provide the average power requirements and also continuously charge the Li-ion battery. The peak power requirements would be taken care of by the Li-ion battery. Standard laptop operations of more than 20 hours have been demonstrated with this hybrid approach.

Micro fuel cells promise the possibility of true tetherless mobility with very long operational times, ultimately exceeding days, and no need for recharging. They are portable miniature power plants that would only need periodic refueling. Fuel cells could also be used as charging devices for rechargeable batteries. Micro fuel cells are poised to revolutionize mobile applications, leading to their broader adoption, although their market penetration should evolve over the next three to five years before spreading more pervasively. All of these developments would further promote the promulgation of fuel cell–capable electronic devices, which in turn would benefit the semiconductor markets.


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