Fuel Cells

Fuel cells are a promising source of power that may be used in future laptops and other portable devices. Fuel cells can be used to either replace or augment battery operation.

A fuel cell is a power-generating device that converts chemical energy into electrical energy. Batteries store electrical energy as chemical energy (during the recharging process), and later convert the stored chemical energy back into electrical energy (while discharging). Fuel cells are like batteries in that they convert chemical energy into electrical energy; however, unlike a battery, a fuel cell is "recharged" by refueling. Therefore, instead of taking hours to recharge, a fuel cell can be refueled in seconds, and can consequently supply power almost continuously.

Fuel cells typically combine a fuel (usually hydrogen) with oxygen to produce electricity. The byproduct of this reaction is pure water, heat, and electrical energy. Fuel cells operate by creating an electrolytic charge between a positively charged anode and a negatively charged cathode separated by an electrolyte. When hydrogen is used as the basic fuel, this reaction yields only water and heat as byproducts while converting chemical energy into electricity, as shown in Figure 7.4.

Figure 7.4. Fuel cell operation.

There are actually several different types of fuel cells using different fuels and electrolytes. Many require dangerous fuels or operate at extremely high temperatures, making them unsuitable for personal use. The type of fuel cell being designed for laptop computers and other portable devices is called a direct methanol fuel cell, or DMFC. Compared to other fuel cell technologies, a DMFC works at lower operating temperatures and uses methanol as a fuel, which has a high hydrogen content and is easy to store.

Current fuel cell technology compares favorably to rechargeable battery technology such as lithium-ion in both energy output and power density, and future fuel cells are expected to improve dramatically (see Table 7.3).

Table 7.3. Fuel Cells Versus Li-ion Batteries

Feature	Li-ion Battery Technology	Current Fuel Cell Technology	Fuel Cell Technology in 2010
Specific Power	50 Watt/kg	30 Watt/kg	100 Watt/kg
Power Density	60 Watt/liter	30 Watt/liter	100 Watt/liter
Energy Density	150 Watt*hr/liter	500 Watt*hr/liter	1,000 Watt*hr/liter
Cost	$3/Watt	$5/W	$3/Watt
Lifetime	300500 cycles	1,000 hours	5,000 hours

Fuel cells have the advantage that they produce energy as long as fuel is continuously supplied, whereas batteries have to be periodically recharged. Fuel cells also do not self- discharge when not in use, and are more environmentally friendly than batteries when it comes to both manufacturing and disposal.

While it may be a few years before fuel cells replace rechargeable batteries in laptops, companies like Toshiba and NEC have been working on fuel cell technology for several years now and have introduced several prototypes . NEC demonstrated the first working notebook PC with a prototype external fuel cell in February 2003, and Toshiba followed with its first external fuel cell prototype in March (see Figure 7.5).

Figure 7.5. The laptop fuel cell prototype shown by Toshiba in March 2003.

These early external fuel cells had an average output of 12W, a maximum output of 20W, and could run about five hours on a replaceable methanol fuel cartridge. Just a few months later in June 2003, NEC unveiled the first prototype laptop with an internal fuel cell (see Figure 7.6).

Figure 7.6. The first prototype laptop with an internal fuel cell shown by NEC in June 2003.

Later on October 19, 2004, NEC announced development of a laptop that included a separate fuel cell unit (see Figure 7.7). This allowed the laptop to dock with the fuel cell as well as to run on internal batteries. This fuel cell had a higher energy density and output compared to the previous models.

Figure 7.7. Protoype laptop with a separate fuel cell shown by NEC in October 2004.

As fuel cell technology has evolved, smaller and smaller cells have become possible. On February 28, 2005, Toshiba announced that Guinness World Records had officially certified its highly compact direct methanol fuel cell (DMFC) as the world's smallest DMFC, with dimensions of only 22x56x4.5mm (9.1mm with fuel tank), which is just about as long and wide as an average thumb (see Figure 7.8).

Figure 7.8. The world's smallest fuel cell shown by Toshiba in February 2005.

This tiny fuel cell is designed to power personal electronics devices such as PDAs (Personal Digital Assistants), cell phones, or MP3 players for as long as 20 hours on a single 2cc charge of highly concentrated methanol.

Fuel cells look to be an excellent future source of energy for laptops, since they can be "recharged" in seconds by merely inserting a new fuel cartridge. While there has been a lot of exciting development occurring in fuel cells over the past few years, it will likely be several more years before fuel cells become commercially viable . Besides cost issues, several technological and safety hurdles must be overcome . For example, since these fuel cells are powered by methanol (a flammable liquid), they may not be allowed on aircraft until the FAA regulations regarding such materials are modified or changed. Once the technological, cost, safety and regulatory problems are solved , fuel cells should be an excellent auxiliary or even main power source for future laptops and other portable computing devices.