Power Electronics

Micro Fuel Cells Strive for Commercialization

In recent months, there's been a lot of interest and discussion about micro fuel cells as a next-generation power source for portable electronics. This attention has been driven by announcements from companies such as NEC and Toshiba on the technical front, as well as the widespread recognition that limited battery life may impede the progress of the wireless lifestyle.

This interest is valid. The power industry needs to develop better, longer-lasting solutions for mobile electronics devices. In spite of this need, commercial fuel-cell products based on traditional designs have yet to emerge in the market. While the potential and prospects for micro fuel cells are enormous, new approaches are required to overcome the technical and business challenges.

Power Gap Issues

The worldwide proliferation of portable electronic devices — including notebook and tablet computers, PDAs, camcorders, mobile phones and other power-hungry products — has created a large and growing demand for energy sources that are compact, lightweight and powerful. Existing rechargeable battery technology, which has greatly matured, simply doesn't meet the needs of users. This gap is expected to widen in the next few years, as devices become more powerful and full featured (Fig. 1).

Similar power-gap conditions exist for other product categories as well, in addition to notebook computers. Current generation lithium-ion (Li-ion) rechargeable battery technology capacity improvements are expected to be modest in the coming years (<5% per year) and will struggle to meet ever-increasing power requirements. This creates an enormous opportunity for new power technologies and products.

At the same time, we're becoming more mobile than ever, widening the power gap. Notebook PCs are the fastest-growing computer segment, and shipments are expected to grow to more than 50 million units in 2006.[1] Widespread Wi-Fi availability has essentially cut the Ethernet tether. Users are looking to cut the last cord as well — our tether to ac power. Mobile users often create work-around solutions to conserve their battery power, such as cutting short a work or e-mail session.

A Viable Solution

Many industry observers have identified direct-methanol fuel cells (DMFCs) as one of the most promising technologies that can bridge the power gap for portable electronics. By combining fuel, such as hydrogen or methanol, with oxygen, a fuel cell generates electricity and can produce electricity continuously as long as fuel and oxygen are supplied from an outside source. The promise is compelling given the high energy density of methanol (Fig. 2).

When fuel cells are commercialized in the near future, they will provide significant improvements in energy storage and allow electronic devices to incorporate new features as well as increase their operating time. Equally important, users can “reload” in a few seconds by replacing the fuel cartridge, as compared to the hours required to recharge a conventional rechargeable battery.

Why not just carry multiple Li-ion batteries if you need additional run-time? This is in fact what many mobile professionals do today. An estimated 30% of notebook PC users have purchased at least one additional rechargeable battery. This is inconvenient, adds to the weight that must be carried and is costly. There is a linear relationship between run-time and volume/weight with batteries. If you want twice the run-time, you carry two batteries, and carry twice the volume and twice the weight.

With a fuel cell, you simply carry one fuel-cell system (Fig. 3) and carry multiple cartridges to extend operating run-time. Instead of carrying three batteries, you can carry three cartridges, which are expected to be at least 50% lighter and significantly smaller than the equivalent battery package.

Extra Li-ion batteries for notebook PCs typically retail for $150 or more per unit. Fuel cartridges are expected to be priced at a level similar to disposable alkaline batteries, perhaps $1 to $3 per cartridge. Thus, there will be a significant cost benefit as well.

Technical Challenges

Though progress has been made in the last few years, significant technical challenges remain to commercialization, including low overall efficiency and power density, miniaturization, ventilation of water vapor and cost.

While the theoretical potential of each individual cell in a fuel-cell “stack” should be 1.24 V, conventional proton exchange membrane (PEM)-based DMFCs are only able to achieve about 30% of this potential. These inefficiencies are driven by several factors that need to be addressed as part of the fundamental design to increase the efficiency of the entire system:

  • Methanol crossover

    Unreacted methanol is readily transported through typical PEMs, reducing the overall reaction efficiency.

  • Membrane operating conditions

    Typical PEMs require a specific level of hydration to perform acceptably, leading to complex water-management schemes and degradation of performance if “dry out” occurs.

  • Catalyst/membrane interface

    In order for a catalyst particle to be utilized in the electrochemical reaction, fuel, catalyst and membrane (electrolyte) must be in mutual contact with each other; this is known as the “3-phase interface.” Because the electrolyte is contained in the PEM, this leads to a narrow, 2-D reaction zone requiring a large surface area (and overall physical volume) for the generation of significant power.

  • Electrode flooding

    Any water condensation on the catalyst structure can block catalyst sites, leading to reaction inefficiencies.

As shown in Fig. 4, all fuel cells create water and carbon dioxide as reaction by-products. Many current fuel-cell designs release water vapor, like a little exhaust pipe on your PC. This can be problematic given the close proximity to other electronic components and, at the very least, can be extremely messy and inconvenient for the user. For certain applications, such as military gear, this is a nonstarter.

The narrow “reaction zone” of most PEM-based fuel-cell designs makes it challenging to miniaturize. Because power is a function of the 3-phase interface, designers have to expand the size of the fuel-cell unit to provide a meaningful amount of power.

Big fuel-cell “engines,” inefficient use of expensive catalyst materials and large size all contribute to drive the cost up for PEM-based fuel-cell designs.

Alternatives to PEM-based Models

Alternative approaches to fuel-cell development must be pursued to overcome these fundamental limitations. Neah Power Systems, for example, is developing a micro fuel cell based upon a novel silicon architecture that is expected to address the traditional challenges of efficiency, size and cost. This approach has the potential to significantly increase power density, which is the key to raising the overall efficiency of the fuel-cell system. With higher efficiency, the entire fuel cell can be miniaturized and costs reduced significantly.

With all fuel-cell systems, power density (the amount of power that can be delivered per cm2 area on the electrode footprint) drives overall efficiency and size of the system. Power density is proportional to the surface area of the 3-phase interface (catalyst, fuels and electrolyte). Neah Power uses an approach that abandons the PEM and attempts to expand the reaction zone through the use of a highly conductive porous silicon (PS) catalyst support structure. Porous silicon exhibits surface area to bulk volume ratios as high as 10,000cm2/cm3. This enables a “thickness” dimension that is not possible with PEM-based systems (Fig. 5).

Using porous silicon, millions of tiny microscopic pores can be etched and catalyst can be applied throughout the structure to create an expanded, 3-D reaction zone. Liquid electrolyte flows through these structures to generate electricity. (Fig. 6).

This design is expected to enable a much higher level of catalytic surface area use and electrochemical activity in a much smaller form-factor. Importantly, a fuel cell constructed this way can capture the water vapor, eliminating venting. The reaction by-products are captured in the fuel cartridge.

Neah Power's out-of-the-box approach has tremendous potential to increase power density by an order-of-magnitude over traditional PEM-based designs. This is one alternative, nontraditional approach, and several should be pursued to increase the likelihood of a breakthrough technology.

Business Challenges: Real Yet Addressable

Unlike many other technology products, a micro fuel cell requires cross-organizational coordination to ensure market acceptance and commercial success. Although these hurdles are not insignificant, they can be managed. Some of the challenges include regulatory modifications, safety, standards, fuel-cartridge distribution and OEM device modification.

First and foremost, methanol fuel cartridges must be safely packaged for consumer and industrial use. The good news is that the battery and consumer products industries have proven track records in packaging various chemicals and materials safely and cost effectively.

Safely packaging the fuel cartridges will be the first step in the regulatory approval process. Methanol fuel cartridges are not permitted on commercial aircraft under current regulations. This is not unusual — when new energy sources are introduced, they frequently require new codes and standards.

Encouragingly, the Department of Transportation has recently ruled that low-concentration methanol can be taken on airplanes, partly clearing the way for commercial acceptance. The U.S. Fuel Cell Council and Underwriters Laboratory (UL) industry panel are working to draft proposed regulations for the appropriate federal and international regulatory agencies.

Ultimately, there must be some standardization on the size, shape and other form-factor dimensions for the industry to take off. Retailers will not want to carry dozens or hundreds of stock-keeping units (SKUs), which would consume valuable shelf space and dilute their inventory turnover.

A two-pronged approach will most likely drive this standardization. First, the market will exert considerable influence on which technologies “win” (competing companies' cartridges tend to have differences in the chemical makeup of the fuel cartridge). On a parallel track, fuel-cell and electronic product companies will work together on some common formats to ensure SKU proliferation is limited and managed in the short-run. NEMA, a standards organization, has already begun this process.

Widespread cartridge availability at retail is critical to mainstream adoption. The challenge is a classic chicken-or-egg scenario. Retailers will be reluctant to carry fuel cartridges until there is critical mass of fuel-cell-enabled devices in the market and proven demand. OEM manufacturers may be reluctant to design-in and offer a fuel-cell option because of the limited availability of replacement fuel cartridges.

So how does the industry get there? Most likely through a staged rollout, beginning with more specific vertical markets and eventually growing into broad horizontal markets and mass mainstream distribution. Targeting a narrow market segment, such as the military market, which has a built-in specialized supply chain, can begin the process. For nonmilitary markets, perhaps you start with an industrial or specialized business application, such as outfitting a mobile sales force. Cartridge distribution could begin in specialized channels, such as office-supply companies, and perhaps even through PC companies' Web sites. As more fuel-cell-enabled devices enter the market, distribution will grow to include more mainstream channels.

OEMs, including PC companies and others creating mobile electronics products, need to design their products to enable them to run on a specific fuel-cell system. Many OEMs, particularly in the PC industry, are understandably taking a wait-and-see attitude on the new technology.

The market could potentially be jump-started in two ways: a) a single OEM invests in the new technology and introduces fuel cells as a new feature (hoping to differentiate their product in a crowded market); or b) industry heavyweights work together to include fuel cells in PC reference designs and actively promote their inclusion and commercialization. There are indications option a) is happening (recent NEC and Toshiba announcements to offer fuel-cell-enabled PCs), though option b) may be the most effective way to facilitate category growth.

Potential Road Map Forward

Smart market segmentation will be the most effective way to bootstrap the micro fuel-cell industry and provide a foundation for growth. It's prudent to focus first on the market segments and applications that have the greatest need and stand to gain the most from adopting fuel cells as an alternative power source. Military applications seem like an early-adopter candidate, given the need for continuous operation and the desire to lighten the battery load for soldiers. Industrial uses, like remote monitoring equipment or warehouse scanning operations, are also promising candidates. Expect to see these early applications in late 2004 or 2005. Establishing traction in these early segments will provide the learning and foundation to penetrate broader markets, such as notebook and tablet PCs, later in 2005 or 2006.

Early industry prototype demonstrations also have shown some external fuel-cell units, which would act as a charger and provide energy for recharging mobile phone, PDA or notebook PC batteries. These may be some of the first micro fuel cells available, possibly in 2004. But their appeal may be limited due to bulkiness and limited energy capacity initially.

The real winners will be the companies that succeed in integrating the fuel cell within the device. To achieve this, creative technical innovations are required to scale up performance and scale down size and cost. Concurrently, business hurdles must be addressed through cross-industry collaboration, as well as focused market segmentation and marketing.

References

  1. Gartner, June 2003/IDC, July 2003.

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