Fuel Cell Technology 101

The following types of fuel cells are commercial viable at this time

• Alkaline - AFC
• Phosphoric Acid - PAFC
• Molten Carbonate - MCFC
• Polymer Electrode Membrane - PEMFC
• Solid Oxide - SOFC
• Direct-Methanol - DMFC

* Alkaline - AFC have one of the highest system efficiencies of all fuel cell types.

Operating temperature is directly linked to material and manufacturing costs i.e. the lower the operating temperature, the lower the cost of the materials needed to create a working and reliable electrode and system.

The fact that Alkaline technology can work perfectly well without the use of precious metals is an insurance against aggressive price hiking in the industry.

• Alkaline technology is the longest established technology having been invented in 1839.
• Alkaline technology is the most reliable of all fuel cell technologies having been selected for both the space and submarine applications over other available technologies.
• Having liquid electrolyte means that we can control the temperature of the system in a cheap and efficient manner.
• Liquid electrolyte also allows us to deal with any CO2 contamination much easier.
• Alkaline fuel cells have a very simple, low component count and architecture

Read more about the different types of fuel cell..

(Source AFC Energy)

*Phosphoric acid fuel cells (PAFC) are a type of fuel cell that uses liquid phosphoric acid as an electrolyte.

• The electrodes are made of carbon paper coated with a finely-dispersed platinum catalyst, which make them expensive to manufacture.
• They are not affected by carbon monoxide impurities in the hydrogen stream.
• Phosphoric acid solidifies at a temperature of 40 °C, making startup difficult and restraining PAFCs to continuous operation.
• However, at an operating range of 150 to 200 °C, the expelled water can be converted to steam for air and water heating.
• Phosphoric acid fuel cells have been used for stationary applications with a combined heat and power efficiency of about 80%, and they continue to dominate the on-site stationary fuel cell market.

Major manufacturers of PAFC technology include UTC Power (also known as UTC Fuel Cells), a unit of United Technologies (NYSE: UTX), as well as HydroGen Corporation (NASDAQ: HYDG).

As of 2005, there were close to 300 "PureCell"® 200 kW units by UTC Power in service globally. (Editors Note: as of 8 December 2008, they no longer manufacture the 200 KW Systems, according to theirs sales department-They are moving to larger systems)

*Molten-carbonate fuel cells (MCFCs) are high-temperature fuel cells, that operate at temperatures of 600°C and above.

• Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas and coal-based power plants for electrical utility, industrial, and military applications.
• MCFCs are high-temperature fuel cells that use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic matrix of beta-alumina solid electrolyte (BASE).
• Since they operate at extremely high temperatures of 650°C (roughly 1,200°F) and above, non-precious metals can be used as catalysts at the anode and cathode, reducing costs.

*Proton Exchange Membrane Fuel Cells, also known as polymer electrolyte membrane (PEM) fuel cells (PEMFC), are a type of fuel cell being developed for transport applications as well as for stationary fuel cell applications and portable fuel cell applications.

• Their distinguishing features include lower temperature/pressure ranges (50-100 degrees C) and a special polymer electrolyte membrane.
• A proton exchange membrane fuel cell transforms the chemical energy liberated during the electrochemical reaction of hydrogen and oxygen to electrical energy, as opposed to the direct combustion of hydrogen and oxygen gases to produce thermal energy.

*A solid oxide fuel cell (SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material and, as the name implies, the SOFC has a solid oxide, or ceramic, electrolyte.

Advantages of this class of fuel cells include:

• high efficiencies
• long term stability
• fuel flexibility
• low emissions
• Cost

The largest disadvantage is:

• the high operating temperature
• which results in longer start up times and
• mechanical/chemical compatibility issues.

*Direct-methanol fuel cells or DMFCs are a subcategory of proton-exchange fuel cells where the methanol (CH3OH) fuel is not reformed as in the indirect methanol fuel cell, but fed directly to the fuel cell operating at a temperature of ca. 90 – 120 °C .

• Storage of methanol is much easier than for hydrogen as it does not need high pressures or low temperatures, because methanol is a liquid from -97.0 °C to 64.7 °C (-142.6 °F to 148.5 °F).
• The energy density of methanol - the amount of energy contained in a given volume - is an order of magnitude greater than even highly compressed hydrogen.
• The waste products with these types of fuel cells are carbon dioxide and water.
• Can still store a high energy content in a small space. This means they can produce a small amount of power over a long period of time.
• Ideal for consumer goods such as mobile phones, digital cameras or laptops.
  

Problems

• The efficiency of current direct-methanol fuel cells is low due to the high permeation of methanol through the membrane materials used, which is known as methanol crossover.
• A new kind of membrane (polymer electrolyte thin films, assembled "layer by layer") has been shown to reduce this problem dramatically.
• Other problems include the management of carbon dioxide created at the anode and the sluggish dynamic behaviour.
• Current DMFCs are limited in the power they can produce, but This makes them presently ill-suited for powering vehicles (at least directly),
• Methanol is toxic and flammable. However, the International Civil Aviation Organization's (ICAO) Dangerous Goods Panel (DGP) voted in November 2005 to allow passengers to carry and use micro fuel cells and methanol fuel cartridges when aboard airplanes to power laptop computers and other consumer electronic devices.

Source for the Above Data is Wikipedia

Of the above technologies, PEMFCs and SOFCs are the two most applicable to small scale systems. SOFCs are widely regarded as the superior technology for stationary applications since:
SOFCS are more efficient.

In actual tests using natural gas as a fuel, SOFCs are over 45% efficient in making electricity, while PEM fuel cells are less than 25% efficient.

• SOFCs can operate on fuels available today.
• PEMFCs require hydrogen to operate, which necessitates an external reformer and hydrogen separator. This makes the use of other fuels such as methane and natural gas inefficient.
• SOFCs reform a wide variety of fuels using steam created as a by-product of the reaction. Additionally, the solid oxide cells are tolerant to CO and thus SOFCs do not require expensive catalysts to remove traces of CO.
• SOFCs have a longer life The stack life of SOFCs has been proven to be much longer than PEMFCs.

Demonstrations is the 100kW class have been operational for over 16,000 hours and showed no signs of degradation in power output.

It is anticipated that SOFCs show the best promise for achieving the reliability necessary to meet commercial needs. Stack life of 50,000 to 100,000 hours is entirely feasible and attainable in the near term.

By contrast,

the average life of 90 PEM fuel cells tested by the Army Corps of Engineers was just 3,000 hours Back to Top

What are the advantages of SOFCs?

In general, all fuel cells are characterized as being low noise, low polluting, and highly fuel-efficient compared to conventional power sources.

However, the SOFC has its own specific set of additional advantages over other types of
fuel cells. A number of these advantages are listed below:

Source Acumentrics