AFC vs PEM

Shelli Zargary

AFC vs. PEM Fuel Cell Technologies

If you’ve been following the news or you’ve read GenCell’s white paper “The Big Deal With Fuel Cells” you know that that fuel cells are a hot topic. With transport responsible for 12% of carbon dioxide emissions in Europe and more than 20% in the USA, there is strong interest by Toyota, Honda, Hyundai and others in proton exchange membrane (PEM) for use in hydrogen fuel cell vehicles (FCVs).  While PEM may have certain benefits for transportation is not necessarily the ideal fuel cell technology to meet the needs of backup energy solutions.

PEM: The Leading Fuel Cell for Transportation

PEM fuel cells have been the most widely publicized and funded low-temperature fuel cells to date. They were invented in the early 1960s by Willard Thomas Grubb and Leonard Niedrach of General Electric for use in NASA’s Gemini space missions. PEM fuel cells consist of two electrodes (an anode and a cathode) with a thin platinum layer of catalyst, bonded to either side of a proton exchange membrane. PEM fuel cells operate at 80-100 degrees Celsius and are relatively small and light-weight. This makes them the leading fuel cell technology used in material handling applications such as forklifts and for transportation applications such as buses, trucks and cars.

Nevertheless, PEM fuel cells are not without their drawbacks. The acidic nature of PEM fuel cells requires the use of platinum cathodes and the water and heat of the fuel cells must be carefully managed to ensure proper performance of the membranes. If there is too little water or too much heat, the membrane will start to dry out and conductivity will decline. If there is too much water, condensation can form and flood the electrodes.

Alkaline Fuel Cells Overcome the Limitations of PEM

Alkaline fuel cells (AFCs) were first developed in 1959 by Francis Thomas Bacon. In the 1960s, AFC fuel cells replaced the PEM fuel cells at NASA for use in the Apollo, Skylab and Space Shuttle programs. In addition to producing electricity, they also produced the drinking water consumed by the astronauts.

Using an alkaline electrolyte such as potassium hydroxide (KOH) in water, AFC are among the most efficient type of fuel cells, reaching up to 60% efficiency (up to 87% combined heat and power).  The circulating liquid electrolyte offers many benefits over more common low temperature membrane-based fuel cells like PEM.

The electrolyte (KOH) used in alkaline fuel cells has a freezing temperature of below -40 degrees Celsius allowing the start up in sub-freezing conditions. Membrane fuel cells typically require water for membrane hydration and therefore must be operated in conditions above freezing (4°C) or be placed in a heated and insulated enclosure.

Liquid electrolyte also avoids many of the challenges with membrane humidification including limited operation in certain high and low humidity conditions and can operate in a greater range of temperature and humidity conditions while maintaining a short start up time demanded by many target applications.

GenCell’s Technical Breakthroughs

GenCell has made a number of patented technical improvements in AFC technology that have substantially reduced the capital and operating expenses of its AFC solution. One improvement is the system’s simple balance-of-plant that minimizes power losses due to the overhead of the system. The system’s unique design makes the electrical efficiency of the entire GenCell system more efficient than other fuel cell powered solutions in its class and as well as more efficient than conventional diesel-fueled generators.

Another improvement is the elimination of platinum as a catalyst and the use of unique CO2 scrubbers. These patented technologies enable the GenCell solution to work with hydrogen that has higher carbon monoxide (CO) concentrations. CO is a common contaminant in hydrogen fuel streams and has a high affinity to platinum.  Fuel cells that rely on a platinum catalyst are susceptible to “CO poisoning” when exposed to fuel streams that contain CO. Due to the costs of removing CO and verifying that the hydrogen is pure enough, there is a considerable cost difference between industrial-grade (99.95%) and medical-grade hydrogen (99.99%).

As GenCell continues to penetrate the backup energy market, the CAPEX and OPEX cost breakthroughs associated with GenCell’s patented technologies will enable GenCell to deliver fuel cell solutions that are affordable for the mainstream.

Written by Shelli Zargary

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