TPACTechnology Policy and Assessment Center
 
 

Technology Decomposition

Table of Contents

This section depicts the structure and relatedness of fuel cell R&D, with particular emphasis on the question: "What does fuel cell technology research look like?"

Technology Mapping Analysis Principle components analysis was conducted on 200 leading keyword terms.

Fig. 14: Fuel Cell Technology Map

Technology Clusters:
Five types of fuel cells, distinguished by type of electrolyte material used, dominate current research and development activities.

Phosphoric Acid Fuel Cells (PAFC):

  • Status: Pre-commercial/commercial; The most mature commercially available fuel cell technology (under development for over 20 years with total worldwide investment in excess of $500 million). Largest unit installed: 11,000kW (200kW units in commerical production).
  • Phosphoric acid is used as the electrolyte and natural gas is used as the fuel.
  • They operate at about 400 degrees F, and their electrical efficiency can exceed 40% LHV.
  • Reforming of the natural gas feedstock to a hydrogen-rich gas occurs outside the fuel cell stacks.
  • Due to PAFC complexity, projected capital costs are high ($1,200-$1,500 per kW) and efficiencies are low.
  • Currently being used in many different types of buildings, ranging from hospitals, hotels, power plants, and an airplane terminal. Possible future applications include buses and locomotives but probably not smaller vehicles.



Molten Carbonate Fuel Cells (MCFC):

  • Status: Pre-commercial; Now being tested in full-scale demonstration plants (e.g., Santa Clara Demonstration Project). Largest unit installed: 2,000kW
  • They offer higher fuel-to-electricity efficiencies (approaching 60% LHV), and operate at higher temperatures (1,200 degrees F).
  • Utilize a lithium/potassium carbonate electrolyte and nickel electrodes.
  • Reforming can occur inside the fuel cell stacks.
  • Main problem with operation and manufacture of MCFC's relates to the design of electrodes; must withstand working for long periods in the electrolyte which is hot and corrosive.
  • Projected capital cost: $1,000-1,200 per kW
  • Seen as an ideal source of large scale power generation.



Solid Oxide Fuel Cells (SOFC):

  • Status: Developmental; Currently being tested in a 100-kilowatt plant.
  • They offer the stability and reliability of all-solid state ceramic construction.
  • The electrochemical conversion process occurs at very high temperature (up to 1800 degress F) and so supports internal reforming; allows more flexibility in the choice of fuels.
  • Moderately high efficiencies (approach 60% LHV) with a high-grade waste heat product; potentially the most efficient type with very useful waste heat.
  • Three fundamental designs - tubular, planar and monolithic types
  • The materials used to make the cells are very difficult to produce, and their manufacture at reasonable cost is a problem yet to be resolved.
  • Projected capital cost: $800-$900 per kW
  • Suited for applications requiring a large amount of power including industrial and large-scale central electricity generating stations.



Proton Exchange Membrane Fuel Cells (PEMFC) or Solid Polymer Fuel Cells

  • Status: Pre-commercial; PEMFC buses operational by Ballard Power Systems in Vancouver.
  • Use a polymer solid-state electrolyte and platinum electrodes. Membrane is made of polyperfluorosulfonic acid (similar to teflon). Pure hydrogen is usually used as the fuel but natural gas and methanol could also be used.
  • Low temperature cell operating at about 200 degrees F.
  • Principal issues related to costs are focused on the electrolyte, known as the 'proton exchange membrane' (PEM) and the bipolar plates.
  • Showing great potential for light-duty vehicles (cars, buses), buildings (heater/chiller units), and very small scale localized power generation (replacement for rechargeable batteries).
  • Direct methanol fuel cells (DMFC) are PEMFC's which use methanol directly as a fuel.



Alkaline Fuel Cells (AFC)

  • Status: Pre-commercial/Commercial; used by NASA for many years
  • Potassium hydroxide is used as the electrolyte and hydrogen as the fuel.
  • High power density and high efficiency (up to 70% efficient).
  • Production costs high due to precious metals required on the electrodes (platinum, palladium, gold).
  • Problems with corrosion, contamination, and carbon dioxide waste products.
  • Very small niche market of power supplies for space vehicles.
  • Possible uses in land vehicles and submarines

Application Clusters:

Materials

  • The use of different materials in the electrolyte is the major distinguishing characteristic of fuel cell types.



Spacecraft

  • Primarily powering space shuttle and related machinery.



Transportation

  • Fuel cells can be applied to four different transportation segments--buses, fleet vehicles (including trucks), passenger vehicles and locomotives.



Cogeneration Plants

  • Fuel cell power plants principally for electric power generation



Mathematical Models

  • Techniques to improve fuel cell efficiency and performance.



Marketing/Economics

  • Issues in cost, feasibility, and viability in commericializing fuel cells.



Environmental Protection

  • Emphasis on reducing emissions by replacing fossil fuel consumption.

Technology Decomposition Co-occurrences and cluster analysis can be conducted on specific technology to decompose the supporting technologies, materials, processes, and applications.  The results of the decomposition of solid oxide fuel cells is shown in Fig. 15.

Fig. 15: Technology Decomposition - Solid Oxide Fuel Cells

The prominent keyword terms match the general literature on SOFC's.  The solid oxide fuel cell uses a ceramic electrode of yttria-stabilized zirconia operating at about 1,800 degrees F. The oxide ions, transported through the electrolyte combine with hydrogen at the anode and produce water vapor and release electrons to the external circuit. While in the cathode, oxygen combines with free electrons to produce oxide ions. Carbon monoxide can also be used instead of hydrogen in these fuels cells to produce carbon dioxide and electrons in the anode.

Of primary importance, is that the electrolyte is in a solid phase and not a liquid electrolyte with its attendant material corrosion and electrolyte management problems. The solid state character of all SOFC components means that, in principle, there is no restriction on the cell configuration. Instead, it is possible to shape the cell according to criteria such as overcoming design or application issues.