Solid Oxide Fuel Cell – More Details

1.) Thermodynamics Principle

-A link to the thermal expansion coefficient and what it means, and how it can be used. My guess is that the thermal expansion coefficient stated in the report means the volume expansion, since the entire system will be under the same conditions for a prolonged time, making each part expand the same.

2.) Best Efficiency

-no need for fuel processing, since they don’t need to worry about fuel contamination from other substances, and be made into usable substances straight in the cell (called internal reformation)

-must be at high temperatures to operate, between 750-1000 celcius

-Possible 80% efficiency

3.) Engineering Details

-must be chemically and physically stable in an oxidizing/reducing environment, chemically compatible with other parts, proper electrical conductivity, similar thermal expansion coefficients to the other parts (to avoid cracking and other damage), low cost, be strong, and easy to make.

-all SOFC use yttria-stalized zirconia as the electrolyte, lanthanum manganite (impurified with strontium) cathode, a nickel/yttria-stabilised zirconia cermet (ceramic and metal alloy) anode, and a lanthanum chromite (LaCrO3) interconnect.

-the interconnect is made to hold each cell together in series and conduct the electricity through it toward the thing(s) to be powered. The interconnect has to have a conductivity similar to that of the other parts of the cell, likewise do all the parts of the cell have to have a similar conductivity to that of the interconnect. So the fact that the cathode has to be impurified means that it’s pure conductivity is higher than that of the rest of the system, and needs to be brought down, or that it’s to low and needs to be brought up.

4.) Environment Impacts

-can take CO straight from source to use as fuel in the cell, cutting down on carbon emissions and recycling the carbon that’s already been made.

Janelle’s Preliminary Research

1. Thermodynamic Principles

  • Electrochemical Process; Molten Carbonate Fuel Cell (MCFC)
    • MCFCs use a molten carbonate salt electrolyte suspended in a porous ceramic matrix of beta-alumina solid.
    • Non-precious metals can be used as catalyst due to high temperature of MCFC opperation (600 deg celcius and above).
    • Can withstand considerable contamination in comparision with other fuel cell types.
    • Blanced Chemical Equations:
      • Internal Reformer:
        • CH4 + H2O –> 3H2 + CO
      • Anode:
        • H2 + CO3  –> H2O + CO2 + 2e
      • Cathode:
        • 1/2 O2 + CO2 + 2e –> CO3
      • Cell Combined Equation:
        • H2 + 1/2 O2 + CO2 –> H2O + CO2

2. Efficiency

  • Due to the high opperating temperature, no additional energy is needed to convert fuels to hydrogen fuel. Fuel is converted to hydrogen fuel inside the cell (internal reforming).
  • MCFC can be utilized for waste streams from other industrial processes.
    • Coal power plant gas. MCFC requires the introduction of CO2 into the cathode, which can be used to reduce the emission of CO2 into the atmopshere.
    • Biogas from the break down of garbage and animal waste can be converted to electrical energy by MCFCs.
    • Natural gas.
  • The gas exiting the cell is around 400 degrees celcius, which makes it an ideal candiate for heat loss reduction by steam powered turbine electricity generation.
  • The efficiency of MCFCs can be close to 60%, and if the waste heat is used to generate steam power, the efficiency can be close to 85%!

3. Engineering Details

  • MCFCs are a fuel cell that has very limited application. They are used solely for the purpose of large-scale energy production.
  • Uses alternate fuels, even waste.
  • Due to the high opperating temperature and corrosivity of the electrolyte, MCFCs degrade quickly and require costly maintentance.
    • Costs are recouped by the ability to use inexpensive metal catalysts, internal reforming, and the potential to recover energy from waste streams.

4. Environmental Concerns

  • Due to the use of fossil fuels, MCFCs produce carbon dioxide gas. A portion of the CO2 gas is reused by the cell, not all.
  • The adoption of MCFCs, while increasing the efficiency of coal-burning power plants, could act as a crutch to slow the complete replacement of fossil fuels by clean, renewable energy sources.
  • Degradation of cell life due to high operating temperature and electroyte corrosivity increases the production of hazardous wastes.

5. Personal Thoughts

  • Due to the incredible efficency of MCFCs, I think that they are a fantasic new resource for the conversion of waste gas from landfills and anerobic digestors to energy.
  • I share the concern, however, that MCFCs will be used to support the continued use of coal burning.
  • The unavoidable production of carbon dioxide gas is a big issue, especially with the push to develope energy sources that do not have greenhouse gas emissions.
  • In all, I think that there are better alternatives for the waste gases from landfills and agriculture. The only real beneficial use of MCFCs is in conjunction with coal burning.

6. MCFC Schematic

7. Nernst Equation:

E = E^o + \frac{RT}{2F}log\frac{P_{H_2}P_{O_2}^{\frac{1}{2}}}{P_{H_2O}}+\frac{RT}{2F}log\frac{P_{CO_2,cathode}}{P_{CO_2,anode}}

8. Sources


Sulley’s Preliminary Work

  1. Thermodynamic Principles
    1. Hydrogen and Oxygen gas ionized by anode (hydrogen) and cathode (oxygen)
      1. anode and cathode are both platinum
    2. Electrolyte containing hydrogen and oxygen ions
      1. electrolyte = liquid that contains ions
      2. chemically react to make water
      3. electrons from ionized reactants then move through external circut
    3. 5 Types
      1. alkaline fuel cells (AFC)
      2. phosphoric acid fuel cell (PAFC)
      3. polymer electrolyte membrane fuel cell (PEMFC) *
        1. aka proton conducting membrane
      4. molten carbonate fuel cell (MCFC)
      5. solid-oxide fuel cell (SOFC) *
  2. Efficiency
    1. SOFC
      1. yttria-stabilized zirconia is cheap and easy to make, also not very reactive with reactants
      2. high temps, increases oxygen ion reception areas
      3. negligible electrical conductivity
      4. generally need operating temp of 850 degrees C
      5. poor durability,
  3. Engineering
    1. alkaline
      1. NaOH or KOH electrolyte
      2. operate at 70 degrees C
      3. carbon and platinum electrocatalyst electrodes
      4. needs very pure hydrogen gas fuel
      5. can use air
    2. phosphoric acid
      1. phosphoric acid electrolyte
      2. operate at 200 degrees C
      3. can work with CO2 and hydrogen gas
      4. can use air
    3. polymer electrolyte membrane
        1. proton conducting polymer membrane electrolyte
        2. requires pure hydrogen and pure oxygen
        3. operate at 80 degrees C
        4. carbon platinum electrocatalyst electrodes
    4. molten carbonate
      1. operates at 650 degrees C
      2. run on CO and hydrogen gas
        1. no pure oxygen or air
    5. solid oxide
      1. solid, ceramic, inorganic oxide electrolyte
      2. operate at 750-1000 degrees C
      3. use hydrocarbon as hydrogen fuel, and air as oxidizing fuel
      4. almost all have yttria-stabilized zirconia electrolyte
  4. Environmental Impacts
    1. SOFC
      1. Adds to carbon footprint, but reduces carbon emissions by 90%
  5. Personal Views
    1. The point of using fuel cells is to cut down on carbon emissions. which the SOFC does, but it still adds to the carbon footprint, which makes it less than ideal to use. And the SOFC generates fewer electrons for each electrolysis reaction than the PEMFC
  6. Sources

* = most practical

There are also likely other things within these articles that I had overlooked, but this is the general info I found.

Suggested Splitting of Work

After doing my preliminary research, I have an idea on how to split the workload for this project:

Of the five topics to cover:

  1. The Thermodynamic Principles at work in Fuel Cells
  2. Fuel Cell Efficiency based on Thermodynamic Principles
  3. Fuel Cell Engineering Details
  4. Environmental Concerns regarding Fuel Cells
  5. Personal Thoughts and Points of View concerning Fuel Cell Technology

I suggest we work on the Thermodynamic Principles (1) together as our primary focus of the research.

Then, we split-up sections 2, 3, 4 and assign one team member to each subject.

We also each provide a few (1-2) personal thoughts for point 5.

Reed’s Prelim Research


  1. Thermodynamic Principles
    1. Electrochemical process:
      1. Simplest example: PEMFC (Proton Exchange Membrane)
        1. Hydrogen (H2) fuel is catalytically oxidized into hydronium ions (H+) and electrons (e-).
        2. Protons are able to pass through a semi-permeable membrane into the electrolyte medium impenetrable by electrons.
        3. Positively charged protons pass through electrolyte and arrive at cathode, creating positive charge.
        4. Conductive circuit is created between Anode and Cathode, allowing electrons to flow from negative anode to positive cathode. The flux of electrons creates a current that can do work.
        5. Protons at the Cathode combine with O2 gas from the atmosphere to produce H2O: 2H2 + O2 –> 2H2O
      2. Thermodynamic relevance:
        1. In order for the fuel cell to continue to produce current, the formation of water reaction in the last step needs to be occurring constantly. Since formation of water is highly exothermic, the fuel cell loses significant amounts of energy to waste heat.
        2. In order to fully investigate the efficiency of the fuel cell, we would need to model the whole system, including:
          1. Current generated by fuel cell
          2. Loss of waste heat
          3. Could this be modeled like a Carnot cycle?
  2. Efficiency
    1. As noted, much energy is lost to waste heat.
    2. Some systems have been established to capture the heat lost and utilize it:
      1. Combined heat and power (CHP) used to capture heat and convert to power or to heat homes or buildings. Increases efficiency to 80-85%
        1. Absorption chillers convert heat to refrigeration
      2. Must consider all inputs and all outputs.
        1. In addition to chemical potential energy of H2 fuel, we must also consider how the fuel is created. Most hydrogen is produced by the decomposition of water, which usually requires energy from electrolysis.
  3. Engineering details – Many types of fuel cells have been designed.
    1. Alternate fuels:
      1. Natural gasses / methanol
      2. Oxides and metal hydrides
      3. Acids (formic, sulfuric, phosphoric)
    2. Stacking methods
      1. Stacking of cathode and anode arrays can be carried out:
      2. In series for higher voltage
      3. In parallel for higher current
      4.  Materials
        1. Catalysts
        2. Cathode and anode materials
        3. Electrolyte medium
    3. Demonstration: Make a model fuel cell?
  4. Environmental Concerns:
    1. Pros
      1. Efficiency higher than fossil fuels
      2. Emissions limited to water vapor
    2. Cons
      1. Hydrogen fuel is very dangerous!
      2. H2 gas must be electrolytically separated, lowering overall efficiency
  5. Personal thoughts:
    1. I had been interested in going in to graduate research on materials of fuel cells (3.B.iv. above), until while doing some digging for a paper in Inorganic, I found this argument from Elon Musk:
    2. Musk makes some very good points about efficiency, and that batteries are already much more efficient. That being said, batteries require rare, often toxic heavy metals that are causing political and human rights issues all over the world.
    3. There is no panacea for fuel efficiency, but renewables or nuclear energy sources seem to be the most sensible. Solar and wind are still very inefficient, but the sun is effectively an infinite source, and should be exploited however possible. Fuel cells do not necessarily utilize renewable energy, but they’re still better than internal combustion.

Preliminary Planning: Thermodynamics of Fuel Cells

Team D Consists of (alphabetically):

  • Reed Heintzkill
  • Sullivan Moreau
  • Janelle Nehs

The five areas to address in this project, with respect to Fuel Cell technology are:

  1. The Thermodynamic Principles at work in Fuel Cells
  2. Fuel Cell Efficiency based on Thermodynamic Principles
  3. Fuel Cell Engineering Details
  4. Environmental Concerns regarding Fuel Cells
  5. Personal Thoughts and Points of View concerning Fuel Cell Technology

Each team member has been asked to perform initial research on each of these topics and to present notes on this blog.  We will then meet to discuss our shared findings and determine which of the points investigated will be followed-up on for the final presentation, and who will be responsible for each of the various sections.