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Questions and Answers
What is one of the challenges facing SOFCs in portable applications?
What is one of the challenges facing SOFCs in portable applications?
What characteristic allows SOFCs to achieve higher power densities in planar designs?
What characteristic allows SOFCs to achieve higher power densities in planar designs?
Which type of SOFC design does not require high-temperature seals to isolate oxidant from the fuel?
Which type of SOFC design does not require high-temperature seals to isolate oxidant from the fuel?
What is a common misconception about the voltage produced by a typical single SOFC cell?
What is a common misconception about the voltage produced by a typical single SOFC cell?
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What issue is a critical area to address for the commercialization of planar SOFCs?
What issue is a critical area to address for the commercialization of planar SOFCs?
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What does the open circuit voltage (OCV) of a hydrogen fuel cell depend on?
What does the open circuit voltage (OCV) of a hydrogen fuel cell depend on?
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Which factor is NOT a cause of voltage drop in a fuel cell?
Which factor is NOT a cause of voltage drop in a fuel cell?
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How is fuel cell efficiency generally defined?
How is fuel cell efficiency generally defined?
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Which of the following accurately describes a reason for efficiency losses in a fuel cell?
Which of the following accurately describes a reason for efficiency losses in a fuel cell?
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In a typical hydrogen fuel cell, which of the following is a consequence of fuel crossover?
In a typical hydrogen fuel cell, which of the following is a consequence of fuel crossover?
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What is the primary challenge of maintaining high voltage in operational fuel cells?
What is the primary challenge of maintaining high voltage in operational fuel cells?
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Which property of fuel cells allows them to be applied to reactions beyond hydrogen?
Which property of fuel cells allows them to be applied to reactions beyond hydrogen?
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What defines the electromotive force (EMF) of a fuel cell?
What defines the electromotive force (EMF) of a fuel cell?
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What are some advantages of solid oxide fuel cells (SOFC)?
What are some advantages of solid oxide fuel cells (SOFC)?
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What does the Open Circuit Voltage (OCV) of a fuel cell represent?
What does the Open Circuit Voltage (OCV) of a fuel cell represent?
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Which of the following best describes the efficiency of a fuel cell?
Which of the following best describes the efficiency of a fuel cell?
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What is a common cause of voltage drop in solid oxide fuel cells?
What is a common cause of voltage drop in solid oxide fuel cells?
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Which historical figure is associated with the first reports on fuel cells?
Which historical figure is associated with the first reports on fuel cells?
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How does the efficiency of solid oxide fuel cells compare to that of reciprocating engines?
How does the efficiency of solid oxide fuel cells compare to that of reciprocating engines?
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What role does the power coefficient (Cp) play in wind-driven generators?
What role does the power coefficient (Cp) play in wind-driven generators?
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In a hydrogen fuel cell, how many electrons are passed for each water molecule produced?
In a hydrogen fuel cell, how many electrons are passed for each water molecule produced?
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Study Notes
Advanced Materials for Energy Conversion Solid Cells (SOFCs)
- Solid oxide fuel cells (SOFCs) convert fuel (hydrogen or hydrocarbons) into electricity through electrochemical reactions, not combustion.
- Fuel: CO, H₂
- Reaction Products: CO₂, H₂O
- Anode Reaction (examples): H₂ + O₂ → H₂O + 2e⁻, CH₄ + 3O₂ → CO₂ + 2H₂O + 6e⁻
- Cathode Reaction: O₂ + 4e⁻ → 2O₂⁻
- Operating Temperature: 1000°C
- Electrolyte: YSZ (Yttria-Stabilized Zirconia)
- Other components: NiZrO₂ cermet, LaMnO₃
History of SOFCs
- Faraday's early investigations of conduction in ceramics (1830s)
- Sir William Grove first reported fuel cells in 1839.
- Walther Nernst observed increased conductivity of mixed oxides (1890s).
- Conceptual development of ion conduction through lattice defects (Schottky and Frenkel) in the 1930s.
- SOFC patent filed by Siemens and Halske.
- NASA's Project Gemini (1961)
- Large stationary fuel cells develop in the 1990s & commercial applications
- Honda begins leasing of Fuel Cell Electric Vehicles (FCV) in 2008
- Fuel cells sold commercially as APU and stationary backup power in 2007
Efficiency and Open Circuit Voltage (OCV)
- Electrical efficiency of SOFCs: ≥40%
- Reciprocating engine efficiency: ≈35%
- Photovoltaic efficiency: 6-20%
- Wind turbine efficiency: ≈25%
- Other advantages of SOFCs: Fuel flexibility, noise-free operation, less pollution, generating excessive heat, effective reduction of greenhouse gas
Wind-Driven Generator
- Input: Kinetic energy of moving air
- Output: Electrical energy
- Power coefficient (Cp): Ratio of wind kinetic power to mechanical power in rotor shaft
- Overall wind turbine efficiency = (Cp) x (electric machine efficiency)
Efficiency of Fuel Cell
- Electrical power and energy output are easily calculated: Power = VI and Energy = VIt
- Using Gibbs free energy calculation ∆Gf = Gf of products – Gf of reactants
- ∆g f = (gfH₂O) – (gfH₂) − ½ (gfO₂)
Hydrogen/Oxygen Fuel Cell
- Basic reaction: 2H₂ + O₂ → 2H₂O
- 'Product' is one mole H₂O
- 'Reactants' are one mole of H₂ and ½ mole of O₂
- Example values of ∆h f, As, and Agf for various temperatures
- Examples of values at 100°C, 300°C, 500°C, 700°C, 900°C, & etc
- Negative ΔGf values indicate energy release
Open Circuit Voltage (OCV)
- OCV formula: E = -∆Gf / 2F
- Example: Hydrogen fuel cell at 200 °C, E = 220,000 / (2 x 96,485) = 1.14 V
- z is the number of electrons transferred per molecule of fuel.
Fuel Cell Efficiency
- Efficiency calculation for different water product forms. Includes different temperatures (e.g. 25°C, 80°C, 100°C, 200°C, 400°C, 600°C, 800°C, & etc.)
- Relationship between Maximum Efficiency (or Reversible Open Circuit Voltage), ∆gf, and ∆h f
Efficiency and Fuel Cell Voltage
- Operating voltage of a fuel cell is easily related to its efficiency
- If all hydrogen fuel energy is transformed into electrical energy, EMF= -∆Hf / 2F
- Cell efficiency = (actual voltage) / E (EMF)
- efficiency = μf Actual Voltage / E
Additional information:
- OCV of hydrogen fuel cell, various losses result in operational voltage (e.g. Activation, Ohmic, and concentration losses)
- Causes of voltage drop in Fuel Cells
- SOFC Design types (Planar and Tubular)
- SOFC Advantages (simpler manufacturing, Higher power densities, High temperature operation & etc) and disadvantages (manufacturing costs, sealing problems, and etc)
- SOFC applications (Small SOFC Systems, Large SOFC Systems, Portable SOFC, and etc)
- SOFC classification by Temperature levels, Cell Type, and Flow
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Description
Test your knowledge on solid oxide fuel cells (SOFCs), their electrochemical processes, and historical milestones in their development. Explore key reactions, materials used, and important figures in the history of fuel cells from the 1830s to the 1990s.
