Molten carbonate fuel cell
Molten-carbonate fuel cells (MCFCs) are high-temperature fuel cells that operate at temperatures of 600 °C and above.
Molten carbonate fuel cells (MCFCs) were developed for
Improved efficiency is another reason MCFCs offer significant cost reductions over phosphoric acid fuel cells (PAFCs). Molten carbonate fuel cells can reach efficiencies approaching 60%, considerably higher than the 37–42% efficiencies of a phosphoric acid fuel cell plant. When the waste heat is captured and used, overall fuel efficiencies can be as high as 85%.[1]
Unlike
Molten carbonate fuel cells are not prone to
The primary disadvantage of current MCFC technology is durability. The high temperatures at which these cells operate and the corrosive electrolyte used accelerate component breakdown and corrosion, decreasing cell life. Scientists are currently exploring corrosion-resistant materials for components as well as fuel cell designs that increase cell life without decreasing performance.[1]
Operation
Background
Molten carbonate FCs are a recently developed type of fuel cell that targets small and large energy distribution/generation systems since their power production is in the 0.3-3 MW range.[2] The operating pressure is between 1-8 atm while the temperatures are between 600 and 700 °C.[3] Due to the production of CO2 during reforming of the fossil fuel (methane, natural gas), MCFCs are not a completely green technology, but are promising due to their reliability and efficiency (sufficient heat for co-generation with electricity). Current MCFC efficiencies range from 60 to 70%.[4]
Reactions[5]
Internal Reformer (methane example):
Anode (hydrogen example):
Cathode:
Cell:
Nernst Equation:
Materials
Due to the high operating temperatures of MCFC's, the materials need to be very carefully selected to survive the conditions present within the cell. The following sections cover the various materials present in the fuel cell and recent developments in research.
Anode
The anode material typically consists of a porous (3-6 μm, 45-70% material porosity) Ni based alloy. Ni is alloyed with either Chromium or Aluminum in the 2-10% range. These alloying elements allow for formation of LiCrO2/LiAlO2 at the grain boundaries, which increases the materials' creep resistance and prevents sintering of the anode at the high operating temperatures of the fuel cell.[6] Recent research has looked at using nano Ni and other Ni alloys to increase the performance and decrease the operating temperature of the fuel cell.[7] A reduction in operating temperature would extend the lifetime of the fuel cell (i.e. decrease corrosion rate) and allow for use of cheaper component materials. At the same time, a decrease in temperature would decrease ionic conductivity of the electrolyte and thus, the anode materials need to compensate for this performance decline (e.g. by increasing power density). Other researchers have looked into enhancing creep resistance by using a Ni3Al alloy anode to reduce mass transport of Ni in the anode when in operation.[8]
Cathode
On the other side of the cell, the
Electrolyte
MCFC's use a liquid electrolyte (molten carbonate) which consists of a sodium(Na) and potassium(K) carbonate. This electrolyte is supported by a ceramic (LiAlO2) matrix to contain the liquid between the electrodes. The high temperatures of the fuel cell is required to produce sufficient ionic conductivity of carbonate through this electrolyte.[3] Common MCFC electrolytes contain 62% Li2CO3 and 38% K2CO3.[11] A greater fraction of Li carbonate is used due to its higher ionic conductivity but is limited to 62% due to its lower gas solubility and ionic diffusivity of oxygen. In addition, Li2CO3 is a very corrosive electrolyte and this ratio of carbonates provides the lowest corrosion rate. Due to these issues, recent studies have delved into replacing the potassium carbonate with a sodium carbonate.[12] A Li/Na electrolyte has shown to have better performance (higher conductivity) and improves the stability of the cathode when compared to a Li/K electrolyte (Li/K is more basic). In addition, scientists have also looked into modifying the matrix of the electrolyte to prevent issues such as phase changes (γ-LiAlO2 to α-LiAlO2) in the material during cell operation. The phase change accompanies a volume decrease in the electrolyte which leads to lower ionic conductivity. Through various studies, it has been found that an alumina doped α-LiAlO2 matrix would improve the phase stability while maintaining the fuel cell's performance.[12]
MTU fuel cell
The German company
See also
References
- ^ a b c d "Types of Fuel Cells". Office of Energy Efficiency and Renewable Energy, United States Department of Energy. Retrieved 2016-03-18.
- ^ "Types of Fuel Cells - Fuel Cell Energy". www.fuelcellenergy.com. Archived from the original on 2013-08-25. Retrieved 2015-11-02.
- ^ a b "NFCRC Tutorial: Molten Carbonate Fuel Cell (MCFC)". www.nfcrc.uci.edu. Archived from the original on 2018-10-08. Retrieved 2015-11-02.
- ^ "Types of Fuel Cells | Department of Energy". energy.gov. Retrieved 2015-11-02.
- ^ "High Temperature Fuel Cells" (PDF). University of Babylon. Retrieved 1 November 2015.
- ^ Boden, Andreas (2007). "The anode and the electrolyte in the MCFC" (PDF). Diva Portal. Retrieved 1 November 2015.
- .
- ISSN 1547-5905.
- ^ Wijayasinghe, Athula (2004). "Development and Characterisation of Cathode Materials for the Molten Carbonate Fuel Cell" (PDF). Retrieved 2 November 2015.
- ^ .
- .
- ^ S2CID 95755022.
- ^ MCFC emission
Sources
External links
- LLNL: The Carbon/Air Fuel Cell Conversion of Coal-Derived Carbons
- DoD
- MTU 240kW fuel cell presented on the Hannover Fair 2006
- Logan Energy Limited integrate, install and operate all fuel cell technologies
- [1] molten carbonate fuel cells distributed generation challenge
- [2] presentation to Fourth Annual Conference on Carbon Capture and Sequestration