Fuel Cell: State-of the-Art Review and Challenges. Pradip Majumdar Professor Department of Mechanical Engineering Northern Illinois University DeKalb, IL 60115. Solid Oxide Fuel Cell. Cathode reaction:
Department of Mechanical Engineering
Northern Illinois University
DeKalb, IL 60115
Flexible in fuel types
No electrolyte depletion
No corrosion of FC components by liquid
Reaction zone has two-phase solid-gas interfaceAttractive Features SOFC
better system match
heat for cogeneration
better system match results
in higher overall conversion
efficiencies - 60%
- May not need the expensive steam reforming and shift conversion
interconnect/Bipolar plates, seals and
SECA - Solid State Energy Conversion Alliance
adding a Sulphonic acid chain
Additional evaluation of Nafion membrane at different temperatures.
Operation at higher temperatures for better thermal management
- up to 120 C for vehicle applications
- above 120 C for stationary application
Membrane that can operate at lower
humidity content ( <10%).
- better water distribution
- reduced resistance
- The concept of one closed end of the tube eliminates
the need for gas seals between cells
- Can provide robust ceramic structure for the cell
- Leads to a relatively long current path around the circumferences of the cells, resulting in higher internal resistances.
- simpler in manufacturing of the flat components
- Potential for higher power densities
Disadvantages of the Planar Design
- Necessity of sealing to avoid crossover of
- increased risk of cell fractures, particularly
during thermal cycling
Planar SOFCs MEM are generally
manufactured in three different
lanthanum strontium cobalt ferrite (LaSrCoFeO).
- YSZ has highest oxide ion conductivity than any other materials:
- lowest electronic conductivity, lowest gas permeability to prevent gas cross over losses.
- typical composition contains 8 % Yttria (y2O3) mixed with Zirconia (ZrO2) for temperature of 800-1000 C.
Yttria introduces high concentration of oxygen vacancies into zirconia crystal structure and results in a higher ion mobility.
- gas concentration distribution
- current density distribution
- mass transport losses.
Tri-layer Membrane Electrode Assembly (MEA) with bipolar plates
NIU design for for Fabrication and Test
Multiple Parallel Channel Design
- Macro channels
- Micro channels
- Straight parallel
- multiple parallel
Velocity vectors along the channel
Gibb’s Free Energy:
= -2E-05*(T3) + 0.042*(T2) + 23.313*T – 239015
Include effect of variation in gas concentrations
Thelocal current density distribution is calculated as using Butler-Volmer equation
Where, i0 = exchange current density
η = over potential
n = number of electrons
= Anodic transfer co-efficient
= Cathodic transfer co-efficient
Detail components of heat and mass fluxes across the SOFC fuel cell
MEA with bi-polar plate with flow channels
Mass and Momentum:
Pressure driven flow through a porous
media is given by Brinkman’s equation
Effective viscosity of the gas in the porous media
Effective diffusion coefficient in a pore structure is given as
Alternate form given by Bruggemann equations
Binary diffusion coefficient is given based on Molecular and Knudsen diffusions
Stefan-Maxwell equation for multi-component diffusion
Water is transported by three mechanisms:
- Electro-osmotic Drag due to the
movement of proton
- diffusion due to water concentration
- Permeation due to pressure
Nernst-Planck Equationto describe flux of species in the membrane pore liquid.
Takes into account of convection velocity given by electro-osmotic drag flux
Where Xo2 - oxygen concentration along electrode-electrolyte interface
Ohmic losses occur due to the resistance to
the ionic flow and electronic flow through the electrolyte and electrodes respectively
Where is constant characterizing the electrolyte material and given as
Mass transfer losses occur at high current densities due
to insufficient supply of the gases.
At the higher current densities the fuel supply may not
sufficient enough to maintain oxygen concentration at
electrode catalyst layer to a positive level to sustain the
This is primarily affected by the gas flow field design in
terms of pressure drop and mass transfer effectiveness.
The mass transfer loss is given by
Where = limiting current density
maintain cell temperature and for better overall efficiency of the fuel cell power generation system.
electrochemical reaction is given as
For single cell
Reversible Heat Generation
Irreversible Heat Generation
Irreversible Heat Generation due to Ohmic heating only
For a single cell
(a) 0.5 Amp/cm2
(a) 0.5 Amp/cm2
Strong two-dimensional variation at the cathode-membrane interface and around the land areas.
Stronger variation across the cell.
Variations are stronger with higher current densities.
(a) 0.5 Amp/cm2
Pickup of water is higher on cathode-side channel compared to anode-side channel.
(b) 1 Amp/cm2
As the current density increases there is a slight increase in pickup of water on anode side.
(c) 1.5 Amp/cm2
Higher accumulation in the land areas around the channels.
a) 0.5 Amp/cm2
Temperature increases from inlet to outlet, indicating that the gas stream is effective in removing heat.
(b) 1 Amp/cm2
Higher temperature at core and cathode side of the fuel cell.
(c ) 1.5 Amp/cm2
Increase in cell temperature at higher current density
transmitted to the wheels through a electrical power train system.
supplies the power to the motors and keeps the battery fully charged
- steam or organic Rankine cycle
- gas turbine cycle
- combination of the two.
- Fuels include ethanol, methanol, diesel, bio-diesel,
natural gas, coal gas.
Need heat for endothermic reaction).
- Steam reforming (SR)
- Partial Oxidation (POX) reforming
- Auto thermal reforming (AR)
Thanks to following graduate students for their work:
This work is supported by:
United States Department of Transportation - (PEMFC)
United States Department of Energy - (SOFC)