Week 2 Challenge
1.Compare four different types of fuel cells and state their applications
| FUEL CELL TYPE | COMMON ELECTROLYTE | OPERATING TEMPERATURE | TYPICAL STACK SIZE | ELECTRICAL EFFICIENCY (LHV) | APPLICATIONS | ADVANTAGES | CHALLENGES |
| Polymer electrolyte membrane (PEM) | Perfluorosulfonic acid | <120°C | <1 kW–100 kW | 60% direct H2;40% reformed fuel |
Backup power Portable power Distributed generation Transportation Specialty vehicles |
Solid electrolyte reduces corrosion and electrolyte management problems Low temperature Quick start-up and load following |
Expensive catalysts Sensitive to fuel impurities |
| Alkaline (AFC) | Aqueous potassium hydroxide soaked in a porous matrix, or alkaline polymer membrane | <100°C | 1–100 kW | 60% |
Military Space Backup power Transportation |
Wider range of stable materials allows lower cost components Low temperature Quick start-up |
Sensitive to CO2 in fuel and air Electrolyte management (aqueous) Electrolyte conductivity (polymer) |
| Phosphoric acid (PAFC) | Phosphoric acid soaked in a porous matrix or imbibed in a polymer membrane | 150°–200°C |
5–400 kW, 100 kW module (liquid PAFC) <10 kW (polymer membrane) |
40% | Distributed generation |
Suitable for CHP Increased tolerance to fuel impurities |
Expensive catalysts Long start-up time Sulfur sensitivity |
| Molten carbonate (MCFC) | Molten lithium, sodium, and/or potassium carbonates, soaked in a porous matrix | 600°–700°C | 300 kW–3 MW, 300 kW module |
50% |
Electric utility Distributed generation |
High efficiency Fuel flexibility Suitable for CHP Hybrid/gas turbine cycle |
High temperature corrosion and breakdown of cell components Long start-up time Low power density |
| Solid oxide (SOFC) | Yttria stabilized zirconia | 500°–1,000°C | 1 kW–2 MW | 60% |
Auxiliary power Electric utility Distributed generation |
High efficiency Fuel flexibility Solid electrolyte Suitable for CHP Hybrid/gas turbine cycle |
High temperature corrosion and breakdown of cell components Long start-up time Limited number of shutdowns |
2.Using a plot with energy density and power density on the X and Y axis, arrange various battery types like lithium ion, lead acid, Nickel Cadmium, Ultracapacitor, fuel cell.
Battery energy density is the amount of energy a battery contains compared to its weight or size. We call this the specific energy density when comparing to weight and volumetric energy density when comparing size.
power density is the amount of power in a given mass. If a system has a high power density, than it can output large amounts of energy based on its mass
From graph we can find out that the lithium ion , lead acid, Nickel Cadmium batteries have low power density and moderate energy density. Ultra capacitors or supercapacitors have moderate power density and moderate energy density. The fuel cell has low power density and high energy density