Fuel Cell

A fuel cell is an electrochemical energy conversion device. It converts chemical energy into electrical energy, water, and heat through electrochemical reactions. The voltage generated by a single fuel cell is small (< 1 volt). So many cells are connected in series to generate the desired voltage.

A fuel cell has two electrodes, one is negative (called anode) and positive (called Cathode). The reaction that generates electricity takes place at the electrode.

Parts of Fuel Cell

Fig. A Fuel Cell
  1. Anode
  2. Cathode
  3. Catalyst
  4. Proton Exchange Membrane

Working of Fuel Cell

  • Fuel (H2) is first transported to the anode of the cell.
  • Fuel undergoes the anode reaction.
  • Anode reaction splits the fuel into H+ (a proton) and e.
  • Protons pass through the electrolyte to the cathode.
  • Electrons can not pass through the electrolyte and must travel through an external circuit which creates a usable electric current.
  • Protons and electrons reach the cathode and undergo the cathode reaction.
  • The oxygen reacts with H+ (a proton) and e− to form water vapour.

Reactions at Electrodes

Anode Reaction

2H2 → 4H+ + 4e

Cathode Reaction

O2 + 4H+ + 4e → 2H2O

Overall Cell Reaction

2H2 + O2 → 2H2O

Types of Fuel Cell

There are different types of fuel cells, differentiated by the type of electrolyte separating the hydrogen from the oxygen. The types of fuel cells are

  1. Alkaline fuel cells (AFC)
  2. Proton Exchange Membrane Fuel Cells (PEMFC)
  3. Phosphoric Acid Fuel Cell (PAFC)
  4. Solid oxide fuel cells (SOFC)
  5. Molten Carbonate fuel cells (MFFC)
  6. Direct methanol fuel cells (DMFC)

1. Alkaline fuel cells (AFC)

  • It operates on compressed hydrogen and oxygen.
  • Its efficiency is about 70 %.
  • Operating temperature is 50 to 100°C.
  • It was used in Apollo spacecraft to provide both electricity and drinking water.
  • AFC require pure hydrogen fuel and have platinum electrode catalysts.

2. Proton exchange membrane fuel cell (PEMFC)

  • Work with a polymer electrolyte in the form of a thin, permeable sheet.
  • Efficiency is about 40 to 50 %.
  • Suitable for homes and cars.

3. Phosphoric acid fuel cell (PAFC)

  • Uses phosphoric acid as the electrolyte.
  • Efficiency ranges from 40 to 80 %.
  • Typically used for stationary power generation.

4. Solid oxide fuel cells (SOFC)

  • Uses a hard, ceramic compound of metal oxides as an electrolyte.
  • Efficiency is about 60%.
  • Operating temperatures are about 1,000 °C, so no reformer is required for extracting hydrogen from fuel
  • Utility applications

5. Molten carbonate fuel cell (MCFC)

  • Uses high-temperature compounds of salt carbonates as an electrolyte.
  • Efficiency ranges from 60 to 80 %.
  • Operating temperature is about 650 °C.
  • Developed for natural gas and coal-based power plants to generate power for industry and military use.

6. Direct Methanol Fuel Cells (DMFC)

  • Use to power cellular phones and laptops.
  • Use a polymer membrane as the electrolyte.
  • The anode catalyst itself draws the hydrogen from the liquid methanol (no reformer needed).
  • The efficiency of about 40%.
  • Typically operate at a temperature between 60-90 °C.
  • Higher efficiencies are achieved at higher temperatures.

Comparison between different Fuel Cell

Fuel cell type Mobile ion Operating Temperature Applications
Alkaline (AFC) OH 50–200°C Used in space vehicles, e.g. Apollo, Shuttle.
Proton exchange membrane (PEMFC) H+ 30-100°C Vehicles and mobile applications, and for lower power CHP systems
Direct methanol(DMFC) H+ 20-90°C Suitable for portable electronic systems of low power, running for long times
Phosphoric acid (PAFC) H+ 220°C Large numbers of 200kW CHP systems in use
Molten carbonate (MCFC) CO32- 650°C Suitable for medium to large scale CHP systems, up to MW capacity
Solid oxide (SOFC) O2- 500-1000°C Suitable for all sizes of CHP systems, 2 kW to multi MW

Advantages of Fuel Cell

  1. Physical Security
  2. High Reliability
  3. Higher Efficiency
  4. Hydrogen fuel cells don’t produce air pollutants or greenhouse gases
  5. Fuel cells can readily be combined with other energy technologies, such as batteries, wind turbines, solar panels, and super-capacitors.
  6. can be refueled in 5 minutes.
  7. 40% higher fuel economy than diesel vehicles.

Applications of Fuel Cell

  1. Power sources for vehicles such as cars, trucks, buses and even boats and submarines.
  2. Power sources for spacecraft, remote weather stations, and military technology.
  3. Batteries for electronics such as laptops and smartphones.
  4. Providing power for base stations or cell sites.
  5. Food preservation.
  6. Small heating appliances.
  7. Used in Hybrid vehicles
Fuel Cell | Working & Applications

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