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Most of the systems that you are surrounded with and use today, draw their power from a very tiny power source. One such source is the Fuel Cell. Fuel Cell is a complex technology and involves a strong chemical reaction to generate electric power. The fuel cell generates electricity through some redox reactions by converting the fuel’s chemical energy with an oxidizing agent into electricity. Let us learn all about fuel cells. It needs a constant supply of two components, a fuel, and an oxidizing agent, to continue the reaction. As soon as the supply is cut off, the reaction stops.
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Key Terms: Cell, Electric Current, Anode, Cathode, Fuel Cell, Chemical reaction, Eelectricity, Oxidizing agent, Electric power
Fuel Cells
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Fuel Cell was invented in 1838 but was used commercially much later by NASA. Typically, they used it in their satellites and other devices for their research to supply power. Today, you will find these being used in commercial and residential premises and industries. It can be used both as a primary or as a secondary source of power.
Fuel Cell
A fuel cell is a tiny device that has two electrodes namely, a cathode and an anode. These electrodes result in an electrochemical reaction inside the cell.
However, a fuel cell needs to have two important components to perform this reaction. These are:
- An oxidizing agent and
- Supply of fuel or an electrolyte.
When these two are cut off, the cell will stop generating electric power. The electrolyte is very important because it supports the movements of ions, to and from the electrodes.
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Working Process of Fuel Cells
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A fuel cell generates electricity via a chemical reaction by simply completing an electric circuit. The entire process is completed in a few steps which are as follows:
- At the anode, Hydrogen atoms are introduced. These atoms are known to carry a positive electric charge. However, these atoms are stripped of their electrons at this stage. These negatively charged electrons move and create a current through the wires.
- At the cathode, Oxygen atoms are introduced. These atoms combine with the leftover electrons of the hydrogen atoms. It can combine with it after it passes through the anode or at this stage itself. It all depends on the type of cell.
Working Process of Fuel Cells
The different reactions that take place involve:
- At Cathode: O2 + 2H2O + 4e- → 4OH-
- At Anode: 2H2 + 4OH- → 4H2O + 4e-
The net result of these two reactions is 2 H2 + O2 → 2H2O.
Sometimes, however, the reaction can be too slow and in such a situation a catalyst is used. Usually, platinum or palladium is used to expedite the reaction.
Types of Fuel Cells
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There are different types of fuel cells available in the market, though the working process is pretty similar in all. The various types of the fuel cell are:
- PEM or Polymer Electrolyte Membrane Fuel Cells, which are also known as Proton Exchange Membrane Fuel Cells, have an operating temperature of 50 to 100 degrees Centigrade while conducting protons. These cells consist of electrodes, bipolar plates, a polymer membrane, and a catalyst.
- Phosphoric Acid Fuel Cells contain phosphoric acid as their electrolyte. The operating temperature of these fuel cells is typically between 150 to 200 degrees Centigrade while they carry the positively charged Hydrogen ions. It is the non-conductive nature of this electrolyte that forces the electrons to pass through the cathode by completing an external circuit. However, the acidic nature corrodes the electrodes and oxidizes during the process.
- Solid Acid Fuel Cells work on either Cesium Hydrogen Sulfate, CsHSO4, or Cesium Dihydrogen Phosphate, CsH2PO4. The molecular structure of the solid acid material works in a specific order at a lower temperature. However, at a high temperature, conductivity can increase significantly due to the phase transition.
- Alkaline Fuel Cells use an aqueous alkaline solution. This solution helps to saturate the permeable milieu and helps in separating the electrodes. These cells operate at a temperature of 90 degrees Centigrade and are very efficient in producing heat and water apart from electric power.
- Solid Oxide Fuel Cells come with a solid oxide or a ceramic electrolyte like the Yttria-stabilized Zirconia. These low-cost cells are also very efficient. However, it operates at a very high temperature. The standard operating temperature of these cells can be 600°C and 1000°C at the two extremes of the temperature scale.
- Molten Carbonate Fuel Cells are powered by natural gas or biogas and use Lithium Potassium Carbonate salt as its electrolyte. It turns liquid at high temperatures to help the carbonate ions move. These cells also have a very high operating temperature of more than 650°C. However, the electrolyte corrodes the anode and cathode of the cells for its high operating temperature.
Applications
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Fuel cell technology is very useful and has a wide and varied range of applications. A few of them include but are not limited to:
- Electric and eco-friendly vehicles
- Spaceships and space expeditions
- Electronic devices and
- Military applications.
The byproducts of the fuel cells, in the form of heat and water, are also very useful. Also, in remote areas, fuel cells are used as a primary electrical source or as a backup. It can also be used to power up cell phones, other appliances, and even households.
Advantages
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There are lots of different advantages of using fuel cells. A few of them are:
- These are more efficient in comparison to any regular combustion engine since they do not undergo a double conversion process.
- These cells save wasteful emissions of greenhouse gases. It not only conserves energy but creates heat and water as its byproducts.
- These cells are consistent and more stable, reliable, and convenient to use because the parts in them or around them need minimal or no movement.
- The working process involves atom separation and is very clean, ergonomic, and is very useful for preserving natural resources.
- These cells are very easy to combine with other technologies such as solar panels and turbines.
- Most importantly, the fuel cells are considered to be extremely scalable in comparison to a traditional cell. Depending on the need, these cells can generate electric power from a few watts to several megawatts.
The advantages and applications of the fuel cells may vary with their type.
Things to Remember
- Fuel cells are the most energy efficient devices for extracting power from fuels.
- Capable of running on a variety of fuels, including hydrogen, natural gas, and biogas, fuel cells can provide clean power for applications ranging from less than a watt to multiple megawatts.
- Fuel cell properties:
- High ionic conductivity (which results in high efficiency)
- Impermeability to gases
- Negligible electronic conductivity
- Chemical stability under a wide range of conditions
- Good mechanical integrity
- Fuel cells are composed of an anode, cathode, and an electrolyte membrane.
- Fuel cells work by passing hydrogen through the anode of a fuel cell and oxygen through the cathode.
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Sample Questions
Ques. What is the need for an electrolyte in a fuel cell? (2 marks)
Ans. The electrolyte in the fuel cells is very important. It helps the ions to travel in the desired proportion between the two electrodes. It also happens to facilitate the chemical reaction in the cell which would have been disrupted if the electrons were allowed to move freely.
Ques. Which is the best fuel cell? (2 marks)
Ans. Typically, there is no winner in this case. The diverse range of fuel cells come with different attributes which make each of them suited for specific applications. It all depends on the purpose when it comes to choosing a fuel cell.
Ques. What is the difference between a fuel cell and a battery? (3 marks)
Ans. The major difference is that the fuel cells need a stable supply of fuel to the reactants but a battery has the reactants closed in it. The fuel cells are, therefore, open systems that can work as long as the fuel is supplied. On the other hand, a battery will need regular replacements, once it dies.
Ques. Do fuel cells make a lot of noise? (2 marks)
Ans. No, fuel cells are not noisy at all because they do not come with any moving internal parts inside them. Whatever is movable is on the outside in the form of small compressors and external pumps that regulate the flow of air and fuel in the cells.
Ques. Are fuel cells safe to use? (2 marks)
Ans. Yes, but fuel cells should be handled with proper care and caution. This is because they use Hydrogen primarily. This is a highly flammable fuel like natural gas. However, it is their properties that make them a safer fuel than other traditional fuels in several situations.
Ques. (a) Calculate ΔrG0 for the reaction
Mg (s) + Cu2+ (aq) → Mg2+ (aq) + Cu (s)
Given : E0cell = + 2.71 V, 1 F = 96500 C mol-1
(b) Name the type of cell which was used in Apollo space programme for providing electrical power. (All India 2014)
Ans. (a) ΔrG0 = – nFE0
= -2 × 96500 × 2.71 (? n = 2)
= -523,030 J mol-1 = -523.03 KJ mol-1
(b) Fuel cell was used in Apollo space programme for providing electrical power.
Ques. Define the following terms :
(i) Limiting molar conductivity (ii) Fuel cell (Delhi 2014)
Ans. (i) Fuel cells : These cells are the devices which convert the energy produced during combustion of fuels like H2, CH4, etc. directly into electrical energy.
(ii) The molar conductivity of a solution at infinite dilution is called limiting molar conductivity and is represented by the symbol Λ°m.
Ques. (a) Define the following terms :
(i) Molar conductivity (Λm)
(ii) Secondary batteries
(iii) Fuel cell (3 marks)
Ans. (a) (i) Molar conductivity Λm): Molar conductivity can be defined as the conductance of the volume V of electrolytic solution kept between two electrodes of a conducting cell at distance of unit length but having area of cross section large enough to accomodate sufficient volume of solution that contains one mole of the electrolyte.
Λm = KV
(ii) Secondary batteries: Those cells which can be recharged on passing electric current through them in opposite direction and can be used again are called secondary batteries, e.g. Lead-acid storage cell.
(iii) Fuel cell : Galvanic cells that are designed to convert the chemical energy of combustion of fuels like hydrogen, methane etc. into electrical energy are called fuel cells, e.g. H2 – O2 fuel cell
Ques. (a) What are fuel cells? Give an example of a fuel cell.
(b) Calculate the equilibrium constant (log Kc) and ΔrG° for the following reaction at 298 K.
Cu (s) + 2Ag+ (aq) → Cu2+ (aq) + 2Ag (s)
Given E0cell = 0.46 V and IF = 96500 C mol-1 (Comptt. All India 2016)
Ans. (a) Cell which converts energy of combustion of fuel directly into electricity.
Example : H2 – O2 fuel cell.
Or
Those cells which convert fuel energy directly into electrical energy.
Example : H2 – O2 fuel cell
Ques. Define the following terms :
(i) Fuel cell
(ii) Limiting molar conductivity (Λ°m) (All India 2014)
Ans. (i) Fuel cells : These cells are the devices which convert the energy produced during combustion of fuels like H2, CH4, etc. directly into electrical energy.
(ii) The molar conductivity of a solution at infinite dilution is called limiting molar conductivity and is represented by the symbol Λ°m.
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