A fuel cell is a device that generates electricity through an electrochemical reaction. The green renewable Fuel cell is attractive due to its salient features like High efficiency, Quiet operation, Compact size, Lower or zero emissions, etc.
The fuel cell uses the chemical energy of hydrogen or other fuels to cleanly and efficiently produce electricity. In the case of the hydrogen fuel cell, hydrogen is the source of fuel and the only products are electricity, water, and heat. Fuel cells do not need to be periodically recharged like batteries, but instead, continue to produce electricity as long as a fuel source is provided.
A fuel cell is composed of an anode, cathode, catalyst, and an electrolyte membrane sandwiched between two electrodes. Oxygen from air passes over one electrode and hydrogen over the other, generating electricity, water, and heat. In a hydrogen fuel cell, a catalyst at the anode separates hydrogen molecules into protons and electrons, which take different paths to the cathode. The electrons go through an external circuit, creating a flow of electricity. The protons migrate through the electrolyte to the cathode, where they unite with oxygen and the electrons to produce water and heat. Bipolar plates on either side of the cell help to distribute gases and collect the electrical current.
In some cases, Fuel cells produce very little voltage which may not be sufficient for most of the applications. In those cases, stacking of fuel cell is required to increase the voltage and hence performance. Individual fuel cells can be collected into a unit and connected to each other in series, resulting in a “stack” of cells that can generate more voltage.
Fuel cells have a number of advantages which includes:
- High efficiency
- Quick refueling
- Quiet operation
- Compact size
- Rapid response to changes in electrical demand
- Long lifetimes
- Longer ranges, increasingly important for larger, heavier vehicles.
- Lower or zero emissions
- High power density
Fuel cells have several benefits over conventional combustion-based technologies currently used in many power plants and vehicles.
The fuel cell can be used in a lot of applications, which includes warehouse logistics, global distribution, utility vehicles, buses, scooters, bicycles, trains, stationary power generation, boats and submarine, and many more. Fuel cells are lightweight, long-lasting, and portable power sources that can be used in backup power applications.
Types of Fuel Cells
- Polymer Electrolyte Membrane Fuel Cell (PEMFC)
- Direct methanol Fuel Cell (DMFC)
- Alkaline Fuel Cell (AFC)
- Phosphoric acid Fuel Cell (PAFC)
- Molten Carbonate Fuel Cell (MCFC)
- Solid Oxide Fuel Cell (SOFC)
Among all these categories, PEMFC and AFC are widely used because of their operational convenience and performance.
Polymer Electrolyte Membrane Fuel Cell (PEMFC)
Among all the types of fuel cells, proton exchange membrane fuel cell (PEMFC) has become widely accepted for powering electric devices and vehicles. Polymer electrolyte membrane (PEM) fuel cells, also called proton exchange membrane fuel cells, use a proton-conducting polymer membrane as the electrolyte.
PEMFC uses water based or mineral acid-based polymer membrane as its electrolyte, with platinum-based electrodes. The water based PEMFC operate at relatively low temperatures (80-100˚C) and can quickly vary their output to meet shifting power demands. The power output for PEMFC fuel cell is in the range of 5-200 kW. Due to their low temperature and use of metal-based electrodes, these cells must operate on pure hydrogen.
A variant of PEMFC which operates at 200˚C can be produced by changing water-based electrolyte to mineral acid based. This is done to overcome some of the current limitations with regard to fuel purity. The low temperature PEMFCs pose serious water management challenges, whereas the high temperature of PEMFCs can operate at dry conditions, and no humidifiers are needed.
Alkaline Fuel Cell (AFC)
AFCs are the first fuel cells to be used widely in space technologies. They have high electrical efficiency and are easy to handle. These fuel cell uses potassium hydroxide in water as electrolyte and for catalyst at anode and cathode they use non- precious metals like nickel and porous gas diffusion as electrode. The electrodes were made of porous powdered nickel that was sintered to make it a rigid structure. To ensure good three-phase contact between the reactant gas, the liquid electrolyte, and the solid electrode, the nickel was made of two layers of different sizes of nickel powders. Alkaline fuel cells consume hydrogen and pure oxygen, to produce potable water, heat, and electricity. They are similar to PEMFC but uses alkaline membrane as electrolyte and not an acidic one. The alkaline environment of AEMFCs allow the use of non-precious metal catalysts such as iron, cobalt, silver, and graphene, which significantly reduces the cost of the fuel cell system. Chemical reaction for AFCs
Anode: 2H2 (g) + 4(OH)- (aq) → 4H2O (l) + 4e-
Cathode: O2 (g) + 2H2O (l) + 4e- → 4(OH)-(aq)
Overall: 2H2 (g) + O2 (g) → 2H2O (l)
AFC fuel cell must contain hydrogen and oxygen as it cannot tolerate a small amount of carbon dioxide in atmosphere. Small amount of CO2 can affect the cell performance and durability since it forms carbonate in presence of CO2. Challenges like Water management issues can be potentially resolved by tuning the properties of the polymer to allow for water diffusion from the anode to the cathode.
Although Fuel cell are great alternate source of renewable energy, but due to low efficiency there is lot of scope of improvement. Researchers are still working in this field. Scientific innovation and improvement is an ongoing process. Fuel cell is great resource for sustainable future.
COURTESY: ULTRANANOTECH PVT. LTD
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