Fuel Cells and its Applications
Fuel cells are environmental friendly renewable source of energy which are capable of generating electricity at an efficiency of greater than traditional energy resources. Fuel cells are scalable and provide everything from few milliwatt to megawatts in number of uses from cellphones to cars and in power generating plants. However, some obstacles exist in the applications of fuel cells. The output voltage of the fuel cell is very low and it varies with age and current, and its efficiency also decrease with the ripple current, no overload capability and no acceptance of reverse current.
History of fuel cells
In 1839, Sir William Robert Grove, a Welsh judge, inventor and a physicist designed the first fuel cell. He mixed hydrogen and oxygen in the presence of an electrolyte which later became known as a fuel cell but the output of the fuel cell is quite low. This basic technology is still used in modern days’ fuel cells.
A fuel cell produces electricity through a chemical reaction, but without combustion. It’s an electro-chemical energy conversion device that produces electricity, water and heat. The reactions that produces electricity happens at electrodes. Every fuel cell has two electrodes, one positive, called the anode, and one negative, called the cathode. These are separated by an electrolyte barrier. Fuel goes to anode side, while oxygen goes to the cathode side. When both of these chemicals hit the electrolyte barrier, they react, split off their electrons which flows through the external circuit. The following reactions shows the basic process:
Anode side: 2H2 => 4H+ + 4e-
Cathode side: O2+ 4H++ 4e-=> 2H2O
Net reaction: 2H2 + O2 => 2H2O
When pure hydrogen is used as a fuel then only water and electricity is produced. This makes fuel cells as an environmental friendly power generation process.
The actual fuel cell is composed of various components as shown in the block diagram. The building block of fuel cells are cylindrical or rectangular tubes that contain the anode, cathode and the membrane which performs the power generation and recombination of electrons. To create fuel cell, stack these tubes are connected in series and parallel fashion. For utility applications where large scale power generation is required, the fuel cell stack can be amassed into tiers. These tiers can be assembled into sub-megawatt megawatt power generation.
Types of fuel cells
Fuel cells are classified on the basis of type of electrolyte used. These are as follows:
- Alkaline fuel cells (AFCs),
- Phosphoric acid fuel cells (PAFCs),
- Proton exchange membrane fuel cells (PEMFCs),
- Molten carbonate fuel cells (MCFCs) and
- Solid oxide fuel cells (SOFCs).
These are described as follows:
- Proton exchange membrane fuel cell (PEMFC): -PEM fuel cells operate at around 80°C and a practical efficiency of 60%. They use hydrogen and oxygen as a fuel and the power output is in the range of 5-200 kW. They are ideal for transportation and portable power. Additional advantages are their high response, small size.An attractive future development is the Direct Methanol Fuel Cell (DMFC). This uses methanol as a fuel for fuel cells by reforming it into hydrogen because of the capacity of safe hydrogen storage and transportation that methanol provides. DMFC is basically used in transportation.
- Phosphoric acid fuel cell(PAFC): - Phosphoric acid fuel cells use liquid phosphoric acid as the electrolyte and operate at about 450°F.PAFCs generate electricity at more than 40% efficiency - and nearly 85% of the steam this fuel cell produces is used for cogeneration. One of the main advantages to this type of fuel cell, besides the nearly 85% cogeneration efficiency, is that it can use impure hydrogen as fuel. PAFCs can tolerate a CO concentration of about 1.5 percent, which broadens the choice of fuels they can use. If gasoline is used, the sulfur must be removed.
- Alkaline fuel cells (AFC): - Alkaline fuel cells use potassium hydroxide as the electrolyte and operate at 160°F. They are very susceptible to carbon contamination, so require pure hydrogen and oxygen. These fuel cells can achieve power generating efficiencies of up to 70%. They were used on the Apollo spacecraft to provide both electricity and drinking water.
- Phosphoric acid fuel cells(PAFCs): - This fuel cells use liquid phosphoric acid as a fuel and operates at 450oF. They have efficiency of more than 40% and the 85% of the steam generated during the operation is used in cogeneration process and unlike PEM fuel cells they can be operate using impure hydrogen as a fuel.
- Microbial fuel cells(MFCs): - A microbial fuel cell (MFC) converts chemical energy into electrical energy by the action of microorganisms. These cells are constructed using bio anode and bio cathode. In these fuel cells the electrons are generated at anode due to oxidation and then these electrons move towards the cathode where reduction takes place. Most of the MFCs using organic donor which oxidized to produce CO2, protons and electrons.
- Solid oxide fuel cells: - These fuel cells use a hard, non-porous ceramic compound as an electrolyte. It operates at a very high temperature range of around 1800OF. They are suitable for stationary applications as well as for auxiliary power units (APUs) to the power electronics based components used in vehicles.
- MCFCs: - These cells use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic lithium aluminum oxide matrix because they operate at a high temperature range of 650oC, non-precious metal can be used as a catalyst, reducing costs. They can reach efficiencies of around 65%.
Applications of fuel cells
- Backup power: - They are used as a backup power source when the primary power supply is interrupted. Some backup applications include computer systems, manufacturing facilities and homes.
- In September 2015, Aditya Birla Group bought more than 200 fuel cells from Ballard industries to power its telecom towers.
- In September 2015, Intelligent Energy announced a deal of € 1.2 billion for the supply of fuel cells to power 27,400 towers in India.
- French rail vehicle manufacturer Alstom with the collaboration with Germany and Canada demonstrated a fuel cell based zero carbon emission train named as Coradia iLint.
- In march 2018 TATA announced India’s first fuel cell powered bus.
- The number of fuel cell vehicles like Toyota myriad, Honda FCX clarity, Mercedes Benz F-Cell, Hyundai ix35 FCEV.
- A world’s first megawatt scale carbonate fuel-cell power plant, built by Toyota and Fuel cell energy to be in operation by 2020 which could generate 2.36 Megawatt of electricity and 1.2 tonnes of hydrogen daily at the port of long beach, California.
- As 2020 Olympics is going to held in Tokyo, Japan. The Japan govt. aims to install 35 hydrogen gas stations in the city with aim to have 6000 fuel cells based cars on the roads and increased the quantities of fuel cell based buses in Tokyo.
- A number of aircrafts like HY4, Lockheed CL-400 sultan are based on fuel cell technology which emits zero carbon emission.
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