FUEL CELLS

WHAT IS A FUEL CELL?

• Fuel Cell is a device that converts chemical energy to electrical energy.
• In short, a fuel cell converts the chemicals hydrogen and oxygen into water, and in the process it produces electricity.
• It is also called as electrochemical energy conversion device.
• It consists of two electrodes i.e. anode and cathode. All the reactions take place at these two places only.

WHAT IS THAT “FUEL CELL” WHICH IS USED IN RELATIONS TO CARS

• A fuel cell is an electrochemical device that combines hydrogen fuel (stored in cars) and oxygen (from air) to produce electricity, heat and water.
• In short, Fuel cell in relation to car is that device that can provide power to run car instead of use of petrol or diesel.

HOW DOES A FUEL CELL WORK

• There are different types of fuel cells available. Hence, each one has different type of working. But the following points try to generalize the idea of working of a fuel cell.
• A single fuel cell consists of three parts:
• a) Anode (that is a negative electrode that provides electrons)
  b) An electrolyte in the center
  c) Cathode (a positive electrode that accepts electrons.


• The hydrogen is supplied to the fuel cell anode catalyst on the anode help separate the hydrogen atoms into protons, hydrogen ions and electrons.
• The electrolyte in the center allows only the proton to pass through the electrolyte to the cathode side of the fuel cell.
• These electrons from the hydrogen can’t pass through the electrolyte and hence pass through a circuit joined between anode and cathode & hence in turn generate electricity that passes through that circuit.
• As oxygen flows into fuel cell cathode, another catalyst causes oxygen protons and electrons to combine to produce pure water & heat.
• This was the working of a single fuel cell.
• Many single fuel cells can be combined to one which can be termed as fuel stack which ultimately can be used for bigger applications like as in cars.

TYPES OF FUEL CELLS

1. Proton Exchange Membrane Fuel Cells (PEMFC)

• Electrolyte: waterbased, acidic polymer membrane.
• Also called polymer electrolyte membrane fuel cells
• Use a platinum-based catalyst on both electrodes
• Generally hydrogen fuelled
• Operate at relatively low temperatures (below 100 degree Celsius)
• High-temperature variants use a mineral acid-based electrolyte and can operate up to 200 degree Celsius.
• Electrical output can be varied, ideal for vehicles

2. Direct Methanol Fuel Cells (DMFC)

• Electrolyte: Polymer membrane (like PEMFC)
• Use a platinumruthenium catalyst on the anode and a platinum catalyst on the cathode
• This catalyst can draw hydrogen atoms from liquid methanol, which is used as fuel instead of hydrogen, giving the cell its name
• Operate in the range from 60 degree Celsius to 130 degree Celsius.
• DMFC are convenient for portable power applications with outputs generally less than 250 W

3. Phosphoric Acid Fuel Cells (PAFC)

• Electrolyte: liquid phosphoric acid in a bonded silicon carbide matrix
• Use a finely dispersed platinum catalyst on carbon
• Quite resistant to poisoning by carbon monoxide
• Operate at around 180 degree Celsius
• Electrical efficiency is relatively low, but overall efficiency can be over 80% if the heat is used.
• Used in stationary power generators (100 kW to 400 kW)

4. Alkaline Fuel Cells (AFC)

• Electrolyte: alkaline solution such as potassium hydroxide in water
• Commonly use a nickel catalyst
• Generally fuelled with pure hydrogen and oxygen as they are very sensitive to poisoning
• Typical operating temperature are around 70 degree Celsius
• Can offer high electrical efficiencies
• Tend to have relatively large footprints
• Used on NASA shuttles thought the space program

5. Solid Oxide Fuel Cells

• Electrolyte: solid ceramic, such as stabilized zirconium oxide
• A precious metal catalyst is not necessary
• Can run on hydrocarbon fuels such as methane
• Operate at very high temperatures around 800 degree Celsius to 1000 degree Celsius
• Best run continuously due to the high operating temperature
• Popular in stationary power generation

6. Molten Carbonate Fuel cells (MCFC)

• Electrolyte: a molten carbonate salt suspended in a porous ceramic matrix
• A precious metal catalyst is not necessary
• Can run on hydrocarbon fuels such as methane
• Operate at around 650 degree Celsius
• Best run continuously due to the high operating temperature
• Most fuel cell power plants of megawatt capacity use MCFC’s as do large combined heat and power plant

ADVANTAGES OF FUEL CELLS

• Less Greenhouse Gas Emissions Fossil fuels do emit a lot of greenhouse gases. Same is not emitted by the fuel cells.
• Reduced oil dependence It provides a best alternative to the already over-pressurized petroleum products. Can also help to solve India’s problem with it’s Current Account Deficit (CAD).
• Less air pollutants Vehicles emit a significant amount of air pollutants which contribute to make smog (smoke + fog). But if fuel cells are used in such vehicles it doesn’t emit such air pollutants thus providing free & non-polluted air.
• Quiet Operation Fuel cells, due to their nature of operation, are extremely quiet in operation. This allows fuel cells to be used in residential or builtup areas where the noise pollution is undesirable.
• High efficiency conversion Fuel cells convert chemical energy directly into electricity without the combustion process. As a result, a fuel cell is not governed by thermodynamic laws, such as the Carnot efficiency associated with heat engines, currently used for power generation.
• High power density: A high power density allows fuel cells to be relatively compact source of electric power, beneficial in application with space constraints. In a fuel cell system, the fuel cell itself is nearly dwarfed by other components of the system such as the fuel reformer and power inverter

DISADVANTAGES OF FUEL CELLS

• High costs compared to other energy systems technology.
• Operation requires a consistent fuel supply.
• The technology is not yet fully developed and few products are available.
• Some fuel cells use expensive materials.
• Fuel cells are currently very expensive to produce, since most units are hand-made.
• Fuel cells are in general slightly bigger than comparable batteries or engines. However, the size of the units is decreasing.
• The refueling and the starting time of fuel cell vehicles are longer and the driving range is shorter than in a “normal” car.
• Reforming hydrocarbons via reformer to produce hydrogen is technically challenging and not clearly environmentally friendly.

SOME CHALLENGES OF USING FUEL CELLS IN CARS

• Vehicle Cost: The current cars with fuel cell technology are very costly as the companies are trying to compensate for the money invested in the Research and Development. So, such cars for now are way beyond the reach of common man. May be in coming years the prices of such cars will fall.
• Onboard Hydrogen Storage: Hydrogen unlike petrol or diesel is very hard to store in cars. So, very scrutinized and secured mechanism has to be developed so that the storage of Hydrogen in cars can be made possible.
• Getting Hydrogen to customers: There is also a problem of how to deliver hydrogen to customers. It can’t be distributed in the way petrol or diesel is distributed i.e. the current infrastructure needs a major makeover.
• Public Education: Fuel cell technology must be embraced by consumers before its benefits can be realized. As with any new vehicle technology, consumers may have concerns about the dependability and safety of these vehicles when they first hit the market. Plus, they must become familiar with a new kind of fuel. Public education can accelerate this process.

NEW DISCOVERY

• An hydrogen fuel cell (HFC) works by consuming hydrogen that reacts with oxygen from the atmosphere over platinum nanoparticles as catalyst to produce water and electricity; the electricity powers a motor stationed in an external circuit between the anode and the cathode of the cell.
• The platinum is dispersed by high surface-area carbon (HSAC) supports. The HSAC supports have a tendency to corrode during vehicle startup and shutdown because of electric potentials at the anode and cathode.
• Carbon has been the substance of choice because it is cheap, abundant, and has high electronic conductivity.
• A new compound has been synthesized called Titanium Ruthenium Oxide (TRO) to support the platinum nano particles. Titanium oxide formed the rigid, corrosion resistant support structure while a coating of ruthenium oxide allowed electrons to be conducted through the frame.
• Neither titanium- or ruthenium-oxide can be further oxidized, leaving them less harmed by corrosion. — an oxidation reaction — which commonly occurs during start-up and shutdown of the cell.
• Compound was also able to prevent the platinum nanoparticles from oxidising. This happens when platinum gets exposed to potentials of 0.9-1 V—values reached when the HFC transitions between full- and no-load, 0.65-0.95 V.
• Even though titanium and ruthenium are costlier than carbon, an analysis by the IIT team found that more than 90 per cent of the cell’s costs were incurred by the use of platinum as catalyst, irrespective of scale.