After the invention of the Digital Versatile Disc [DVD], the true digital sound effect and high clarity video effects were brought to all homes.  But the hunger for high-definition videos and audio along with a high-capacity storage disc led to the invention of the Blu-ray Disc [BD]. They have the same capabilities of a DVD, storing audio, video as well as photos.

TAKE A LOOK : WORKING OF DIGITAL VERSATILE DISC (DVD)

TAKE A LOOK : WORKING OF FLEXPLAY DVD

Blue-ray disc

Blu-ray Disc – Definition

A Blu-ray Disc is a high density optical disc storage medium, which is used for the storage of all high-definition digital formats like audio, video, and play-station games and so on. They have the same physical appearance as a DVD. The name “BLU-RAY” is actually a combination of the colour “blue” and “ray”. Here blue refers to the blue colour of the laser that is used for its reading and ray refers to the optical ray. While trade marking a product, you are not supposed to include a common or everyday used word. Thus the letter ‘e’ from the word “blue” was omitted.

Blu-Ray Disc Specifications

1. BD is present in both single layer and double layer. The single layer Blu-Ray Disc has a capacity of up to 25 GB and double layer has a capacity of 50 GB. Though this is a practical storage capacity meant for the present Blu-Ray players, there are BD’s that have capacities up to 200 GB. These discs, though not marketed yet, can be played in any Blu-Ray player without any additional equipment.
2. Blu-Ray Disc needs a wavelength of 400 nanometer violet-blue laser for its reading at different speeds like 4.5 MBPS, 9 MBPS, 18 MBPS, 27 MBPS, 36 MBPS and 54 MBPS.
3. Blu-Ray disc can run formats that are encoded in MPEG-4 and MPEG-2.
4. BD is used for data storage, playing 1080p HD video and audio, 3-D Stereophonic and so on.

Blu-Ray Technology – History

There have been many questions on who invented the Blu-Ray technology. But this can be explained only by explaining the history of Blu-Ray technology.

Even though the High Definition TV was invented, there was no particular storage format, recorder or player for it. Thus companies like Toshiba started experiments on making a bigger size DVD. Lately, they released their own Blu-Ray player. During this war for HD technology, researches proved that short wavelengths (shorter than that of a DVD Blu-ray Disc) were enough to make discs with higher storage capacities along with optical capabilities. It was at this time that a researcher, Shuji Nakamura invented the violet-blue laser diode which was apt for a Blu-Ray Disc.

This invention was first applied by Sony Company. They were able to create Ultra Density Optical and also DVR Blue along with the help of Pioneer. These were considered to be the first replicas of Blu-Ray Disc. This was later exhibited to the world at February 2002 and an association was formed. It consisted of nine members, who were considered to be the inventors of Blu-Ray disc. The association was called the Blu-ray Disc Association. This association has now expanded with more than 5000 members all over the world. This association consists of many makers of electronic goods, computer hardware’s and also motion pictures.

Blu-Ray Disc (BD) vs DVD

• Both of them have the same physical appearence. [Thickness = 1.2 mm]
• The single layer Blu-ray disc can store up to 27 GB data. A singe layer DVD can hold only 4.7 Gb of data. Thus a BD can hold almost 13 hours of normal video and 2 hours of high-definition video. A double layer BD gas a storage capacity of 50 GB which can play almost 20 hours of normal video and 5 hours of HD.
• A DVD needs two substrates and they should be bonded. But a Blu-ray disc requires only one substrate.
• The production cost of Blu-ray is lesser than that of a DVD because there is no need for bonding of substrates. Thus the production materials are lessened. This causes a lesser production time than that for a DVD.
• The Blu-Ray disc uses violet-blu laser with improved lens specifications, while a DVD uses red laser. This causes the focus to increase, thus helping in the recording of both small and high density pits on the BD.
• The wavelength used for BD is 400 nanometers. DVD has a wavelength of 650 nanometers. This decrease in wavelenth helps in high density medium storage.
• The layer in a blu-Ray disc is very close to the laser lens on its player. Thus the precision of the data displayed will be higher with less distortion than a DVD.

Take a look at the comparison between DVD and BD from the figures below.

Types of Blu-Ray Disc

Similar to a DVD, BD also has different versions according to its application. The common types are

1. Read only memory Blu-Ray disc [BD-Rom] – This type of BD can only be read but cannot be written over. The content will be pre-recorded.
2. Recordable Blu-Ray disc [BD-R] – This BD is mainly used for storage of PC data.
3. Re-writable Blu-Ray disc [BD-RW] – This BD is mainly used for storage of PC data. The contents in this disc can be written over and over.
4. Re-writable Blu-Ray disc [BD-RE] – This BD is mainly used for recording of data to be used in HDTV. This disc can also be written over again and again.

Construction and Working of Blu-Ray Disc

Like a DVD, the BD also has pits and bumps. The only difference is that the pits and bumps are smaller and very closely packed. Blu-ray disc also has spiral tracks running from the centre to the edges of the disc. The information is stored in these tracks in the form of audio and video. These audio and video are introduced into the DVD after encoding it.

As told earlier a blue laser is used to focus on the DVD. The laser has a small wavelength of precisely 405 nanometers and must be highly accurate because the pits and bumps are smaller and packed closely. The information stored in the Blu-Ray disc is usually very small in size. They are only 0.15 x 10-6 meters long. Since all these are very small in size, a single-layer itself is more than enough to hold more than 25 GB of data. Thus if a double layer is used, they can easily hold information up to 5o GB.

The Blu-Ray disc does not have these issues because the data is stored on top of a poly-carbonate layer which is about 1 millimeter thick. This stops the problem of birefringence and causes no distortion to the reading of data. This also has an advantage in regard to the closeness of the data to the objective lens. Due to this closeness to the surface, the BD has a outside hard cover to prevent scratching and finger prints.

Because the data is closer to the surface, a hard coating is placed on the outside of the disc to protect it from scratches and fingerprints. The simple design helps in manufacturing these discs at a cheaper rate than a DVD. There is no need of moulding like a DVD.

Advantages of Blu-Ray Technology

• The sleek design helps in skipping from any part of the disc to the other
• Multiple programs like using the same disc for watching a video as well as recording on it  can be done at the same time.
• Watch HD in its maximum quality with very little loss.
• You can make your own playlists.
• The programs present on the disc can be re-ordered in any way you like.
• Use of subtitles is possible for movies.

To know more about Flexplay DVDs, you must also know the working of a normal DVD. Click at the link below to know more.

TAKE A LOOK : WORKING OF DIGITAL VERSATILE DISC (DVD)

What is Flexplay DVD?

In most foreign countries, people rent a lot of DVD’s from the shop. All you have to do is watch the movie and return the DVD back within the agreed time. But, if we are pretty much unorganized, we tend to forget about the DVD. This is where the DVD rental shop makes money. They take late fees and this money sums up to a large amount equal enough to buying a DVD. This disadvantage can be overcome by using a Flexplay DVD.

The Flexplay DVD, introduced by a company called Flexplay Technologies is a special type of DVD that can be rented and need not be returned back. The rental prices will be the same as that of a normal DVD. But this does not mean that you can keep watching the movie all your life. The Flexplay DVD has a fixed life, after which the DVD destroys itself. That is, there is an in-built stopwatch which starts automatically when you start playing the disc. The stopwatch is chemical in nature and is designed to destroy the DVD after a fixed time.

Advantages of Flexplay DVD

1. You are actually buying the Flexplay DVD for the same price as the rental DVD.
2. You need not return the DVD. So there is no tension on extra charges.
3. As there is no risk involved in selling it like a rental DVD, Flexplay DVD’s can be sold in any store.

How Flexplay DVD Works?

The working of a Flexplay DVD is very much the same as that of a Digital Versatile Disc [DVD], except for an additional component. Just like a DVD, the sound and video are digitally encoded into the Flexplay DVD. This information will be stored in the disc in the bumps and trenches in the DVD and thus form a long track of information. Like the normal DVD, Flexplay DVD will also have the tracks spiral in nature. These tracks will then be covered with the help of protective layers like poly-carbonate plastic and then a gold layer n top of it.

Like a normal DVD, this DVD also has two tracks with the same information holding capacity. They will also have two reflective layers out of which one is inside and the other is outside. The outside reflective layer will be semi-transparent. These two layers are stuck together with the help of resin adhesive, thus making a two-layer single disc.

DVD vs Flexplay DVD

The only difference between them is in an additional layer inside the disc. This layer is situated on the front side of the inside reflective layer. This layer is made up of a special transparent chemical compound that reacts with the external atmospheric oxygen to form another chemical compound.

The resultant chemical compound obtained is opaque in nature. When the laser beam of a DVD player passes through the different layers, the layers that are reflective causes it to read the DVD. But after the reaction, the opaque nature stops the DVD player from reading the disc. Thus the DVD shows the sign “No Disc”. The special layer cannot be easily setup inside the disc. For this, the manufacturers made a special adhesive that bonds the two separate layers with this layer.

In the beginning, when you purchase the Flexplay DVD, it is sold as an air-tight package. Thus, the DVD will not have any contact with the atmospheric oxygen. As soon as you open the package, the oxygen starts a slow reaction with the chemical. Though the reaction starts slowly, it later reacts quickly when it nears the expiry period. When the expiry period is near the special layer becomes opaque. This change can be understood easily by just looking at the disc. When the disc is take n out of the package it will have a red colour. After the complete reaction, the colour changes to black.

The expiry period of the disc is decided by the manufacturer and the chemical compound can be balanced accordingly.

Usually, there will be small chemical reactions even if the disc is kept in an air-tight package. But still the disc will be working properly for as long as one year, before it is opened. The special adhesive used in the bonding process helps in keeping the disc usable for a maximum of 48 hours without being damaged.

Though this technology has not yet been marketed, it will surely be a replacement for the rental DVD stores in future.

Disadvantages

Though the Flexplay discs can be economical to us, it  will not be so economical to the manufacturers. When each DVD is disposed off after watching, you will have to make many more copies for others as well. Though this may sound like profit, the selling of these DVD’s for cheap rental cash makes it a loss.

Recycling Options

The use and dispose of a large number of Flexplay DVD’s can cause serious environmental pollution. But the company has made tie-ups with many environmental organizations like Greendisk and Geo-tech polymers so that they can fully recycle the waste and thus maintain the environmental standards. All the wasted discs will be collected and the poly-carbonate plastic present in it will be recycled and later used for high-end applications. The company also claims that the pollution caused by the discs are not so harmful compared to the energy emitted due to the use of a vehicle to return the DVD back to the rental store.

Working of DVD

What is a DVD?

A Digital Versatile Disc/Digital Video Disc [DVD], is an optical disc storage medium like a compact disc [CD], but with greater data storage and high quality audio and video formats. The clarity, when comparison with a CD is almost six times higher.

A DVD can be termed in different ways according to their applications.

• If they are used for storing data that can only be used to read and cannot be written, it is called a DVD-ROM, where ‘ROM’ stands for ‘Read Only Memory’.
• If a DVD is used to record data [audio, video or a combination of both] and then work as a DVD-ROM, it is termed as DVD-R, where ‘R’ stands for ‘recordable’. In a DVD-R, the data is can be inputted only once.
• If a DVD can be read and again be written over it, it will be called a DVD-RW, where ‘RW’ stands for’re-writable’. The data in a DVD-RW can be erased and re-written and also can be written on the remaining space in a DVD.

Specifications of DVD

• DVD has a total capacity of 4.7 GB.
• It can run a high-quality video for a maximum of 133 minutes.
• DVD has a video compression ratio of 40:1 with an MPEG-2 compression.
• DVD can use subtitles in almost 32 languages with a soundtrack in 8 languages.
• Wavelength of a DVD is almost 650 nanometres laser diode light.
• DVD’s can be written at a speed of almost 18x to 20x. [1x = 1318 Kbps].

Advantages of DVD

• The picture quality is far better than a CD.
• Most DVD’s have Dolby Digital or DTS. Thus the clarity of the sound will be nearly equal to that in a theatre.
• Though the technology of CD is gone, they were made with a compatibility with audio CD’s.
• The DVD has a special on-screen index quality which helps you to take a closer look at important scenes of a movie which was earlier indexed by the publisher of the movie. This method is not common.
• Unlike a CD player, the DVD player is specialised in taking you to the correct part which you prefer to see. Thus, there will be no need of fast-forwarding.
• The format of a DVD can be changed according to the type of view you need. It can be a standard TV size format and also a wide-screen TV format.

Structure of a DVD

The manufacturing methods and materials used for manufacture as the same as that of a CD. The DVD has a number of layers of plastic pieces with a total thickness of 1.2 millimetres. Clear poly-carbonate plastic is basically used for making these layers. Apart from the original plastic, there will be some impressions of microscopic bumps on the layers. Naturally, with the formation of bumps, there will also be pits. Thus a long spiral of data can be created which is together called a track. The track in any DVD is only 740 nanometers thick. There are several tracks in a DVD. Thus the bumps will be smaller than the track with a width of 320 nanometers, a length of 400 nanometers a height of and 120 nanometers. Although the bumps are often mistaken for pits, it should be noted that they only appear as pits when seen from the aluminium side.  They are actually bumps when read from the laser side.

DVD-Pits

At the inner layers of the plastic, the bumps and pits are covered with the help of a reflective aluminium layer. But their outer layers are protected with the help of a very thin layer of semi-reflective gold. Thus the lasers that hit the DVD are made to completely focus on the outer and also into the inner layers. On top of all these layers a coating of lacquer is also put. The lacquer is strongly bonded with the help of infrared light.

There are DVD discs which are single-sided as well as double-sided. For the former, the outer label is silk-screened onto the side that is not readable. For the latter there are no labels except at the area which is not readable near the middle hole.

In the case of DVD’s that are writable, each track in the DVD is spiral and has data stored in it. These tracks also have a unique direction. For single-sided discs, the circling will be from the inside to the outside. Take a look at the diagrams illustrated below.

DVD structure

Thus, it is clear why DVD’s are capable of storing more data than a CD. The high density of tracks and smaller size of the pits and bumps is the main reason. In a CD, a lot of valuable space is simply wasted in codes, so as to avoid errors in the information. These codes are actually a repetition of the information that is already present in the disc. This shows that the method is not only efficient, but a wastage of storage space as well. But DVD’s does not need such error correction codes.

DVD Video Format

It must be noted that a movie video can never be stored in a DVD without being compressed. The movies are usually compresses with the help of MPEG-2 format, which is accepted internationally. Though the coding is done to compress the video, it also has to be decoded, which is actually done by the DVD.

Decrease in Data size using MPEG-2 Format

When a movie is being filmed, they use either a PAL format or a NTSC format. These formats are distinguished according to the number of frame rates that are displayed on a movie screen for a particular second. For NTSC format the frame rate is 30 and for NTSC the frame rate is 50. Thus, it is clear that there will be a difference in the resolution as well. Thus the MPEG-2 format must be compatible to both the above said formats.

While using an MPEG format, each frame is carefully studied by the compressing file and a possible solution of encoding is finally decided. There are mainly three ways of encoding a file.

1. One method is called the intra-frame format. This format contains all the image data for that particular frame. This type of coding provides lesser compression than the other two.
2. The second method is the predicted frame format. The most recently displayed frame [either intra-frame or predicted frame] will be shown to the DVD player and will be told to predict the frame based on it.
3. The third method is called bi-directional frame, in which a method of interpolation is carried out in such a way that the exact position and colour of each pixel is given from the nearest frames. For this frame the help of the other two frames are needed.

DVD Audio Format

The audio and video formats in a DVD are completely different. Audio DVD discs are not much in sale because, to play such a disc you will need a 192 kHz/24-bit digital-to-analog converter (DAC) compatible DVD player. This is rarely sold. Our usual DVD players have only a 96 kHz/24-bit DAC.

Though an audio DVD is not as perfect as the original sound, it is far better than the sound from an audio CD. Whether it is a DVD or an audio CD, each bit is represented by a digital response from the DAC according to the voltage level it needs to output. As the sound is sampled at different frequencies, it is sure to lose small pieces of data and hence the difference.

To get the best sound from an audio DVD, you will have to use a 5.1 home theatre along with a Dolby digital decider implanted receiver.

To know the detailed working of fuel processors, you must first know more about fuel cells. To know about fuel cells click o the link below.

TAKE A LOOK : WORKING OF FUEL CELLS

In the blog post on fuel cells I have explained the way hydrogen and oxygen react to produce electricity with water as a by-product. There also some disadvantages with this method. The problems include the improper storing and distribution of hydrogen.

What is a fuel processor?

When comparing a hydrogen fuel cell to that of a gasoline fuel, the density of hydrogen is lesser. Meaning, it has a very less energy/unit volume compared to gasoline. This makes it practically impossible to store enough hydrogen and process it and hence make it drive a car to a maximum distance. Though this problem can be solved by using liquid hydrogen, which has a density more than normal hydrogen it has problems regarding its storing temperature. The storing temperature of liquid hydrogen is extremely low and also needs a high pressure. This problem makes the cost of production higher and also a difficulty in the mode of transportation.

Another important note about hydrogen is that its molecular structure is present in all natural gases like methanol, ethanol, and gasoline and so on. If these molecular structures could be easily removed from these natural fuels and thus used for making a fuel cell, all the above said problems could be solved.

Thus, a fuel processor, commonly known as a steam reformer is used to produce hydrogen from natural fuels. This is carried out by a device called reformer. This device is used to react the natural fuel along with steam at very high temperatures.

Need for Fuel Processors

We speak about using fuel cells because they do not create pollution in any way. They are also highly efficient. So, if the hydrogen is readily available for the fuel cells, it will turn out to be one of the biggest innovations of this century. So, the fuel processor is needed to provide pure hydrogen to make it practically applicable in fuel cells. By making the fuel processor possible, the transportation and storage will also become easier.

For this, the fuel processors should be highly efficient. Otherwise there will be no profit in replacing gasoline fuel with fuel cells.

Other than hydrogen experiments with methanol is also been carried out. Since methanol can be stored as a liquid fuel, it is easy to store in cars. It clearly replaces large tanks that are used for carrying gasoline.

The natural fuel called propane is also applicable for use in homes.  Nowadays many houses have direct pipelines coming from propane tanks.

Working of a Fuel Processor / Steam Reformer

Steam reformers are mainly of two types. They are

1. Methanol Reformer

In a methanol reformer, methanol [CH3OH] is mixed with water at a very high temperature such that they vaporize. This vaporized mixture is later sent to a high temperature chamber and mixed with a catalyst. This process is carried out so as to extract as much hydrogen as possible and at the same time reduce the emission of pollutants like carbon monoxide [CO] as much as possible.

Both the hydrogen and carbon monoxide are produced in the heated chamber. Out of this the carbon monoxide is reacts with oxygen to form carbon-dioxide. Oxygen is formed by splitting water vapour into hydrogen and oxygen.

The chemical equation of the entire reaction is shown below.

CH₃OH – CO + 2H₂

H₂O + CO – CO₂ + H₂

Methanol – CH3OH

Hydrogen – H₂

Carbon Monoxide – CO

Water – H₂O

2. Methane Reformer

Natural gases contain molecules of methane. This methane is extracted and then a similar process like a methane reformer is carried out. The methane present in the natural gas is extracted and then reacted with water vapour to get carbon monoxide and hydrogen. Then the carbon monoxide is converted to carbon dioxide like the methanol reformer. The reactions taking place in the process is shown below.

CH₄ + H₂O – CO + 3H₂

H₂O + CO – CO₂ + H₂

Methane – CH₄

Water – H₂O

Carbon Monoxide – CO

Hydrogen – H₂

Combination of fuel cells and fuel processors

As the fuel cells have to provide the electricity constantly, the fuel processors have to work in parallel with it.

Suppose you want to drive a car that is powered with fuel cells. When the accelerator is pressed, the controller of the motor supplies current to the electric motor. This helps the electric motor in generating more torque. For the controller to supply power, the fuel call has to work in order to make electricity. When the amount of hydrogen becomes less, the fuel processor starts its mechanism and extracts the hydrogen from methanol. Though such a system has never been adapted properly, we can expect this to happen soon.

Drawbacks of Fuel Processors

Though the amount of carbon dioxide is not emitted as much as other technologies, it is still considered a threat to global warming. As fuel processors are used to provide the hydrogen, the emission of CO₂ is sure. If the pure hydrogen could be used this disadvantage would not have happened.

Though the efficiency of the fuel processor is less, the overall efficiency when connected to a fuel cell is very less. Most of the energy is wasted in the form of heat and high pressure.

What is a Fuel Cell?

Fuel Cell is an electrochemical device that is used to convert an open source fuel into electricity. An electrolytic process has to take place inside a cell in which there is an open source fuel [hydrogen] and an oxidant [oxygen]. Both the fuel and oxidant reacts in the presence of an electrolyte. Both the fuel and oxidant are introduced into the cell, where they react and the output product is carried out of the cell and stored. The electrolyte is left as it is inside the cell. This process can take place non-stop for a long time as long as the flow of resources are maintained.

The result obtained by combining hydrogen and oxygen is water. As a result of this process, electricity is formed. Although batteries are also electrochemical devices, they are different from a fuel cell. They use reactants from an external source and the chemicals have to be stored inside the battery. These chemicals react to each other to produce the electricity. Thus they use closed source fuel. As the device stores the required energy in a chemical form, the battery has to be recharged at intervals or have to be replaced.

Other than hydrogen the other types of fuels commonly used are hydrocarbons and even alcohol. The most commonly used oxidants are oxygen, chlorine and also chlorine dioxide.

Need of Fuel Cells

The main reason for the use of fuel cell is the increasing dependency on the use of fossil fuels. The whole world has burnt so much fossil fuel like oil to such an extent that they have become one of the main reasons for the pollution. This pollution has eventually resulted in the global warming and extreme climate change. Other than the environmental problems, the use of oil has become large enough that the sources of production have become less. As a result more challenging expeditions will have to be made for oil deposits which results in a very high oil price.

Fuel cells are surely an alternative to the above said problems. They are a clear solution to the dependency of fossil fuels. The best feature of fuel cells is that they produce pure water as the by-product. As a result they are pollution free as well.

As a part of making hydrogen fuel cell dependent vehicles possible in the most efficient and cheapest way, American president George Bush announced the Hydrogen Fuel Initiative program (HFI) in the year 2003. The country has also spent nearly one billion dollars for the research of better fuel cells. The technology will surely become practical soon and thus bring a solution to the rising oil problems.

Basic design and Working of a Fuel Cell

For any type of fuel cell, there are mainly three segments.

1. Anode
2. Cathode
3. Electrolyte

The type of electrolyte used is what defines the type of fuel cell used. Whatever may be the type of fuel cell, their basic operation is always the same.

With the combination of the three segments, two main chemical reactions take place. A catalyst will be present at the anode. This anode catalyst, mostly platinum powder, is used to oxidise the hydrogen fuel. Thus the hydrogen gas turns into ions and electrons. Out of these, the ions make way through the electrolyte to the cathode. As soon as they reach the cathode, they combine with the cathode and then react with the oxidant to produce water.  The electrons pass through a wire producing the electricity. Nickel is mostly used as the cathode catalyst. Thus the electricity is formed at the load and water is obtained as the by-product.

Though a fuel cell can normally produce only up to 0.7 volts at full load, the desired amount of voltage can be obtained by combining the fuel cells in series. For obtaining the desired amount of current, the fuel cells can be connected in parallel.

The fuel cell also has certain losses which causes a lesser amount of voltage to be produced at a higher current rate. Some of the losses are ohmic loss. Activation loss and also the loss due to the mass depletion of reactants called mass transport loss.

Different Types of Fuel Cells

The type of fuel cell differs mainly according to their operating temperature and the different electrolytes used. Some of the most common are given below.

Polymer Electrolyte Membrane Fuel Cell (PEMFC)

Polymer Electrolyte Membrane Fuel Cell (PEMFC) uses electro-chemical reaction to react both hydrogen and oxygen to form water as a by-product and also electricity. The device is said to be completely pollution free and with an efficiency of more than 50%. As the name suggests, in between the anode and cathode terminals is a sandwiched membrane called the proton-exchange polymer membrane. This will act as the electrolyte. This membrane can conduct only positive charged ions and stops electrons from passing through. To use this electrolyte in this device, the membrane should be in the hydrated form so as to be in the stable form.

The anode, a cathode and the membrane are together called as the Membrane Electrode Assembly [MEA]. The earlier mentioned catalysts are used here as well. But the anode catalyst will be assembled in a carbon fibre substrate.

In the anode, the hydrogen gas reacts with the anode catalyst causing it to split into protons and electrons. The protons are then carried to the oxidant region where they react together form multi-facilitated proton membranes. The electrons travel through another wire and react with the oxygen as well as protons and thus water is produced. When the electron travels through the external circuit, electricity is also produced. Take a look at the diagram given below.

As usual the voltage produced will be very low [0.5 volts to 1 volt]. The wanted voltage can be obtained by adding fuel cells in series. This device is mostly efficient at low temperatures from 50 to 70 degree Celsius and also a high power density.

Alkaline fuel cell (AFC)

This type of fuel cell was been introduced since the early 1960’s. As the electrolyte used for this device is aqueous alkaline solution like potassium hydroxide, the procedure for electricity consumption is rather expensive.

Direct Methanol Fuel Cell (DMFC)

This device has somewhat the same characteristics as that of a Polymer Electrolyte Membrane Fuel Cell (PEMFC). But the only difference is in the percentage of efficiency. It has lesser efficiency [<30%] and also needs a huge amount of anode catalyst and thus highly expensive. The device uses Polymer membrane, mostly ionomer as the electrolyte.

Molten-Carbonate Fuel Cell (MCFC)

Molten alkaline carbonate like sodium bicarbonate is used as the electrolyte. They can produce high powers up to 100 Mega Watts. Thus they can be used as high power generators. They can also be operated at high temperatures up to 650 degree Celsius. They are not so expensive in production and hence can be used for commercial uses.  It has an efficiency of almost 55%.

Phosphoric Acid Fuel Cell

Molten phosphoric acid is the electrolyte used in this type of fuel cell. It operates at high temperature up to 200 degree Celsius. It has an efficiency of up to 55%. This type of fuel cell is most commonly used in commercial cars.

Solid oxide Fuel Cell (SOFC)

This is one of the most commercially used fuel cell as they have the highest operating life. It has a very high operating temperature of 1,000 degrees Celsius. But other parts of the fuel cell may not be able to withstand at this temperature making it highly unstable. But, when used in a continuous state they can be highly reliable. At high temperatures the device can produce water in the form of steam which can be easily transported through steam turbines to produce more electricity, thus increasing the efficiency of the system. This device is also special in the case where a wide variety of fuels can be used. Most of the petroleum products can be used as the fuel. The electrolyte used in the cell is called yttria stabilized zirconia (YSZ). This electrolyte is good for large scale power generation and has the same characteristics as all the other electrolytes.

As the device has a very high operating temperature, there are some disadvantages as well. There may be unwanted number of reactions taking place inside the cell due t the high temperature. As a result of these reactions carbon dust and also graphite may be built up on the anode making it insufficient from reacting with the catalyst.

Fuel Cells – Advantages

• It is compact, light weight and has no moving parts. Thus it is 99.9% reliable.
• Pollution is reduced by 99%. This is the lowest pollution rate when compared to batteries as well as gasoline powered devices.
• If the device is used to power cars, it means that the efficiency level of all the three components will be different. Though the basic components of the car like tyre, transmission and so on are the same the efficiency is define on the power produced and the power converted to mechanical power. In the beginning almost 80% efficiency is produced by converting hydrogen into electricity. When this electricity is converted to mechanical energy to run the device, motor/motors and also an inverter will be needed. This will also have a efficiency of 80%. Thus the overall efficiency will be almost 65%, which is a high efficiency when compared to battery and gasoline. The overall efficiency of a battery is considered to be 60% and that of a gasoline powered vehicle is 40%.

Fuel Cells –Disadvantages

1. Cost

The overall production cost of a fuel cell is very costly. The anode catalysts like platinum and also gas diffusion layers almost hold up to 75% of the total cost. When compared to batteries and gasoline powered vehicles, they tend to be the costliest. If a kilowatt of power produced by the fuel cell comes around $35 to $40, it can be used. Currently, it costs up to $75. This can be done only by extensive research in replacing platinum with some other cheaper substance.

2. Durability

Most of the fuel cells that are used in cars, like PEMFC does not operate well enough in higher temperatures. As a result they have less tolerance level and less stability under running conditions.

3. Bad infrastructure

In order to make vehicles with fuel cells enough amount of hydrogen has to be generated. After generation process, they must also be carefully transported from the generating plants. This can be done only by transportation or pipelines. For this a proper infrastructure has not yet been developed.

Fuel Cells – Applications

• Can be used as power sources in remote areas.
• Can be used to provide off-grid power supplies.
• Can be applicable in both hybrid and electric vehicles.