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TECHFOCUS Fuel Cells

Power sources of tomorrow

Nah id Akhter
WHAT would it be like if all the world's cars stopped harmful emissions and all our power needs were met by a single battery a fuel cell that would give us tiie power to charge our portables as well as provide all the electricity needs for our homes? This is not a dream, as scientists insist that fuel cells are the power sources of the future.
Efficient and environment-friendly power sources have become the need of the day. With growing concerns over Global Warming and depletion of fossil fuels, it has become a necessity to find a technology that will deliver energy efficiently and cleanly. Experts believe that fuel cells can provide an ideal solution to all these concerns. They convert energy more efficiently than conventional power sources such as the internal combustion engine-some of them more than twice as efficiently. Secondly, fuel cells produce almost no pollution.
They also have engineering advantages. Because there are no moving parts inside a fuel cell, there's none of the noise and vibration associated with spinning turbines and moving pistons. That makes fuel cells quiet, and less prone to wear and tear.
Problems remain, however, primarily with cost, reliability and power density-the amount of power fuel cells produce for their volume or mass. They also have to compete with long-established technologies. Vehicles Dowered by fuel cells could require whole new refueling infrastructures, and all fuel cells will need qualified and trained support staff. Then again, that's what happens when any new technology is introduced.
Although there are many types of fuel cells, they all work in essentially the same way. The basic set-up consists of two electrodes separated by an electrolyte-a substance that conducts electricity. A fuel such as hydrogen, natural gas or methanol enters at one electrode, and an oxidant, usually oxygen from the air, at tire other. These undergo a redox reaction across the electrolyte, releasing energy which pushes electrons round an external circuit. Because the fuel doesn't actually burn, fuel cells don't produce the pollutants associated with combustion, such as carbon monoxide, soot and oxides of nitrogen. Cells that use fossil fuels produce water and carbon dioxide as waste products. Cells that use hydrogen generate only water.
To understand in detail how fuel cells work, it's worth considering one type, the proton exchange membrane cell, which is widely regarded as the most promising for light-duty transportation. Here, hydrogen gas flows through channels to the anode, where a catalyst causes the hydrogen molecules to separate into protons and ‘electrons. The membrane allows only the protons to pass through it While ’'the protons are conducted through . the membrane to the other side of the cell, the stream of negatively-charged electrons follows an external circuit to the cathode. This flow of electrons is electricity that can be used to do work, 'such as power a motor.
On the other side of the cell, oxygen ‘gas, typically drawn from the outside air, flows through channels to the ^cathode. When the electrons return from doing work, they react with oxygen and the hydrogen protons (which have moved through the membrane) at the cathode to form water. .This union is an exothermic reaction, generating heat that can be used outside the fuel cell.
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The power produced by a fuel cell depends on several factors, including the fuel cell type, size, temperature at which it operates, and pressure at which gases are supplied. A single fuel cell produces approximately 1 volt or less barely enough electricity for even the smallest applications. To increase the amount of electricity generated, individual fuel cells are combined in series to form a stack. (The term "fuel cell" is often used to refer to tire entire stack, as well as to the individual cell.) Depending on the application, a fuel cell stack may contain only a few or as many as hundreds of individual cells layered together. This "scalability" makes fuel cells ideal for a wide variety of applications, from laptop computers (50-100 Watts) to homes (l-5kW), vehicles (50-125 kW), and central power generation (1-200 MW or more).
Some of the PEM cell's main features are its ability to start quickly and to run at moderate temperatures, which means that it does not need to heat up very much in order to run. The PEM friel cell is compact and lightweight a big advantage for cars. Furthermore, its maximum efficiency of 60% (energy delivered from hydrogen to motor as electricity) is about 3 times greater than the efficiency of internal combustion engines (most of the energy from combustion is lost in heat and friction before it even pushes
down on the pistons).
Fuel cells themselves are very safe. No combustion or detonation takes place, and the only moving parts are those pumping the fuel and oxidant around, so catastrophic failures such as turbine blades breaking or pistons seizing are impossible. However, the main danger-as with today's enginesis the fuel. Hydrogen is combustible in air at a wide range of concentrations, but the flame radiates almost no heat. In a hydrogen-vehicle fire, almost nothing other than the fuel should ignite. In addition, hydrogen disperses very rapidly, and fires burn out more quickly than petrol fires.
Some companies like Mercedes-Benz, BMW, Mazda, and Ballard Power Systems have already introduced their hydrogen fueled vehicles on the road. Buses powered by PEM fuel cells have been successfully tested in Vancouver and Chicago. Passenger cars in California have being built by Ford, General Motors and DaimlerChrysler in response to California's zero-emission laws.
Fuel cells are also being demonstrated as stationary pow.er sources. A few houses in Japan, Germany and the US use PEM systems to provide electricity and heat. Larger systems are also in operation. A police statiorf in Central Park, New York, relies on a 200-
kilowatt phosphoric acid fuel cell to provide its electricity and heating. The system was built by US company International Fuel Cells and cost about $1 million, but that's less than it would have cost to dig up the park and lay electricity cables.
At the moment, cost-reduction and durability enhancement are the two most significant challenges to fuel cell commercialization. Fuel cell systems must be cost-competitive with, and perform as well or better than, traditional power technologies over the life of the system. Ongoing research is focused on identifying and developing new materials that will reduce the cost and extend the life of fuel cell components. Low cost, high volume manufacturing processes will also help to make fuel cell systems cost competitive with traditional technologies
Legislative bodies around the world seem certain to follow California's lead and introduce laws demanding zeroemission vehicles, and this will probably ensure that fuel cells make it into some parts of the transport market in the near future. Although for Bangladesh and other developing nations, it will require some time for the fuel cell technology to commercialise, it is something worth thinking about, considering the rising demand for fuels and their diminishing supplies.