HYDROGEN FUEL CELL TECHNOLOGY

Transcription

1 HYDROGEN FUEL CELL TECHNOLOGY Vikash, Vipin Yadav, Vipin Badgaiyan Dronacharya College of Engineering, Gurgaon Abstract: - Whereas the 19th century was the century of the steam engine and the 20th century was the century of the internal combustion engine, it is likely that the 21st century will be the century of the fuel cell. Full cells are now on the verge of being introduced commercially, revolutionizing the way we presently produce power. Fuel cells can use hydrogen as a fuel, offering the prospect of supplying the world with clean, sustainable electrical power. The article discusses fuel cells technology and PEM fuel cells. Fuel cell applications in transportation, distributed power generation, residential and portable power are discussed. The science of the PEM fuel cell is mainly discussed in this artical. Index Terms: fuel cell, PEM (proton exchange membrane) INTRODUCTION Fuel cells and fuel cell components produce electricity and heat electrochemically by combining oxygen from the air with a fuel, preferably hydrogen, from methanol, natural gas, or petroleum. Reformers are often used in conjunction with hydrogen fuel cells. There many are types of fuel cells and fuel cell components. Examples include a proton exchange membrane (PEM) fuel cell, direct methanol fuel cell (DFMC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), and solid oxide fuel cell (SOFC). Selecting fuel cells and fuel cell components requires an understanding of hydrogen fuel cell technologies. A proton exchange membrane (PEM) fuel cell or PEM fuel cell uses hydrogen as the anode gas and pure or atmospheric oxygen as the cathode gas. PEM fuel cells use a solid polymer membrane as the electrolyte, which is much easier to handle and use than a liquid counterpart. A direct methanol fuel cell (DMFC) uses methanol in a solution of water as the anode gas and atmospheric oxygen as the anode gas. The electrolyte is made of a solid polymer membrane. A phosphoric acid fuel cell (PAFC) uses a phosphorous electrolyte to provide high reliability, quiet operation, and improved efficiency. Molten carbonate fuel cells (MCFC) use hydrogen or methane as the anode gas and atmospheric oxygen as the cathode. Alkalicarbonates such as carbonate-salt-impregnated ceramic matrix are used as an electrolyte. Solid oxide fuel cells (SOFC) are fuel cells and fuel cell components that use hydrogen or methane as anode gas and atmospheric oxygen as cathode gas and ceramic oxide electrolyte. Selecting fuel cells and fuel cell components requires an analysis of performance specifications and end-user applications. Performance specifications include percent efficiency, working temperature, components and subsystems, and materials of construction. The catalyst, a fuel cell component that activates the chemical reaction between electrodes, is also an important consideration. A PEM fuel cell typically uses a thin platinum catalyst. In terms of applications, some fuel cells and fuel cell components are designed for use with a fuel cell car or fuel cell vehicle. roton exchange membrane fuel cell Diagram of a PEM fuel cell IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 718

2 Proton exchange membrane fuel cells, also known as polymer electrolyte membrane (PEM) fuel cells (PEMFC), are a type of fuel cell being developed for transport applications as well as for stationary fuel cell applications and portable fuel cell applications. Their distinguishing features include lower temperature/pressure ranges (50 to 100 C) and a special polymer electrolyte membrane. PEMFCs operate on a similar principle to their younger sister technology PEM electrolysis. They are a leading candidate to replace the aging alkaline fuel cell technology, which was used in the Space Why Do We Need a New Fuel Source? Currently our machinery runs on oil Oil pollutes and there are limited supplies Hydrogen is the most abundant element in the known universe Hydrogen fuel cells do not pollute How A Hydrogen Fuel Cell Works The fuel cell is composed of an anode, an electrolyte membrane in the center, and a cathode. Hydrogen flows into the fuel cell anode. Platinum coating on the anode helps to separate the gas into hydrogen ions and electrons. The electrolyte membrane allows only the protons to pass through the membrane to the cathode side of the fuel cell. The electrons cannot pass through this membrane and flow through an external circuit in the form of electric current. Reactions A Proton exchange membrane fuel cell transforms the chemical energy liberated during the electrochemical reaction of hydrogen and oxygen to electrical energy, as opposed to the directcombustion of hydrogen and oxygen gases to produce thermal energy. A stream of hydrogen is delivered to the anode side of the membrane electrode assembly (MEA). At the anode side it is catalytically split into protons and electrons. This oxidation half-cell reaction or Hydrogen Oxidation Reaction (HOR) is represented by: At the Anode: The newly formed protons permeate through the polymer electrolyte membrane to the cathode side. The electrons travel along an external load circuit to the cathode side of the MEA, thus creating the current output of the fuel cell. Meanwhile, a stream of oxygen is delivered to the cathode side of the MEA. At the cathode side oxygen molecules react with the protons permeating through the polymer electrolyte membrane and the electrons arriving through the external circuit to form water molecules. This reduction half-cell reaction or oxygen reduction reaction (ORR) is represented by: IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 719

3 At the cathode: Overall reaction: The reversible reaction is expressed in the equation and shows the reincorporation of the hydrogen protons and electrons together with the oxygen molecule and the formation of one water molecule. Polymer -electrolyte membrane discovered, and platinum is the best option. One promising catalyst that uses far less expensive materials iron, nitrogen, and carbon has long been known to promote the necessary reactions, but at rates that are far too slow to be practical. [2] Recently, a Canadian research institute has dramatically increased the performance of this type of iron-based catalyst. Their material produces 99 A/cm 3 at 0.8 volts, a key measurement of catalytic activity. That is 35 times better than the best nonprecious metal catalyst so far, and close to the Department of Energy's goal for fuelcell catalysts: 130 A/cm 3. It also matches the performance of typical platinum catalysts. The only problem at the moment is its durability because after only 100 hours of testing the reaction rate dropped to half. Another significant source of losses is the resistance of the membrane to proton flow, which is minimized by making it as thin as possible, on the order of 50 µm. A cheaper alternative to platinum is Cerium(IV) oxide catalysator used by professor Vladimír Matolín in the developement of PEMFC. To function, the membrane must conduct hydrogen ions (protons) but not electrons as this would in effect "short circuit" the fuel cell. The membrane must also not allow either gas to pass to the other side of the cell, a problem known as gas crossover. Finally, the membrane must be resistant to the reducing environment at the cathode as well as the harsh oxidative environment at the anode. Splitting of the hydrogen molecule is relatively easy by using a platinum catalyst. Unfortunately however, splitting the oxygen molecule is more difficult, and this causes significant electric losses. An appropriate catalyst material for this process has not been The PEMFC is a prime candidate for vehicle and other mobile applications of all sizes down to mobile phones, because of its compactness. However, the water management is crucial to performance: too much water will flood the membrane, too little will dry it; in both cases, power output will drop. Water management is a very difficult subject in PEM systems, primarily because water in the membrane is attracted toward the cathode of the cell through polarization. A wide variety of solutions for managing the water exist including integration of electroosmotic pumps. Furthermore, the platinum catalyst on the membrane is easily poisoned by carbon monoxide (no more than one part per million is usually acceptable) and the membrane is sensitive to things like metal ions, which can be introduced by corrosion of metallic bipolar plates, metallic components in the fuel cell system or from contaminants in the fuel/oxidant. PEM systems that use reformed methanol were proposed, as in Daimler Chrysler Necar 5; reforming methanol, i.e. making it react to obtain hydrogen, is however a very complicated process, that requires also purification from the carbon monoxide the reaction produces. A platinum-ruthenium catalyst is necessary IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 720

4 as some carbon monoxide will unavoidably reach the membrane. The level should not exceed 10 parts per million. Furthermore, the start-up times of such a reformer reactor are of about half an hour. Alternatively, methanol, and some other biofuels can be fed to a PEM fuel cell directly without being reformed, thus making a direct methanol fuel cell (DMFC). These devices operate with limited success. CONCLUSION Its an green technology because its by product is water. And this technology can be easily implemented in cars, buses & trucks. The most commonly used membrane is Nafion by DuPont, which relies on liquid water humidification of the membrane to transport protons. This implies that it is not feasible to use temperatures above 80 to 90 C, since the membrane would dry. Other, more recent membrane types, based on polybenzimidazole (PBI) or phosphoric acid, can reach up to 220 C without using any water management: higher temperature allow for better efficiencies, power densities, ease of cooling (because of larger allowable temperature differences), reduced sensitivity to carbon monoxide poisoning and better controllability (because of absence of water management issues in the membrane); however, these recent types are not as common. APPLICATION & ADVANTAGES Hydrogen Powered Cars Hydrogen cars run clean. 500 cubic tons of carbon removed from atmosphere by 2040 New design possibilities because of compact hydrogen fuel cell stack Stack of 200 cells is the size of a home PC 500 metric tons of carbon saved each year by 2040 Reduce demand for oil by 11 million barrels per day by 2040 Child born in 2003 to drive a hydrogen car at age 16 IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 721

5 IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 722