The simple statement that water is made from hydrogen and oxygen doesn’t give us a very clear picture of what really goes into the creation of a molecule of water.
A quick look at the chemical equation for the formation of water tells us more. 2H2 + O2 = 2H2OIt takes two molecules of the diatomic hydrogen gas, combined with one molecule of the diatomic oxygen gas to produce two molecules of water.In other words the ratio of hydrogen to oxygen is 2:1, the ratio of hydrogen to water is 1:1, and the ratio of oxygen to water is 1:2. There’s something more though that doesn’t show up in the equation. Energy. The formation of water from its elements produces, in addition to water, a tremendous amount of energy, 572 kJ to be exact. 2H2 + O2 = 2H2O + EnergyThis is an example of an exothermic reaction, a reaction that produces energy.
It is also an example of what is called a combustion reaction, where a substance (in this case hydrogen gas) is combined with oxygen.You are probably familiar with this reaction through two tragic examples of the unleashed energy of the combustion reaction of hydrogen, the Hindenburg, and the space shuttle Challenger. Hydrogen Fuel? Yes – hydrogen is a good, clean fuel, producing only water as a by-product. Unfortunately it produces so much energy that it can get out of control, resulting in an explosion. But let’s forget about that explosive part for a minute and think about the possibilities – Hydrogen as a New Clean Fuel – it could be the end of the energy crisis – but where would we get the hydrogen?Can we create Hydrogen from Water? Oh Yes! It’s the same chemical reaction, but run in reverse: 2H2O + ENERGY = 2H2 + O2 Notice now that the requirement is for energy to be ADDED TO the reactants. This is an example of an Endothermic reaction.
This means that we could use Water as a Fuel! IF (and this is a big if) we could find an easy way to convert the water to hydrogen and oxygen, then the hydrogen could be used as a clean fuel. One way to convert Water to Hydrogen and Oxygen is through the process of Electrolysis – using electricity as the source of energy to drive the reaction.Let’s take a look at what that might look like: Isn’t this rather circular? Using Energy to break water to form hydrogen to combine oxygen to form Energy – in this way is rather circular. In fact, because of the laws of thermodynamics, you can’t break even in this exchange of energy. However, there exist better ways to disassemble water – namely using CATALYSIS. What does a catalyst do? A catalyst is a chemical compound that acts to speed up a reaction, but in the process is not itself changed.
Therefore the catalyst, at the end of the reaction, is free to act again to assist another reactant through the reaction.Catalysts work by lowering the energy barrier between the reactants and the products. In this case: 2H2O + ENERGY = 2H2 + O2 where it normally takes a tremendous amount of energy to convert reactants to products – the addition of a catalyst can decrease the amount of energy required and therefore speed the reaction up! 2H2O + CATALYST+ energy = 2H2 + O2 + CATALYST Does this catalyst really exist? Have you ever wondered how a plant uses water and carbon dioxide to create glucose and oxygen? This too is an endothermic reaction, an energy producing reaction run in reverse.Normally we would think of using glucose as a fuel, through oxidation we could produce carbon dioxide, water and energy – In fact this is what OUR bodies do to provide us with the energy we need for maintaining all of our bodily functions including THINKING! The kind of fuel cell shown here is routinely used in the space program. If this technology ever becomes viably available to the common person, the estimated cost of a fuel-cell hydrogen powered car would be less than half that of your current gas-mobile.
In addition, it would be simpler, require less maintenance, and be environmentally friendly! | | Fuel cell A fuel cell is an electrochemical cell that converts a source fuel into an electric current. It generates electricity inside a cell through reactions between a fuel and an oxidant, triggered in the presence of an electrolyte. The reactants flow into the cell, and the reaction products flow out of it, while the electrolyte remains within it. Fuel cells can operate continuously as long as the necessary reactant and oxidant flows are maintained.Fuel cells are different from conventional electrochemical cell batteries in that they consume reactant from an external source, which must be replenished – a thermodynamically open system. By contrast, batteries store electrical energy chemically and hence represent a thermodynamically closed system. Many combinations of fuels and oxidants are possible.
A hydrogen fuel cell uses hydrogen as its fuel and oxygen (usually from air) as its oxidant. Other fuels include hydrocarbons and alcohols. Other oxidants include chlorine and chlorine dioxide.
2] Design Fuel cells come in many varieties; however, they all work in the same general manner. They are made up of three segments which are sandwiched together: the anode, the electrolyte, and the cathode. Two chemical reactions occur at the interfaces of the three different segments.
The net result of the two reactions is that fuel is consumed, water or carbon dioxide is created, and an electric current is created, which can be used to power electrical devices, normally referred to as the load.At the anode a catalyst oxidizes the fuel, usually hydrogen, turning the fuel into a positively charged ion and a negatively charged electron. The electrolyte is a substance specifically designed so ions can pass through it, but the electrons cannot. The freed electrons travel through a wire creating the electric current. The ions travel through the electrolyte to the cathode. Once reaching the cathode, the ions are reunited with the electrons and the two react with a third chemical, usually oxygen, to create water or carbon dioxide.The most important design features in a fuel cell are: * The electrolyte substance. The electrolyte substance usually defines the type of fuel cell.
* The fuel that is used. The most common fuel is hydrogen. * The anode catalyst, which breaks down the fuel into electrons and ions. The anode catalyst is usually made up of very fine platinum powder.
* The cathode catalyst, which turns the ions into the waste chemicals like water or carbon dioxide. The cathode catalyst is often made up of nickel. A typical fuel cell produces a voltage from 0. 6 V to 0. 7 V at full rated load.Voltage decreases as current increases, due to several factors: * Activation loss * Ohmic loss (voltage drop due to resistance of the cell components and interconnects) * Mass transport loss (depletion of reactants at catalyst sites under high loads, causing rapid loss of voltage).  To deliver the desired amount of energy, the fuel cells can be combined in series and parallel circuits, where series yields higher voltage, and parallel allows a higher current to be supplied. Such a design is called a fuel cell stack.
The cell surface area can be increased, to allow stronger current from each cell.Proton exchange fuel cells In the archetypal hydrogen–oxygen proton exchange membrane fuel cell (PEMFC) design, a proton-conducting polymer membrane, (the electrolyte), separates the anode and cathode sides. This was called a “solid polymer electrolyte fuel cell” (SPEFC) in the early 1970s, before the proton exchange mechanism was well-understood. (Notice that “polymer electrolyte membrane” and “proton exchange mechanism” result in the same acronym. ) On the anode side, hydrogen diffuses to the anode catalyst where it later dissociates into protons and electrons.These protons often react with oxidants causing them to become what is commonly referred to as multi-facilitated proton membranes. The protons are conducted through the membrane to the cathode, but the electrons are forced to travel in an external circuit (supplying power) because the membrane is electrically insulating. On the cathode catalyst, oxygen molecules react with the electrons (which have traveled through the external circuit) and protons to form water — in this example, the only waste product, either liquid or vapor.
In addition to this pure hydrogen type, there are hydrocarbon fuels for fuel cells, including diesel, methanol (see: direct-methanol fuel cells and indirect methanol fuel cells) and chemical hydrides. The waste products with these types of fuel are carbon dioxide and water. Construction of a high temperature PEMFC: Bipolar plate as electrode with in-milled gas channel structure, fabricated from conductive plastics (enhanced with carbon nanotubes for more conductivity); Porous carbon papers; reactive layer, usually on the polymer membrane applied; polymer membrane.The materials used in fuel cells differ by type.
In a typical membrane electrode assembly (MEA), the electrode–bipolar plates are usually made of metal, nickel or carbon nanotubes, and are coated with a catalyst (like platinum, nano iron powders or palladium) for higher efficiency. Carbon paper separates them from the electrolyte. The electrolyte could be ceramic or a membrane. Proton exchange membrane fuel cell design issues * Costs.
In 2002, typical fuel cell systems cost US$1000 per kilowatt of electric power output.In 2009, the Department of Energy reported that 80-kW automotive fuel cell system costs in volume production (projected to 500,000 units per year) are $61 per kilowatt.  The goal is $35 per kilowatt. In 2008 UTC Power has 400 kW stationary fuel cells for $1,000,000 per 400 kW installed costs. The goal is to reduce the cost in order to compete with current market technologies including gasoline internal combustion engines.
Many companies are working on techniques to reduce cost in a variety of ways including reducing the amount of platinum needed in each individual cell.Ballard Power Systems have experiments with a catalyst enhanced with carbon silk which allows a 30% reduction (1 mg/cm? to 0. 7 mg/cm? ) in platinum usage without reduction in performance.
 Monash University, Melbourne uses PEDOT as a cathode.  * The production costs of the PEM (proton exchange membrane). The Nafion membrane currently costs $566/m?. In 2005 Ballard Power Systems announced that its fuel cells will use Solupor, a porous polyethylene film patented by DSM.  * Water and air management (in PEMFCs).In this type of fuel cell, the membrane must be hydrated, requiring water to be evaporated at precisely the same rate that it is produced.
If water is evaporated too quickly, the membrane dries, resistance across it increases, and eventually it will crack, creating a gas “short circuit” where hydrogen and oxygen combine directly, generating heat that will damage the fuel cell. If the water is evaporated too slowly, the electrodes will flood, preventing the reactants from reaching the catalyst and stopping the reaction.Methods to manage water in cells are being developed like electroosmotic pumps focusing on flow control. Just as in a combustion engine, a steady ratio between the reactant and oxygen is necessary to keep the fuel cell operating efficiently. * Temperature management. The same temperature must be maintained throughout the cell in order to prevent destruction of the cell through thermal loading. This is particularly challenging as the 2H2 + O2 -> 2H2O reaction is highly exothermic, so a large quantity of heat is generated within the fuel cell. Durability, service life, and special requirements for some type of cells.
Stationary fuel cell applications typically require more than 40,000 hours of reliable operation at a temperature of -35 °C to 40 °C (-31 °F to 104 °F), while automotive fuel cells require a 5,000 hour lifespan (the equivalent of 150,000 miles) under extreme temperatures. Current service life is 7,300 hours under cycling conditions.  Automotive engines must also be able to start reliably at -30 °C (-22 °F) and have a high power to volume ratio (typically 2. kW per liter).
* Limited carbon monoxide tolerance of the cathode. Fuel cell applications Fuel cells are very useful as power sources in remote locations, such as spacecraft, remote weather stations, large parks, rural locations, and in certain military applications. A fuel cell system running on hydrogen can be compact and lightweight, and have no major moving parts. Because fuel cells have no moving parts and do not involve combustion, in ideal conditions they can achieve up to 99. 999% reliability.  This equates to around one minute of down time in a two year period.
Since electrolyzer systems do not store fuel in themselves, but rather rely on external storage units, they can be successfully applied in large-scale energy storage, rural areas being one example. In this application, batteries would have to be largely oversized to meet the storage demand, but fuel cells only need a larger storage unit (typically cheaper than an electrochemical device). One such pilot program is operating on Stuart Island in Washington State.
There the Stuart Island Energy Initiative has built a complete, closed-loop system: Solar panels power an electrolyzer which makes hydrogen. The hydrogen is stored in a 500 gallon tank at 200 PSI, and runs a ReliOn fuel cell to provide full electric back-up to the off-the-grid residence. Cogeneration Micro combined heat and power (MicroCHP) systems such as home fuel cells and cogeneration for office buildings and factories are in the mass production phase.The system generates constant electric power (selling excess power back to the grid when it is not consumed), and at the same time produces hot air and water from the waste heat. MicroCHP is usually less than 5 kWe for a home fuel cell or small business.  A lower fuel-to-electricity conversion efficiency is tolerated (typically 15-20%), because most of the energy not converted into electricity is utilized as heat. Some heat is lost with the exhaust gas just as in a normal furnace, so the combined heat and power efficiency is still lower than 100%, typically around 80%.
In terms of exergy however, the process is inefficient, and one could do better by maximizing the electricity generated and then using the electricity to drive a heat pump. Phosphoric-acid fuel cells (PAFC) comprise the largest segment of existing CHP products worldwide and can provide combined efficiencies close to 90% (35-50% electric + remainder as thermal) Molten-carbonate fuel cells have also been installed in these applications, and solid-oxide fuel cell prototypes exist.Advantages of Hydrogen Fuel When hydrogen is burned, the only emission it makes is water vapor, so a key advantage of hydrogen is that when burned, carbon dioxide (CO2) is not produced. Clearly, hydrogen is less of a pollutant in the air because it omits little tail pipe pollution.
Hydrogen has the potential to run a fuel-cell engine with greater efficiency over an internal combustion engine. The same amount of hydrogen will take a fuel-cell car at least twice as far as a car running on gasoline.