ALKALINE AND DIRECT METHANOL

FUEL CELL

FUEL CELL:

A fuel cell is an electrochemical cell that converts energy from a fuel into electrical energy. Electricity is generated from the reaction between a fuel supply and an oxidizing agent. 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.

DESIGN OF FUEL CELL:

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.

A block diagram of a fuel cell

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.

ALKALINE FUEL CELL:

The alkaline fuel cell (AFC), also known as the Bacon fuel cell after its British inventor, is one of the most developed fuel cell technologies and is the cell that flew Man to the Moon.

NASA has used alkaline fuel cells since the mid-1960s, in Apollo-series missions and on the Space Shuttle. AFCs consume hydrogen and pure oxygen producing potable water, heat, and electricity. They are among the most efficient fuel cells, having the potential to reach 70%.

HISTORY OF ALKALINE FUEL CELL:

The history of fuel cell (FC) begins with Sir William Grove who completed experiments on the electrolysis of water in 1839. From 1889 until the early twentieth century, many people tried to produce a Fuel Cell that could convert coal or carbon to electricity directly. These attempts failed because not enough was known about materials or electricity. The Alkaline Fuel Cell developed for space application was based, in large part, on work initiated by F.T. Bacon in the 1930s. By 1952 construction and performance testing of a 5-kW alkaline fuel cell, operations on H2 and O2, was completed.

The large boost in Fuel Cells technology came from NASA. In the late 1950's, NASA needed a compact way to generate electricity for space missions. Nuclear was too dangerous, batteries too heavy and solar power too cumbersome. The answer was Fuel Cells. NASA went on to fund 200 research contracts for Fuel Cell technology. Both the alkaline and polymer electrolyte fuel cells have demonstrated their capabilities in the Apollo, Gemini and Space Shuttle manned space vehicle programs.

DIAGRAM:

CONSTRUCTION AND CHEMISTRY:

An alkaline fuel cell consists of an alkaline electrolyte, typically potassium hydroxide (KOH), sandwiched between an anode (negatively charged electrode) and a cathode (positively charged electrode). The processes that take place in the fuel cell are as follows:

1. Hydrogen fuel is channelled through field flow plates to the anode on one side of the fuel cell, while oxygen from the air is channelled to the cathode on the other side of the cell.

2. At the anode, a platinum catalyst causes the hydrogen to split into positive hydrogen ions (protons) and negatively charged electrons.

3. The positively charged hydrogen ions react with hydroxyl (OH-) ions in the electrolyte to form water.

4. The negatively charged electrons cannot flow through the electrolyte to reach the positively charged cathode, so they must flow through an external circuit, forming an electrical current.

5. At the cathode, the electrons combine with oxygen and water to form the hydroxyl ions that move across the electrolyte toward the anode to continue the process.

OPERATING TEMPERATURE OF ALKALINE FUEL CELL:

There are both low temperature and high temperature AFC’s. Low temperature AFC’s operate at temperatures as low as 25°C up to 75°C. High temperature AFC’s operate at 100°C up to 250°C.

ELECTROLYTE:

The two electrodes are separated by a porous matrix saturated with an aqueous alkaline solution, such as potassium hydroxide (KOH). Aqueous alkaline solutions do not reject carbon dioxide (CO2) so the fuel cell can become "poisoned" through the conversion of KOH to potassium carbonate (K2CO3). Because of this, alkaline fuel cells typically operate on pure oxygen, or at least purified air and would incorporate a 'scrubber' into the design to clean out as much of the carbon dioxide as is possible. Because the generation and storage requirements of oxygen make pure-oxygen AFCs expensive, there are few companies engaged in active development of the technology. There is, however, some debate in the research community over whether the poisoning is permanent or reversible. The main mechanisms of poisoning are blocking of the pores in the cathode with K2CO3, which is not reversible, and reduction in the ionic conductivity of the electrolyte, which may be reversible by returning the KOH to its original concentration. An alternate method involves simply replacing the KOH which returns the cell back to its original output.

BASIC DESIGNS:

Because of this poisoning effect, two main variants of AFCs exist: static electrolyte and flowing electrolyte. Static, or immobilized, electrolyte cells of the type used in the Apollo space craft and the Space Shuttle typically use an asbestos separator saturated in potassium hydroxide. Water production is managed by evaporation out the anode, as pictured above, which produces pure water that may be reclaimed for other uses. These fuel cells typically use platinum catalysts to achieve maximum volumetric and specific efficiencies.

Flowing electrolyte designs use a more open matrix that allows the electrolyte to flow either between the electrodes (parallel to the electrodes) or through the electrodes in a transverse direction (the ASK-type or EloFlux fuel cell). In parallel-flow electrolyte designs, the water produced is retained in the electrolyte, and old electrolyte may be exchanged for fresh, in a

manner analogous to an oil change in a car. In the case of "parallel flow" designs, greater space is required between electrodes to enable this flow, and this translates into an increase in cell resistance, decreasing power output compared to immobilized electrolyte designs. A further challenge for the technology is that it is not clear how severe is the problem of permanent blocking of the cathode by K2CO3, however, some published reports indicates thousands of hours of operation on air. These designs have used both platinum and non-noble metal catalysts, resulting in increased volumetric and specific efficiencies and increased cost.

The EloFlux design, with its transverse flow of electrolyte, has the advantage of low-cost construction and replaceable electrolyte, but so far has only been demonstrated using oxygen.

Further variations on the alkaline fuel cell include the metal hydride fuel cell and the direct borohydride fuel cell.

REACTIONS:

ANODE:

At the anode, hydrogen is oxidized according to the reaction:

2 H2 + 4 OH- => 4 H2O + 4 e-

producing water and releasing four electrons.

CATHODE:

The electrons flow through an external circuit and return to the cathode, reducing oxygen in the reaction:

O2 + 2 H2O + 4 e- => 4 OH-

producing hydroxide ions.

OVERALL REACTION:

The net reaction consumes one oxygen atom and two hydrogen atoms in the production of one water molecule. Electricity and heat are formed as by-products of this reaction.

2H2+O2 => 2H2O + electrical energy + heat

ADVANTAGES:

AFCs are the cheapest of fuel cells to manufacture. AFCs are among the most efficient in generating electricity at nearly 70%. The catalyst required for the electrodes can be any of a number of different chemicals that are inexpensive compared to those required for other types of fuel cells. The commercial prospects for AFCs lie largely with the recently developed bi-polar plate version of this technology,

considerably superior in performance to earlier mono-plate versions. The world's first Fuel Cell Ship HYDRA used an AFC system with 6.5 kW net output. In addition to this, the major advantage of AFCs is that pure hot water is produced as the ‘waste’ product. Another advantage of AFCs is their high performance which is due to the rate at which chemical reactions take place in the cell. They have also demonstrated efficiencies near 60% in space applications. Many other prominent advantages

include Low material costs – plastics, carbon, base metals and metal oxides; no

platinum, Long life span – 2000-plus hours currently, Superior electrochemical conversion efficiency to other fuel cells and the internal combustion engine, Quick start, even in sub-freezing temperatures down to minus 40 degrees C, Simpler heat and water management when compared to other fuel cell technologies.Like other fuel cells, it is odorless and quiet for enclosed applications

DISADVANTAGES:

The disadvantage of this fuel cell type is that it is easily poisoned by carbon dioxide (CO2). In fact, even the small amount of CO2 in the air can affect this cell's operation, making it necessary to purify both the hydrogen and oxygen used in the cell. This purification process is costly. Susceptibility to poisoning also affects the cell's lifetime (the amount of time before it must be replaced), further adding to cost.

USES:

Another very interesting recent development (though not necessarily for high power applications) is the solid-state alkaline fuel cell, utilizing alkali anion exchange membranes rather than a liquid. AFCs were used on Apollo space missions to provide electricity for the on-board needs of the shuttle. Therefore, on the shuttle in addition to providing electricity the AFCs provided Heat, Cooling, Hot water, and ultimately – drinking water for the astronauts. They also have significant applications in electric vehicles. Low temperature, silent operations, and no poisonous exhausts are the big selling characteristics of Alkaline Fuel Cells for defence applications.

DIRECT METHANOL FUEL CELL:

The technology behind Direct Methanol Fuel Cells (DMFC) is still in the early stages of development, but it has been successfully demonstrated powering mobile phones and laptop computers—potential target end uses in future years.

DMFC is similar to the PEMFC (Proton Exchange Membrane Fuel Cell) in that the electrolyte is a polymer and the charge carrier is the hydrogen ion (proton). Direct-methanol fuel cells or DMFCs are a subcategory of proton-exchange fuel cells in which methanol is used as the fuel.

THE CELL:

In contrast to indirect methanol fuel cells, where methanol is reacted to hydrogen by steam reforming, DMFCs use a methanol solution (usually around 1M) to carry the reactant into the cell; common operating temperatures are in the range 50–120 °C, where high temperatures

are usually pressurized. DMFCs themselves are more efficient at high temperatures and pressures, but these conditions end up causing so many losses in the complete system that the advantage is lost therefore, atmospheric-pressure configurations are preferred nowadays.

Because of the methanol cross-over, a phenomenon by which methanol diffuses through the membrane without reacting, methanol is fed as a weak solution: this decreases efficiency significantly, since crossed-over methanol, after reaching the air side (the cathode), immediately reacts with air; though the exact kinetics are debated, the end result is a reduction of the cell voltage. Cross-over remains a major factor in inefficiencies, and often half of the methanol is lost to cross-over.

Other issues include the management of carbon dioxide created at the anode, the sluggish dynamic behaviour, and the ability to maintain the solution water.

The only waste products with these types of fuel cells are carbon dioxide and water.

HISTORY:

Fuel cells have been around for over 150 years. Sir William Robert Grove conceived the first fuel cell In 1839.   Sir Grove was a Welsh gentleman, scientist and judge.   His fuel cell used porous platinum electrodes and sulfuric acid as the electrolyte bath. His mixture of hydrogen and oxygen in the presence of an electrolyte produced electricity and water. Unfortunately, his invention didn't produce enough electricity to be useful.

In 1889, Ludwig Mond and his assistant Charles Langer, attempted to build a working fuel cell using air and industrial coal gas.

Around that time, a fuel cell constructed by William White Jaques (who incidentally coined the term fuel cell), substituted phosphoric acid in the electrolyte bath.

In the 1920s, fuel cell research in Germany paved the way to the development of the carbonate cycle and solid oxide fuel cells of today.

In 1932, Dr. Francis T. Bacon made a significant contribution to fuel research.   Early cell designers used porous platinum electrodes and sulfuric acid as the electrolyte bath. Using platinum was expensive and using sulfuric acid was corrosive.   Bacon used an inexpensive nickel electrode and a less corrosive alkaline electrolyte.    It took Bacon until 1959 to perfect his design and demonstrated a five-kilowatt fuel cell that could power a welding machine.   Francis T. Bacon, a direct descendent of the other well known Francis Bacon, named his famous fuel cell design the "Bacon Cell."

In October of 1959, Harry Karl Ihrig, an engineer for the Allis - Chalmers Manufacturing Company, demonstrated a 20-horsepower tractor that was the first vehicle ever powered by a fuel cell.

During the early 1960s, General Electric produced the fuel-cell-based electrical power system for NASA's Gemini and Apollo space capsules. General Electric used the principles found in the "Bacon Cell" as the basis of its design. Today, the Space Shuttle's electricity is provided by fuel cells, and the same fuel cells provide drinking water for the crew.

Dr. Lawrence H. DuBois of the U.S. Department of Defense and the Defense Advanced Research Projects Agency (DARPA) envisioned the development of a fuel cell that could operate on various types of liquid hydrocarbons (methanol, ethanol, etc.,).   He called on Dr. Surya Prakash a world-renowned super acid specialist and Nobel laureate Dr. George A. Olah, both of the University of Southern California's Loker Hydrocarbon Institute to invent such a fuel cell. USC, in a collaborative effort with Jet Propulsion Laboratory (JPL) / California Institute of Technology (Caltech) proceeded to invent the direct oxidation of liquid hydrocarbons subsequently coined as DMFC, Direct Methanol Fuel Cell Technology.

DTI acquired the exclusive worldwide license for Direct Oxidation of Liquid Hydrocarbons, DMFC Technology.   DTI's President and CEO, Todd Marsh, saw the future impact that a clean alternative to fossil fuels was being born and offered to steward this technology and help commercialize it.  

DMFC technology has become widely accepted as a viable fuel cell technology that offers itself to many applications.

METHANOL:

Methanol is a liquid from -97.0 °C to 64.7 °C at atmospheric pressure. The energy density of methanol is an order of magnitude greater than even highly compressed hydrogen, and 15 times higher than Lithium-ion batteries.

Methanol is toxic and flammable. However, the International Civil Aviation Organization's (ICAO) Dangerous Goods Panel (DGP) voted in November 2005 to allow passengers to carry and use micro fuel cells and methanol fuel cartridges when aboard airplanes to power laptop computers and other consumer electronic devices. On September 24, 2007, the US Department of Transportation issued a proposal to allow airline passengers to carry fuel cell cartridges on board. The Department of Transportation issued a final ruling on April 30, 2008, permitting passengers and crew to carry an approved fuel cell with an installed methanol cartridge and up to two additional spare cartridges. It is worth noting that 200 ml maximum methanol cartridge volume allowed in the final ruling is double the 100 ml limit on liquids allowed by the Transportation Security Administration in carry-on bags.

PRINCIPLE:

A DMFC works in the same way as a Polymer Electrolyte Membrane Fuel Cell (PEMFC), with the difference that methanol and water are split into protons, electrons and carbon dioxide at the anode (negative electrode).The voltage generated by a single DMFC cell is 0.3-0.9 Volts depending on load. The voltage level appropriate to a specific application is achieved by combining a number of single cells into a stack, in which graphite-based bipolar flow-plates supply the fuel to the Membrane Electrode Assemblies (MEAs) of each cell and serve as electrical interconnectors between the cells in the stack.

Illustration of Direct Methanol Fuel Cell (DMFC) in Principles.

REACTIONS:

At the anode methanol reacts with water to produce carbon dioxide and 6 hydrogen ions losing six electrons. Reduction takes place at the cathode in which oxygen reacts with 6 hydrogen ions and accepts 6 electrons to produce water. In the net reaction oxygen and methanol react together to produce carbon dioxide and water.

ADVANTAGES:

Their main advantages are the ease of transport of methanol, an energy-dense yet reasonably stable liquid at all environmental conditions, and the lack of complex steam reforming (used to generate Hydrogen from fossil fuels) operations. Efficiency is presently quite low for these cells, so they are targeted especially to portable applications, where energy and power density are more important than efficiency. Using methanol as a primary fuel has its advantages over pure hydrogen. One of the most significant is that fact that methanol can be stored as a liquid over a wide temperature range (-97°C to 64.7°C) and therefore avoids many of the pitfalls of hydrogen storage. Liquid methanol on the other hand can be stored in cheap plastic containers and is an excellent carrier fuel that hydrogen can be extracted from to power fuel cells. Pure methanol, because it exists in liquid form, also has a significant energy density by volume advantage over highly compressed hydrogen gas allowing DFMC’s to exist in a very compact form. This size factor makes DFMC’s ideal for consumer electronics, but probably prevents their use in vehicle propulsion applications.

DISADVANTAGES:

One of the drawbacks of the DMFC is that the low-temperature oxidation of methanol to hydrogen ions and carbon dioxide requires a more active catalyst, which typically means a larger quantity of expensive platinum catalyst is required than in conventional PEMFCs. This

increased cost is, however, expected to be more than outweighed by the convenience of using a liquid fuel and the ability to function without a reforming unit.

One other concern driving the development of alcohol-based fuel cells is the fact that methanol is toxic. Therefore, some companies have embarked on developing a Direct Ethanol Fuel Cell (DEFC). The performance of the DEFC is currently about half that of the DMFC, but this gap is expected to narrow with further development.

Because water is consumed at the anode in the reaction, pure methanol cannot be used without provision of water via either passive transport such as back diffusion (osmosis), or active transport such as pumping. The need for water limits the energy density of the fuel.

USES:

Current DMFCs are limited in the power they can produce, but can still store a high energy content in a small space. This means they can produce a small amount of power over a long period of time. This makes them presently ill-suited for powering large vehicles (at least directly), but ideal for smaller vehicles such as forklifts and tuggers and consumer goods such as mobile phones, digital cameras or laptops. Military applications of DMFCs are an emerging application since they have low noise and thermal signatures and no toxic effluent. These applications include power for soldier-carried tactical equipment, battery chargers, and autonomous power for test and training instrumentation. Units are currently available with power outputs between 25 watts and 5 kilowatts with durations up to 100 hours between refuelling. DMFCs are relatively low range fuel cells which make them attractive for tiny to mid-sized applications.

ENDLESS POSSIBILITIES FOR DMFC:

Direct Methanol Fuel Cell technology (DMFC) can be applied in a variety of products.   Obviously, our environment would benefit from fuel cell powered cars and buses.   There is an equal or greater demand for clean efficient energy in many other applications.   Lawnmowers, weed whips, chain saws, snow and leaf blowers, and jet skis can all be converted to DMFC, Direct Methanol Fuel Cell technology.   Marine applications such as boats, tankers, luxury liners and at-sea platforms have significant power needs. Micro fuel cells, using DMFC, Direct Methanol Fuel Cell technology, in cellular phones, laptop computers and portable electronics will provide longer usability.   Wastewater treatment plants and landfills are using direct methanol fuel cells to convert the methane gas they produce into electricity. The possibilities are endless.

STATIONARY APPLICATIONS OF DMFC:

The opportunities and demand for Direct Methanol Fuel Cells in stationary applications are extraordinary. More than 2500 fuel cell systems have been installed all over the world -- in hospitals, nursing homes, hotels, office buildings, schools, utility power plants, and airport terminals, providing primary or backup power. Every country on Earth has stationary power and consumer electronics needs. Producing immediate stationary, decentralized power by using Direct Methanol Fuel Cell technology for absolutely every electrical need, makes sense not only logistically, but also monetarily. In large-scale building systems, fuel cells can reduce energy costs by 20% to 40% over conventional energy service.   Additionally, DMFCs are an excellent choice for backup power needs such as UPS and APU devices.

RESIDENTIAL APPLICATIONS OF DMFC:

Developing nations need reliable power in their cities, villages, and homes. Direct Methanol Fuel Cells are ideal for power generation, either connected to the electric grid to provide supplemental power and backup assurance for critical areas, or installed as a grid-independent generator for on-site service in areas that are inaccessible by power lines.   The average home operates on two to three kilowatts per day for all its electrical needs.   The refrigerator runs twenty-four hours per day to prevent food spoilage and uses power accordingly.   Small stand-alone, seven to ten kilowatt per hour DMFC generators emit no pollutants as a byproduct and can be used to provide hot water or space heating for a home.

TRANSPORTATION APPLICATIONS OF DMFC:

All the major automotive manufacturers have a fuel cell vehicle either in development or in testing right now.   Honda and Toyota have already begun leasing vehicles in California and Japan.   Automakers and experts speculate that the DMFC fuel cell vehicles will be widely commercialized by 2010.   Direct Methanol Fuel Cell technology, DMFC, is being incorporated into buses, trains, scooters and golf carts on a faster time line.

PORTABLE POWER APPPLICATIONS OF DMFC :

Possibly the most wide spread uses of Direct Methanol Fuel Cell technology, DMFC, are in the area of portable power.   Also known as Micro Fuel Cells, Direct Methanol Fuel Cells, DMFC, will change the telecommuting world, powering laptops and palm pilots hours longer than batteries and allowing up to a month of talk time on a cellular phone. Other applications for micro DMFC fuel cells include pagers, video recorders, portable power tools, and low power remote devices such as hearing aids, smoke detectors, burglar alarms, hotel locks and meter readers.

LANDFILL/WASTEWATER TREATMENT USING DMFC:

Direct Methanol Fuel Cells, DMFC, currently operate at landfills and wastewater treatment plants across the country, proving themselves as a valid technology for reducing emissions and generating power from the methane gas they produce.

MARINE APPLICATIONS OF DMFC:

Luxury liners and tankers can power themselves across the oceans using Direct Methanol Fuel Cell, DMFC, technology to power all their on-ship needs from the "engine room" -- which will likely be renamed the "energy room"-- to kitchen, bath, staterooms, laundry rooms and so on.   Yachts and fishing boats can have on-board power for personal comforts (hair dryers, a/c and heating) without the dreadful noise and fumes of combustion generators.   Furthermore, the use of methanol, a biodegradable fuel, will rescue our oceans from the pollution caused by the dumping of other fuels.

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