As we move towards a greener future, fuel cells is the direction to 15 go for in terms of alternative forms of renewable energy and is a potential solution to our depleting fossil fuel dependency, hence reducing greenhouse gases release and the dangers of global warming. This review article looks into the future developments of fuel cells; particularly polymer electrolyte membrane fuel cells (FEMME), in terms of cost and technological advancement of the cell components, In an alma to cost effectively deliver sustainable energy via fuel cells. 1. 0 Introduction 25
Ever since the world was introduced to internal combustion engines, there have been many attempts made to replace this form of combustion powered engines in powering vehicles. Combustion engines have two major drawback which results in further research in alternative forms of energy system to power up vehicles. The first problem of Internal combustion engines are, the emissions from these engines, primarily, have been proven to harm the environment, causing world problems such as global warming, due to CA emissions, and smog, caused 30 by Incomplete combustion of hydrocarbon fuels.
The second more obvious problem Is he depletion of fossil fuels, which is the primary source of fuel for transportation alternative forms of energy to provide a sustainable future for the global energy demands. 35 This report looks into the potential future developments in the established technology of portable energy storage for vehicle application which utilities fuel cell technology powered by hydrogen as the fuel.
There are various forms of fuel cells that can be employed for this application, and through thorough evaluation, the best fuel cell technology to utilize is the Proton Exchange Membrane (POEM) fuel cell, also now as Polymer Electrolyte Membrane fuel cell. 1. 1 Fuel Cell Theory The theory behind POEM fuel cell consists of reacting pure hydrogen gas with oxygen from air to produce electricity, water and waste heat.
H 2 (g 20 2 ) + Electricity + waste Heat 45 Fuel other than pure hydrogen can be used but pure hydrogen as a fuel, only produces water, electricity and waste heat eliminating greenhouse gases and other pollutants to be emitted to the environment. 50 The hydrogen fuel is fed continuously to the anode (negatively charged electrode) and the oxygen is also fed continuously to the cathode (positively charged electrode). At the anode the pure hydrogen fuel is split into a positively charged hydrogen proton and negatively charged electrons with the help of platinum catalyst.
This Journal is O The University College London [2009] Kansas Jam*, Fall Latin, Reran Furious, Karachi K. Kampala, Mohamed Mohamed Renewable energy technology (2009) The positively charged hydrogen proton then reacts with oxygen on the cathode to produce water which flows out of the fuel cell, while the negatively charged electrons travel along an external circuit to the cathode creating electricity. 20 Figure 1. 1 Diagram showing how a typical polymer electrolyte fuel cell works 25 Although fuel cells in general can be used for various applications, POEM fuel cell is best suited for automobiles such as vehicles etc.
In vehicles the fuel cell system provides its generated electricity to the electric drive train which consists of: An electric motor, The motor’s controls, DC to AC inverter and DC to DC converter, A transmitter. The power generated from the motor is then transmitted to the wheels. Some of the benefits why POEM fuel cells is used for automobiles are, it operates at low temperature (60 to 800 C), reasonably good efficiency, have high power density and has zero or low greenhouse and other greenhouse emissions. 0 Figure 1. 2 Schematic diagram showing how the fuel cell system is integrated in the vehicle. 5 2 2. 0 Polymer Electrolyte Membrane Fuel Cell (FEMME) one of the most promising fuel cell power source for widespread applications such as residential and housing, automotive, mobile, electronic (1) 5 applications etc, due to its high efficiency, high power density and low emissions . Poems are exceptionally responsive to varying loads (such as driving) and are increasingly cheap to manufacture. The POEM fuel cell uses an advanced plastic electrolyte (typically Info) to shuttle protons from the anode to the cathode.
By employing a solid electrolyte makes FEMME more user friendly and easier to handle rather than a 10 liquid counterpart, and its low operating temperature allows for a quick start-up of the system. A thin platinum catalyst chemically activates the reactions at the electrodes. In the past, the use of platinum is the main cause of these devices being prohibitively expensive, but new application technologies have dramatically thinned the platinum layer, allowing these devices to deliver electricity for less than $3000/k.
POEM fuel cells are (30) 15 best suited for 1 k to skew applications The limitations of the FEMME system are mainly in terms of high manufacturing costs and complex water management issues. The stack contains hydrogen, oxygen and water. If the polymer electrolyte membrane is dry, the input resistance is high and water must be added to get the system going. However, the level of hydration is 20 very sensitive as too much water causes flooding of the membrane. The warm-up process is slow and the performance is poor when cold.
The POEM fuel cell requires heavy accessories. Operating compressors, pumps and other apparatus consumes 30% of the energy generated. The POEM stack has an estimated service life of 4000 hours if operated in a vehicle. The 25 relatively short life span is caused by intermittent operation. Start-up and stop conditions induce drying and wetting, which contributes to membrane stress. In the case of a stationary stack, it is estimated that it can run for bat 40,000 hours (30). The POEM fuel cell requires pure hydrogen.
There is little tolerance for contaminates such as sulfur compounds or carbon monoxide as they can poison the system. A decomposition of the membrane takes place if different grade fuels are used. The complexity of repairing a fuel cell stack becomes apparent when considering that a happily IV, 50 k stack contains about 250 cells. 2. 1 Future developments The developments over recent years have brought the current densities up to around 1 Acm 2 or more, while at the same time reducing the use of platinum by a factor of over 100.
These improvements have led to huge reduction in cost per kilowatt of power, and much improved power density. Femmes, not only are being actively applications, it is also being developed for combined heat and power (CAP) systems There are on going scientific and technical developments to accommodate the huge increasing demands of fuel cell systems for various applications. The high performance, low cost, greater durability, better water management and (3) 45 the ability to function at higher temperatures are some challenges that must be addressed . . 2 Industrial Players 55 In the early sass, the General Electric Company (US) started the development of polymer electrolyte membrane fuel cells (Femmes) as power sources in space shuttle for space explorations. In the sass, the development of Femmes progressed greatly by introduction of Inflow, from the parent Du Pond company. Since then, many companies, including Siemens (Germany) and Ballard (Canada), have developed FEMME technology. According to a new research written by Business Communications Co. US market value of polymer electrolyte membrane and other components of FEMME stacks have reached $149 million in 2004. The research also stated that the market will expand at an average annul growth rate (AGAR) of 26% over the next five years to reach $475 million by 2012 (4). 3 3. 0 Research Developments in FEMME 3. 1 Membrane electrode assembly (MEA) The Membrane Electrode Assembly (MEA) part of a POEM is essential to the overall effectiveness of the cell, as it contains three elements required for the chemical reduction of electricity.
The two gas diffusion layers namely anode and cathode, ensure movement of the hydrogen fuel and oxygen; a thin layer of platinum applied in a carbonated ink catalyst to allow for the chemical reaction to occur, and a proton exchange membrane (Info) (5). 10 There are three published types of MEA production. Firstly, an MEA with catalyst ink applied directly to the gas diffusion layers. Secondly, an MEA with catalyst 15 ink applied directly to the proton exchange membrane. And finally, a catalyst coated membrane made through use of the decal method.
The overall effectiveness of each en can be found by testing the electronic load to determine the amounts of voltage and current produced and hence the current density. It has been found that membranes coated using decal method has more application than catalyst ink, since it ensures that almost all parts of the membrane are coated with catalyst. Therefore, it is clear that membrane coated through the decal method produces a greater current density than other types of MEA. The maximum current density observed from the latter was estimated at 25 Local this is quite high density and its encouraging.
However, more tests are required to confirm this finding (6). . 1. 2 Future developments The improved efficiency of the MEA through effective catalyst application is highly important for future success. One of the most unattractive aspects of the fuel cell is the use of platinum as a catalyst. Therefore it is believed that 30 by producing an MEA with effective ink will reduce the amount of platinum and hence cutting the costs and increasing the overall appeal of fuel cell (6). 3. 2 Catalyst The major problems for the development of Proton Electrolyte Membrane Fuel Cells are durability and production cost of the fuel cells itself.
The main contributor to the total cost of a Proton Electrolyte Membrane Fuel Cell is the cost of the platinum, which is used as the catalyst for the electrolyte. Based on a literature survey done, the typical loadings of platinum in the electrode today are about 0. 4-0. 8 MGM platinum/CM 2, which is significantly lower than 25 2 40 MGM/CM with early platinum black catalysts One alternative currently being explored is the use of platinum-WAC alloy catalysts (X=Co, Fee, N’, or other transition metals. Apt-Co/C, for instance, has shown a twofold activity enhancement for oxygen reduction allowing a reduction in platinum loading from 0. 0 MGM/CM to 0. 0 MGM/CM (11). 45 The cost of platinum in year 2005 was $900/trot ($28,936/keg) and there is an cost is $1 ,080/trot ($34,723/keg) (8). Another concern raised by the Proton Electrolyte Membrane Fuel Cell is the durability of platinum itself. The platinum catalyst has low carbon monoxide tolerance. Its low carbon monoxide tolerance has been improved by (13) 50 using functional catalysts comprising alloys of Platinum with Ruthenium, Molybdenum and Rhenium . The following section will discuss further the recent technologies which have been developed.
According to a report by Technology Tracking, utilizing unstructured arbor such as informers, annotates, etc. As supports may help realize the target to reduce the amount of platinum catalyst used (11). Several novel approaches 55 being pursued in the US and worldwide hold promise to boost catalytic activity and may potentially reduce the loading to as low as 0. 1 MGM/CM (11). 4 Fuel cells could become smaller, more efficient and cheaper, if carbon annotates replaced the expensive platinum catalysts that the current cells rely on (7).
A team from University of Dayton, Ohio has discovered that bundles of annotates doped with nitrogen shows better voltage performance compared to pure annotates itself 7). Other materials also have been studied to replace platinum as the catalyst. One potential material is Molybdenum Carbide (MOM C). Apart from its high cost, the platinum based electrodes also suffer from susceptibility to dementedness drift and carbon dioxide deactivation (10). Moreover, a mixture of platinum and ruthenium gave a significant hope to reducing the utilization of platinum.
