A Comprehensive Review of the Fuel Cells Technology and Hydrogen Economy

The degrading of the air quality resulting from the emissions of the existing energy conversion devices, in addition to the recent instability of the oil prices forced the need to a more stable zero-emission distribution generation technology or combination of technologies which allows a clean, cost effective supply of energy, on demand on a large scale and in any location. Thus, renewable energy generation or the decentralized power systems like wind, photovoltaic, as well as new hydrogen and fuel cells technologies are developing nowadays to take over from fossil hydrocarbons combustion. Fuel cell is an emerging technology which could allow a clean, cost effective supply of energy on demand on a large scale and in any location. This paper will act as a literature survey to the fuel cell technology. It will introduce the different fuel cell types with their advantages and disadvantages, and their suitability for different applications. It will also discuss the technical and economic issues facing the spread of this technology, and how to move to a worldwide hydrogen technology. It will also brief the current state of fuel cells with both drivers and barriers to its market growth. Further recommended work for the advance and spread of use of the fuel cells will be also highlighted.


INTRODUCTION
temperatures TH then the thermal energy is used to generate mechanical energy and some of the heat energy Fuel cells can potentially replace conventional power is rejected to a heat sink at a low temperature TL, thus its equipment in many cases as stationary power generation, efficiency is subject to the Carnet efficiency limitation; transportation and battery replacement. They are already while fuel cells directly convert fuel chemical energy into commercially available, at high costs, for applications electrical energy. The voltage produced from one cell is such as portable power sources and small-scale power (0-lV); for higher voltages a number of cells are stacked generation and transportation. At present there are in series. different fuel cell types at various stages of intensive development by several manufacturers around the world.
3. HISTORY OF FUEL CELLS As fuel cells reduce the dependence on fossil fuels thus having a significant environmental and national security, Sir William Grove developed the first fuel cell in 1839. they are the centre of interest for excessive research.
The principle was discovered by accident during an electrolysis experiment, when he disconnected the battery 2. WHAT IS A FUEL CELL?
from the electrolyser and connected the two electrodes together he found a current flowing in the opposite A fuel cell is a device that directly converts the chemical direction consuming the gases of hydrogen and oxygen; energy of a gaseous fuel into electrical energy. Any fuel he called this the "Gas-Battery". In 1842 he connected a (solid, liquid, or gas) can be used in fuel cells; however it number of gas batteries in series to form a "gas chain" and should pass first through a reformer to get out pure used the electricity produced to power an electrolyser in hydrogen [1, 2 and 3]. The fuel cell is analogous to a order to split water into hydrogen and oxygen. battery however battery reactants are stored internally and when used up battery must be replaced or recharged, while reactants of fuel cells are stored externally and can easily be recharged. Like a battery each fuel cell has two electrodes and an electrolyte that allows protons to pass through while blocking electrons [4]. Generally hydrogen is fed to the anode where it splits into a proton and electron; the protons pass through the electrolyte to the circuit creating electricity. The hydrogen protons andFrniBaoatCmideUvrsythnpdudte electrons combine with oxygen from air at cathode prdcn uewtr an a smal amun of het Thfe first practical fuel cell in 1950, which was alkaline [5, 6, cell reactions [5]: by polymer properties and for water management for Fig. 4 a prototype direct methanol fuel cell provides up membrane hydration. The low temperature means that to 20 watts electrical power only hydrogen rich gas with the minimal CO (poison) can be used as a fuel. PEM fuel cells delivers high power density, rapid start-up, offers low weight and cost, and 5. WHY FUEL CELLS? contain no corrosive fluids which make them ideal for transport applications, smaller units for powering laptops Fuel cells combine the best features of engines and and other low power devices.
batteries; like an engine they can operate for as long as fuel is available and like a battery they produce electricity .~~~~~~directly from fuel without combustion (reducing | . , , . 2 l~~emissions and noise) and without intermediate steps ill: ir 3Ww i:ir~~~~~~~~supplementing batteries in a variety of applications in the _g~~~~~~~~~~~~equally reliable and cost competitive. Some of the main F::>Xyrrl:r~~~~1. They convert hydrogen and oxygen directly into Fig. 3. A single PEM fuel cell electricity and water and heat with no combustion resulting in an efficiency which is double that of an 2. Alkaline FC (AFC): The electrolyte is concentrated internal combustion engine (ICE). potassium hydroxide. AFC was the first type of fuel cells 2. They emit low levels of pollutants thus contributing developed and is still used in the space shuttles. These substantially to a global low carbon dioxide cells require a hydrogen supply containing no other economy. reactive constituents, which result in their high cost.
3. They are quiet with no noise pollution. Thus anytime the sun shines, the wind blows or water To create a worldwide hydrogen economy with fuel cells flows the electrolyser can produce hydrogen. This is a providing clean safe electrical energy to be used on board closed system as none of the products or reactants (water, of vehicles, at neighbourhood fuelling stations, in hydrogen and oxygen) are lost to the outside environment.
electronic portable devices as well as in stationary 3. Biological Methods: Biogases produced from installations to provide electricity for homes & businessbiomass, landfill, or anaerobic digestion contain a confirmation about the safety of hydrogen and the fuel mixtures of methane, C02, and nitrogen together with cell systems that rely on it should be first achieved. varies organic materials are attractive to fuel cells.

Fears came from Hydrogen explosiveness and
Also Bio liquids such as methanol and ethanol are flammability potential stems that resulted from hydrogen attractive for some fuel cell systems. bombs [18,19,20 and 21]. Also fears came from the cause of the Hindenburg airship destroyed by fire in New Jersey. But examinations suggested that the airship did not 8. FUEL CELLS APPLICATIONS AND USES explode but rather burned in omni directional patterns as a result of static electricity and not from a leak in hydrogen This includes the following applications [23 -33]: tank. The blue glow of electrical activity witnessed before the fire started indicates an extremely high temperature 1. Military: typical to a corona discharge; and the colour of fire wasn't characteristic of hydrogen. The National Hydrogen The efficiency, versatility, extended running time and Association (NHA) also explains that to induce the quiet operation make fuel celle or the power needs nuclear fusion reaction of a hydrogen bomb, the rare H2 of military services from portable handheld devices used isotope, tritium, plus extreme heat are necessary and this in the field to land and sea transportation and would has no resemblance to the simple chemical reactions dramatically reduce the level of fuel required during associated with fuel cells. manoeuvres.
The basic properties of hydrogen in light of safety in 2. Space: handling include 1221: The combination of low weight, reliable supply of 1. Hydrogen is lighter than air and diffuses rapidly. Its electricity and heat without significant noise and vibration rapid dispersion rate is its greatest safety asset. and the added advantage of drinking water production 2. Hydrogen flames have low radiant heat which can gave fuel cells considerable advantages in space reduce the risk of secondary fires.
applications. 3. It does not explode when ignited as a result of putting it under pressure or low temperature (in compressed tanks). It quickly rises and dissipates.

Portable:
corrosion, their low operating temperature (80°C) that Miniaturised fuel cells will offer key advantages over makes them reach the operating temperature quickly, their conventional batteries such as increased operating times, rapid response to varying loads that raise their efficiency reduced weight and ease of recharging. Direct methanol to 60% where the ICE efficiency is 25%. PEM fuel cells fuel cells (DMFC) offers a great advantage over solid need an uncontaminated hydrogen fuel. batteries in that recharging will just involve refilling with the liquid fuel, not plugging into an external electric supply. Its disadvantage is the cost of the platinum 9. THE MARKET FOR FUEL CELLS catalyst required.
The fuel cell market has only just begun to emerge with 4. Residential: few FC in operation. Drivers and barriers for the market These are smaller units typically below 50 kW. All the growth can be summarised as follows. heat and power requirements of private households or small business could be met by a low temperature 9.1 Drivers forMarketeGrowth: PEMFC or a cheaper PAFC. At present only few homes * Favourable Characteristics: Their high efficiency, in the USA, Japan and Germany are powered by PEM good part load characteristics, rapid load flowing, cells.
flexibility of fuel supply and flexibility of load factor gives fuel cells a strong position in a wide range of applications.
G*overnment market stimulation programs: The *l l | 11 F-F growing scientific consensus that increasing levels of greenhouse gas emissions are changing the earth's climate, forced programmes for clean energy (currently mainly for transport applications). facilities. In future high temperature fuel cells, such as * A hydrogen infrastructure must be developed in order MCFC and SOFC, may be adapted for MW-scale power to for hydrogen technologies to spread; but a generation. The high operating temperatures (600hydrogen infrastructure will not develop until there is 1 100°C) cells can tolerate a contaminated source of a sufficiently large adoption of hydrogen hydrogen and hence can use unreformed natural gas, technologies.
diesel or gasoline. Also, the heat generated can be used to produce additional electricity by driving steam turbines. technology. In order to help the move to a hydrogen economy, further work is recommended to simulate the Fuel Cell dynamic performance. As it is clear from the 10. CURRENT STATE OF FUEL CELLS given survey, PEMFC has high power densities, high efficiencies, rapid start-up, long cell and stack life, low The number of complete systems (defined as a unit weight and cost, contain no corrosive fluids, useful for capable of independent power production) since 1995 up almost all applications, exhibit most of the basic fuel cell till 2004 is slightly over 10,000. Recently, there was an properties and finally incorporates the essential physical increase in the importance of DMFC Also, apart from the and electrochemical processes that happen in a fuel cell continued romance with PEM units, SOFC exhibited a along its operation. Thus developing a reliable model for continued importance especially in stationary units [34]. the simulation, and performance evaluation of PEMFC is recommended as a further work.