ALKALINE FUEL CELL (AFC)

Alkaline Fuel Cell (AFC) using an electrolyte solution (KOH) or alkaline solution. Operating temperature between 150 °C - 200 °C using hydrogen fuel and pure oxygen and free of CO_2. Because impurities can cause side reactions and CO₂ reacts with the electrolyte to form a precipitate carbonate will seal the surface of the catalyst and inhibit the reaction at the surface of the anode and cathode. Alkaline fuel cell (AFC) has been used as a source of power for spacecraft since 1960.

Alkaline systems operate well at room temperature, yield the highest voltage (at comparable current densities) of all fuel cell systems, and cell and electrodes can be built from low-cost carbon and plastics. Because of a good compatibility with many construction materials AFCs can achieve a long operating life

Complete reaction can be seen as below:

Anode reaction:

2H₂ + 4OH^- à 4H₂O + 4e^-

Cathode reaction:

O₂ + 2H₂O + 4e^- à 4OH^-

The overall reaction: 

2H₂ + O₂ à 2H₂O

Started working mechanism of the reaction of water and oxygen at the cathode generates hydroxyl ions (OH^-)^. Hydroxyl ions through the electrolyte transferred to the anode side. On the anode side hydrogen reacts with hydroxyl ions produce water and liberate electrons. Electrons generated at the anode side out of the system and used as electric power and then back to the cathode. On the cathode side the electrons react with oxygen. To more clearly below show the mechanism of action (AFC): 

Figure 1.

AFC structure

The AFCs for remote applications (space, undersea, military) are not strongly constrained by cost. On the other hand, the consumer and industrial markets require the development of low-cost components to successfully compete with alternative technologies. Much of the recent interest in AFCs for mobile and stationary terrestrial applications has addressed the development of low-cost cell components. 

PROTON EXCHANGE MEMBRANE FUEL CELL (PEMFC)

Among the six types of fuel cells are known at this time, the hydrogen fuel cell electrolyte membrane (PEMFC) most of the attention throughout the country because it has advantages compared with conventional engines and other fuel cells. This cell uses the so-called solid electrolyte (Proton Exchange Membrane, PEM) so easy to make, energy efficiency is almost doubled compared with the efficiency of conventional engines. Results of electrochemical reaction only water (zero emission), modular, no corrosion problems, the life of 11.000 hours, no sounds and can be applied to a moving tool and tools that is not easy to move.

Anodes in PEMFC fuel cell as a negative pole of an electrode that will drain off electrons from hydrogen molecules. These electrons can be used outside the circuit. At the anode material are channels that hydrogen gas can spread to the entire surface of the catalyst.

PEMFC cathode in a fuel cell pole positive electrode has a channel that will spread to the entire surface of the catalyst oxygen. Cathode also plays a role in the flow of electrons from the external circuit into the circuit. Electrons from the external circuit (load) combine with hydrogen ions and oxygen to form water to the entire surface of the catalyst.

Electrolyte PEMFC is a proton exchange membrane (proton exchange membrane / PEM). Shaped electrolyte material such as plastic wrapping which can only drain the positively charged ions. Electrons are negatively charged will not be through this membrane (membrane would hold electrons).

The catalyst in PEMFC is used to facilitate the reaction of oxygen and hydrogen. Catalysts made ​​of a sheet of carbon paper by a thin layer of platinum powder. The catalyst surface is always porous and rough so that the entire surface area of the platinum can be achieved hydrogen and oxygen. Platinum catalyst layer directly adjacent to the positive ion exchange membrane. 

Figure 1.

PEMFC Structure

Working Principle of PEMFC

-      Hydrogen gas that has a certain pressure enters the fuel cell at the anode.

-      The hydrogen gas will react with the catalyst to boost the pressure.

-      When the H₂ molecule contacts with the platinum catalyst, the molecules will separate into two H⁺ ions and two electrons (e^-)^.

-      Electrons will flow through the anode, the electrons will make a point outside the circuit of fuel cell and perform electrical work, and then flows back to the cathode in a fuel cell.

-      On the other hand, on the cathode fuel cell, oxygen gas (O₂) is driven style press then reacts with a catalyst to form two oxygen atoms.

-      Each oxygen atom has a very large negative charge. This will attract the negative charge two H⁺ ions out of the membrane PEM,

-      These ions combine with one atom of oxygen and electrons from the external circuit to form a water molecule (H₂O).

APPLICATION OF FUEL CELL

In many developed countries, the technology of fuel cell has not new anymore. Countries like the United States (US), Japan, Germany or the UK have developed this technology for a long time. In this country that triggered the use of hydrogen as a vehicle fuel is environmental issues and energy conservation. Vehicle manufacturers such as General Motors (GM) for example has released a prototype hydrogen-fueled cars. The car is scheduled commercially in 2010 using fuel cell-shaped wafer that serves to separate the hydrogen atoms into protons and electrons. By using electrons as electric current, coupled protons with oxygen from the air, so that the side only water vapor. To generate the necessary driving power car series consisting of 372 cells wafer. Although already able to apply these technologies, it does not mean everything went smoothly. GM claims that driving over a tank of compressed hydrogen is very uncomfortable compared with the above the gas tank. The car that was exhibited in the arena Alberto Fujimori American International Auto Show can cover a distance of almost 500 kilometers before having to recharge the fuel. In addition there are obstacles in the areas of comfort, hydrogen cars are relatively expensive, which is about 700.000 dollars.

Canadian company launched the generator fuel cell model of E8 Portable Power module containing two fuel cell PowerStack MC250. This portable power station has a capacity of 2,4 kW with voltage of 48 VDC at 50 A current and an electrical efficiency of over 50 percent. This plant is intended for stationary application such as backing up to Curacao response for commercial and military users.

Not only motor vehicles are considered to be feasible utilizing the fuel cell, but also information technology (IT). Manufacturers of portable computer from Japan, for example, to develop this technology on a number of products. Not all fuel cell can be used for a portable electronic device, only fuel cell from direct methanol (direct methanol fuel cell) which includes alkaline fuel cell  who can. If mass-produced, the price of the fuel cell can compete with Lithium-ion batteries are now widely used. Energy density can even be 5-10 times greater Lithium-ion battery.

A well-known manufacturer of electronic equipment in the United States, during the 1960s to produce electric power-based fuel cell to power NASA space shuttle as that Gemini and Apollo. Fuel cell system used in these tools based on Bacon cell. Until now, the energy used in the spacecraft still use fuel cell because the fuel cell energy used is not too complicated such as a battery or nuclear power are quite risky. In terms of technology research fuel cell, NASA has funded more than 200 research.

Not only that, the technology fuel cell that is found also be varied, such as the discovery of fuel cells are more efficient at generating hydrogen gas by increasing number doubled. This technology involves even by microbial fermentation processes that were previously impossible once in fuel production.

Obstacles still restrict the use of fuel cell, among others:

1.    If the use of hydrogen fuel, it takes a thick-walled safety tank and has a safety valve. Also required compressor to enter into the tank.

2.    If that is taken is liquid hydrogen, then there will be trouble of having to be maintained at a temperature of -253,15 °C at a pressure of 10⁵ Pa.

3.    If the use of methanol instead of hydrogen, then the required reformer. But efficiency is lowered.

4.    The temperature is quite high when operating between 60 °C -120 °C

DEVELOPMENT OF FUEL CELL

Fuel cells are a source of electric power using hydrogen and methanol as fuel and oxygen as oxidant produce water. The concept is very simple: to change the electrochemical energy into electrical energy. This concept was first invented by Sir William Grove in 1839. The rationale Grove is the reverse process of electrolysis. He discovered an idea to split water into oxygen and hydrogen by using electric power and generate the return force by combining the two gases. He uses sulfuric acid and platinum as a generator.

Cells created by Grove named gas voltaic battery. The cell consists of two rod electrodes (anode and cathode) are different, and between the two electrode rods are connected by a series of conductive electrons. Grove cell produces a voltage of 1,8 volts and the current 12 Amphere.

Then, scientists Ludwig Mond and Charles Langer has tried discovery Grove on a practical tool, with its findings to be named a fuel cell. In 1932, Francis T. Balcon has been researching the financing of the fuel cell through the cell and finally they tried to commercial it. In 1959, in collaboration with a company Balcon garden equipment from Milwaukee to make a wheel. In addition, in early 1950 Pennsylvania General Electric formed an SBA program for the purpose of moving the generator. The scientists General Electric (GE) at the time tried to use air as the source of oxygen. In 1965, the SBA as a reserve power source to the spaceship Gemini 5. Since then, Francis Balcon cooperating with Pratt and Whitney (P&W) to make the SBA program space as a source of power (Hall & Kerr 2003).

Throughout the 1970s, the technology SBA increasingly popular among industrial users of electric power so that the SBA is applied to devices other industries. In 1973 and 1979, Blocking oil has prevailed and the United States (USA) seeking a new alternative to generate power that is not dependent on petroleum importing. Some unions and organizations have begun a study commercial SBA (Tsuchiya & Kobayashi, 2004).

Studies undertaken to understand the optimum material resources and lower the price of this technology. Throughout the 1980s, the technology from the initial SBA tested for usability principles and manufacture of automobiles. In 1993, Ballard has produced and marketed vehicles using fuel cells fire.

In terms of marketing, Johnson Matthey reports that this type of technology is quite suitable for the automobile sector as well as other purposes. In addition, the EG&G Services (2004) also reported that the SBA has the power of a high enough power. Therefore, the United States formed a new automobile association program (USCAR) to develop SBA automobile technology and hydrogen infrastructure reserve as a refueling point hydrogen flame. In addition, several international magazines such as Parade Magazine, Business fuel cell Meet Big Business, Tansportation SAE 200 is also planned that the SBA as an energy alternative to burning energy.

This fact can be accepted by virtually all countries in the world because every gallon of fossil flame used in the combustion energy will generate 20 lb CO₂ polluting the state. For example, the United States produces 10,700 lb CO₂ and pollute the air with a quarter of the air density.

With these developments, many countries in the world do the investigation and development of the SBA. In the early 2000s, Universiti Kebangsaan Malaysia (UKM) and Universiti Teknologi Malaysia (UTM) combine to produce SBA. In 2005, SMEs have been doing prototypes motosikal that use SBA. Until now, this has been known 6 fuel cells that are differentiated based on the electrolyte used and the operating conditions (temperature and pressure) cells. The sixth of these cells is: Proton Exchange Membrane Fuel Cell (PEMFC), Alkaline Fuel Cell (AFC), Molten carbonate fuel cell (MCFC), Posphoric Acid Fuel Cell (PAFC), Solid Oxide Fuel Cell (SOFC), Direct Methanol Fuel Cell (DMFC).

Institutions that have developed and sell fuel cell including the International Fuel Cell, Avista Labs, Energy Partners, H Power, Energy Research Corporation, Allied Signal (US), Ballard (Canada), Mitsubishi, Toshiba, Ishikawajima-Harima Heavy Industries, Fuji Electric (Japan), DeNora (Italy), Rolls-Royce (UK), Siemens (Germany), Ceramic Fuel Cell (Australia), and Siemens-Westinghouse (Germany-US).

Hydrogen as a fuel is a material that is non-toxic, colorless, and when it is burned with the air will react and produce only water. A source of hydrogen is widely available in nature as a material that can be renewable for example biomass, water, industrial waste (steel and soda), waste city gas, vegetable oil besides petroleum fractions such as (gasoline, naphtha, methanol, ethanol, natural gas, etc.). Hydrogen is a chemical element that brings energy. Hydrogen can be marketed in the form of a liquid or a gas. In addition to fuel boilers and steam turbines, hydrogen can normally be used for the fuel cell as a power plant, because it can generate an electrical efficiency of up to 40%-60%. The application of hydrogen energy, among others:

- As the fuel in the fuel cell.

- As a material for the chemical industry.

- As fuel boiler and steam turbine.

Hydrogen fuel cells are one of the tools that change the energy-producing electrochemical energy directly into electrical energy. Results of electrochemical reaction is water, in contrast to conventional engines produce exhaust gases that are toxic such as (CO_2, CO, SO_X, NO_X, VOM) and other gases are very harmful to the environment. Besides, the fuel cell produces high power efficiency compared to conventional machines because there is no friction loss shaft.

WORKING PRINCIPLE OF FUEL CELL

Fuel cell is a device electrochemical energy conversion that will convert hydrogen and oxygen into water, simultaneously generating electrical energy and heat in the process. Fuel cell is a form of simple technologies such as rechargeable batteries fuel to get his energy back, in this case the fuel is oxygen and hydrogen.

Just like a battery, any kind of fuel cell has positive and negative electrodes also called cathode and anode. The chemical reaction that produces electricity occurs on the electrode. In addition to electrodes, one unit there electrolyte fuel cell that will carry electrical charges from one electrode to the other electrode, and a catalyst that will accelerate the reaction at the electrode. Generally distinguish the types of material electrolyte fuel cell is used. Electric current and heat is generated every type of fuel cell is a by-product of chemical reactions that occur in the cathode and anode.

 Figure 1.

Diagram of Fuel Cells

Because the energy produced by the fuel cell is a chemical reaction forming water, an electrochemical energy conversion device will not produce side effects that are harmful to the environment as conventional energy conversion devices (eg combustion processes in the engine). In terms of energy efficiency, the application of fuel cells inportable batteries such as mobile phones or laptops will hold ten times longer than lithium batteries. And to replenish the energy will be faster because the energy is used instead of electricity, but the fuel is liquid or gas.

The working principle of the fuel cell is the reverse process of electrolysis, where hydrogen reacted with oxygen and produce electricity.

2H₂ + O₂ à 2H₂O

In the aforementioned reaction liberated heat energy can then be generated electrical energy. The resulting electrical current is very small. This is due to several things:

(a)    The low contact area between gas, electrode and electrolyte;

(b)   The long distance between the electrodes and the electrolyte causing the electrical current prisoners. So as to improve the performance of electrodes made ​​into a plate with a thin layer of electrolyte (as shown in Figure 2). Electrode structure made ​​from porous materials that cause electrolyte on one side and the other side can penetrate. 

Figure 2.

The Basic Structure Of The Fuel Cell

At the anode, the acid from the electrolyte, the hydrogen will produce ionized electrons and hydrogen ions (protons). This reaction will liberate energy.

2H₂ à 4H⁺ + 4e^-

While at the cathode, oxygen reacts with the electrons extracted from the electrodes and protons (hydrogen ions) to form water.

O₂ + 4e^- + 4H⁺ à 2H₂O

The above reaction takes place continuously, the electrons produced at the anode should be able to pass through the electric circuit to the cathode. Likewise, hydrogen ions (protons) must be able to pass through the electrolyte.

FUEL CELL

Fuel cells are a source of electric power using hydrogen as fuel and oxygen as oxidant that produces exhaust is water, electrochemical energy is converted directly into electrical energy. In contrast to batteries that work is not continuous, the fuel cell can work continuously while fuel is supplied into the cell. The most important part in the fuel cell is two layers of electrodes and electrolyte. Electrolytes are substances that can conduct ions. Hydrogen gas (H₂) supplied to the anode, platinum (Pt) contained in the anode serves as a catalyst that will take electrons from hydrogen atoms. H⁺ ions are formed will pass through the electrolyte, while the electrons remain behind in the anode. Oxygen is supplied to the cathode, then H⁺ ions pass through the electrolyte binds with oxygen produces water (H₂O). This reaction would take place if there are electrons at the anode, while the cathode requires electrons. If the anode and the cathode connected to the electrons will flow and reduction-oxidation reactions will take place. The process is the basic principle of a fuel cell work.

One unit fuel cell consists of two electrodes and an electrolyte Pt – called single cell. The voltage obtained from a single cell is equal to about 1 volt dry cell, to be able to produce a high voltage or desired then the cells can be arranged in series or parallel. A collection of many single cell is called a stack. Stack made ​​of single cells and cell separator. Stack can be used for electronic equipment and household purposes, for example in mobile phones that require single cells, while for household use needed 20 more single cells and to car needed 200 more single cells. Currently the price of these materials are very expensive, so as to be applied to cars is still relatively expensive.

 

Figure 1.

Fuel Cell Structure

Based on the difference in electrolyte used, fuel cells can be divided into six types, i.e. polymer electrolyte fuel cell (PEFC), alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC), and direct methanol fuel cell (DMFC). The sixth type, temperature and scale have different energy. Six types are then split into two, namely fuel cells working at high temperature and fuel cells that work at low temperatures. Every cell type has its own advantages and disadvantages. Excess cells work at temperatures below 2000 °C (AFC, PEMFC, DMFC and PAFC) is the start up and shut down faster, easy to make, and its use is widespread. The disadvantage, the catalyst is deactivated by impurities, especially CO in the hydrogen can react with the catalyst. Other losses are not able to use a liquid fuel directly. Cell SOFC and MCFC operates at temperatures above 2000 °C allows the use of solid fuels such as coal or liquid fuels such as gasoline directly without going through the reformer. Waste heat can be utilized as a steam generator. The catalyst does not need precious metals and catalysts are more resistant to CO. Weakness of these cells operate at high temperatures so that the start up and shut down a long, hard look for materials that are resistant to high temperature and because of the difference in temperature start up and shut down relatively large, it is possible that the cells will rupture. Use of a cell is limited to providing large-scale power centers e.g. power plants.

HYDROGEN GAS AS FUEL

The problems facing the world today is the problem of air pollution due to the use of fuel and fuel mineral crisis (petroleum). As we know that the ability of countries in the world to provide fuel progressively decreases and at some point will reach its peak, as almost all areas containing oil have been discovered and explored. While the demand for fuel continues to rise sharply, so that the world's oil reserves are running low.

Along with the expensive and limited petroleum and greenhouse effects are globalized, the use of alternative energy that are environmentally friendly and simple is needed. One of them is a hydrogen energy. Hydrogen is one of the important chemical substances, simplest, and most widely in nature, which is consumed by the world reached 50 million tons / year. The energy possessed by hydrogen can be converted into electrical energy with the help of a device called a fuel cell. The most important part in the fuel cell is two layers of electrodes and electrolyte.

Hydrogen bound in organic matter and water makes up 70% of the earth's surface. Hydrogen gas is a gas that is colorless, odorless, and tasteless in normal environmental conditions. The reason for hydrogen gas is used as fuel because hydrogen has a molecular weight that is light and has a high energy content.

Hydrogen gas can be obtained from the reaction of a hydrocarbon reformer at this time is obtained from large plants. Hydrogen gas can also be obtained from methanol after decomposed into carbon dioxide and hydrogen, then the CO gas is oxidized to CO₂ and water. Hydrogen gas has difficulty to be stored and transport due to small molecule making it difficult for liquefied and flammable.

Another way to produce hydrogen is by electrolysis. Electrolysis can separate the element of water (H and O) with the provision of electric current to the water. The addition of electrolytes such as salt can increase water conductivity and improve process efficiency. Payload break the chemical bonds between the hydrogen and oxygen, creating charged particles called ions. Ions are formed on two poles: an anode, a positively charged and a negatively charged cathode. Hydrogen is collected at the cathode and oxygen at the anode. A voltage of 1,24 volts needed to separate the hydrogen from the oxygen in pure water at 77 °F. The voltage will increase or decrease depending on changes in temperature and pressure.

Motor vehicles can use hydrogen as a fuel. Burning hydrogen creates air pollution that is more environmentally friendly than gasoline or diesel. Hydrogen also has a higher burning speeds, flammable, blasting high temperatures, and requires little energy to burn than gasoline alone. This means that hydrogen burns faster, but it is quite dangerous. Hydrogen as a vehicle fuel has the advantages of higher energy, the vehicle engine is not noisy, and produces exhaust (H₂O) that are environmentally friendly.