Fuel Cell Practical

INTRODUCTION

Unlike normal batteries fuel cells supply electricity as long as it supplied with fuel. Inside the fuel cell electricity generate by chemical reaction. Fuel cell consist of three major parts anode, cathode electrolyte and catalyst make reactions faster. Electrolyte act as iron exchanging medium .Different types of fuel cells are designed using different types of electrolytes.

APPERATUS

·         PEM fuel.

·         Two Multimeters.

·         Rheostat.

·         Electrolyzes to provide Hydrogen.

PROCEDURE

·         Container is filled with distill water up to indicated mark.

·         Use battery and solar panel parallel to generate power which requires generating H_2.

·         After sufficient amount of H₂ production connects electrolyzer to the one end of the fuel cell while other end of the fuel cell closed.

·         Measure the voltage and currents varying the resistance of the external circuit.

CALCULATION

Resistance (Ω)	Voltage (V)	Current (mA)	Power (W)
Open circuit	4.21	0	0.00
330	3.84	10	0.04
100	3.56	30	0.11
50	3.3	70	0.23
31	3.17	100	0.32
1.1	1.08	150	0.16
0.55	0.18	180	0.03
0	0.1	180	0.02

Maximum power =0.27 (W)

Current at maximum power = 100mA

Voltage at maximum power =1.2V

Resistance at maximum power =12Ω

Discussion

1. Types of fuel cells and their difference, use and performances

1.1Alkaline Fuel Cell

 Alkaline fuel cell is most historical fuel cell which is developed. In these types of fuel cells KOH is used as the electrolyte. Inside the cell OH- irons travelsfrom cathode to anode and react with hydrogen gas hence produce water and release electrons near the anode. Electrons migrate through an external circuit to cathode and reacts with oxygen and produce OH- irons.

1.1.1Performance

·         Efficiency around 60-70% which is considered as high efficiency.

·         Typically used to generate power 10-100kW.

·         Operating at 65-220C temperature.

        1.1.2 Advantages

·         High performance due to fast cathode reaction.

·         Wide range of electro catalysts can be used.

·         Low cost components.

·         Produce water as a byproduct.

1.1.3 Disadvantages

·            React with CO₂ so fuel and air must be CO₂ free.

·            Using expensive catalyst like platinum.

1.1.4 Applications

·            Used for military and space applications. Mainly due to material durability issues commercially this technology to be used.

1.2 Polymer Electrolyte Membrane (PEM) Fuel Cells.

  In PEM fuel cells used solid polymer as an electrolyte, porous carbon electrodes and platinum catalyst. Unlikealkaline fuel cells oxygen is directly taken from atmosphere but pure hydrogen is required. Catalyst platinum is highly sensitive to CO so hydrogen which is derived from hydrocarbon or alcohol must be filtered.H₂ divided into protons and electrons at anode. Then electrons travel to cathode through the external circuit while H+ irons travels through the electrolyte. H+ irons and electrons react with the oxygen and produce water.

1.2.1Performance

·         Efficiency around 60-35%.

·         Generate power up to 1–100kW.

·         Operating at very low temperature which is 50-100C.

1.2.2        Advantages

·         Solid electrolyte reduces corrosion& electrolytemanagement problems.

·         Quick startup.

·         Low operating temperature.

·         Produce water as a byproduct.

·         Low power to weight ratio.

1.2.3 Disadvantages

·            React with CO so fuel must be CO free.

·            Using expensive catalyst like platinum.

1.2.4 Applications

·            Special electric vehicle batteries.

·            Portable and backup power

·            Transportation.

1.3Phosphoric Acid Fuel Cells.

   Anode and cathode reactions are similar to the PEM fuel cells but electrolyte is different.Liquid phosphoric acid as an electrolyte is used. This type of fuel cells is used for stationery power genera ration. As a fuel cellit has very low efficient but by cogeneration electricity and heat it can reach 85% efficiency.

1.3.1Performance

·         Efficiency around 40%.

·         Generate power up to 100–400kW.

·         Operating at 150-200C temperature.

       1.3.2Advantages

·         Very high efficiency as cogenerating heat and electricity.

·         Can withstand fuel impurities.

1.3.3 Disadvantages

·            Platinum catalyst

·            Long start up time

·            Low current and power.

1.3.4 Applications

·            Special electric vehicle batteries.

1.4 Molten Carbonate Fuel Cells.

These types of fuel cells used in coal-based power plants for their electricity requirement. Molten carbonate fuel cells contain molten carbonate salt mixture and use ceramic lithium aluminum oxide as a catalyst. Because of the high operating temperatures non-precious metals can be used.

                 Anode reaction: CO₃2- + H₂ => H₂O + CO₂ + 2e-

                 Cathode Reaction:  CO₂+ 1/2O₂ + 2e- => CO₃2-

Molten carbonate melts in high temperatures generating carbonate irons. Because of high operating temperature startup time is very low.

        1.4.1Performance

·         Efficiency around 45-50%.

·         Generate power up to 300kW–3MW.

·         Operating at 600-700C temperature.

        1.4.2Advantages

·         Very high efficiency as cogenerating heat and electricity.

·         Can use variety of catalyst.

·         Fuel flexibility.

1.4.3 Disadvantages

·            High temperature can reduce lifespan of the battery.

·            Long start up time

·            Low current and power.

1.4.4 Applications

·            Distributed generation.

·            Electric utility.

1.5Solid Oxide Fuel Cell.

These types of fuel cells have solid electrolyte which is made of non-porous ceramic compound. no need for plate type cell constructionBecause of the solid electrolyte. Fuel operating temperature is very high so need to have expensive metals which reduce cost of the fuel cell. By cogenerating electricity and heat high efficiency can be achieved. It has very slow start up time mainly due  totime taken to reach high temperatures. Because of the temperature and weight can’t use for portable operations.

                 Anode Reaction: 2 H₂ + 2 O^2- => 2 H₂O + 4 e^-

                 Cathode Reaction: O₂ + 4 e^- => 2 O^2-

         1.4.1Performance

·         Efficiency around 60%.

·         Generate power up to 1–3MW.

·         Operating at 600-1000C temperature.

        1.4.2Advantages

·         Very high efficiency as cogenerating heat and electricity.

·         Can use variety of catalyst.

·         Fuel flexibility.

·         Solid electrolyte.

1.4.3 Disadvantages

·            High temperature can reduce lifespan of the battery.

·            Long start up time

·            Low current and power.

·            Can’t use for portable applications.

1.4.4 Applications

·            Distributed generation.

·            Electric utility.

·            Auxiliary power.

2.Shortcomings of existing fuel cell technology.

Main problem is most of the fuel cell use H₂ as fuel which is not naturally existing gas which need to be generated. If there is an fuel cell which take CO₂ as fuel then its become very effective. Another is space requirement for H₂ storage and H₂ is very flammable gas so extra precautions need to be taken which reduce portability of the fuel cell. Most of the fuel s is operating at high temperatures which restrict the applications.

3. Performance ofIC engine vs. Fuel cell automobile engine.

H₂ is considered as renewable energy mainly because it can be generated by water. For generating H₂ electricity is required and natural source like solar power can be used to generate the electricity. Storing H₂ is much effective than storing electricity but more risky than other fuels. .Fuel cell is the one that convert H₂ into electricity. Hydrogen fuel cells in vehicles proved to be more efficient than Ic combustion engine.

Toyota Highlander FCHV-adv hydrogen fuel cell vehicle achieved an incredible average fuel economy of 68.3 miles per kilogram of hydrogen In the other hand Toyota Highlander Hybrid that is powered by gasoline gets an EPA-estimated 26 miles per gallon.

             Weight of a 1L liquid hydrogen = 0.070752Kg.

             Weight of a 30L liquid hydrogen = 2.12Kg.

So weight of liquid hydrogen is much lower than gasoline .so energy that can be carrying by gasoline is much higher than gasoline. But carrying hydrogen is much risky and special costly storages are required. Hydrogen fuel cells like PEM operates at very low temperature while internal combustion engine has high temperatures which resulting thermal energy lost But IC engine convert chemical energy directly to motion while fuel cells convert chemical energy into electric energy and it need to be converted in to kinetic energy.