Presented by

biPin guPta

A fuel cell is an electrochemical energy conversion device that converts hydrogen and oxygen into electricity, heat, and water as a result of a chemical reaction.

1. Introduction

•Fuel and air react when they come into contact through a porous membrane (electrolyte) which separates them.

•This reaction results in a transfer of electrons and ions across the electrolyte from the anode to the cathode.

Fuel CellChemical Energy

Electrical Energy

Fuel

Water

• If an external load is attached to this arrangement, a complete circuit is formed and a voltage is generated from the flow of electrical current.

(+) (-)

Anode Cathode Electrolyte

2.Parts of a fuel cell.

A fuel cell configuration

There are 4 main parts• Anode• Cathode• Catalyst• Proton exchange

membrane (or)• Solid oxide electrolyte

The anode is the negative post of the fuel cell. It conducts the electrons that are freed from the

hydrogen molecules so that they can be used in an external circuit.

It has channels etched into it that disperse the

hydrogen gas equally over the surface of the catalyst

The cathode is the positive post of the fuel cell. It has channels etched into it that distribute the

oxygen to the surface of the catalyst. It also conducts the electrons back from the

external circuit to the catalyst, where they can recombine with the hydrogen ions and oxygen to form water.

The catalyst is a special material that facilitates the reaction of oxygen and hydrogen.

It is usually made of platinum powder very thinly

coated onto carbon paper or cloth. The catalyst is rough and porous so that the maximum surface area of the platinum can be exposed to the hydrogen or oxygen.

The platinum-coated side of the catalyst faces the

PEM.

The electrolyte is the proton exchange membrane. This is a specially treated material that only

conducts positively charged ions. The membrane blocks electrons.

11Fuel Cell Stack

3. Types of fuel cellsThere are different types of fuel cells, differentiated by the type of electrolyte separating the hydrogen from the oxygen. The types of fuel cells are:

• Alkaline fuel cells (AFC)• Direct methanol fuel cells (DMFC)• Molten carbonate fuel cell (MFFC)• Phosphoric acid fuel cells (PAFC)• Polymer electrolyte membrane fuel cells (PEMFC)• Solid oxide fuel cells (SOFC)

Used in spacecraft to provide drinking water and electricity

Electrolyte: Aqueous solution of alkaline potassium Hydroxide

Output of 300W -5KW

Power generation efficiency of about 70%

Too expensive for commercial applications

Used in hospitals, nursing homes and for all commercial purposes

Electrolyte: Liquid Phosphoric acidCatalyst: platinumElectrical efficiency of 40% Advantages :using impure hydrogen as fuel and

85% of the steam can be used for cogeneration

Also called as Solid Polymers and used for quick startup in automobiles, light duty vehicles and potentially to replace rechargeable batteries

Electrolyte :Solid organic polymer poly-perflourosulfonic acid.

Catalyst: Metals (usually platinum) coated on both sides of membrane act as catalyst

Advantages: Use of solid electrolyte reduces corrosion and management problems

Majorly used for electric utility applications

Electrolyte: Liquid solution of lithium, sodium and/or potassium carbonates.

Catalyst: Inexpensive metals can be used as catalyst other than Platinum

Advantages: High operating temperature allow for inexpensive catalysts

Highly promising fuel cell

Used in big, high-power applications including industrial and large-scale central electricity generating stations

Some developers also see SOFC use in motor vehicles

Power generating efficiencies could reach 60% and 85%

Principle:The fuel is oxidized on

the anode and oxidant reduced on the cathode. One species of ions are transported from one electrode to the other through the electrolyte to combine there with their counterparts, while electrons travel through the external circuit producing the electrical current.

Electrons (e-)

Fuel Permeable

Anode

Electrolyte

Oxidant Permeable

Cathode

Fuel Oxidant

Cations (+ve)

Anions (-ve)

4. Principle, construction and working of H2-O2 fuel cell

WorkingThe Fuel gas (hydrogen rich) is passed towards the anode where the following oxidation reaction occurs:

H2 (g) = 2H+ + 2e-

The liberated electrons from hydrogen in anode side do not migrate through electrolyte.

Therefore, they passes through the external circuit where work is performed, then finally goes into the cathode.

On the other hand, the positive hydrogen ions (H+) migrate across the electrolyte towards the cathode.

At the cathode side the hydrogen atom reacts with oxygen gas (from air) and electrons to form water as byproduct according to:

H2 + 1/2 O2 +2e- H2O + Heat

fuel + oxidant product + Heat

The overall cell reaction is

PEM CELL

Mechanism of SOFC’s

Reactions:

At Anode:2H2 + 2O–2 → 2H2O + 4e–

At Cathode:O2 + 4e– → 2O–2

Overall Reaction: 2H2 + O2 → 2H2O

The liberated electrons from the hydrogen are responsible for the production of electricity.

The water is produced by the combination of hydrogen, oxygen and liberated electrons and is sent out from the cell.

The DC current produced by fuel cell is later converted into AC current using an inverter for practical application.

The voltage developed in a single fuel cell various from 0.7 to 1.4 volt.

More power can be obtained by arranging the individual fuel cell as a stack. In this case, each single cell is sandwiched with one another by a interconnect.

Therefore, electricity power ranging from 1kW to 200 kW can be obtained for domestic as well as industrial application.

(a) Anode:

(b) Cathode:

• Cermet of Ni and type of electrolyte.• Thickest and strongest• Oxidize the H2 Fuel

• Lanthanum Strontium Magnetite(LSM)• Similar thermal coefficient as of electrolyte.• Reaction occurs at triple phase boundary.

(a)Electrolyte:

(d) Inter Connect :

• The interconnect can be either a metallic or ceramic layer that connects each individual cell.• Chromium and steel-based alloys are mostly used.• 95Cr-5Fe alloy.

The electrolyte is a dense layer of ceramic that conducts oxygen ions.Most Popular Electrolytes are :• Yttria Stabilized Zirconia (YSZ)• Gadolinium Doped Ceria (GDC)

HydrogenOxygen

Electrical power production by fuel cell

Rotating shaft connected to generator for electricity production

Advantages • Zero Emissions: a fuel cell vehicle only emits water

vapour. Therefore, no air pollution occurs.

• High efficiency: Fuel cells convert chemical energy directly into electricity without the combustion

process. As a result, Fuel cells can achieve high efficiencies in energy conversion.

• High power density: A high power density allows fuel cells to be relatively compact source of electric power, beneficial in application with space constraints.

5. Advantage, disadvantage and applications

• Quiet operation: Fuel cells can be used in residential or built-up areas where the noise pollution can be avoided.

• No recharge: Fuel cell systems do not require recharging.

Disadvantages • It is difficult to manufacture and store pure hydrogen at higher pressure.

• It is very expensive as compared to battery

The high temperature limits applications of SOFC units and they tend to be rather large

While solid electrolytes cannot leak, they can

crack. Complex materials

AssemblingMaintenanceDesign Cost & choice of material

Major Application(a) Chemical Industries and Power Plants:

(a) Stationary energy resources:•Power for municipalities, rural areas and industries.•Heat and electricity for homes.•Long-lasting mobile power for computers, cell phones and other electronics(b) Transportation:•Non polluting automobiles•Inexpensive fuels (c) Military applications:• Fuel cells could significantly reduce deployment costs

Other Applications

1. Portable applications

• They used in portable appliances and power tools

• They can be used in small personal vehicles

• They are used Consumer electronics like laptops, cell

phones can be operated

• They can be used in Backup power

A laptop using a fuel cell power source can operate for up to 20 hours on a single charge of fuel (Courtesy: Ballard Power Systems

2. Transportation applications• They can be used for transport application in the

following areas,

• Industrial transportation

• Public transportation

Commercial transportation

(truck, tractors)

• Marine and Military

transportation

3 . Power distribution application

• Fuel cells can be used for the distribution of power in various fields such as,

• Homes and small businesses

• Commercial and industrial sites

• Remote, off-grid locations (telecom towers, weather

stations)

Research • Research is going now in the direction of lower-temperature SOFC (400°C) in order to decrease the materials cost, which will enable the use of metallic materials with better thermal conductivity.

• Research is also going on in reducing start-up time to be able to implement SOFCs in mobile applications.

• Research is currently underway to improve the fuel flexibility of SOFCs.