Fuel Cell Technology


This paper investigates the physics behind the fuel cells.Starting from it's meaning ,it's historical origin,to frequently asked questions associated with it ,then we go into some research work performed on it and try to understand it's results .Concluding the paper with discussing our own understanding in the topic.

Introduction:

Fuel Cell, device in which the energy of a chemical reaction is converted directly into electricity. Unlike a battery, a fuel cell does not run down; it operates as long as fuel and an oxidant are supplied continuously from outside the cell.
A fuel cell consists of an anode, the negative end of an electric circuit, and a cathode, the positive end of an electric circuit, separated by an electrolyte. Electrolytes are substances that allow ions (particles formed when a neutral atom or molecule gains or loses one or more electrons) to pass through them. Fuel flows to the anode, and an oxidant flows to the cathode. The chemical reaction between the fuel and the oxidant produces an electric current. Fuel cells are different from conventional electrochemical cell batteries in that they consume reactant from an external source, which must be replenished -a thermodynamically open system. By contrast, batteries store electrical energy chemically and hence represent a thermodynamically closed system.

Historical origin:

In 1800, British scientists William Nicholson and Anthony Carlisle had described the process of using electricity to decompose water into hydrogen and oxygen. But combining the gases to produce electricity and water was, according to Grove, "a step further that any hitherto recorded." Grove realized that by combining several sets of these electrodes in a series circuit he might "effect the decomposition of water by means of its composition." He soon accomplished this feat with the device he named a "gas battery"– the first fuel cell.
William Robert Grove (1811 -1896), a Welsh lawyer turned scientist, won renown for his development of an improved wet-cell battery in 1838. The "Grove cell," as it came to be called, used a platinum electrode immersed in nitric acid and a zinc electrode in zinc sulfate to generate about 12 amps of current at about 1.8 volts.

“Despite their modern high-tech aura, fuel cells actually have been known to science for more than 150 years. Though generally considered a curiosity in the 1800s, fuel cells became the subject of intense research and development during the 1900s.”
SOURCE: PR-Inside.com

Some FAQ'S(Frequently Asked Questions):

(i) What is so interesting about fuel cells?

Ans. • Direct energy conversion (no combustion)
• No moving parts in the energy converter
• Quiet
• Demonstrated high availability of lower temperature units
• Siting ability
• Fuel flexibility
• Demonstrated endurance/reliability of lower temperature units
• Good performance at off-design load operation
• Modular installations to match load and increase reliability
• Remote/unattended operation
• Size flexibility
• Rapid load following capability

(ii) Being so good and energy efficient why can’t I go out and buy a fuel cell?

Ans. The basic workings of a fuel cell may not be difficult to illustrate. But building inexpensive, efficient, reliable fuel cells is a far more complicated business.Many of the choices facing fuel cell developers are constrained by the choice of electrolyte. The design of electrodes, for example,and the materials used to make them depend on the electrolyte.

(iii) What is the future potential of fuel cells technology?

Ans. Fuel cells in vehicles combine very high-energy efficiency with zero exhaust emissions and potentially low noise without diminishing its performance and range.
In the medium to long term, fuel cells have a strong energy saving potential for decentralised co- generation in households and buildings and for power production.
In the long term they could replace a large part of the current combustion systems in all energy end use sectors.

Different Types of fuel cells:

Alkali fuel cell
Molten carbonate fuel cell
Phosphoric Acid fuel cells (PAFC)
Proton Exchange Membrane (PEM) fuel cells
Solid oxide fuel cell

Alkali fuel cells operate on compressed hydrogen and oxygen.Molten Carbonate fuel cells (MCFC) use high-temperature compounds of salt (like sodium or magnesium) carbonates (chemically, CO3) as the electrolyte.Phosphoric Acid fuel cells (PAFC) use phosphoric acid as the electrolyte.Proton Exchange Membrane (PEM) fuel cells work with a polymer electrolyte in the form of a thin, permeable sheet.Solid Oxide fuel cells (SOFC) use a hard, ceramic compound of metal (like calcium or zirconium) oxides (chemically, O2) as electrolyte.Alkali fuel cells have maximum efficiency(70-80%).

Fig1.1: Alkali Fuel cell Fig1.2: Molten Carbonate Fuel cell

Fig1.3: Phosphoric Acid and P.E.M fuel cell

Table 1.1 Electrochemical Reactions in Fuel Cells

Fuel Cell
Anode Reaction
Cathode Reaction
Alkaline
H2 + 2(OH)(-) ? 2H2O + 2e-
H2 + 2(OH)- ? 2H2O + 2e- 1?2 O2 + H2O + 2e- ? 2(OH)-
Molten Carbonate
H2 + CO3(2-) ? H2O + CO2 + 2e-
CO + CO3(2-) ? 2CO2 + 2e-
1?2 O2 + CO2 + 2e- ? CO3 (2-)

Polymer Electrolyte and Phosphoric Acid
H2 ? 2H(+) + 2e-
1?2 O2 + 2H+ + 2e- ? H2O

Solid Oxide
H2 + O(2-) ? H2O + 2e-
CO + O(2-)? CO2 + 2e-
CH4 + 4O(2-) ? 2H2O + CO2+8e-
1?2 O2 + 2e- ? O(2-)

In the next section , I am breifly discussing on a major problem related to
fuel cell i.e storage of fuel , as we know hydrogen fuel cell is a potent energy source for future but it's storage is a big challenge for scientists even today.

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