Fuel cell

Chemistry Digital Assignment

Vinit Shahdeo

15BIT0335

What is Fuel Cell..???

A fuel cell produces electricity through a chemical reaction, but without combustion. It converts hydrogen and oxygen into water, and in the process also creates electricity. It’s an electro-chemical energy conversion device that produces electricity, water, and heat. Fuel cells operates much like a battery, except they don’t require electrical recharging. A battery stores all of its chemicals inside and coverts the chemicals into electricity. Once those chemicals run out, the battery dies. A fuel cell, on the other hand, receives the chemicals it uses from the outside; therefore, it won’t run out. Fuel cells can generate power almost indefinitely, as long as they have fuel to use. The reactions that produce electricity happen at the electrodes. Every fuel cell has two electrodes, one positive, called the anode, and one negative, called the cathode. These are separated by an electrolyte barrier. Fuel goes to the anode side, while oxygen (or just air) goes to the cathode side. When both of these chemicals hit the electrolyte barrier, they react, split off their electrons, and create an electric current. A chemical catalyst speeds up the reactions.

How does Fuel Cells

Work..??? Hydrogen molecules are delivered to the anode side of the

fuel cell.

Electrons are stripped from the molecules and forced to

travel through a circuit, producing electricity.

The leftover protons pass through the fuel cell and are

recombined with the lost electrons on the cathode side,

producing water molecules.

Working of Fuel Cell

• Pressurized hydrogen gas (H2) enters cell on anode side.

• Gas is forced through catalyst by pressure.

• When H2 molecule comes contacts platinum catalyst, it

splits into two H+ ions and two electrons (e-).

• Electrons are conducted through the anode

• Make their way through the external circuit (doing

useful work such as turning a motor) and return to the

cathode side of the fuel cell.

• On the cathode side, oxygen gas (O2) is forced through the

catalyst

• Forms two oxygen atoms, each with a strong negative

charge.

• Negative charge attracts the two H+ ions through the

membrane,

• Combine with an oxygen atom and two electrons from

the external circuit to form a water molecule (H2O).

Fuel Cells Vs Conventional Power Sources

FC is an electrochemical device in which the energy of fuel and

oxidant continuously supplied to electrodes is directly converted

into electricity without low-efficient combustion process.

As there is no heat/power conversion in these devices, their

energy efficiency is much higher than that of traditional power

units, and can reach 90%.

Benefits of fuel cells

Environmental Performance

Since hydrogen fuel cells don’t produce air pollutants or greenhouse gasses, they can significantly improve our environment. Energy Efficiency Fuel cells are 2 to 3 times more efficient than combustion engines. For co-generation applications, where fuel cells generate both heat and electricity, efficiencies can be close to 80%.

Versatile Fuel cells are scalable, and provide everything from mill watts to megawatts of power in a variety of uses - from cellphones, to cars, to entire neighborhoods. Health Benefits Hydrogen fuel cells only produce heat and water – no toxins,

particles, or greenhouse gasses, which means cleaner air for us

to breathe.

Fuel Flexibility There are many types of fuel cells, and each can operate in a clean manner using different fuels including hydrogen, natural gas, methanol, ethanol, and biogas.

Complementary

Fuel cells can readily be combined with other energy technologies, such as batteries, wind turbines, solar panels, and super-capacitors.

Some Limitations

Hydrogen:

o Not readily available, must use other energy sources to

convert

o Infrastructure not in place

o Difficult to store/distribute

High Capital Cost

Non-technical barriers

o Could have dramatic impact

Future of Fuel Cells

2015 – 2025- Substantial markets for

Hydrogen-powered vehicles likely to

Start developing

2020: 5 to 10 million

Hydrogen-powered cars

2030: 50 million

Hydrogen powered cars

2040: 150 million

Hydrogen-powered cars

Types of Fuel Cells

Polymer electrolyte membrane (PEM) fuel cells

Direct methanol fuel cells Alkaline fuel cells Phosphoric acid fuel cells Molten carbonate fuel cells Solid oxide fuel cells Reversible fuel cells

POLYMER ELECTROLYTE MEMBRANE FUEL CELLS

Polymer electrolyte membrane (PEM) fuel cells—also called proton exchange membrane fuel cells—deliver high power density and offer the advantages of low weight and volume compared with other fuel cells. PEM fuel cells use a solid polymer as an electrolyte and porous carbon electrodes containing a platinum or platinum alloy catalyst. They need only hydrogen, oxygen from the air, and water to operate. They are typically fueled with pure hydrogen supplied from storage tanks or reformers.

PEM fuel cells operate at relatively low temperatures, around 80°C (176°F). Low-temperature operation allows them to start quickly (less warm-up time) and results in less wear on system components, resulting in better durability. However, it requires that a noble-metal catalyst (typically platinum) be used to separate the hydrogen's electrons and protons, adding to system cost. The platinum catalyst is also extremely sensitive to carbon monoxide poisoning, making it necessary to employ an additional reactor to reduce carbon monoxide in the fuel gas if the hydrogen is derived from a hydrocarbon fuel. This reactor also adds cost.

PEM fuel cells are used primarily for transportation applications and some stationary applications. Due to their fast startup time and favorable power-to-weight ratio, PEM fuel cells are particularly suitable for use in passenger vehicles, such as cars and buses.

DIRECT METHANOL FUEL CELLS

Most fuel cells are powered by hydrogen, which can be fed to the fuel cell system directly or can be generated within the fuel cell system by reforming hydrogen-rich fuels such as methanol, ethanol, and hydrocarbon fuels. Direct methanol fuel cells (DMFCs), however, are powered by pure methanol, which is usually mixed with water and fed directly to the fuel cell anode.

Direct methanol fuel cells do not have many of the fuel storage problems typical of some fuel cell systems because methanol has a higher energy density than hydrogen—though less than gasoline or diesel fuel. Methanol is also easier to transport and supply to the public using our current infrastructure because it is a liquid, like gasoline. DMFCs are often used to provide power for portable fuel cell applications such as cell phones or laptop computers.

ALKALINE FUEL CELLS

Alkaline fuel cells (AFCs) were one of the first fuel cell technologies developed, and they were the first type widely used in the U.S. space program to produce electrical energy and water on-board spacecraft. These fuel cells use a solution of potassium hydroxide in water as the electrolyte and can use a variety of non-precious metals as a catalyst at the anode and cathode. High-temperature AFCs operate at temperatures between 100°C and 250°C (212°F and 482°F). However, newer AFC designs operate at lower temperatures of roughly 23°C to 70°C (74°F to 158°F). In recent years, novel AFCs that use a polymer membrane as the electrolyte have been developed. These fuel cells are closely related to conventional PEM fuel cells, except that they use an alkaline membrane instead of an acid membrane. The high performance of AFCs is due to the rate at which electro-chemical reactions take place in the cell. They have also demonstrated efficiencies above 60% in space applications.

PHOSPHORIC ACID FUEL CELLS

Phosphoric acid fuel cells (PAFCs) use liquid phosphoric acid as an electrolyte—the acid is contained in a Teflon-bonded silicon carbide matrix—and porous carbon electrodes containing a platinum catalyst. The electro-chemical reactions that take place in the cell are shown in the diagram to the right.

The PAFC is considered the "first generation" of modern fuel cells. It is one of the most mature cell types and the first to be used commercially. This type of fuel cell is typically used for stationary power generation, but some PAFCs have been used to power large vehicles such as city buses.

MOLTEN CARBONATE FUEL CELLS

Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas and coal-based power plants for electrical utility, industrial, and military applications. MCFCs are high-temperature fuel cells that use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic lithium aluminum oxide matrix. Because they operate at high temperatures of 650°C (roughly 1,200°F), non-precious metals can be used as catalysts at the anode and cathode, reducing costs.

Improved efficiency is another reason MCFCs offer significant cost reductions over phosphoric acid fuel cells. Molten carbonate fuel cells, when coupled with a turbine, can reach efficiencies approaching 65%, considerably higher than the 37%–42% efficiencies of a phosphoric acid fuel cell plant. When the waste heat is captured and used, overall fuel efficiencies can be over 85%.

SOLID OXIDE FUEL CELLS

Solid oxide fuel cells (SOFCs) use a hard, non-porous ceramic compound as the electrolyte. SOFCs are around 60% efficient at converting fuel to electricity. In applications designed to capture and utilize the system's waste heat (co-generation), overall fuel use efficiencies could top 85%.

SOFCs operate at very high temperatures—as high as 1,000°C (1,830°F). High-temperature operation removes the need for precious-metal catalyst, thereby reducing cost. It also allows SOFCs to reform fuels internally, which enables the use of a variety of fuels and reduces the cost associated with adding a reformer to the system. SOFCs are also the most sulfur-resistant fuel cell type; they can tolerate several orders of magnitude more sulfur than other cell types can. In addition, they are not poisoned by carbon monoxide, which can even be used as fuel. This property allows SOFCs to use natural gas, biogas, and gases made from coal. High-temperature operation has disadvantages. It results in a slow startup and requires significant thermal shielding to retain heat and protect personnel, which may be acceptable for utility applications but not for transportation. The high operating temperatures also place stringent durability requirements on materials.

Fuel Cells vs. Batteries

Designed to be continuously powered

Fuel source can be re-supplied without interrupting power

Unlike batteries, the fuel source is not contained inside the fuel cell - increases shelf life and decreases time before replacement is necessary

Produces water waste only

Environmentally friendly - companies such as Dell must currently offer recycling programs for batteries in order to comply with government environmental regulations

More efficient than batteries

Automotive Industry & Hydrogen

GM and others are looking to capitalize on the next generation of cars

After enormous success of rivals like Honda and Toyota with hybrid vehicles

GM, along with other domestic automotive makers Face serious threats of bankruptcy, making a large

R&D push difficult.

Rivals such as Toyota and Honda are already ahead of GM and Ford

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Submitted by

Vinit Shahdeo

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NAME- VINIT SHAHDEO

REG. NO.-15BIT0335

B.TECH-IT

VIT UNIVERSITY

VELLORE