Week 2 Challenge(Fuel cells and its energy & Power density)

WEEK 2 CHALLENGE

Objective:

1)To Compare different types of fuel cells and the applications using them.

2)Comparing the energy density and power density of various battery types,

• Lithium ion.
• Lead acid.
• Nickel cadmium.
• Ultracapacitors.
• Fuel cells.

Discussions:

1)Comparing different types of fuel cells and their appications.

Fuel cells are classified primarily classified by the kind of electrolyte they employ.This classification determines,

• The kind of electrochemistry reactions that take over in the cells.
• The kind of catalyst required.
• The fuel required and other factors.

These characteristics inturns,affect the applications for which these cells are more suitable.There are several types of fuel cells currently under deelopment,each with its own advantages and limitations,potential applications.

The major four types of fuel cells in present onfields are,

• Polymer Electrolyte Membrane Fuel cells.
• Alkaline Fuel cells.
• Solid Oxide Fuel cells.
• Direct Methanol fuel cells.

Fuel cell type	Common Electrolyte	Operating temperature	Typical stack size	Electrical efficiency	Applications
Polymer Electrolyte Membrane (PEM)	Perfluorasulphonic acid incorporated into solid memprane.	<120 deg C	<1KW-100KW	60% in using direct H2,40% in using reformed fuel	Distributed generation,Backup Power,Portable power,Transportation,Special vehicles.
Alkaline (AFC)	Aqueous potassium hydroxide soaked in porous matrix or alkaline polimer membrane.	<100 deg C	1-100KW	60%	Military,Space,Backup power,Transportation.
Solid Oxide (SOFC)	Ceramic solid oxide zirconia	500-1000 deg C	1KW-2MW	60%	Auxilary power,Electric utility,Distributed generation.
Direct Methanol(DMFC)	Sulphonic acid incorporated into solid membrane or sulphuric acid solution.	30-130 deg C	1-100W	97% for electronic equipment operations.	Portable Electronic equipments like charging laptops,cell phones,etc..

Advantages and challenges of each type of cells:

Polymer Electrolyte Membrane(PEMFC):

Advantages-

• Solid electrolyte reduces corrosion and electrolyte management problems.
• Operating in low temperatures.
• Quick start-up and load following.

Challenges-

• Expensive catalyst(platinum used as catalyst).
• Sensitive to fuel impurities.

Alkaline(AFC):

Advantages-

• Wide range of stable materials allows lower cost components.
• Operate in low temperatures.
• Quick start-ups.

Challenges-

• Sensitive to CO2 in fuel and air.
• Aqueous challenges in electrolyte management system.
• Conductivity of electrolyyte as due polymer.

Solid Oxide(SOFC):

Advantages-

• High efficiency.
• Fuel flexibility.
• No aqeuous challenges as the usage solid electrolyte.

Challenges-

• High temperature corrosion.
• Breakdown of cell components.
• Low start-up time.
• Limited number of shutdowns.

Direct methanol(DMFC):

Advantages-

• Methanol is much easier to store than hydrogen.
• It doesnot need high temperature or pressure.

Challenges-

• Methanol is more toxic and highly flammable.
• Methanol is made of non-renewable fossile fuels.
• Poduction of CO2
• Low efficiency as it passes through the membrane material.

2)Comparison of Power density and Energy density.

Here we will discuss about the characteristics of various energy supplying and storing devices based on its energy densities and power densities.

Power density refers to how quickly a device can discharge its energy, while energy density refers to how much energy a device contains.

The devices are,

• Lithium ion batteries.
• Lead acid batteries.
• Nickel cadmium batteries.
• Ultracapacitors.
• Fuel cells.

Li-ion batteries:

A lithium-ion battery is a type of rechargeable battery that is charged and discharged by lithium ions moving between the negative (anode) and positive (cathode) electrodes.

Because lithium-ion batteries are suitable for storing high-capacity power, they are used in a wide range of applications, including consumer electronics such as smartphones and PCs, industrial robots, production equipment and automobiles.

Lead acid batteries:

A lead acid battery consists of a negative electrode made of spongy or porous lead. The lead is porous to facilitate the formation and dissolution of lead.

The positive electrode consists of lead oxide. Both electrodes are immersed in a electrolytic solution of sulfuric acid and water.

In case the electrodes come into contact with each other through physical movement of the battery or through changes in thickness of the electrodes, an electrically insulating, but chemically permeable membrane separates the two electrodes.

This membrane also prevents electrical shorting through the electrolyte.

• These are employed in emergency lightening to provide power for sump pumps.
• Used in electric motors
• Submarines
• Nuclear submarines

Ni-cadmium batteries:

The nickel-cadmium battery is the same as lead acid-based batteries. It consists of three fundamental layers.

The first one is a nickel layer, then the separator layer, and the cadmium layer. The nickel acts as a positive electrode collector and the cadmium layer acts as a negative layer collector.

The separator layer between the two layers is made up of KOH or NaOH. Its purpose is to provide OH ions.

It also consists of a safety valve, sealing plate, insulation ring, insulation gasket, and an outer case. The purpose of the insulator ring is to provide insulation between the two layers.

The insulator gasket is the place where the insulation ring is kept nearby. The separator layer is connected to this ring.

It has various applications like toys, small DC motors, calculators, fans, computers, etc.

Ultra capacitors:

Supercapacitors, Ultracapacitors or EDLC (Electric Double Layer Capacitors) as they are also called, look very much like batteries.

They have double layer construction consisting of two carbon electrodes immersed in an organic electrolyte.

During charging, the electrically charged ions in the electrolyte migrate towards the electrodes of opposite polariity due to the electric field between the charged electrodes created by the applied voltage.

Thus two separate charged layers are produced. Although similar to a battery, the double layer capacitor depends on electrostatic action.

Since no chemical action is involved the effect is easily reversible and the typical cycle life is hundreds of thousands of cycles.

They are majorly used in all EV's to initiate high torque requirements and many other low/high power equipments.

Fuel cell:

Fuel cells work like batteries, but they do not run down or need recharging. They produce electricity and heat as long as fuel is supplied.

A fuel cell consists of two electrodes—a negative electrode (or anode) and a positive electrode (or cathode)—sandwiched around an electrolyte.

A fuel, such as hydrogen, is fed to the anode, and air is fed to the cathode.

The electrons go through an external circuit, creating a flow of electricity. The protons migrate through the electrolyte to the cathode, where they unite with oxygen and the electrons to produce water and heat.

Comparison based on its energy density Vs Power densities from the above plot:

Here from the plot we can summarize that,

• The Fuel cells are having high energy density but the power density is very less when compared to other types of batteries.As they produce the electrical energy based on their fuel supply, its reaction time given as 100Hrs.Here shown the energy density as 1000Wh/Kg where as its power density produced given as nearlly 10W/Kg.They requires boost converters to match load requirements.

• The Lithium ion batteries having high energy density and also its power density matching its load requirements with out boost converters.Here shown for 100Wh/Kg energy density,the power density is given as nearly 100W/Kg.They are in equal ratio.
• For lead acid batteries ,the energy density and power density are nearly in equal ration.Here given for energy density of 10Wh/Kg the power density is also 10W/Kg.Thus increase in energy density also increases the power density in equal ratio as Li-ion batteries.
• For Ni-cd batteries the energy density are quite high as same as Li-ion and Lead acid battery types. But its specific power is less when compared with other batteries. Here given the energy density as 50Wh/Kg but its power density is only near 9W/kg. Thus they are used in less power consuming devices.
• Ultracapacitors/Supercapacitors are having less energy density but they will produce high power in short duration of time. Here shown supercapacitors as having nearly 1 Wh/Kg of energy density produces nearly 5KW/kg of specific power or said to be its power density. Thus they are used in certain applications needs high power requirement in short duration of time.Its reaction time is given as 0.36 seaconds.
• Capacitors are normally using in most of the electronic devices to produce high power balancing regions. Thus they are having nearly 0.05Wh/Kg as energy density but power output as extremely higher.Its reaction time as given 3.6 micro seconds.

Thank you

Submitted by,

Praveen Kumar L V,

Date:30/08/2021.