Fuel cells, lithium cells

What are the conditions of a standard electrode potential?

• 298 K

• 100 kPa

• 1.00 moldm-3 solution of ions

What are the (simplified) electrode reactions in a lithium cell?

Positive electrode:

Li+ + CoO2 + e- —> Li+[CoO2]-

Negative electrode:

Li —> Li+ + e-

What are fuel cells used for and what is a feature of them?

• fuel cells are used to generate an electric current

• and do not need to be electrically recharged

At the positive electrode, where are the electrons in the half equation?

• in the reactants

• electrons are taken in

At the negative electrode, where are the electrons in the half equation?

• in the products

• gives out electrons

Is CO2 acidic or alkaline?

acidic

What does a hydrogen-oxygen fuel cells consist of?

• a reaction chamber with separate inlets for hydrogen and oxygen gas

• an outlet for the product - water

• an electrolyte of aqueous sodium hydroxide

• a semi-permeable membrane that separates the hydrogen and oxygen gases

What are the benefits of fuel cells (and give the overall equation)?

Overall equation:

2H2 + O2 —> 2H2O

Benefits:

• water is the only reaction product (environmental advantage)

• the reaction takes place at room temp without combustion, so all bond energy is converted into electrical energy instead of heat

• no harmful oxides of nitrogen produced (usually formed in high temp combustion)

What are the risks/problems of fuel cells?

Risks/problems:

• hydrogen is a highly flammable gas, production and storage of hydrogen is a safety hazard

• very thick walled cylinders and pipes are needed to store hydrogen - economic impacts

• production of hydrogen is a byproduct of the crude oil industry, so it relies on a non-renewable resource

• its use is fuel cells is limited by hydrogen being expensive to make

• hydrogen needs large containers compared to liquid fuels (has low energy density per unit volume)

Why is lithium used in lithium ion cells?

It has a very low density and a relatively high electrode potential

What does a lithium cell consist of?

• a positive lithium cobalt oxide electrode

• a negative carbon electrode

• a porous polymer membrane electrolyte

What are some issues with lithium ion cells?

Issues:

• a global shortage of lithium is likely to make lithium ion cells unsustainable, as demand for lithium exceeds supply

• if cells are not recycled and are thrown away, a huge amount of lithium is lost

• safety - lithium ion cell fires

Why does lithium have a high electrode potential?

Because it is a very reactive element in group 1

Why don’t fuel cells need to be recharged?

There is a continuous supply of reactants

What does the type of cells used in commercial applications depend on?

• the voltage required

• the current needed

• the size of the cell

• the cost

What’s the most common type of non-rechargeable cell, and what does it consist of?

Zinc-carbon cells

• a zinc casing which acts as the negative electrode

• a paste of ammonium chloride which acts as an electrolyte as well as the positive electrode

• a carbon rod which acts as an electron carrier in the cell