MADE TO BE MADE AGAINCHEMISTRY FOR A CIRCULAR ECONOMY

Car batteries: Is there a circular solution?

Lesson objectives:•Describe how an electrochemical cell works.•Explain the redox reactions that take place in an electrochemical cell.•Evaluate the benefits and risks to society of each type of cell and the alternative.

Is this the future? Renault Fluence Z.E. is UK’s

cheapest electric carFluence costs under £18k but

you lease the battery

An electrochemical cell

Electrochemical cells

Electrochemical cells commonly consist of two different metals in salt solutions of their own metal ions, connected by a wire.

Electrons flow through the wire from the most reactive metal to the least reactive metal (i.e. zinc loses electrons and is oxidised, while copper gains electrons and is reduced).

A salt bridge is often filter paper soaked in an ionic solution that allows ions to flow and balance out the charges.

Electrochemical cells

Electrochemical cells

• The reactions at each electrode are reversible:

Zn2+ (aq) + 2e- Zn(s)

Cu2+ (aq) + 2e- Cu(s)

• Which direction the reaction goes in depends on how easily each metal is oxidised.

• How easily a metal loses electrons is measured using electrode potential – the more easily oxidised, the more negative the electrode potential.

• The metal with the more negative electrode potential will be the one that is oxidised, i.e. the reaction will go in the reverse direction in the equations above.

Electrochemical cells

• There is a convention for drawing electrochemical cells:

1) The half-cell with the more negative potential goes on the left.

2) The oxidised forms go in the centre of the cell diagram:

Zn(s) Zn2+ (aq) Cu2+

(aq) Cu(s)

Changes go in this directionreduced oxidised oxidised reduced

• The cell potential is the electrode potential of the right hand side (more positive) – the electrode potential of the left hand side (more negative).

• Eѳcell = (Eѳ

right hand side – Eѳ left hand side )

• The cell potential will always be a positive voltage.

Conditions affect the value of the electrode potential:

Half-cell reactions are reversible so the equilibrium position is affected by changes in temperature, pressure and concentration. Changing the equilibrium position changes the cell potential.

The standard electrode potential of a half-cell is the voltage measured under standard conditions (298K, 100kPa, 1.00mol dm-3) when the half-cell is connected to a standard hydrogen electrode.

Over to you…

Follow the instructions on the practical sheet to make your own electrochemical cells and use the notes taken in the lesson to help you to answer the questions.

Group work

Renault Fluence Z.E. is the UK’s cheapest electric car.Fluence costs under £18k but you lease the battery.

•Discuss the pros and cons of a shift from petrol to electric.•Pay close attention to choices around batteries – leasing, battery swap, purchase, overall mileage contract hire. •Gather each person’s view point and discuss the prospects of shifting the linear automotive economy to a more circular one.

Use the help sheets to prompt your discussion.