Cells, Batteries and Fuel Cells

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CognitoElectrochemical cells and fuel cells

Key facts & methods

Electrochemical cells

An electrochemical cell converts chemical energy into electrical energy.
Made of two different metals (or a metal and a non-metal) in an electrolyte solution.
Electrons flow from the more reactive metal (negative electrode) to the less reactive metal.
The greater the difference in reactivity, the greater the voltage produced.
Salt bridge completes the circuit by allowing ion flow between half-cells.
E.g. zinc-copper cell: Zn is more reactive, loses electrons, acts as negative electrode.

Batteries

A battery is two or more cells connected in series.
Non-rechargeable (primary) cells: chemical reactions are not easily reversible. E.g. alkaline AA batteries.
Rechargeable (secondary) cells: reactions can be reversed by passing current through. E.g. lithium-ion in phones.
Advantages of rechargeable: less waste, lower long-term cost.
Lithium-ion: high energy density, lightweight, widely used in EVs and electronics.

Fuel cells

Fuel cells use a continuous supply of fuel (usually hydrogen) and oxygen to produce electricity.
Overall reaction: H2 + O2 → H2O. Only product is water.
Hydrogen fuel cell: H2 loses electrons at negative electrode; O2 gains electrons at positive electrode.
Unlike batteries, fuel cells do not run down — fuel supplied continuously.
High efficiency compared to combustion engines.

Advantages and disadvantages of hydrogen fuel cells

Advantages: only water produced (clean). Higher efficiency than combustion. Quiet.
Disadvantages: hydrogen is explosive (safety concern). Hard to store and transport.
Most hydrogen currently produced from natural gas (not renewable).
Fuel cell vehicles (FCEVs) compared to battery electric vehicles (BEVs): faster refuelling, longer range.
Infrastructure: few hydrogen refuelling stations currently exist.

Exam questions — 4 questions · 10 marks · AQA 8462 style

3 marksFuel cell advantagesAQA 8462 style

Give two advantages and one disadvantage of hydrogen fuel cells compared to petrol engines for powering vehicles. (3 marks)

Hint: Two specific advantages over petrol (emissions, efficiency). One clear disadvantage (storage, production or infrastructure).

+30 XP

1 markCell voltageAQA 8462 style

Two metals are used to make an electrochemical cell. What determines the voltage produced?

A The temperature of the electrolyte

B The volume of the electrolyte solution

C The difference in reactivity between the two metals

D The colour of the metals used

3 marksRechargeable vs non-rechargeableAQA 8462 style