Hydrogen Fuel Cells

What Hydrogen Fuel Cells covers

Hydrogen Fuel Cells is examined in Unit A2 1, Building and Managing a Sustainable Future, a written examination. It covers hydrogen as a fuel: properties and storage, hydrogen production: steam reforming, electrolysis and photocatalysis, how a fuel cell works and the PEM cell, alkaline, phosphoric acid, molten carbonate and solid oxide fuel cells and fuel cell applications and the challenges of hydrogen.

The 5 subtopics

Each one has its own page.

• Hydrogen as a fuel: properties and storageHydrogen as an energy carrier, its reaction with oxygen, energy per kilogram against petrol, low density with worked volume and energy calculations, leaks and embrittlement, fire hazards, and compressed, liquid, hydride and bulk storage.Open →
• Hydrogen production: steam reforming, electrolysis and photocatalysisSteam methane reforming and the water-gas shift, reforming equations and carbon dioxide per kilogram, grey, blue and green hydrogen, electrolysis and its half-equations, electrolyser efficiency, and photocatalytic water splitting.Open →
• How a fuel cell works and the PEM cellWhat a fuel cell is and how it differs from a battery, efficiency against engines, the redox reaction, the PEM cell's electrolyte, half-equations and operating temperature, hydrogen purity, stacks, and model fuel cell calculations.Open →
• Alkaline, phosphoric acid, molten carbonate and solid oxide fuel cellsThe electrolyte, charge-carrying ion and half-equations of alkaline, phosphoric acid, molten carbonate and solid oxide cells, carbon dioxide poisoning, space use, stationary CHP, running on natural gas, and a comparison of the five types.Open →
• Fuel cell applications and the challenges of hydrogenBackup, remote and telecommunications power, fuel cell cars, buses in Belfast, trains, boats and portable generators, backup efficiency, round-trip efficiency and car emissions calculations, and the cost, transport and storage of hydrogen.Open →

What you need to know

Answer each one before you reveal it.

Take Hydrogen Fuel Cells further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Anode vs Cathode

  Anode: the electrode where oxidation releases electrons into the external circuit. Cathode: the electrode where reduction takes up electrons from the external circuit.

• Grey hydrogen vs Blue hydrogen

  Grey hydrogen: fuel made from natural gas with its carbon dioxide released to the atmosphere. Blue hydrogen: fuel made from natural gas with most of its carbon dioxide captured and stored.

• Steam methane reforming vs Electrolysis

  Steam methane reforming: a high-temperature reaction of natural gas with water vapour over a nickel catalyst. Electrolysis: the splitting of water into its elements by passing an electric current.

Questions from this topic

Each one with the model answer underneath.

1. 1

   Why is hydrogen described as an energy carrier rather than an energy source?

   Model answer

   Hydrogen is almost never found free on Earth, because it is locked up in water and hydrocarbons. Energy must be spent to release it, and the hydrogen then carries that energy to where it is used.

2. 2

   How does hydrogen react with oxygen, and what is the only product?

   Model answer

   Hydrogen reacts with oxygen to form water and nothing else: 2H₂ + O₂ → 2H₂O. The reaction is strongly exothermic, whether the hydrogen is burned or used in a fuel cell.

3. 3

   Why does a mixture of hydrogen and air not react at room temperature until it is ignited?

   Model answer

   The H–H bond is strong, so the reaction needs activation energy to start. A spark, a flame or a catalyst supplies that energy, and the reaction is then rapid.

4. 4

   How does hydrogen's energy content per kilogram compare with that of petrol?

   Model answer

   Hydrogen releases about 120 MJ per kilogram, the highest of any common fuel. Petrol releases about 44 MJ per kilogram, so hydrogen holds nearly three times as much by mass.

5. 5

   Why is hydrogen's very low density a problem for its use as a fuel?

   Model answer

   Hydrogen is the least dense gas, so a kilogram fills a huge volume at normal pressure. The gas must be compressed, liquefied or bound into another material before a useful amount fits in a tank.

6. 6

   The density of hydrogen is 0.0899 kg/m³ at 0°C and atmospheric pressure. What volume does 1 kg of hydrogen occupy?

   Model answer

   One kilogram of hydrogen occupies about 11.1 m³. The working is 1 ÷ 0.0899 = 11.1 m³.

What is inside Levo

Six ways to work the same material.

Hydrogen Fuel Cells revision questions

What does Hydrogen Fuel Cells cover in CCEA A-Level Environmental Technology?

5 subtopics: hydrogen as a fuel: properties and storage, hydrogen production: steam reforming, electrolysis and photocatalysis, how a fuel cell works and the pem cell, alkaline, phosphoric acid, molten carbonate and solid oxide fuel cells and fuel cell applications and the challenges of hydrogen. Each one has its own page with questions and model answers.

How is Hydrogen Fuel Cells organised?

By the CCEA 3930 specification, subtopic by subtopic, so it matches the order you are taught it in.