Practice Questions

Question 1

• What are the advantages and disadvantages of using hydrogen as an energy carrier compared to other options like electricity?
• How can hydrogen production be integrated into a clean energy system?
• Briefly describe the process of transporting and storing hydrogen.
• Are there any new or advanced ideas for hydrogen storage being explored?

Answer 1

• Advantage: Clean burning, high energy density
• Disadvantage: Infrastructure cost, energy loss during conversion
• Integrate with renewable energy sources (solar, wind) for electrolysis
• Transportation: Pipelines, ships; Storage: Compressed gas, liquefaction, chemical carriers (e.g., ammonia)

Question 2

• Explain the basic operation of a fuel cell.
• What are the main challenges associated with material selection and fabrication for fuel cells?
• How do different types of fuel cells compare in terms of properties like efficiency and operating temperature?
• Are there any broader issues to consider when implementing fuel cell technology besides the technical challenges?

Answer 2

• Electrochemical conversion of hydrogen and oxygen into electricity
• Challenges: Material cost, durability, degradation
• Different types: PEMFC (low temp), SOFC (high temp)
• Broader issues: Safety, hydrogen availability

Question 3

• How can hydrogen fuel cells be used to power zero-emission electric vehicles?
• What other components are needed besides the fuel cell?

Answer 3

• Generate electricity to power electric motor
• Other components: Battery (auxiliary power), electric motor, control systems

Question 4

1. Compare and contrast the use of batteries versus hydrogen fuel cells for electric vehicles, considering factors like range, weight, and refueling time.
2. What are the different options for storing hydrogen?
3. Discuss the advantages and disadvantages of each method, including compressed hydrogen gas, metal hydrides, liquid hydrogen, and chemical hydrogen carriers.

Answer 4

• Batteries: Shorter range, slower recharging, lower energy density
• Hydrogen: Longer range, fast refueling, high energy density
• Compressed gas: Simple, low density; Metal hydrides: Reversible storage, complex; Liquid hydrogen: High density, boil-off losses; Chemical carriers: High density, complex conversion

Question 5

Currently, most hydrogen is produced from methane.
1. How does this method compare to “green hydrogen” production methods in terms of environmental impact?
2. What are the different options for hydrogen production, and how are they categorized based on their environmental footprint (e.g., grey hydrogen, blue hydrogen, green hydrogen)?

Answer 5

• Grey hydrogen (fossil fuels)
• Green hydrogen (renewable energy)
• Blue hydrogen (fossil fuels with carbon capture)
• Grey > Blue > Green (environmental impact)

Question 6

List and explain two methods for purifying hydrogen gas streams.

Answer 6

• Zeolites (adsorption)
• Palladium membranes (diffusion)

Question 7

Why does the size and structure of magnesium particles affect their ability to absorb and release hydrogen?

Answer 7

• Larger grain size slows down hydrogen diffusion
• Smaller grain size (e.g., from ball milling) increases surface area and allows for faster hydrogen absorption and release at lower temperatures

Question 8

What are the trade-offs between using ball-milled magnesium hydrides and smaller nanoparticles for hydrogen storage?

Answer 8

• Ball-milled magnesium hydrides offer faster hydrogen absorption/desorption and lower temperatures
• Nanoparticles may have lower hydride density (can store less hydrogen per unit volume)

Question 9

Why are specific conditions necessary for using complex hydrides like alanates and borohydrides for hydrogen storage?

Answer 9

• Incorrect conditions can lead to unwanted reactions

Question 10

How does the combination of magnesium hydride with other materials like MgB2 improve hydrogen storage properties?

Answer 10

• Creates an intermediate stage (MgB2) that destabilizes the complex hydride and improves hydrogen release