Hydrogen Economy and Production Flashcards

1
Q

What are the main features of the Hydrogen Economy? Describe a feature of each.

A

Hydrogen Production - SMR is currently the most popular

Storage and Transport - As compressed gas, liquid H2 or chemical storage

Applications - Using H2 as a net 0 carbon fuel in transport, industry, residential

Environmental Impact - currently, H2 production by SMR is very carbon intense

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the equation for combustion of H2 in air

(Overall reaction of a Fuel Cell)

A

H2 + 0.5 O2 = H2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the equation for the combustion of CH4 in air

A

CH4 + 2O2 = CO2 + 2H2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are issues with the hydrogen economy

A

Technology - exists and we understand the challenges but not ready for nation wide application, expensive/experimental and small scale

Financial - H2 production is expensive, infrastructure for commercial storage and transport doesn’t exist

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why is H thought to be a better fuel than conventional fuels

A

The carnot efficiency of H is much greater than that of conventional fuels such as diesel/petrol engines or combined cycle plants.

Using H does not produce any greenhouse gases (ignoring steam). So thought to be a green replacement.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the cathodic reaction of a hydrogen fuel cell, and what is the potential

A

Reduction of Oxygen into water
O2 + 4e- + 4H+ = 2H2O

Ec = +1.23 V

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the anodic reaction of a hydrogen fuel cell, and what is the potential

A

Oxidisation of Hydrogen
H2 = 2H+ + 2e-

Ea = 0 V

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the total potential of a hydrogen fuel cell.

Using G = - n * F * Ecell find the efficiency

H(H) = -285 kJ/mol
F = 96485

A

Ecell = Ec - Ea = 1.23 V

G = - 2 * 96485 * 1.23 = -237 kJ/mol

Eff_elec = desired/input
= G/H = -237/-285 = 0.83

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is Steam Methane Reforming, and what is the fundamental reaction and byproduct. How can the byproduct be removed/converted.

A

Production of Hydrogen using the reforming of CH4

Steam Reforming
CH4 + H2O = CO + 3H2

CO is produced as a byproduct and can be converted using the following reaction

Water Shift Reaction
CO + H2O = CO2 + H2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Write the equation for steam reforming, what conditions does this reaction take place at?

A

Steam Reforming
CH4 + H2O = CO + 3H2

At high temperatures and pressures

Uses Ni/Al2O3 catalysts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Write the equation for water shift reaction, what conditions does this reaction take place at?

A

Water Shift Reaction
CO + H2O = CO2 + H2

High Shift at 350 deg
Low Shift at 250 deg

High Shift using Fe-Cr catalyst
Low Shift using Cu-Zn/Al2O3 catalyst

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are main considerations of SMR

A

Produces lots of CO2, for every 1kg of H we produce around 9-12 kg of CO2

CH4 is a valuable resources and is non-renewable

Output (80% H2) needs purification

Economical Viable and well-established

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Explain Coal Gasification, whats the feedstock and what are the 2 main reactions (and their sub reactions).

A

Feedstock = Coal

Coal is superheated in fuel rich conditions and turned into syngas that is rich in H2, this can be used to produce electricity through gas turbines or H2 through further processing.

Oxidisation (exothermic)
C + 0.5O2 -> CO
CO + 0.5O2 -> CO2
H2 + 0.5O2 -> H2O

Gasification (endothermic)
C + H2O -> CO + H
C + CO -> 2CO2
C + 2H2 -> CH4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What dictates if combustion or gasification occurs.

A

The amount of O2 in the reaction.

Lots of O2 (fuel lean) results in combustion where CO2 and H2O are produced.

Little O2 (fuel rich) results in gasification where CO and H2 are produced.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is Methane Pyrolysis

A

The decomposition of methane into carbon (coal) and hydrogen.

CH4 -> C + 2H2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the feedstock of methane pyrolysis and what conditions are needed

A

feedstock = methane (natural gas)

high temperatures = 1100/1200 deg

no catalysts needed

no air needed (pyrolysis is burning with no oxygen)

17
Q

What occurs in the reactor of methane pyrolysis

A

natural gas is feed into the reactor

nat gas is bubbled through a column of molten salt/metal

nat gas decomposes into carbon (coal) and hydrogen

hydrogen escapes through the top of the reactor

coal remain in the molten column and has to be separated once the column becomes too carbon rich

18
Q

Pros and Cons of Methane Pyrolysis

A

+ves

Carbon is produced as coal so no carbon capture is required

High hydrogen purity

-ves

Can have proplems seperating the solid
carbon from the molten salf/metal

Creates a stockpile of coal

19
Q

Pros and Cons of Coal Gasification

A

+ves

Cleaner alternative to standard coal combustion

-ves

Carbon still produced as a byproduct so need carbon capture

difficult to control reaction

20
Q

Overall reaction of water electrolysis and potential

A

H2O -> H2 + 0.5O2

Ecell = -1.23 V

21
Q

Half reactions of water electrolysis in acidic electrolyte

A

Opposite of fuel cell

Cathode (Ec = 0 V)
H -> 2H+ + 2E-

Anode (Ea = 1.23 V)
2H2O = O2 + 4e- + 4H+

22
Q

Half reactions of water electrolysis in alkaline electrolyte

A

Cathode (Ec = -0.828 V)
2H2O + 2e- = H2 + 2HO-

Anode (Ea = 0.401 V)
2OH- = 0.5O2 + H2O + 2e-

23
Q

Consideration of alkaline and acidic water electrolysis

A

acidic
fast dynamic response
suitable for variable renewable energy support

alkaline
slower dynamic response
less suited for variable renewable energy support
has some applications that could be scaled up

24
Q

Nernst Equation

A

Ecell = Ec - Ea - RT/nF * ln(

25
Q

What are the 2 types of Hydrogen storage, give examples of each

A

Physical Storage
Compressed gas
Liquid Hydrogen and cryogenic storage

Material Based Storage
‘Chemical based storage’ in hydrides
Liquid organic

26
Q

Give more detail on the examples of material based storage

A

Hydrides
Hydrogen stored in interstitial states
can be released at high tempertures
ie when burnt
M + (x/2)H2 = MHx

Absorbtion
Bonding of hydrogen onto a surface via weak Wan-der-val forces
required cryogenic tempertures

27
Q

How is hydrogen delivered

A

Trucks ?
Pipelines -> repurpose CH4 lines for LH
Shipping -> most common

28
Q
A