hydrogen

Why Engineers Study Hydrogen: Chemistry and Industrial

Relevance?

1. Foundation for Clean Energy Technologies

Hydrogen is the "fuel of the future", used in fuel cells, hydrogen vehicles, and

energy storage.

Engineers need to understand its production, storage, and conversion chemistry to

design efficient and safe systems, such as electrolyzers and fuel cells.

3. Environmental and Sustainable Applications

Hydrogen is a "zero-carbon fuel"; understanding its chemistry aids in developing

sustainable energy systems and combating climate change.

4. Safety and Engineering Design

Hydrogen's "high flammability" requires engineers to understand its reactivity

and safe handling methods.

use

fuel cells, hydrogen vehicles, and

energy storage.

hydrogen is

Hydrogen is the lightest and most abundant element in the universe, constituting

about 70% of the total mass of the universe.

10th most abundant by mass

on earth oceans, minerals and all forms of life.

H2 occurs at trace level in our atmosphere (0.5 ppm).

occurance

Molecular state

Exists freely as H₂ gas

Hydrogen gas (H₂)

Combined state

Chemically combined with

other elements

H₂O, CH₄, NH₃, HCl

chem properties

Hydrogen is a colourless, odourless, non-metallic, tasteless, highly flammable

diatomic gas with the molecular formula H2.

◦ It is also the lightest element with a molecular mass of 2.016 kg/kmol.

◦ Hydrogen is a fuel with a gross calorific value of 141,800 kJ/kg and a net

calorific value of 120,000 kJ/kg.

◦ However, hydrogen is not an energy source like coal, oil, and natural gas since

there are no hydrogen reserves in the earth. Although hydrogen is the most

plentiful element in the universe, making up about three quarters of all matter,

free hydrogen is scarce. Hydrogen must be produced from other fuels such as

natural gas or from water through electrolysis by consuming electricity.

Therefore, hydrogen should be called an energy carrier rather than an energy

source (each H-H bond stores 436 kJ mol-1 energy).

Oxidation number or states

1, −1

Ionization energy

1st: 1312.05 kJ mol−1

Flammability

Highly flammable forms explosive mixture with air

(4-75%)

Thermal conductivity

High — used as a cooling gas in generators and

reactors

physical

Physical state

Colourless, odourless, tasteless gas

State at 20 °C

Gas

Melting point

−259.16 °C, −434.49 °F, 13.99 K

Boiling Point

−252.88 °C, −423.18 °F, 20.27 K

Density

0.0899 g/L at STP (lightest gas known)

Solubility

Slightly soluble in water

Diffusion

Diffuses very rapidly due to small molecular size

protium

Protium or hydrogen (H): It is the most common isotope of hydrogen and

constitutes 99.9% of all available hydrogen in nature. The molecule of ordinary

hydrogen is diatomic. The nucleus of the atom consist of single proton and no

neutron with one electron.

Most common isotope of hydrogen.

Has one proton and no neutron.

The molecules of ordinary hydrogen is diatomic (H2)

Found in water (H₂O) and organic compounds.

Non-radioactive and stable.

deuterium

Deuterium (D): Deuterium or heavy hydrogen consists of 0.016% total hydrogen

occurring in nature. The nucleus of heavy hydrogen contains a single proton and a

neutron with one electron. Water containing deuterium is called heavy water.D2O

is used as moderator in nuclear power industry to slow down the speed of emitted

neutrons. Deuterium is also used for determining Kinetics of a reaction and

reaction mechanism substituting hydrogen. It is used as a tracer. Deuterium

water(D2O) is used as a reference in spectroscopy.

Has one proton and one neutron.

The molecules of heavy hydrogen is diatomic (D2)

Found in heavy water (D₂O).

Used in nuclear reactors, tracers in chemical

reactions (to study kinetics and mechanism), and

fusion research.

Stable and non-radioactive.

tritium

Tritium (T): The molecule of tritium is T2. The nucleus consists of 1 proton and 2

neutrons with 1 electron. It is radioactive in nature. Deuterium and tritium are used

for generation of energy from nuclear fusion. It is used for self-powered lighting

devices and is used in hydrogen bombs and nuclear weapons. It is radioactive in

nature and its halflife is 12.4 years.

Has one proton and two neutrons.

Radioactive (half-life ≈ 12.4 years).

Produced in nuclear reactions.

Used in nuclear weapons, self lighting devices,

self-luminous paints, and fusion energy research.

prep by (a) From acids and metals

A common method is the reaction of a metal, such as zinc, with a dilute acid

like hydrochloric acid ((HCl) or sulfuric acid (H2SO4).

Zn + 2HCl → ZnCl2 + H2↑

Zn + H2SO4 → ZnSO4 + H2↑

(b) From alkali metals and water

(b) From alkali metals and water

In the laboratory, hydrogen can be prepared by the reaction of electropositive

metals like Al or Si with hot alkali solutions such as sodium hydroxide (NaOH)

or potassium hydroxide (KOH)

2Al + 2NaOH + 6H2O → 2Na[Al(OH)4] + 3H2↑

Sodium meta-aluminate

Si + 2KOH + H2O → K2SiO3 + 2H2↑

Potassium silicate

carbides

The reaction of metal hydrides with water is another convenient method to

generate small amounts of hydrogen gas (H₂), especially outside the

laboratory or in field conditions

CaH2 + 2H2O → Ca(OH)2 + 2H2↑

Such hydrides can be used as portable hydrogen generator.

fossil fuels

1. Production of Hydrogen from Fossil Sources

Hydrogen can be produced from fossil fuels such as natural gas, coal etc.

through various chemical processes. These are the most common

industrial methods today.

steam refining meth

Steam Reforming is the main industrial method of producing large

amount of hydrogen from fossil fuels, especially natural gas.

1. Steam Reforming of methane

Methane reacts with steam (H₂O) at high temperature (700-1100 °C) in

the presence of a Ni/Cu catalyst, producing H2 and CO.

CH4 + H2O Ni, 800°C CO + 3H2

Water-Gas Shift Reaction

The CO formed in the first step reacts further with steam to produce more

hydrogen and carbon dioxide (CO₂).

CO + H2O → CO2 + H2 (exothermic)

Overall Reaction : CH4 + 2H2O → CO2 + 4H2

more

To satisfy the needs of the industry, where H2 is used as a feedstock, Steam

reforming is the main commercial process.

◦ The catalysed reaction of H2O (as steam) and hydrocarbons (CH4)

at high temperatures (700-1000 ° C) using Ni/Cu as catalyst:

CH4 (g) + H2O (g) → CO(g) + 3H2 (g)

o H2 produced in this reaction can be directly used in Haber's process for ammonia

production.

o Coal or coke can be used for above reaction at 1000° C

C (s) + H2O (g) → CO(g) + H2 (mixture is called water gas)

Water gas shift reaction takes place in a shift converter:

CO (g) + H2O (g) → CO2 (g) + H2

It contains iron/Cu catalyst and CO is converted to CO2 and more H2. Capturing

CO2, we can minimize the greenhouse gas to escape into the atmosphere.

adv and dis

High hydrogen yield.

Mature, well-established

technology.

Produces large amounts of CO₂ .

Requires high temperature and energy input.

steam of coke

When coke or coal reacts with steam at high temperature, hydrogen is

produced along with carbon monoxide.

This process is also known as coal gasification or steam-carbon reaction

This produces a mixture of carbon monoxide and hydrogen, called water

gas or syngas

Water-Gas Shift Reaction

The carbon monoxide formed reacts further with steam to produce more

hydrogen and carbon dioxide

Applications

Industrial hydrogen production.

Fuel for synthesis of ammonia (Haber process) and methanol.

Source of syngas for Fischer-Tropsch synthesis.

C + H2O(g) 1000 °C CO + H2

CO + H2O → CO2 + H2

2. Electrolysis of Water

Electrolysis of water is the decomposition of water (H2O) into oxygen (O2) and

(H2) due to an electric current being passed through the water.

Electrolysis Process (Alkaline electrolyzer)

Hundreds of electrolytic cells are stacked together

operating at 2 V each and at 85º C.

Ni is anode and Fe is anode.

NaOH/KOH is used as electrolyte to increase efficiency

of electrolysis.

H2 is liberated at cathode and O2 at anode and the

gases are collected separately.

Anode: 2OH- → H2O + ½ O2 + 2e-

Cathode: 2H2O + 2e- → 2OH- + H2

Overall Reaction: H2O → H2 + ½ O2

Electrolysis of water is the decomposition of water (H2O) into oxygen (O2) and

(H2) due to an electric current being passed through the water.

Electrolysis Process (Alkaline electrolyzer)

Alkaline electrolyzers are suitable

for stationary applications.

more (electrolusis)

To drive this reaction a large overpotential is required to offset the sluggish electrode

kinetics esp for O2 .Pt is expensive although best catalyst.

Due to their use of water, a readily available resource, electrolysis and similar water-splitting

methods have attracted the interest of the scientific community. With the objective of

reducing the cost of hydrogen production, renewable sources of energy have been targeted

to allow electrolysis, e.g. wind, solar energy

Water electrolysis can operate between 50-80 °C, while steam methane reforming requires

temperatures between 700-1100 °C.

The difference between the two methods is the primary energy used; either electricity (for

electrolysis) or natural gas (for steam methane reforming).

++

-◦Electrolysis consists of using electricity to split water into hydrogen and oxygen.

It is a

70-80% efficient (a 20-30% conversion loss) while steam reforming of natural

gas has a thermal efficiency between 70-85%. The electrical efficiency of

electrolysis is expected to reach 82-86% before 2030, while also maintaining

durability as progress in this area continues at a pace.

◦ Water electrolysis can operate between 50-80 °C, while steam methane

reforming requires temperatures between 700-1100 °C.

◦ The difference between the two methods is the primary energy used; either

electricity (for electrolysis) or natural gas (for steam methane reforming).

◦ Hundreds of electrolytic cells are stacked together operating at 2 V each and at 85o C.

◦ Ni is anode and Fe is cathode. NaOH/KOH is used as electrolytes to increase

efficiency of electrolysis.

◦ H2 is liberated at cathode and O2 at anode and the gases are collected separately.

Hydrogen stores a tremendous amount of energy and so offers great potential as a

sustainable, carbon-free source of power as it is largely present on earth as water.

Electrocatalysis can separate the hydrogen atoms from the oxygen atoms, but a crucial

consideration is a process known as oxygen evolution. The rate of oxygen creation is

known to affect the overall production rate of hydrogen, so scientists are searching for a

catalyst to enhance this reaction.Noble metals like Pt, Ir,Ru etc. are effective but quite

expensive. Cu, Ni,Cr,nickel oxide is being tested.

The cell reaction can be represented as given below:

◦ Anode: 2OH- → H2O + 1⁄2 O2 +2e-

◦ Cathode 2H2O + 2e- → 2OH- + H2

..........................................................

H2O → H2 + 1⁄2 O2, .................G੦ = + 237 kJ/mol

BLUE HYDROGEN

CO2 formed is easily removed by dissolving in water under pressure or reaction

with K2CO3 or using various types of aqueous solutions of amines to form solid

NH4CO3 or with ethanolamines to capture 40% industrial CO2.

Steam

reforming +

Carbon capture

Fossil fuels +

CCS

Low

Cleaner than grey; CO₂

captured and stored

gg green grey

Electrolysis of

water

Renewable

energy (solar,

wind)

None

Cleanest and most

sustainable form

The cleanest form. It's produced using electrolysis (splitting

water into hydrogen and oxygen) powered by renewable energy sources like wind or

solar. This process is emissions-free.

Grey

Hydrogen

Steam

reforming of

natural gas

Fossil fuels

High

Most common but polluting

The most common type in use today. It's produced the same

way as blue hydrogen (from natural gas via SMR) but the resulting CO2 is released

into the atmosphere.

11

It is cheap but carbon-intensive.

bp blackpink

Coal

gasification

Coal

Very high

Dirtiest form; high carbon

footprint

Electrolysis of

water

Nuclear energy

None

Stable, low-carbon hydrogen

from nuclear-powered

electrolysis

Produced through electrolysis, like green hydrogen, but the

electricity is supplied by nuclear power. This is also a low-carbon source.

ty torquise yellow white

Methane

pyrolysis

Thermal

energy

None (solid

carbon formed)

Promising low-emission

method

Yellow

Hydrogen

Electrolysis of

water

Grid electricity

(mixed source,

often solar)

Depends on

grid mix

Cleaner if renewable share

is high

🌎 A naturally occurring, geological H2 found in underground

deposits. It is not man-made, but its potential is being explored.

application of hyd

1. It is a raw material for production of Ammonia, methanol etc.

2. It is used for hydrogenation of fats.

3. It is used in the manufacture of organic chemicals.

4. It is used in metallurgical operations to obtain reduction of metals to

zerovalent state.

5. Hydrogen is the primary fuel to power fuel cells. Fuel cell-powered cars,

bikes, stationary and portable generators, electronic devices such as

computers and cell phones can all use hydrogen as the fuel. A mobile

phone powered by a fuel cell using hydrogen as the fuel can have several

months of battery life compared to just several days with the current

batteries.

6. Hydrogen can be used in a variety of applications including electricity

generation plants, and various industrial, commercial, and residential

uses.

fuel industrial and labrotory

Fuel Cells: H2+½O2→H2O + Energy; clean power

for vehicles and spacecraft.

Rocket Fuel: Liquid H₂ with LOX used as

high-energy propellant.

Clean Fuel: Zero-carbon fuel producing only water

vapor on combustion.

Ammonia Synthesis: N2 + 3H2 → 2NH3 ; used for fertilizer production.

Methanol Production: CO + 2H2 → CH3OH.

Hydrogenation: Converts oils to fats and reduces metal oxides.

Petroleum Refining: Used in hydrocracking and desulfurization to improve fuel

quality

Used as a reducing agent in various chemical and metallurgical processes.

Employed as a carrier gas in gas chromatography.

PHYSICAL STORAGE compressed gas

In this method, hydrogen is stored in its molecular form (H₂ gas or liquid).

It involves compressing or cooling hydrogen without changing its chemical composition.

Compressed Gas Storage Method:

Hydrogen is compressed to high pressures (typically 350-700 bar) and stored in cylinders or

tanks made of steel or carbon-fiber composites.

Advantages: Simple, mature technology; quick refueling.

Disadvantages: Requires heavy, high-pressure tanks; safety concerns at high pressure.

Use: Common in fuel cell vehicles and laboratories.

Compressed H2 : It has good energy density by weight (gravimetric energy

density) but low volumetric density hence large tanks are required to store and

that increases the weight.

◦ H2 gas is pressurized under several hundreds of atm and stored in pressure

vessel. It can thus be stored in a compressed state.

◦ Increasing gas pressure would improve energy density by volume making it

smaller but not lighter. Compression of hydrogen requires about 2.1 % of energy.

Liquid Hydrogen Storage Method:

Hydrogen is cooled to -253°C (20 K) and stored as a cryogenic liquid.

Advantages: Higher energy density than compressed gas.

Disadvantages: High energy needed for liquefaction (~30% of hydrogen's energy); boil-off

losses due to evaporation.

Use: Rockets, space missions, and high-demand transport systems.

form: H2 can be stored at low temperatures (-253 0C) in cryogenic tanks. The

liquefaction tanks are lighter. But liquefaction imposes a large energy loss

(energy to cool and liquefy hydrogen gas)

◦ The tanks must be insulated since B.P of H2 is low so to prevent boil off and

this adds to the cost.

difficulties w storage

Liquefied H2 is DENSER than gaseous H2. Similar sized

liquid H2 tanks can store H2 than compressed gas tanks but it takes energy to

cool and liquefy H2.

◦ Difficult to liquefy due to low density (0.07g/cc) and low B.P. of 20.4 K at atm

pressure. Hence risky to store & transport hydrogen gas. For example, the

storage of hydrogen in liquid form requires very low TEMP(about 20 K

or −253°C) which are expensive to achieve and maintain.

◦ Its storage in gas form at high pressure, on the other hand, involves low

density, and a full tank will have a low range of mileage. Extensive tests

indicate that pressures as high as 70 MPa can safely be used for compressed

hydrogen storage in commercial vehicles.

◦ Cost of onboard storage of H2 is high compared to petrol. Energy

efficiency is a challenge for all H2 systems and durability is inadequate.

◦ Hydrogen stored in a metal hydride solid can absorb only about 3.5 percent of

its mass as hydrogen.

Storing hydrogen in liquid form in cryogenic temperatures

and metal hydrides are not as commercially ready technologies as compressed

hydrogen gas.

Liquefied H₂ is denser than gaseous H₂, but

cooling and liquefaction require high energy.

Low density (0.07 g/cc) and very low boiling

point (-253°C) make liquefaction difficult.

Needs well-insulated cryogenic tanks to prevent

boil-off losses.

Decarburization of steel at high pressure makes

tanks brittle and prone to failure.

Lightest gas — only small amounts can be stored

even under pressure.

Highly flammable due to low ignition temperature.

Suitable only for short-term storage, as

continuous evaporation occurs.

Overall, risky to store and transport because of

flammability and cryogenic handling.

CHEMICAL STORAGE OF HYDROGEN

onboard/off

On-board Storage:

Hydrogen is stored within the vehicle itself to supply fuel during its operation.

It uses compressed gas cylinders, liquid hydrogen tanks, or metal hydrides.

Example: Hydrogen fuel cell car storing H₂ in a 700-bar tank.

Off-board Storage:

Hydrogen is stored outside the vehicle, usually at production, storage, or refueling

stations.

It is later transferred to the vehicle when required.

Example: Hydrogen stored in large cryogenic tanks at a refueling station.

chemical storage

🔹 Hydrogen Storage in Solid State (Chemical Storage)

Hydrogen can be stored in large amounts within small volumes using solid materials. This is important for applications like fuel cells (PEMFC) and onboard hydrogen storage.

🔸 Types of Solid Hydrogen Storage Materials

Complex Hydrides

Chemical Hydrides

Metal Hydrides

🔹 Summary (Quick Revision)

Metal hydrides → reversible, low temp storage

Borohydrides → high storage but regeneration issues

LiBH₄ → highest capacity but not reversible ❌

NaBH₄ → economical but regeneration challenge

Ca(BH₄)₂ → better due to lower decomposition temp ✔

Alanates (NaAlH₄) → practical, ~5.5 wt%, suitable for PEMFC

Catalysts (Ti, Zr) → improve kinetics and reversibility

metal

🔹 1. Metal Hydrides

📌 Concept

Metals or alloys react with hydrogen to form metal hydrides:

Metals/alloys + H₂ → Metal hydrides

Hydrogen can be released by heating:

Metal hydrides → (Δ heat) → Metals/alloys + H₂

📌 Key Feature

Store and release hydrogen at low temperature and pressure

Suitable for on-board hydrogen storage

📌 Examples

LaNi₅H₆

CaH₂

MgH₂

TiFeH₂

LiH

borohydrides

3. Borohydrides (Important Complex Hydrides)

📌 General Property

Very high hydrogen storage density

📊 Storage Capacities

CompoundStorage CapacityRemarksLiBH₄~18.5%❌ Not reversibleZn(BH₄)₂~8.4%ModerateNaBH₄~10.8%High temp requiredCa(BH₄)₂~8.3%Lower decomposition temp ✔

🔸 Key Observations

✔ LiBH₄

Very high storage (~18.5%)

❌ Not reversible → Not suitable

Catalysts (Ti, Mg) can improve performance

✔ NaBH₄

Good storage (~10.8%)

❌ Requires high decomposition temperature

✔ Economical and simple method

❗ Major issue: Regeneration problem

✔ Ca(BH₄)₂

Storage: ~8.3%

✔ Decomposes at lower temperature → Better option

🔹 Decomposition Reactions of Borohydrides

Let M = Na, Li, K

Step 1:

M(BH4)n→nMH+nB+32nH2M(BH₄)_n → nMH + nB + \frac{3}{2}nH₂M(BH4)n→nMH+nB+23nH2

Step 2:

nMH+nB→nB+nM+12nH2nMH + nB → nB + nM + \frac{1}{2}nH₂nMH+nB→nB+nM+21nH2

📌 Final Products

Elemental Boron (B)

Binary metal hydride (MH)

🔹 Regeneration Issue (NaBH₄)

After hydrogen release, regenerating NaBH₄ is difficult

However:

✔ Method is simple and economical

✔ Using MgH₂ reduces cost 34 times

✔ Regeneration efficiency ≈ 68.5

alantes

🔹 4. Alanates (Complex Metal Hydrides)

Example: NaAlH₄

📌 Key Features

Theoretical storage capacity: ~5.5 wt%

Suitable for PEM Fuel Cells (~80°C)

Good thermodynamics

🔸 Hydrogen Release Reactions

Step 1:

3NaAlH4↔Na3AlH6+2Al+3H23NaAlH₄ ↔ Na₃AlH₆ + 2Al + 3H₂3NaAlH4↔Na3AlH6+2Al+3H2

✔ Occurs above 33°C

✔ Releases 3.7 wt% H₂

Step 2:

2Na3AlH6↔6NaH+2Al+3H22Na₃AlH₆ ↔ 6NaH + 2Al + 3H₂2Na3AlH6↔6NaH+2Al+3H2

✔ Occurs above 110°C

✔ Releases 1.8 wt% H₂

📌 Total Hydrogen Released

3.7% + 1.8% = ~5.5 wt%

role of cata

🔹 Role of Catalysts (Ti, Zr)

📌 Why Needed?

Improve reverse kinetics (hydrogen absorption)

Enhance reaction speed

📌 How They Work

Reduce crystal size

Increase surface area

Improve hydrogenation rates

🔹 Hydrogen Storage in Carbon Nanostructures

Hydrogen can also be stored by physical adsorption on porous carbon materials.

📌 Key Idea

Hydrogen molecules are adsorbed on the surface (not chemically bonded)

material

🔹 Types of Carbon Materials Used

Activated carbon

Graphite

Fullerenes

Carbon nanotubes (CNTs)

Graphite nanofibers

🔹 Why Carbon Materials are Suitable?

📌 Important Properties

✔ Small size

✔ High surface area

✔ Porous structure

✔ Low density

✔ Chemically inert

👉 These properties allow high hydrogen uptake

what and how

🔹 Carbon Nanotubes (CNTs)

📌 Importance

Strong candidates to compete with metal hydrides for hydrogen storage

📌 Types

Single-Walled Carbon Nanotubes (SWNTs)

Multi-Walled Carbon Nanotubes (MWNTs)

🔹 1. Fullerenes

📌 Structure

Closed spherical molecules made of 60 carbon atoms (C₆₀)

Ball-like structure

📌 Properties

✔ Can be hydrogenated and dehydrogenated reversibly

✔ Storage capacity ≈ 5 wt% H₂

🔹 2. Multi-Walled Carbon Nanotubes (MWNTs)

📌 Structure

Made of multiple concentric graphene cylinders

Hollow core

Number of layers: 2-50

📌 Storage Capacity

Alkali-doped MWNTs can store ≈ 7.7 wt% H₂

🔹 3. Single-Walled Carbon Nanotubes (SWNTs)

📌 Structure

Single layer of graphene rolled into a tube

📌 Key Concept

Hydrogen storage increases with surface area

Larger tube diameter → higher H₂ uptake

conditions

📊 Storage Behavior

At Normal Conditions (1 atm)

❌ Very low storage: < 1 wt%

At Cryogenic Conditions (low temperature)

✔ Storage increases to 1 - 2.4 wt%

📌 Enhanced Storage (With Coatings)

Titanium-coated CNTs → ~8% (by volume)

Lithium-coated carbon spheres (buckyballs) → ~9% (by volume)

👉 Doping improves hydrogen adsorption significantly

graphite nano fibre

🔹 4. Carbon & Graphite Nanofibers

📌 Structure

Layered graphitic nanostructures

Stacks of graphene plates

📌 Storage Capacity

Range: < 1 wt% to 10 wt%

📌 Key Observation

Graphite nanofibers can achieve:

~6.5% H₂ adsorption

1. Preparation of H₂ by alkaline electrolysis

1. Preparation of H₂ by alkaline electrolysis

Electrolysis of water using NaOH/KOH electrolyte improves conductivity.

Electrodes: Ni (anode), Fe (cathode)

Reactions:

Cathode: 2H2O+2e−→2OH−+H22H_2O + 2e^- → 2OH^- + H_22H2O+2e−→2OH−+H2

Anode: 2OH−→H2O+12O2+2e−2OH^- → H_2O + \frac{1}{2}O_2 + 2e^-2OH−→H2O+21O2+2e−

Overall: H2O→H2+12O2H_2O → H_2 + \frac{1}{2}O_2H2O→H2+21O2

2. Laboratory preparation from acid and alkali + justification

2. Laboratory preparation from acid and alkali + justification

Hydrogen is prepared in the lab by reacting electropositive metals with acids or alkalis.

(a) From aqueous acids:

Zn+2HCl→ZnCl2+H2Zn + 2HCl → ZnCl_2 + H_2Zn+2HCl→ZnCl2+H2

Also: 2Na+2H3O+→2Na++H2+2H2O2Na + 2H_3O^+ → 2Na^+ + H_2 + 2H_2O2Na+2H3O+→2Na++H2+2H2O

(b) From alkali:

2Al+2NaOH+6H2O→2Na[Al(OH)4]+3H22Al + 2NaOH + 6H_2O → 2Na[Al(OH)_4] + 3H_22Al+2NaOH+6H2O→2Na[Al(OH)4]+3H2

Why not used industrially:

Uses expensive metals (Zn, Al)

Not economical for large-scale production

Produces small quantities only

Not continuous process

coke2

Industrial production using coke + colour classification

Hydrogen is produced by coal gasification (steam-carbon reaction):

C+H2O(g)→CO+H2C + H_2O (g) → CO + H_2C+H2O(g)→CO+H2

The mixture of CO + H₂ is called water gas (syngas).

Water gas shift reaction:

CO+H2O→CO2+H2CO + H_2O → CO_2 + H_2CO+H2O→CO2+H2

This increases hydrogen yield.

Colour of hydrogen produced:

This method gives Black hydrogen, as it uses coal and produces high CO₂ emissions.

Why hydrogen is a future fuel

High calorific value (~141,800 kJ/kg)

Produces only water → zero carbon emission

Suitable for fuel cells and clean energy systems

Heavy water in nuclear reactors

🔹 Role in nuclear reactors:

Heavy water acts as a moderator.

A moderator is a substance used to slow down fast neutrons produced during nuclear fission.

🔹 Why slowing neutrons is important:

Slow (thermal) neutrons are more effective in sustaining chain reactions.

This ensures controlled nuclear fission.

🔹 Why heavy water is preferred:

Deuterium has low neutron absorption capacity.

It slows neutrons without capturing them, maintaining neutron availability.

🔹 Additional points:

Used in nuclear power plants for efficient energy generation.

Also used in fusion research and tracer studies.

✅ Conclusion: Heavy water is used because it efficiently moderates neutrons while maintaining the chain reaction.

2. Tritium in self-powered lighting devices

Tritium (³H) is a radioactive isotope of hydrogen.

🔹 Key properties:

Contains 1 proton and 2 neutrons

Radioactive with half-life ≈ 12.4 years

Emits low-energy beta radiation

🔹 Working in lighting devices:

Tritium emits beta particles continuously

These particles excite a phosphorescent material

The material emits visible light

🔹 Why it is useful:

No external power source needed

Continuous illumination for years

Reliable and maintenance-free

🔹 Applications:

Emergency exit signs

Watch dials

Military equipment

✅ Conclusion: Tritium is used because its radioactive decay provides a continuous, self-sustained light source.

3. CO₂ separation in steam reforming process

During steam reforming, CO₂ is formed after the water gas shift reaction:

CO+H2O→CO2+H2CO + H_2O → CO_2 + H_2CO+H2O→CO2+H2

🔹 Need for CO₂ removal:

CO₂ is an undesirable impurity

Reduces hydrogen purity

Contributes to greenhouse gas emissions

🔹 Methods of separation (as per notes):

Absorption in water under pressure

Reaction with potassium carbonate (K₂CO₃)

Absorption using amine solutions (ethanolamines) → forms carbonate/bicarbonate compounds

🔹 Importance:

Produces high purity hydrogen

Enables carbon capture (blue hydrogen)

Reduces environmental impact

✅ Conclusion: CO₂ is separated to improve hydrogen purity and reduce emissions.

4. Need for water gas shift reaction

Reaction:

CO+H2O→CO2+H2CO + H_2O → CO_2 + H_2CO+H2O→CO2+H2

🔹 Why it is necessary:

Increases hydrogen yield

Converts CO into additional hydrogen

Removes toxic carbon monoxide

CO is poisonous and undesirable

Improves purity of hydrogen

Essential for industrial applications (e.g., ammonia synthesis)

Makes process more efficient

Maximizes hydrogen production from same raw material

🔹 Industrial significance:

Essential step after steam reforming and coal gasification

✅ Conclusion: The shift reaction is crucial to maximize H₂ production and remove CO impurity.

5. Why NaOH/KOH is added in electrolysis

Electrolysis of pure water is inefficient because water has low conductivity.

🔹 Role of NaOH/KOH:

Acts as an electrolyte

Provides OH⁻ ions for conduction

🔹 Functions:

Increases electrical conductivity

Facilitates ion movement

Improves efficiency of electrolysis

Reduces energy loss

🔹 In electrochemical reactions:

OH⁻ ions participate in anode and cathode reactions

🔹 Why specifically NaOH/KOH:

Strong electrolytes

Stable and effective in alkaline medium

✅ Conclusion: NaOH/KOH is added to make electrolysis efficient and feasible.

6. Hydrogen as a future fuel for vehicles + On-board & Off-board reforming

🔹 Why hydrogen is a future fuel:

Zero carbon emission

Produces only water:

H2+12O2→H2O+energyH_2 + \frac{1}{2}O_2 → H_2O + energyH2+21O2→H2O+energy

High calorific value

~141,800 kJ/kg

Clean and sustainable

Especially when produced as green hydrogen

Efficient energy conversion

Used in fuel cells with high efficiency

🔹 Reforming in hydrogen vehicles

(A) On-board reforming

Hydrogen is produced inside the vehicle

Fuel like methanol/natural gas is converted into H₂ in real time

Features:

No need for hydrogen storage tanks

More complex system

(B) Off-board reforming

Hydrogen is produced outside the vehicle

Stored and supplied at refueling stations

Features:

Vehicle stores hydrogen directly

Simpler vehicle design

Requires infrastructure (storage + transport

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