---
title: "Hydrogen production processes"
subject: "Energy Resources"
chapter: 6
key: "semester_6/energy_resources:hydrogen-production-methods"
source: https://www.bctengineer.com/q/semester_6/energy_resources/hydrogen-production-methods
site: BCT Engineering
---

# Hydrogen production processes

Energy Resources · Chapter 6: Non conventional forms of energy and batteries

- Asked in: year not given, 6 marks
- Video: [Hydrogen Industry Overview - How is Hydrogen Produced?](https://www.youtube.com/watch?v=UHYmBFICDSY) — Primerli
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/energy_resources/hydrogen-production-methods
- Whole chapter: https://www.bctengineer.com/md/semester_6/energy_resources/chapter-6

## Question

Describe the main processes for producing hydrogen: steam methane reforming, water electrolysis and gasification of coal or biomass. Compare the processes in brief and mention one other emerging method.

## Short answer

Steam methane reforming (CH4 + H2O → CO + 3H2 then shift) is cheapest, 70-80% efficient, emits CO2. Electrolysis splits water: ~50-55 kWh/kg, zero emission if renewable. Coal/biomass gasification yields syngas. Emerging method: photoelectrochemical splitting.

## Answer

Hydrogen is not found free in nature; it is an energy carrier made from water or hydrocarbons, so how clean it is depends on the source of energy used.

#### 1. Steam methane reforming (SMR)
Natural gas reacts with steam over a nickel catalyst at 700–900 °C and 3–25 bar:

$$
CH_4 + H_2O \rightarrow CO + 3H_2 \quad (\text{endothermic})
$$

This is followed by the water-gas shift reaction at 200–400 °C: $CO + H_2O \rightarrow CO_2 + H_2$. Pressure swing adsorption purifies the H₂. Natural gas reforming is the main industrial route (about two-thirds of world hydrogen, and about 95 % in the USA), with an efficiency of 70–80 % and CO₂ emissions of about 9–10 kg per kg of H₂ ("grey hydrogen"; with carbon capture it is "blue").

#### 2. Water electrolysis
Direct current splits water:

- Cathode: $2H_2O + 2e^- \rightarrow H_2 + 2OH^-$
- Anode: $2OH^- \rightarrow \tfrac{1}{2}O_2 + H_2O + 2e^-$
- Overall: $H_2O \rightarrow H_2 + \tfrac{1}{2}O_2$

Types: alkaline, PEM and solid oxide electrolysers. It needs about 50–55 kWh of electricity per kg of H₂. With electricity from hydro, solar or wind, the product is "green hydrogen" of very high purity (above 99.9 %).

#### 3. Gasification
Coal or biomass is heated with limited oxygen and steam at 800–1500 °C to form syngas (CO + H₂), mainly by $C + H_2O \rightarrow CO + H_2$; the CO is then shifted to more H₂ and the gas is purified. It suits places where coal or biomass is cheap; coal gasification gives high CO₂ emissions.

#### Comparison

| Process | Feed | Cost | Emission |
|---|---|---|---|
| SMR | Natural gas | Lowest | High CO₂ |
| Electrolysis | Water + electricity | High | Nil if renewable |
| Gasification | Coal / biomass | Medium | High (coal), low (biomass) |

#### Other methods
Thermochemical cycles (sulphur-iodine) using high-temperature nuclear or solar heat, photo-electrochemical water splitting and biological (algae) production are under development.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the first reaction in steam methane reforming?
   A. CH4 + H2O -> CO + 3H2 over a nickel catalyst at 700-900 C (endothermic)
   B. CO + H2O -> CO2 + H2 at 900 C
   C. 2H2O -> 2H2 + O2
   D. C + O2 -> CO2
   Answer: A. Methane reacts with steam to give CO and H2; the water-gas shift then converts CO to more H2. (Key point: Steam methane reforming)

2. What is the purpose of the water-gas shift step after reforming?
   A. To remove nitrogen from air
   B. To convert CO and steam into extra H2 and CO2
   C. To liquefy hydrogen
   D. To heat the methane
   Answer: B. CO + H2O -> CO2 + H2 raises the hydrogen yield. (Key point: Role of water-gas shift)

3. Why is hydrogen from electrolysis called green only in some cases?
   A. Because electrolysis needs no electricity
   B. Because green hydrogen needs electricity from hydro, solar or wind
   C. Because electrolysis uses natural gas
   D. Because the hydrogen is coloured
   Answer: B. Hydrogen is an energy carrier, so its cleanliness depends on the energy source used. (Key point: Colour of hydrogen)

4. Which describes gasification of coal or biomass?
   A. Heating with excess air to burn fully to CO2
   B. Heating with limited oxygen and steam at 800-1500 C to give syngas (CO + H2)
   C. Splitting water with direct current
   D. Using algae in sunlight
   Answer: B. Limited oxygen produces syngas, which is shifted and purified to get hydrogen. (Key point: Gasification)

5. Which correctly compares the emissions of the processes?
   A. SMR emits nil CO2
   B. Electrolysis with renewable power has nil emission; SMR and coal gasification emit high CO2
   C. Coal gasification is lowest in CO2
   D. All three emit the same CO2
   Answer: B. SMR (grey) and coal give high CO2; electrolysis from renewables gives none. (Key point: Comparison of methods)

## Related in Energy Resources

- [Hydrogen storage and infrastructure requirements](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Ahydrogen-storage-infrastructure) — Energy Resources, chapter 6
- [Biochemical conversion of biomass to fuels](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Abiomass-biochemical-conversion) — Energy Resources, chapter 3
- [Fuel cell voltage, efficiency and hydrogen use](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Afuel-cell-stack-numerical) — Energy Resources, chapter 6
- [Sizing a family biogas plant](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Abiogas-plant-sizing-cattle-dung) — Energy Resources, chapter 3

## Related in other subjects

- [Hydrogen production and storage](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Ahydrogen-production-storage) — Energy Environment and Society, chapter 3
- [Electrochemistry basics, hydrogen production](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aelectrochemistry-hydrogen-production) — Energy Environment and Society, chapter 3
- [Steam main with two insulation layers: overall coefficients](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Asteam-main-two-layer-lagging-overall-u) — Fundamental of Thermodynamics & Heat Transfer, chapter 7
- [Euler's formula: one end fixed, other hinged](https://www.bctengineer.com/question.md?key=semester_3%2Fstrength_of_materials%3Aeuler-one-fixed-one-hinged) — Strength of Materials, chapter 8, asked 2×