---
title: "Electrochemistry basics, hydrogen production"
subject: "Energy Environment and Society"
chapter: 3
key: "semester_7/energy_environment_and_society:electrochemistry-hydrogen-production"
source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/electrochemistry-hydrogen-production
site: BCT Engineering
---

# Electrochemistry basics, hydrogen production

Energy Environment and Society · Chapter 3: Renewable Energy Sources

- Asked in: 2074 Chaitra, 2+4 marks
- Video: [Electrochemistry](https://www.youtube.com/watch?v=2VT5rl8P84M) — Professor Dave Explains
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/electrochemistry-hydrogen-production
- Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-3

## Question

What are the basics of electrochemistry? Explain about hydrogen production and storage.

## Short answer

Electrochemistry studies chemical-electricity conversion. In an electrolytic cell, water electrolysis splits water into hydrogen and oxygen using DC, requiring >1.23 V (practical ~1.8–2.0 V) and about 50–55 kWh per kg H2. Hydrogen can be stored as compressed gas (350–700 bar), liquid at –253°C, in metal hydrides or underground caverns.

## Answer

#### Basics of electrochemistry
**Electrochemistry** is the branch of chemistry dealing with the relation between chemical reactions and electrical energy.
- **Redox reactions:** oxidation is loss of electrons, reduction is gain of electrons. They always occur together.
- **Electrochemical cell:** two electrodes (anode and cathode) in an electrolyte. *Anode:* oxidation takes place; *cathode:* reduction takes place.
- **Galvanic (voltaic) cell:** a spontaneous chemical reaction produces electricity (batteries, fuel cells).
- **Electrolytic cell:** electricity forces a non-spontaneous reaction (electrolysis, electroplating, hydrogen production).
- **Electrode potential (E°) and cell voltage:** E°cell = E°cathode − E°anode. For the hydrogen–oxygen cell, E°cell = 1.23 V at 25 °C.
- **Faraday's laws:** mass deposited m = (M · I · t) / (n · F), where F = 96,485 C/mol.
- **Nernst equation** gives the potential at non-standard conditions.
- **Electrolyte:** a substance whose ions carry current in the cell.

#### Hydrogen production (electrolysis of water)
```text
        DC supply
       -|  |+
    cathode  anode
    2H2O+2e- -> H2+2OH-   (cathode)
    2OH- -> 1/2 O2+H2O+2e- (anode)
  Overall: 2H2O -> 2H2 + O2
```
At least 1.23 V is needed in theory (about 1.8–2.0 V in practice) to split water. About 50–55 kWh of electricity is needed per kg of H₂. Types: alkaline, PEM, and solid oxide electrolysers. Other methods include steam methane reforming and biomass gasification.

#### Hydrogen storage
- Compressed gas (350–700 bar) in cylinders.
- Liquefied hydrogen (−253 °C).
- Solid-state storage in metal hydrides and chemical carriers (ammonia).
- Underground salt caverns for large scale.
The main challenge is the low volumetric energy density of hydrogen.

## Check yourself

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

1. In an electrochemical cell, what occurs at the anode and cathode?
   A. Reduction at the anode, oxidation at the cathode
   B. Oxidation at the anode, reduction at the cathode
   C. Oxidation at both
   D. Reduction at both
   Answer: B. Oxidation (loss of electrons) occurs at the anode; reduction (gain) at the cathode. (Key point: Anode and cathode)

2. How does an electrolytic cell differ from a galvanic cell?
   A. Electricity forces a non-spontaneous reaction, as in electrolysis
   B. It produces electricity spontaneously
   C. It has no electrodes
   D. It does not need an electrolyte
   Answer: A. Galvanic cells (batteries, fuel cells) produce electricity; electrolytic cells consume it. (Key point: Galvanic vs electrolytic)

3. What voltage is needed to split water in theory and in practice?
   A. 1.23 V theoretical, about 1.8-2.0 V in practice
   B. 12 V theoretical, 1.8 V practical
   C. 0.5 V in both
   D. 1.23 V in both
   Answer: A. Losses raise the practical voltage above the 1.23 V theoretical minimum. (Key point: Electrolysis voltage)

4. Which is the expression of Faraday's law for deposited mass?
   A. m = M I t / (n F)
   B. m = n F / (M I t)
   C. m = I t F / M
   D. m = M n / (I t F)
   Answer: A. Mass is proportional to molar mass, current and time, and inversely to n and F (96,485 C/mol). (Key point: Faraday's law)

## Related in Energy Environment and Society

- [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

## Related in other subjects

- [Hydrogen storage and infrastructure requirements](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Ahydrogen-storage-infrastructure) — Energy Resources, chapter 6
- [Hydrogen production processes](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Ahydrogen-production-methods) — Energy Resources, chapter 6