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Electrochemistry basics, hydrogen production

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.

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

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)

        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.

✓ Answer checked by Claude Opus 5.5 (high effort)

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