An electrolyzer is a device that uses electricity to drive non-spontaneous chemical reactions, converting electrical energy into chemical energy through direct current. It plays a key role in the chemical, metallurgical, and energy industries. Its core principle is to use the electric field between cathode and anode electrodes to induce ion migration in an electrolyte solution or molten salt, leading to redox reactions on the electrode surfaces, thereby achieving decomposition, synthesis, or purification of substances.
Basic Structure and Working Principle
The basic structure of an electrolyzer consists of a cell body, electrodes (anode and cathode), electrolyte, and power supply system. The cell body is typically made of corrosion-resistant materials (such as PP plastic, steel-lined glass, or titanium alloy) to contain the electrolyte and isolate the reaction environment. Electrodes are made of different materials depending on process requirements. For example, the chlor-alkali industry often uses titanium-coated anodes and graphite cathodes, while aluminum electrolysis uses carbon anodes and steel cathodes.
When direct current is applied, cations in the electrolyte (such as Na⁺ and Al³⁺) migrate to the cathode, gaining electrons and being reduced, while anions (such as Cl⁻ and O²⁻) migrate to the anode, losing electrons and being oxidized. Taking chlor-alkali electrolysis as an example, salt water (NaCl solution) decomposes in the electrolyzer into hydrogen (cathode), chlorine (anode), and sodium hydroxide. This process supports approximately half of the world's caustic soda and chlorine production capacity.
Main Types and Applications
Depending on the state of the electrolyte, electrolyzers can be divided into three categories: aqueous solution electrolyzers, molten salt electrolyzers, and solid electrolyte electrolyzers:
1. Aqueous Solution Electrolyzer
This is the most common type, used in applications such as the chlor-alkali industry, electroplating, and water treatment. For example, alkaline water electrolysis (AEL) and proton exchange membrane electrolysis (PEM) are currently the mainstream technologies for green hydrogen production. They split water to produce hydrogen and oxygen, providing clean energy for fuel cell vehicles and the chemical industry.
2. Molten salt electrolysis cells are used for the electrolysis of high-temperature molten metals or oxides, with a typical application being aluminum electrolysis (Hall-Héroult process). In this cell, aluminum oxide (Al₂O₃) is dissolved in a molten salt called cryolite (Na₃AlF₆). Liquid aluminum and carbon dioxide are then electrolyzed at a carbon anode. This process produces over 90% of primary aluminum globally. The extraction of light metals such as magnesium and lithium also relies on similar technology.
3. Solid electrolyte electrolysis cells
Utilizing ceramic or polymer solid electrolytes (such as yttrium-stabilized zirconia (YSZ), these cells can conduct ions (such as O₂⁻ or H⁺) at high temperatures. They are used in cutting-edge fields such as solid oxide fuel cells (SOFCs) and carbon dioxide electroreduction, and are a potential key technology for future zero-carbon energy systems.
Technological Challenges and Development Trends
Although electrolyzer technology is relatively mature, significant room for improvement remains:
Energy Efficiency Improvement: Traditional aluminum electrolyzers consume as much as 13,000-15,000 kWh/ton. New-generation inert anode technology can reduce energy consumption and carbon emissions.
Material Innovation: Platinum catalysts for PEM electrolyzers are expensive, and developing non-precious metal catalysts is a breakthrough.
Large-Scale and Intelligent: The chlor-alkali industry has seen a rise in single-cell capacity from a few hundred amperes decades ago to hundreds of thousands of amperes today, with precise control enabled by digital twin technology.
Driven by the "dual carbon" goals, electrolyzers are becoming core equipment in the new energy industry chain. Whether it's green hydrogen production, battery material production, or the design of tritium breeder layers for future nuclear fusion reactors, these "electrochemical factories" provide essential support. With advances in materials science and power electronics, the performance boundaries of electrolyzers will continue to expand, driving global industry towards greener and more efficient processes.
