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Detailed Explanation of Alkaline Water Electrolysis for Hydrogen Production | Understanding How Green Hydrogen is Made
Release time:
2025-05-07
With the advancement of the "dual-carbon" goals, alkaline water electrolysis has become a core pathway for large-scale green hydrogen production due to its mature technology and low cost. This article breaks down the entire process from "water" to "high-purity hydrogen" in the simplest terms!
1. Raw Water Treatment: Providing "Purified Water" for the Electrolyzer
Ordinary water contains impurities like calcium and magnesium, which can corrode equipment and reduce efficiency if directly electrolyzed. Therefore, industrial soft water undergoes ultrafiltration and dual-stage reverse osmosis treatment to remove 99% of ions and particles, achieving ultra-pure water with a conductivity of ≤0.1 μS/cm (close to laboratory-grade purity).
The purified water is mixed with a 30% potassium hydroxide (KOH) solution and stored in an alkali tank, becoming the "nutrient solution" for the electrolyzer—conductive while protecting the equipment from rust.
2. Electrolysis Reaction: Water Molecules "Split" in an Electric Field
The electrolyzer is the "heart" of the system, consisting of hundreds of stacked electrode plates. The plate surfaces are covered with textured protrusions to evenly distribute the electrolyte and reduce resistance. When direct current (1.6–2.0V) is applied, water molecules "split" at the electrodes:
Cathode (hydrogen side): Water molecules gain electrons, decomposing into hydrogen (H₂) and hydroxide ions (OH⁻).
Anode (oxygen side): Hydroxide ions lose electrons, forming oxygen (O₂) and water.
*(Reaction equation: 2H₂O → 2H₂↑ + O₂↑)*
The electrolyte temperature is maintained at around 85°C, with a pressure of about 1.6 MPa, ensuring efficient and stable reactions.
3. Gas-Liquid Separation: Hydrogen and Alkali Solution "Go Separate Ways"
The hydrogen and oxygen produced carry high-temperature alkali solution out of the electrolyzer. In the hydrogen/oxygen separator, leveraging the principle that gas is lighter than liquid, hydrogen "rises" to the top pipeline, while the alkali solution "sinks" to the bottom and is pumped back into the electrolyzer.
The separator also contains a magnetic filter at the bottom to adsorb metal impurities like rust, protecting the equipment.
4. Gas Purification: "Washing and Drying" the Hydrogen
The hydrogen exiting the separator is still at 80°C and contains tiny alkali droplets:
Cooling: A shell-and-tube heat exchanger reduces the temperature to 30–40°C, liquefying most water vapor.
Washing: The gas enters a mist eliminator, where ultra-pure water rinses away residual alkali droplets (purity increases to 99.5%).
Oxygen Removal: At 200°C, hydrogen passes through a palladium (Pd) catalyst bed, reacting with trace oxygen to form water *(2H₂ + O₂ → 2H₂O)*.
Drying: Molecular sieves adsorb remaining moisture, lowering the dew point to below -40°C and achieving 99.999% purity.
5. Intelligent Control: "Full-Service" Monitoring
The system automatically monitors key parameters via PLC:
Electrolyte concentration: Replenishes pure water and alkali in real time.
Temperature and pressure: Maintains ±2°C temperature and ≤0.05 MPa pressure fluctuations.
Safety measures: Nitrogen purging for explosion prevention, emergency power cutoff.
Why Choose Alkaline Electrolysis Technology?
Low cost: No precious metal catalysts required; only 4–5 kWh of electricity per cubic meter of hydrogen.
Long lifespan: Nickel-based electrodes + polyphenylene sulfide (PPS) diaphragms ensure over 15 years of service.
Renewable energy compatibility: Current can flexibly adjust from 20% to 110%, perfectly accommodating fluctuating green power.
With its mature process chain and low electricity cost (~4–5 kWh/Nm³ H₂), alkaline water electrolysis has become the preferred technology for large-scale green hydrogen production. In the future, with optimized diaphragm materials and increased current density, its efficiency and adaptability will further improve, supporting the realization of carbon neutrality goals!
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