Currently, hydrogen production technology through water electrolysis mainly follows four routes, with their respective principles, characteristics, and development stages as follows:
1. Hydrogen production from alkaline electrolysis of water (ALK)
Principle: Using KOH or NaOH as the electrolyte solution, water is decomposed into hydrogen and oxygen under the influence of an electric field, and the hydrogen and oxygen are separated by a diaphragm.
Advantages: The most mature technology and low cost (equipment cost is about 1/3 to 1/5 of PEM);
The single-tank hydrogen production system has a large scale (up to 3000 Nm³/h), making it suitable for large-scale applications.
Challenge
Low current density (approximately 1,500A/m²) and high energy consumption (direct current power consumption of 4.2-5.5kWh/Nm³);
Slow response speed (over 1 hour for cold start) makes it difficult to match renewable energy fluctuations;
Alkali solution has strong corrosivity, requires complex maintenance, and poses environmental risks.
Application stage: mature commercialization, accounting for about 60% of the current market share.
2. Proton Exchange Membrane Water Electrolysis for Hydrogen Production (PEM)
Principle: Using perfluorosulfonic acid membrane as the solid electrolyte, pure water is electrolyzed, and hydrogen ions (H⁺) migrate through the membrane to the cathode to generate hydrogen gas. advantage
1. High efficiency and low energy consumption: The electrolysis efficiency reaches 70%-80% (with a direct current power consumption of 4.0-4.5 kWh/Nm³), which is significantly higher than that of traditional alkaline electrolytic cells (around 50%).
High current density (typically exceeding 10,000A/m²) results in stronger hydrogen production capacity per unit area.
2. Quick response and flexibility
The cold start time is only 20-30 minutes, with a wide load adjustment range (5%-125%), second-level response speed, and adaptability to fluctuating renewable energy sources such as wind and solar.
The system boasts a compact structure, with a volume and weight only accounting for 1/3-1/5 of alkaline electrolytic cells, making it ideal for distributed and mobile scenarios.
3. High purity and safety
The purity of hydrogen produced reaches 99.99%, eliminating the need for additional purification treatment, and pure water electrolysis poses no risk of alkali solution pollution.
The proton exchange membrane exhibits excellent gas tightness, preventing the cross-permeation of hydrogen and oxygen, thus ensuring higher safety.
4. Strong pressure adaptability
It can operate directly under high-pressure conditions (such as above 30 bar), reducing the energy consumption for subsequent hydrogen compression.
challenge
1. High cost due to dependence on precious metals
The anode requires an iridium (Ir)-based catalyst, while the cathode requires a platinum (Pt)-based catalyst. Additionally, the proton exchange membrane relies on imported perfluorosulfonic acid materials (such as Nafion membrane), making the equipment cost 3-5 times that of alkaline electrolytic cells.
2. The localization rate of core materials is low
Key materials such as membrane electrodes and catalysts rely on imports, and domestic technology is not mature enough. The maximum production capacity of a single tank is only 200 Nm³/h (while it has reached 500 Nm³/h abroad).
3. Material lifespan and stability issues
Strongly acidic and highly oxidizing environments accelerate catalyst dissolution (such as Ir³+ loss) and membrane material degradation, resulting in equipment lifetimes generally shorter than those of alkaline electrolytic cells.
4. Bottlenecks in large-scale applications: Megawatt-scale projects are still dominated by European and American companies (such as Plug Power and Siemens). Most domestic commercial projects are in the demonstration stage, relying on technological iteration and localization of supply chains to reduce costs.
Application stage
Current positioning: In the early stage of commercialization, with a global installed capacity share of about 10%, mainly relying on European and American technologies.
Typical scenario:
Renewable energy coupled hydrogen production: For example, the PEM electrolyzer of Jidian shares is applied to wind and solar power stations to enhance the economic efficiency of green hydrogen.
Hydrogen supply in the transportation sector: Providing on-site hydrogen production for hydrogen fuel cell vehicles at hydrogen refueling stations to meet high purity requirements, such as the demonstration project of Changchun Lvdong Hydrogen Energy Company.
Industrial decarbonization: Deploying megawatt-scale equipment in the steel and chemical industries, combined with waste heat utilization, to achieve low-carbon production, such as the demonstration project of Huaneng Jiuquan Power Plant.
Future trends: The development of low-iridium/non-precious metal catalysts (such as nickel-based alloys) and the localization of non-fluorinated proton exchange membranes are key to cost reduction.
3. Solid oxide electrolysis of water for hydrogen production (SOEC)
Principle: It operates at high temperatures ranging from 700 to 1000℃, using a solid oxide (such as 8mol% yttria-stabilized zirconia, YSZ) as the electrolyte. Water vapor is electrolyzed into hydrogen gas and oxygen ions at the cathode, and the oxygen ions pass through the electrolyte layer to the anode where they combine to form oxygen gas.
Advantage:
The reaction kinetics is significantly enhanced at high temperatures, and the electrolysis efficiency can reach 85%-90% (when combined with waste heat input);
Non-precious metal catalysts (such as nickel-based electrodes) can be used to reduce material costs;
Adapt to industrial waste heat or high-temperature energy sources (such as nuclear energy and solar thermal collection) to achieve energy cascade utilization.
Challenge
High-temperature operation leads to stringent requirements for equipment materials (such as short lifespan of high-temperature resistant sealing materials);
The startup/shutdown time is long (requiring several hours), making it difficult to quickly respond to fluctuations in renewable energy;
The technology is not yet mature and is currently in the demonstration stage, with high costs for large-scale application.
Application stage: The focus is mainly on technology verification and demonstration projects, with a relatively small global installed capacity, and commercialization has not yet been achieved.
4. Hydrogen production by water electrolysis using anion exchange membrane (AEM)
Principle: An anion exchange membrane (such as Aemion+) is used to replace the traditional separator, allowing the migration of hydroxide ions (OH⁻). Pure water or low-concentration alkali solution is used as the electrolyte, and a non-precious metal catalyst (such as transition metal) is employed to reduce costs.
Advantage:
Combining the advantages of ALK and PEM: no need for strong alkali solution (environmentally friendly), lower cost than PEM, and higher current density than ALK;
The operating temperature is close to room temperature (70-90℃), with a simple system design and convenient maintenance;
The potential application scenarios are extensive, such as distributed hydrogen production and mobile hydrogen supply.
Challenge
The stability of anion exchange membranes is insufficient (due to poor chemical/mechanical properties), resulting in a short lifespan;
Low membrane conductivity and slow catalytic kinetics result in limited efficiency and current density;
Core materials (such as membranes and catalysts) rely on imports, with a low localization rate.
Application stage: Currently, the focus is mainly on laboratory research and development. Companies like ENAPTER in Italy have commercialized miniaturized products, but large-scale application still requires technological breakthroughs.
