PEM Water Electrolysis Hydrogen Production: Structure Breakdown and Cost Analysis

In our previous discussions, we analyzed the fundamental differences between alkaline (ALK) and proton exchange membrane (PEM) electrolysis, particularly focusing on the types of electrolytes used—liquid for ALK and solid for PEM. Given the century-long development of water electrolysis technology, why has PEM consistently attracted the attention of high-end players and investors? This article will delve into various aspects of PEM technology.
Key Components and Terminology
Differences in Design Pressure
The materials used in PEM electrolysis cells vary depending on the design pressure. For low-pressure electrolysis cells, carbon-based materials may replace titanium-based materials. This article primarily focuses on high-pressure industrial PEM electrolysis cells. A complete PEM electrolysis cell consists of several components arranged from left to right, with larger cells being formed by connecting multiple smaller chambers:

Bolt: Fastening nut
Compression Plate: End plate (also known as the end plate)
Insulation Layer: Insulating layer
Bipolar Plates (BPs): Bipolar plates
Insulation Rubber Ring: Insulating rubber ring
Large-hole Titanium Mesh: Titanium mesh with large holes (>500μm)
Medium-hole Titanium Mesh: Titanium mesh with medium holes (100-500μm)
Small-hole Titanium Mesh: Titanium mesh with small holes (micron level, e.g., 50-100μm)
Titanium Felt: Titanium fiber felt
Electrode Plate: Electrode plate

Common Terminology
In literature, we often use specific terms to simplify the introduction of components based on their functions:


Gas Diffusion Layer (GDL): Also known as the current collector, it serves as an electronic conductor between the Membrane Electrode Assembly (MEA) and Bipolar Plates (BPP), ensuring effective mass transfer of liquids and gases between the electrodes and BPP. Typically made of titanium fiber felt.


Membrane Electrode Assembly (MEA): The core component, with catalyst layers coated on both sides—anode catalyst layer (OER, oxygen evolution reaction) and cathode catalyst layer (HER, hydrogen evolution reaction). At the anode, water is oxidized to produce oxygen and protons, which then migrate to the cathode. Electrons flow through an external circuit to the cathode, where protons gain electrons and are reduced to form hydrogen gas.


Catalyst Choices

Anode: Iridium (Ir) or iridium oxide (IrO₂) is considered the most advanced catalyst for PEM water electrolysis.
Cathode: Generally, platinum (Pt) or platinum-carbon (Pt/C) catalysts are used.

Cost Analysis
The high cost of PEM electrolysis is primarily attributed to four major components:


Proton Exchange Membrane (PEM): Cost share: approximately 20-30%. The use of perfluorosulfonic acid resin (such as Nafion) complicates production and relies on imports, with high purity requirements.


Catalyst Layer: Cost share: approximately 30-40%. Anode: iridium or iridium oxide; cathode: platinum here or platinum-carbon.


Bipolar Plates: Cost share: approximately 10-15%. Made from titanium-based materials (due to corrosion resistance) and requiring precision machining (e.g., flow channel design).


Gas Diffusion Layer (GDL): Cost share: approximately 5-10%. Made from carbon paper or carbon cloth substrates treated for hydrophobicity, with high-performance carbon paper (like Toray TGP-H series) used, and titanium-based materials for high-pressure systems.


Advantages of PEM Technology
Despite the high costs, PEM technology offers several advantages that make it attractive for long-term investment:


Higher Efficiency and Current Density: PEM electrolysis cells maintain high efficiency (>70-80%) at high current densities (>20000 A/m²), while ALK cells typically operate at lower efficiencies (60-70%) and current densities (1000-4000 A/m²).


Rapid Dynamic Response: PEM electrolysis can respond to power fluctuations (e.g., from wind or solar energy) in seconds, whereas ALK systems may take tens of minutes to hours to start up.


Superior Gas Purity and Safety: The solid membrane of PEM effectively prevents hydrogen-oxygen crossover, achieving hydrogen purity levels of 99.999%, while ALK systems often require additional purification. Additionally, PEM avoids the risks associated with alkaline liquid leaks and corrosion.


Direct High-Pressure Hydrogen Production: PEM electrolysis can generate hydrogen at pressures of 3-6 MPa, eliminating the need for external compression, which reduces energy consumption and costs.


Compact Size and Weight: PEM systems have a power density 3-5 times that of ALK, requiring less space and making them suitable for distributed or mobile applications (e.g., hydrogen refueling stations, ships).


Wide Load Operating Range: PEM can operate stably at as low as 10% rated power, while ALK systems usually require a minimum of 30% to avoid electrode passivation.


Environmental Benefits and Low Maintenance Costs: PEM systems do not use alkaline electrolytes, reducing waste disposal costs. Key materials (like Nafion and titanium bipolar plates) are highly corrosion-resistant, with lifespans exceeding 60,000 hours (compared to around 40,000 hours for ALK systems).


Conclusion
This article provides a detailed introduction to the core equipment of PEM water electrolysis—electrolysis cells—covering key components, terminology, cost analysis, and a comparison of advantages over ALK technology. In the following sections, we will further explore the operational cost (OpEx) advantages of PEM electrolysis. Due to its numerous benefits and technological barriers, PEM technology remains a focal point in the field of green hydrogen production.