In alkaline water electrolysis hydrogen production equipment, bipolar plates play an extremely crucial and multifunctional role. They are not only the physical foundation of the electrolyzer stack structure, but also the core components for current conduction, gas separation, fluid distribution, and structural support. Understanding bipolar plates is crucial to understanding the working principle and performance of alkaline electrolyzers.

　　 1. Definition and Core Concepts

　　● Meaning of "Bipolar": Bipolar plates are so named because one side serves as part of the anode chamber, while the other side serves as part of the cathode chamber of the adjacent electrolysis cell. In an electrolyzer stack composed of multiple electrolysis cells connected in series, the bipolar plate simultaneously has the dual identities of "anode" and "cathode".

　　● Structural Core: It is the main repeating unit in the electrolyzer stack, and together with the electrodes (anode, cathode), diaphragm, and sealing gasket, it constitutes a complete "single cell". Multiple single cells are connected in series and stacked to form the electrolyzer body.

　　 2. Core Functions

　　Bipolar plates undertake several indispensable functions in alkaline electrolyzers:

　　● Current Conduction and Distribution:

　　o Conductive Bridge: As the main conductive path inside the electrolyzer stack, the bipolar plate is responsible for efficiently conducting current from the cathode to the anode.

　　o Current Distribution: Its internal conductive structure and flow field design help to distribute the current evenly across the entire active area of the electrode, avoiding local hot spots and efficiency losses.

　　● Reaction Chamber Separation and Gas Separation:

　　o Physical Isolation: The bipolar plate and diaphragm work together to strictly separate the oxygen produced on the anode side and the hydrogen produced on the cathode side into two independent chambers. This is a key safeguard to prevent hydrogen and oxygen gas mixing (explosion risk).

　　o Gas Flow Channels: Specific flow fields are designed on the plate surface to provide channels for the produced gas to exit, guiding the gas smoothly away from the reaction zone and collecting it into the respective gas manifolds.

　　● Electrolyte Distribution and Circulation:

　　o Fluid Channels: The flow field structure on the bipolar plate (usually on the other side or a different area on the same side) is also used to guide the alkaline electrolyte (such as KOH solution) to flow evenly over the electrode surface. This ensures that the reactants (water) can fully reach the electrode surface and carry away the reaction products (gas) and reaction heat.

　　o Concentration Maintenance: Promoting electrolyte circulation throughout the electrode area helps maintain the relative uniformity of electrolyte concentration and temperature.

　　● Structural Support and Sealing Interface:

　　o Mechanical Framework: Provides solid support for the relatively thin electrodes and diaphragms, withstanding the clamping force of the entire stack and maintaining the rigidity and stability of the electrolyzer structure.

　　o Sealing Base: The surface of the bipolar plate is usually the main location for placing sealing gaskets (such as rubber O-rings), cooperating with adjacent components to form a reliable seal and prevent electrolyte and gas leakage.

　　● Thermal Management (Auxiliary): The electrolyte flowing through the bipolar plate helps to carry away some of the reaction heat. Some designs may also consider integrating cooling channels inside the bipolar plate to enhance heat dissipation.

　　 3. Materials and Manufacturing

　　The working environment of alkaline electrolyzers (high temperature, high concentration alkaline solution, certain pressure) places stringent requirements on bipolar plate materials:

　　● Core Requirements:

　　o Excellent Corrosion Resistance: Must be able to withstand long-term high temperature (70-90°C) and strong corrosion from high-concentration alkaline solutions.

　　o High Conductivity: Minimize ohmic losses and improve the overall efficiency of the electrolyzer.

　　o Good Mechanical Strength: Withstand assembly clamping force and internal pressure.

　　o Good Machinability: Easy to manufacture complex flow field structures.

　　o Gas Tightness: Prevent gas permeation.

　　o Cost Control: Bipolar plates are a significant cost component of the electrolyzer.

　　 4. Flow Field Design

　　The flow channel pattern (flow field) design on the surface of the bipolar plate has a significant impact on the performance of the electrolyzer. Common flow field types in alkaline electrolyzers include:

　　● Parallel Flow Field: Simple structure, low pressure drop. However, the gas discharge capacity is relatively weak, easily forming "gas pockets", affecting the uniformity of electrolyte distribution.

　　● Serpentine Flow Field: Forces gas and liquid to flow along a tortuous path, with strong gas discharge capacity and relatively uniform distribution. However, the flow resistance (pressure drop) is larger, increasing pump power consumption.

　　● Interdigitated Flow Field: Forces the fluid to pass through the electrode diffusion layer, enhancing mass transfer. However, the pressure drop is large, and its application in alkaline cells is relatively less.

　　● Porous Structure/Mesh Flow Field: Provides a large number of contact points to support the electrode and promote mass transfer. However, the flow channels are not clear, and the control of gas discharge and electrolyte distribution is relatively complex.

　　● Composite Flow Field: Combines the advantages of different flow field types, such as using parallel flow channels in the inlet/outlet areas to reduce pressure drop and serpentine flow channels in the main reaction area to enhance defoaming.

　　Design choices need to strike a balance between gas discharge efficiency, electrolyte distribution uniformity, pressure drop (pump consumption), current distribution uniformity, structural strength, manufacturing difficulty, and cost.

　　 Summary

　　Bipolar plates are indispensable multifunctional core components in alkaline water electrolysis hydrogen production electrolyzers. They are not only the "backbone" of the stack structure, connecting various electrolysis cells in series, but also key executors of efficient current conduction, strict gas separation, uniform fluid distribution, and reliable structural sealing. The material selection (mainly nickel-coated carbon steel) and precise flow field design directly determine the electrolyzer's efficiency, safety, lifespan, and cost. As alkaline electrolyzer technology develops towards higher current density, larger scale, and lower cost, the optimization of bipolar plates (such as more corrosion-resistant and conductive materials, more efficient flow field designs, and lower-cost manufacturing processes) will continue to be a key research area.