Impact of Channel Designs and Configurations on Material Flow in Bipolar Plates for Hydrogen Electrolysis
Green hydrogen is powering the future. Hydrogen electrolysis, the process of producing hydrogen by splitting water molecules using electrical energy, is leading the way when it comes to hydrogen power.
Flow field plates, also called bipolar plates, are critical to the hydrogen electrolysis process. These plates ensure efficient electrochemical reactions as materials flow through them. These plates are typically made of graphite or metal and feature a series of channels on their surfaces that facilitate the flow of liquids or gasses.
In hydrogen electrolysis, bipolar plates ensure that water is evenly distributed over the membrane or electrode, maintaining a consistent reaction across the entire surface. They also enable efficient removal of hydrogen and oxygen from the reaction sites, preventing gas bubbles from forming and disrupting the flow of reactants – reducing the efficiency of the process.
Since these components play such a critical role in the efficiency of several key processes in hydrogen electrolysis, the design of the channels can have a significant impact on the efficiency and quality of the results.
Impact of Channel Design
Channel design on flow field plates can have a multitude of effects on the efficiency of the plate and ultimate process outcome. First, poorly designed channels can result in uneven water distribution. If the channels leave dry spots, the active surface area is reduced.
Channel design also impacts the effectiveness of product removal – if gas bubbles form, reactant flow can be reduced, leading to lower output efficiency.
Finally, channel design can have an impact on the flow pressure throughout the plate. Low pressure spots or high pressure drops reduce flow and flow efficiency, so finding the right balance of flow pressure is a key aspect of channel design.
Pros & Cons of Channel Design Types
While there are many options for channel design, there are a two general patterns that are most commonly used on bipolar plates designed for hydrogen electrolysis. Understanding the impact that channel design can have on the outcome is key to choosing the right channel design for your budget, needs and volume.
Parallel Channels
Parallel channels consist of straight channels that run from inlet to outlet. There are a number of advantages to this design style:
- Simple design lowers production costs for hard-tooled plated
- Low pressure drops compared to more complex designs
- Lower energy pumping requirements
- Uniform reactant distribution and consistent performance across the plate
Due to its simplicity, parallel channel design also has some downsides compared to other methods:
- Inadequate product removal, leading to gas bubbles obstructing flow
- Reduced contact time could lead to incomplete reactions
- Ineffective heat distribution, leading to hotspots and non-uniform reactions
Serpentine Channels
Serpentine channels create a winding path across the surface of the flow field plate, with many options for specific path and design complexities available. Like parallel channels, there are pros and cons to this more complex design style:
Reactants are very evenly distributed across the surface- Improved reactant contact improves reaction efficiency
- Product removal is more effective than parallel channels
- Better water management leads to a more stable electrolysis process
- A controlled flow rate helps mitigate pressure drops for more uniform pressure distribution
- Heat distribution is more even, for better cooling facilitation and fewer hotspots
The complexity of these designs can also result in some disadvantages or challenges:
- Higher energy requirements due to higher pressure drops
- Pumping systems may need to be more robust
- Manufacturing can be a challenge, the more complex the design
- Intricate designs may be more prone to flow blockage
- More variation in channel lengths can lead to maldistribution of flow
Other Design Considerations
In addition to the channel path, there are other design properties that can have an impact on the effectiveness and efficiency of hydrogen electrolysis flow field plates.
Channel Depth & Width
Larger channels reduce pressure drop and have increased flow rate capacity, but may compromise reactant distribution. Shallower, narrower channels have more uniform distribution, but may lead to higher pressure drops.
Single vs. Multi-Pass Channels
A single pass channel flows in one continuous path from inlet to outlet. Multi-pass channels may have several directional changes between inlet and outlet. Single pass channels are simpler and easier to design and maintain, but multi-pass channels enhance reactant distribution but increase design complexity.
Interdigitated Channels
Interdigitated channels have intersections between inlet and outlet paths. In interdigitated channels, reactants are forced through the porous membrane, improving reactant utilizations. Interdigitated designs add additional layers of design complexity, but can significantly increase the efficiency of your bipolar plates.
Material & Manufacturing
The material you choose for your plate also impacts the ultimate result of your design. Most bipolar plates are made from graphite (non-metal conductor) or stainless steel, each of which have limitations in terms of thickness, weight and design flexibility.
How your bipolar plates are manufactured has a significant impact on design capabilities. Traditional methods like stamping tend to limit your design complexity, while more innovative methods like photochemical machining (PCM) open up your channel design options to explore far more intricate, complex options, including symmetrical or asymmetrical dual-sided plates, tighter channel radii, and more intricate channel paths.
Ultimately, the channel design you choose needs to meet your needs and priorities. While any design will have some pros and cons, not every factor will be of equal importance to your goals.
To get expert design support for your hydrogen electrolysis or fuel cell flow field plates, reach out to Switzer to learn more about our capabilities and consult with an engineer.
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