Hydrogen fuel cells, heralded as a cornerstone of clean energy, are receiving a significant boost in performance thanks to an unlikely source of inspiration: the humble lizard. By mimicking the sophisticated water-transport mechanisms found in the skin of certain desert-dwelling reptiles, scientists are developing novel flow field plates that dramatically improve a fuel cell’s power density and operational stability, particularly under challenging humid conditions.
This innovative biomimetic approach addresses one of the primary limitations of Proton Exchange Membrane Fuel Cells (PEMFCs)—water management—paving the way for more efficient and durable hydrogen-powered technologies.
The Critical Role of Flow Field Plates in Hydrogen Fuel Cells
Flow field plates, often referred to as bipolar plates, are integral components within hydrogen fuel cell stacks. They are responsible for distributing reactant gases (hydrogen and oxygen) uniformly across the catalyst layers, collecting the electrical current generated, and facilitating the removal of water produced during the electrochemical reaction. These plates represent a substantial portion of a fuel cell stack’s weight and cost, making their design crucial for overall performance and economic viability.
Challenges with Traditional Flow Field Designs
Despite their critical function, traditional flow field designs, such as parallel and serpentine patterns, face inherent challenges. These include:
- Uneven Reactant Distribution: Gases may not be distributed uniformly, leading to “hot spots” and reduced efficiency across the membrane electrode assembly (MEA).
- Water Flooding: The electrochemical reaction at the cathode produces water. If this water accumulates in the flow channels faster than it can be removed, it can block the reactant gas pathways, a phenomenon known as “flooding”. Flooding is particularly problematic at high relative humidity and can significantly degrade fuel cell performance, leading to mass transfer losses and accelerated component aging.
- Pressure Drop: Complex channel designs aimed at improving gas distribution can lead to a higher pressure drop, requiring more energy to pump reactants through the cell, thus reducing overall efficiency.
Addressing these issues is paramount for enhancing the power density and longevity of PEMFCs, making them more competitive for widespread application in portable devices, automotive, and stationary power generation.
Biomimicry: Nature’s Solution to Engineering Problems
Biomimicry, the practice of emulating nature’s designs and processes to solve human problems, offers a powerful paradigm for innovation. In the realm of fuel cells, researchers have turned to organisms that have mastered fluid dynamics and water management in extreme environments: desert lizards.
The Texas Horned Lizard: A Master of Water Harvesting
Several species of lizards inhabiting arid regions, including the Australian thorny devil, the Arabian toad-headed agama, and most notably, the Texas horned lizard ( Phrynosoma cornutum), possess remarkable adaptations for collecting and transporting water. These lizards can harvest moisture from their surroundings—be it dew, rain, or even moist sand—using their specialized skin.
The secret lies in a sophisticated capillary system integrated within their integument (skin and scales). Under an electron microscope, researchers have observed tiny channels extending between the lizard’s scales. These micro-channels are not uniform; they periodically narrow and widen, creating a passive, directional flow that funnels water towards the lizard’s mouth, even against gravity, without requiring active energy expenditure. Furthermore, the honeycomb-like micro-ornamentation on the scales renders the surface superhydrophilic, significantly improving moisture absorption and condensation.
Lizard-Inspired Flow Fields: A Breakthrough in Water Management
Scientists, including those at the Institute for Biology at the University of Aachen (RWTH Aachen) and University College London (UCL), have investigated these natural designs to translate them into technical applications. By recreating the geometric principles of the lizard’s capillary channels on artificial surfaces, they have developed “lizard-inspired” flow field plates.
Enhanced Performance and Flood-Free Operation
The implementation of these biomimetic designs in PEMFCs has shown promising results. Researchers have laser-engraved microchannels, inspired by the lizard’s skin structure, onto graphite plates used as flow fields. This innovative water management strategy leverages capillary pressure to rapidly and passively remove generated water from the fuel cell, rather than relying solely on gas flow.
Key improvements observed with lizard-inspired flow field plates include:
- Increased Power Density: Studies have demonstrated a significant increase in current and peak power density. For instance, one study reported a ~60% increase in current (~1.9 A cm⁻²) and peak power density (~650 mW cm⁻²) compared to conventional serpentine flow-field based PEMFCs. Another found a 20% and 30% increase in maximum current and power density, respectively, for lung-inspired flow fields with this water management strategy.
- Flood-Free Operation: A critical advantage is the ability to operate PEMFCs flood-free at 100% relative humidity (RH). This is a major breakthrough, as traditional designs often suffer severe performance degradation under fully humidified conditions.
- Improved Reactant Distribution: By effectively managing water, these designs ensure more uniform distribution of reactants across the catalyst layer, leading to more stable and efficient electrochemical reactions.
- Lower Pressure Drop: Some nature-inspired flow fields have also demonstrated substantially less pressure drop compared to commercial serpentine flow fields, contributing to higher overall system efficiency.
Research conducted by teams, including Panagiotis Trogadas, Jason I. S. Cho, and Marc-Olivier Coppens at UCL, has highlighted the effectiveness of integrating these lizard-inspired microchannel structures with other optimized flow fields, such as lung-inspired designs, to achieve robust, high-performance PEMFCs. The University of Sevilla in Spain has also contributed to the field with biomimetic bipolar plate designs showing remarkable performance at high relative humidity.
The Future of Hydrogen Fuel Cells
The integration of lizard-inspired flow field plates marks a significant step forward in hydrogen fuel cell technology. By addressing the long-standing issue of water flooding and improving reactant distribution, these biomimetic designs unlock higher power densities and enable more stable operation, even in challenging environments. This research underscores the immense potential of looking to nature for innovative solutions to complex engineering problems, accelerating the transition towards a cleaner, hydrogen-powered future.
