Plant leaves inspire design of improved fuel cell

Hydrogen fuel cells convert hydrogen and oxygen into electricity, heat, and water. Because this conversion process doesn’t generate any carbon emissions, fuel cells are seen as a valuable source of green energy that could be key in addressing climate change.

However, there’s an obstacle standing in the way of their use in large-scale applications—powering electric trucks for long-haul transport, for example, or replacing diesel generators to provide electricity in remote, northern communities. Current fuel cells have reached a ceiling in the amount of electricity they can generate because their internal structure cannot adequately manage all of the water that cells create as a byproduct.

Researchers from the University of Toronto’s Department of Mechanical and Industrial Engineering looked to a novel source when they were brainstorming for ideas to improve the design of the channels—called “flow fields”—that direct water inside the cell. Their work is published in the journal Applied Energy.

Ph.D. student Eric Chadwick says that, instead of starting from scratch, he turned to nature for inspiration (“biomimicry”). “Rather than trying to come up with a brand-new design, I decided to look toward nature, as often some organism has already, through evolution, optimized a process.”

In this case, the process was moving water in a single direction. He found evidence of this on the skin of lizards and the leaves of certain plants. “Lizards living in dry, arid climates have scales that have evolved to trap condensation from air and channel it to their eyes and mouth,” says Chadwick. “Similarly, on certain types of leaves the veins catch water and move it to tips of the leaves so that it falls down, so the roots can absorb it.”

He and his team incorporated these patterns from nature into the channels within their new cell, to more effectively move water from the porous layer inside the cell to the outside of the cell.

Using the Canadian Light Source at the University of Saskatchewan, Chadwick and his colleagues found the nature-inspired design resulted in a 30% increase in the peak power density they could reach in the fuel cell, compared to existing designs. The new cell design showed a more even distribution of water within the cell, with no buildup, which also meant more even distribution of the reactants (oxygen and hydrogen)—”so the fuel cell is using the catalyst (platinum) more effectively.”

The researchers also found that, because the new design removed excess liquid water from the porous layer, the channels served as additional pathways for more reactant to get to the catalyst layer.

With the high-energy X-rays at the CLS, Chadwick and the team were able to generate richly detailed, cross-sectional images of their new fuel cell while it was operating. “We were able see exactly where the water is going, how much is remaining in the cell, with the different designs we tested,” says Chadwick.

“In the old design, we used to have this heterogeneous distribution of water. Now we have a much more homogeneous layer of water, which in turn means we have a much more homogeneous distribution of the reactants and we’re using the catalyst in the fuel cell much more effectively and evenly.”

The next step, says Chadwick, will be to build and test a bigger cell. He and his team will use computer modeling to determine how to adapt their designs for a large system.” We took these designs from nature and optimized them, but there’s always room for more (improvement). “I think modeling could really help assist this work and drive it in the field.”

“What I find really satisfying and really interesting about this, is that we can take these designs directly from nature, and use them to, in a way, help us lessen our impact on nature.”