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“Electrify everything.” Among those seeking to reduce the world’s reliance on fossil fuels, this phrase has become a rallying cry. We can see the electrification imperative in action all around us, as hybrid gas–electric vehicles (HEVs) and battery–electric vehicles (BEVs) are now familiar sights on the highway. But even as many automakers ramp up HEV and BEV production, one company is dedicated to developing electric cars that do not rely primarily on batteries for energy storage. Instead, these cars carry hydrogen, which provides electricity when combined with oxygen from the air inside a fuel cell.
The company pursuing this alternate route is Toyota. The commercialisation of hydrogen-fuelled vehicles faces many obstacles, but if anybody can put the world on fuel cell-powered wheels, it could be the world’s largest automaker (Ref. 1). Toyota is directing great financial, physical and human resources toward automotive fuel cell research, but it sees vehicle development as only the beginning of a long journey. The company’s vision leads far beyond cars; it foresees the emergence of a global “hydrogen society”. In this proposed society, fossil fuel-burning engines, heating systems and generators would be replaced by fuel cells that extract electric current from hydrogen. Toyota’s efforts to reach this destination are as far-sighted as its adoption of the Japanese city of Susono as a hydrogen-tech test bed, and as focused as its refinement of a generative design methodology for optimising fuel cell performance.
Generative Design Enabled by Simulation
Toyota Research Institute of North America (TRINA) has developed a simulation-driven generative design method and applied it to the design of flow field microchannel plates, which direct the movement of fluid reactants in microreactors like hydrogen–oxygen fuel cells. While much of Toyota’s fuel cell R&D is necessarily confidential, the TRINA team has published an article in Chemical Engineering Journal (Ref. 2) about their simulation-enabled “inverse design” process. Applying this process to flow field plates resulted in four distinctive microchannel designs, as shown in Figure 1.
Figure 1. Simulation results from the TRINA team’s model, built using the COMSOL Multiphysics® software, showing the pressure distributions resulting from four different microchannel flow field designs.
Each of the four designs has particular merits; all of them outperform existing benchmark designs in terms of key metrics. Just as important, they exemplify the power of process. TRINA has shown how generative design enabled by simulation can accelerate innovation — even when a project’s ultimate destination may be far into the future.
“We think that the inverse approach can revolutionise current design practice,” says Yuqing Zhou, a research scientist at TRINA. “We are enabling the next step in a long journey, even though we cannot know exactly where that journey will lead.”
Cleaner Powertrain Options
Considering this spirit of open-ended inquiry, perhaps it is understandable that Toyota is sustaining its decades-long pursuit of fuel cell research, even as most automakers have committed exclusively to battery power for electric vehicles. As Chairman Akio Toyoda put it in a November 2022 interview (Ref. 3): “Think of Toyota as a department store offering every available powertrain.”
Figure 2. A schematic of the important components of a hydrogen fuel cell-powered vehicle. Image in the public domain, via the U.S. Department of Energy.
While a hydrogen–oxygen fuel cell may seem like an exotic way to supply power to a car (Figure 2), the technology itself is not new and its operation is appealingly straightforward. Figure 3 presents the fundamentals of a generic fuel cell in action.
Figure 3. A schematic of a generic fuel cell design. One flow field plate distributes hydrogen gas toward the anode–electrolyte–cathode stack while the other plate distributes oxygen to the stack and channels away water. Note: While this illustration shows the oxygen-side fuel plate on top of the stack assembly and the hydrogen-side plate below, the actual orientation of a fuel cell can vary.
As hydrogen gas flows across the anode, it encounters a catalyst, which separates it into hydrogen ions and electrons. Whereas the hydrogen ions move through the electrolyte to reach the cathode, the electrons move through a conductor outside the fuel cell. It is this electric current that can be harnessed to perform useful work.
As oxygen gas from the air flows across the cathode, it encounters the hydrogen ions and returning electrons at the surface of the cathode. Here, the oxygen molecules split and combine with the hydrogen ions and electrons to form water.
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