Researchers from Washington University in St. Louis are developing high-power fuel cells to advance electrification of the transportation sector. A focus on liquid-fueled instead of hydrogen-powered devices eliminates the need to pressurize, store and transport the gas and has resulted in the design of a high-power direct borohydride fuel cell.

The device design and performance reflect the use of an approach to optimize the flow field architecture, flow rates and residence times to realize high power operation. The reactant-transport engineering method applied by the researchers addresses primary barriers to direct borohydride fuel cell deployment, including effective oxidant and fuel distribution and parasitic reaction mitigation. The assembled cell maintains a sharp pH differential using a pH gradient-enabled microscale bipolar interface.

As reported in Cell Reports Physical Science, the fuel cell delivered a 1.4 V or higher single-cell operating voltage. The device can therefore reach an operating voltage twice that of hydrogen fuel cells, which have peak levels approaching 1 W/cm². Doubling the voltage would allow for a smaller, lighter and more efficient fuel cell design, which translates to significant gravimetric and volumetric advantages when assembling multiple cells into a stack for commercial use.

During technology comparison tests, a polymer electrolyte membrane fuel cell delivered a power density of 295 mW/cm² at 0.75 V. The re-engineered direct borohydride system with icroscale bipolar interface provided a 2.4 times higher power density of 705 mW/cm² at double the operating voltage of 1.5 V. At the same operating current density, the voltage efficiency of the redesigned fuel cell is about 78%, markedly higher than the 57% demonstrated for the polymer electrolyte membrane fuel cell.