(625g) Tuning Palladium Hydride Formation with Hypophosphite: A Sustainable Hydrogen Source for Fuel Cells

Fuel cells are a promising technology for clean electrical energy production from energy dense fuels without harmful emissions. The utilization of hydrogen as a fuel for fuel cell devices is well known, however, challenges associated with the use of gaseous, reactive fuels has driven the search for alternative solid and liquid fuels that can be coupled to a fuel cell architecture. Hypophosphite salts have recently gained attention as a promising solid fuel for sustainable fuel cells due to its ease of handling, stable storage characteristics, and extremely negative reduction potential. Further, these hypophosphite salts can be used to efficiently generate palladium hydride (Pd-H), which has attracted considerable basic science and applied research interest as a catalyst in a variety of reactions.

Herein, we have studied a hypophosphite fuel coupled to palladium catalysts to understand the mutual relationship between hypophosphite concentration, Pd-H structure and electrochemical performance. Our results indicate that hypophosphite can produce significantly negative voltages relative to reversible hydrogen electrode(RHE) on palladium electrodes, with the open-circuit voltage(Voc) dependent on the hypophosphite concentration. These observed Voc values are equivalent to extremely high hydrogen headspace pressures (>200 bar) in the absence of hypophosphite. We further found that a decrease in the palladium particle size corresponds to a more negative open-circuit voltage. Specifically, our experiments yielded Voc of -0.35 V vs. RHE and -0.14 V vs. RHE with Pd nanoparticulates and bulk Pd disks, respectively. Lastly, we compared the ability of the palladium hydride synthesized using hypophosphite and its electrochemical counterparts to generate hydrogen. Our study provides a framework for understanding the potential of hypophosphite as a sustainable fuel for fuel cells, and lays the foundation for further research in both alternative fuel cell fuels and Pd-H catalysis.