Direct liquid fuel cells (DLFCs) are promising power sources for future portable, wearable or implantable electronic devices owing to their high energy density and low emissions. Large efforts have been given for the development of DLFCs since 1990s, however the wide spread commercialization of DLFCs is still limited by the high cost coming from the expensive noble metal catalysts and proton exchange membranes. Furthermore, the safety risks related to organic fuels (methanol, ethanol and formic acid), such as toxicity and flammability, bring up tremendous consideration in fuel cell design, fuel distribution and transportation ^[1]. Finally, the emission of CO₂ is inevitable by using organic fuels, which escalates to Green House Effect.

In this work, we proposed a new category of inorganic fuels for DLFCs. Hypophosphite is a type of food additive, therefore no safety hazards at all, and is also a strong reductant whose electrochemical oxidation reactivity is strongly correlated to metallic palladium ^[2]. Moreover, the inorganic fuels could realize “Zero Emission” after “Burning”. From thermodynamic calculations, the theoretical cell voltage and volumetric energy density at 1M are 2.05 V and 188 Wh/L at standard conditions, which are comparable and even better than the data of DMFCs (Direct Methanol Fuel Cells).

The unique electrochemical oxidation behavior of hypophosphites on Pd catalyst brings advantages in simplifying fuel cell structure and broadening our selections of cathodic catalysts for ORR (Oxygen Reduction Reaction). Herein, we report the investigation of catalyst design and cell design of a novel membrane-free Direct Hypophosphite Fuel Cell (DHPFC), which showed an open circuit voltage of 1.0 V and a maximum power density of 32 mW cm^-2 under air flow at 25 ^oC. The oxidation mechanism of hypophosphites on Pd was also studied in this work.

This work is financially sponsored by Solvay and “Shanghai Rising-Star Program” (16QB1404600).

Reference:

[1] G. L. Soloveichik, Beilstein J. Nanotechnol. 2014, 5, 1399-1418.

[2] N. Fujiwara, Z. Siroma, T. Ioroi, K. Yasuda, J. Power Sources 2007, 164, 457-463.