Although fuel cells are used as power sources in aerospace systems such as unmanned aerial vehicles (UAVs) and spacecrafts, the existing proton exchange membrane fuel cells (PEMFCs) limit the mission ability of the aerospace systems because of some problems (low energy density of gaseous hydrogen and limited storage period of liquid hydrogen). Because the direct sodium borohydride/hydrogen peroxide fuel cells (direct NaBH4/H2O2 fuel cells) use liquid fuels like NaBH4 and H2O2 solution with high volumetric energy density and long storability, they can solve the problems of PEMFCs. In this study, the direct NaBH4/H2O2 fuel cell was developed based on basic research and performance of the fuel cell was evaluated.
First, the electrodes for the direct NaBH4/H2O2 fuel cell were developed based on basic research. Some catalysts can decompose fuels (NaBH4 and H2O2 solution) and produce gas (hydrogen and oxygen), which can reduce performance of the fuel cell. Therefore, the electrocatalyts for direct oxidation of NaBH4 and reduction of H2O2 have to be selected to develop the direct NaBH4/H2O2 fuel cells with high performance. The catalysts such as rhodium, ruthenium, platinum, gold, silver, palladium, nickel, and copper were used in this study. The effects of catalyst supports on fuel cell performance were investigated. Then, various metal/γ-Al2O3 catalysts were manufactured and reacted with the NaBH4 and H2O2 solution to evaluate activity of various catalysts on fuel decomposition. Also, electrodes with various catalysts were manufactured by the conventional method, and their ability on direct oxidation and reduction was evaluated through unit cell tests. Finally, NaH2PO2 was used as reducing agent to improve catalyst durability.
Second, effects of operating conditions on performance were also investigated. Operating conditions such as NaBH4 concentration, H2O2 concentration, and operating temperature were determined based on test results. Most suitable membrane was sele