Studies On Direct Hydrazine Fuel Cell

The direct hydrazine fuel cell (DHFC) has attracted much attention as a potential candidate of high power device due to its high theoretical energy density (5.42 Wh g^-1), high theoretical electromotive force (1.61 V) and high theoretical energy conversion rate (100%). Electrocatalysts as a key part of DHFC have a direct impact on the cell performance of DHFC. In this work, the anode catalyst, cathode catalyst and oxidant of DHFC were systematically studied in order to improve the cell performance of DHFC further. The electrocatalytic performance and mechanism of anode and cathode catalyst towards N₂H₄ oxidation reaction and oxygen reduction reaction were investigated by cyclic voltammery and constant current discharge. Moreover, a novel DHFC using H₂O₂ as oxidant was developed and designed and the operated voltage and power density of DHFC was improved.It was found that the oxidation peak of N₂H₄ on Ni was 0.32 V, but the oxidation peaks of N₂H₄ on Pt were located at -0.628 V and 0.16 V. This was attributed to that the adsorption state of N₂H₄ and attraction of H and N on different catalysts. It was proposed that the bond breaking of N₂H₄ on Ni surface is that N-N bond break and form adsorption species NH₂(ad). On the other hand, the bond breaking of N₂H₄ on Pt surface is two different manners which is that the N-H bond break and form adsorption species NH(ad) in the negative potential and the N-N bond break and form adsorption species NH₂ (ad) in the positive potential.The electrochemical performance of Pt/C, Pd/C, Co-PPY-C and Au/C as the DHFC cathode catalyst were investigated and compared. The Co-PPYC-C exhibited the best performance during these cathode catalysts. This was attributed to that the Co-PPY-C not only exhibited good electrocatalytic activity towards oxygen reduction reaction but also had good resistance to the crossover of N₂H₄.The effects of electrolyte membrane, fuel concentration, temperature and fuel flow rate on the the performance of DHFC were evaluated. A DHFC using Nafion 211 membrane as the electrolyte, 10 wt.% N₂H₄-15 wt.% NaOH solution as the fuel achieved the maximum output power density of 627 mW cm^-2 when it operated at 80℃. A DHFC using Ni-Pt/C as the anode catalyst, Au/C as the cathode catalyst, Nafion 211 membrane as the electrolyte and H₂O₂ as the oxidant had been explored. This single cell achieved a open-circuit voltage of 1.75 V and a maximum output power density of 1.02 W cm^-2 when it operated at 80℃. The result of rotation disk electrode cyclic voltammery confirmed that the number of electrons of H₂O₂ electrochemical reduction reaction on Au/C is close to the theoretical value of 2.