Study On The Alkaline Hydrazine Fuel Cell

It is considered that the direct hydrazine fuel cell(DHFC) is a potential candidate for mobile and portable applications due to easiness of fuel transport and fuel storage, high energy density and high energy conversion efficiency.It is no harm to environment because only N₂ and H₂O are produced after hydrazine is electro-oxidized.The hydrazine cross-over is an important factor that limits the development of DHFC because hydrazine cross-over reduces the performance of DHFC.Aiming to suppress the hydrazine cross-over during operation,this thesis has studied the effects of fuel composition modification,electrolyte selection and applied catalysts on the DHFC performance based on the research results on electrochemical reaction mechanism of hydrazine.The main results are described as follows:It was found that NaOH addition in the anolyte effectively improved the open circuit voltage and the performance of the DHFC.The cell performance was mainly influenced by anode polarization when using alkaline N₂H₄ solutions with low NaOH concentrations.However,when using alkaline N₂H₄ solutions with high NaOH concentrations as the fuel,the cell performance was mainly influenced by cathode polarization.The increase of the anolyte viscosity would decrease the movability of charge carrier in the anolyte,which lead to decrease the cell performance.A cell performance comparison of the cells using cation exchange membrane (CEM) or using anion exchange membrane(AEM) as the electrolyte has been carried out in this study.Results showed that cell performance of the DHFC using AEM as the electrolyte was higher than that of the DHFC using CEM due to that crossover of N₂H₄ and Na⁺ was suppressed when AEM was used as the electrolyte.The power density of the test cell reached up to 88mW/cm² at ambient conditions。It was found that hydrazine was electro-oxidized following a 4-electron anodic reaction at Ni,Pd/C and Zr-Ni alloy and Pd/C based on gas evolution rate via current. Pd/C demonstrated a high catalytic activity and a high cell performance have been achieved when using Pd/C as the anodic catalyst.A preliminary study has been done on the decrease of precious metal loading in cathode.It was found that the DHFC performance was improved when cathode catalyst of Pt was partially substituted by COCl₂.The achievements in this study provide some ways to solve the hydrazine crossover in the DHFC.It is considered that this thesis has made a certain contribution to the development of DHFC technology.