| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 97 === In the past decades, since the rise of environmental consciousness around the world, many efforts have been devoted into the discovery and development of clean energy technologiesm. Within them, solar energy、hydrogen energy and fuel cell, which are environment-friendly and zero-polluted, are the three mainstreams. Zinc-air fuel cell is one of the focal point of fuel cell studies. The performance of zinc-air fuel cell significantly depends on the characteristic of electrode、electrolyte and catalyst. Hence, the investigation of improving the transformation rate of catalyst plays a significant role to decide the range of future application of zinc-air fuel cell. H3PMo12O40．xH2O (PMo12) catalyst was widely to be applied into various electrochemical applications. There are several references has been reported to reveal that adding phosphomolybdic acid hydrate PMo12 in the electrode of proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cell (DMFC) could promote performance. Under this concept, the study aims to add H3PMo12O40．xH2O (PMo12), a strong oxidizing agent, into the cathode of zinc-air fuel cell to serve as catalyst to improve the electrocatalytical efficiency by increasing the oxygen reduction rate that can increase the current density.
The PMo12/C cathodes are prepared by liquid impregnation method and then compared with MnO2/C cathodes for analyzing the effects of PMo12/C. Thereafter, the efficiency of PMo12/C cathodes for zinc-air fuel cell in different annealing temperatures、different loading currents and different electrolytes is investigated. The discharging behavior under the steady current of 50 mA and the life time properties were measured by the Galvanostat system at 1 atm and 27 ℃. The structure and surface morphologies of PMo12/C cathodes were characterized by using X-ray diffractometer (XRD) and field emission scanning electron microscopy (FE-SEM).
According to the results, PMo12/C cathodes show the same catalysis ability as MnO2/C cathodes, but PMo12/C cathodes reveal better efficiency. Therefore, the result proves the idea that PMo12/C serves as the cathode catalyst in zinc-air fuel cell is practical. In the single cell test, the potential is going down with increasing loading current, and the life time is becoming shorter. Specifically, form the results evidences, the annealing temperature is a factor of structure and catalysis of PMo12/C. From the XRD and TGA/DTA results, we know the PMo12 structure changes into molybedenum oxide (MoO3) at 375℃. And from the single test results, it is found the best electrochemical performance on unannealing PMo12/C cathode. Moreover, in single cell test with different electrolytes, it is also found the best cell behavior with potassium hydroxide (KOH) electrolyte.
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