A Study Of Fuel Cells Using Non-Pt Catalysts

Due to the clean and efficient advantages, fuel cells are considered to be a promising candidate of power source in future. Proton exchange membrane fuel cell (PEMFC) is advantageous in high power density, quick starting-up and compactibility, and thus will be ideal to power the vehicles. Despite the success in the last decades, the commercialization of PEMFC has been hindered by the use of Pt catalyst, a highly limited resource in earth. Recently, alkaline polymer electrolyte fuel cell (APEFC) has attracted much research interest, because it can in principle combine the advantages of PEMFC and alkaline fuel cell (AFC). Specifically, it can also be compact in size and of no leakage trouble of liquid electrolytes, more importantly, non-precious metal catalyst can be used. The mission of this research is to develop polymer electrolyte fuel cells without Pt catalysts. After a systematic study on some non-Pt and non-precious metal catalysts, we finally achieve at two types of fuel cells:PEMFC using non-Pt catalysts and APEFC using non-precious metal catalysts. The progress of this work is summarized in the following.1. PEMFC using non-Pt catalystsBecause of the strong acid enviroment of PEMFC, only precious metal catalysts can be relatively stable. Considering Pd is40times rich than Pt in earth, as well as only of a quarter of the price of Pt, we try to replace Pt completely with Pd in both the anode and the cathode. In this study, Pd is alloyed with some transition metals, so as the electronic property of Pd is tuned, which leads to an improvement in the catalytic activity toward both the oxygen reduction reaction(ORR) and the hydrogen oxidation reaction (HOR). Finally, two Pd alloy catalysts were used to make a PEMFC prototype. Main conclusions of this part are as follows.a) A series of PdAu/C, PdNi/C, and PdCu/C catalysts were prepared using an impregnation method. The samples were characterized by XRD, etc.. Among these catalyts, Pd90Cu10/C exhibits the highest mass-specific catalytic activity toward the ORR; while Pd85Ni15/C and Pd80Cu20/C is the best for the HOR. Because of the easiness in synthesis, we has chosen PdgoCu2o/C as the anode catalyst for the subsequent test of single cell.b) PEMFC completely based on Pd or Pd-alloy catalysts are achieved for the first time.. For PEMFC using Pd catalysts, the maximum power density is178mW/cm2, while for PEMFC using Pd-Cu alloy catalsyts, the maximum power density is204mW/cm2. The prototype runs stably in a period of test more than100hours.2. APEFC using non-precious metal catalystsWithout the acidic media, non-precious metal catalysts can now be used in APEFC. Many non-noble metal catalysts can be used as the catalyst for the ORR. In the present work, the M-N_x/C catalyst was selected due to its relatively high activity and stability. Whereas for the HOR, the choice of non-noble metal catalysts is much less, to develop new non-precious metal catalysts is hence an urgent mission. We found Ni-W anode catalyst is a promising one. Finally, non-precious metal catatlysts prepared in this work are used for both the anode and the cathode of the APEFC prototype. Main results are summarized as follows.a) Non-precious metal cathode catalyst for APEFCWe studied the M-Nx/C type of cathode catalyst, and investigated the preparation process influenced by the type of transition metal, conductive polymers, and carbon supports. It turned out that Co-PPY-BP2000was the best, it catalyzes the ORR through a4-electron pathway. The preparation parameters of Co-PPY-BP2000were then optimized thoroughly.b) Non-precious metal anode catalyst for APEFCNiWO4was used as the precursor for the Ni-W catalyst which exhibited a relatively high activity and stability for the HOR. Analyses on the composition and structure of this catalyst showed that Ni is the catalytic component, while W functions in stabilized the Ni through modifying its electronic structure. The apparent activation energy of Ni-W catalyst for the HOR is17.95kJ/mol, far lower than that of other Ni-based catalysts. c) APEFC using non-precious metal catalystsPt/C catalyst was first used to optimize the working condition of APEFC, and the maximum power density of this prototype reached265mW/cm2at75℃. Co-PPY-BP2000and Ni-W were then used in the cathode and the anode, respectively, the resulting prototype exhibited a maximum power density of40mW/cm2at70℃.