Preparation Of Carbon Fibers Using Polyurethane Foam As Substrate And Investigations On Fuel Cell Electrocatalysis Applications

Proton exchange membrane fuel cell(PEMFC) is a power generation device which directly converts chemical energy into electrical energy. PEMFC has been attractive widespread because of its advantages such as high energy conversion efficiency, low pollution and high power density. Although PEMFC has found some applications, its largescale deployment was limited due to the well-known technical bottlenecks(catalytic activity and lifetime) and high price. It is out of question that platinum-based catalysts are the best catalysts with acceptable performance. However, platinum was occurred on the earth with very limited reserve, therefore, improvement on its utilization efficiency is a critical issue to be resolved at present. On the other hand, enhancement on the catalytic activity and stability is another approach to improve the utilization of platinum.This thesis is therefore targeted to improve the activity and stability of the catalyst. Firstly, polyurethane foam was used as a substrate for electroless nickel plating. In doing so, polyurethane foam was pre-treated through a series of pre-treatment processes and then was electrolessly-plated with a layer of Ni-P to produce nickel foam. The as-prepared nickel foam was used as a catalyst to decompose ethylene gas by chemical vapor deposition(CVD) method to produce carbon nanofibers(CNF). The effects of different reaction conditions on the carbon nanofiber materials were systematically explored. Secondly, by changing the chemical plating solutions, various metal foams such as copper and cobalt were prepared in a similar way and these foams were used to prepare carbon nanofibers with different morphologies. Nitrogen, phosphorus and boron atoms were incorporated in the resulted carbon nanofibers during formation process and these doped fibers were then used to support platinum catalysts for PEMFC applications.Effects on CVD temperature(from 500 oC to 700 oC) and time(from 2-4 h) were systematically studied. In this work, it has been found that the reaction condition is optimized at 600oC and 3h for growth of carbon nanofibers with better physical properties. The specific surface area of carbon nanofibers was found to be 168.6 m2 g-1. X-ray diffraction(XRD) and Raman analysis showed the as-prepared carbon nanofibers have certain degree of graphitization and are consisted of some defect sites, which are very suitable to anchor Pt electrocatalyst. The home-made carbon nanofibers exhibit good hydrophilic properties without any pre-treatment. Electrochemical tests found that oxygen reduction reaction(ORR) onset potential of the homemade carbon nanofibers was positively shifted for 30 mV relative to that of commercial carbon nanotubes.Copper foams have been prepared by variations on the electroless plating solutions. The resultant carbon nanofibers prepared using Cu foams were incorporated with boron(B), nitrogen(N) and phosphorus(P) dopants. These carbon nanofibers were used as supports to load platinum by ethylene glycol reduction method(Pt/CNF). Pt particles were dispersed on the carbon nanofibers with high uniformity, with an average particle size of 3.2 nm. When compared with a commercial counterpart Pt/C-JM, the Pt/CNF showed higher stability in an accelerated stability test. ORR catalytic activity for Pt/CNF also surpassed that of Pt/C-JM as demonstrated by more positive on-set reduction potential. It can be concluded that the homemade carbon nanofibers was applicable as supports for proton exchange membrane fuel cell.