Abstract
Energy crisis not only causes conflicts between nations, but also affects the world economy. Inflation and air-pollution both devaluate the living environment of human being. As crude oil price keeps increasing, many alternative energy systems become competitive for commercialization, such as the hybrid car from Toyota, solar, and wind power in European countries, etc. They are the hope to solve for the many problems people are encountering now. This study focuses on two building blocks of green energy: fuel cell and hydrogen storage. Hydrogen fuel cell requires platinum (Pt) catalyst to accelerate the reaction, and most of the commercial Pt catalysts are deposited on amorphous carbon black for greater reaction surface area. With a hope to increase the activity and stability of Pt catalyst, another approach was made in this study by depositing Pt on multi-walled carbon nanotubes (MWNTs), which retain good mechanical and electrical properties. MWNTs were first surface modified with a mixture of nitric and sulfuric acid to produce surface functional groups. By either precipitation of Pt particles in a solution with an appropriate pH or direct reduction of Pt particles using sodium borohydride, Pt particles can be dispersed uniformly on the surface of modified MWNTs and carbon nanohorn (CNH). Moreover, the diameters of Pt can be controlled at 1 to 3 nm and 2 to 4 nm, respectively. In contrast, without surface modification, the Pt particles would tend to aggregate on the surface defects and tubular-ends of MWNTs. The cell performance with (17%) Pt/MWNT as the catalyst is 0.25 W/cm2, while that of commercial E-TEK (20%) Pt/XC-72 is 0.28 W/cm2. Unlike the optimal Nafion® loading in Pt/XC-72 gas diffusion electrode (GDE), the optimal Nafion® loading in Pt/MWNT GDE is determined to be between 10 and 20%. As for hydrogen storage material, vanadium (V) can absorb a large amount of hydrogen; however, the high cost of V is its drawback. By alloying V with inexpensive titanium (Ti) and chromium (Cr), they turn into an inexpensive hydrogen storage alloy with respectable hydrogenation properties. In this study, 0.1 at% to 5 at% of boron (B) or carbon (C) was doped into the interstitial sites of the bcc Ti25V35C40 alloy, hoping to increase the effective desorption capacities for fuel cell application. The samples were prepared by arc melting and homogenized by annealing at 1200oC for 2 hours in vacuum. From X-ray diffrection and optical microscopic analyses, all specimens formed a bcc phase with the presence of some minor second phases. The effective desorption capacity of Ti25V35Cr40 is 0.80 H/M. The specimens that added with 1% B or 0.1% C exhibit greater effective desorption capacities, with values of 0.86 H/M and 0.87 H/M, respectively. The 9% increase of effective desorption capacity can reduce the weight of metal hydride in fuel cell vehicles by 60 to 80 kg, that demonstrates a greater potential for commercial applications.