Effects of Functionalize Carbon Nanofibers Supported Catalysts on Oxygen Reduction Reaction in Alkaline Medium

Abstract

Fuel cells are attractive because they provide clean and efficient energy for stationary and portable applications. Among the various types of fuel cells, the proton-exchange membrane fuel cells (PEMFC) have a high energy density and a fast start-up, but the cost of noble-metal catalysts and perfluorinated membranes is high. Anion-exchange membrane fuel cells (AEMFC) are attractive because they have enhanced the oxygen reduction and methanol oxidation kinetics at high pH, which makes the use of non-noble catalysts possible. Carbon nanofibers (CNFs) have outstanding structural, mechanical and electrical properties, and are widely used as catalyst supports in fuel cells. CNFs are also considered to be good material for the oxygen reduction reaction catalysts in alkaline fuel cells because of their high surface area, thermal stability and electrical conductivity. In this work, we use CNFs as the support for fuel cell catalysts in hybrid fuel cells, which combine alkaline and acidic conditions at the different electrodes. Functional groups were added onto the CNFs, including carboxyl groups (CNF-OX), carbonyl groups (CNF-CO), hydroxyl groups (CNF-OH) and nitrogen-containing groups (CNF-ON). In previous studies, they were tested them in half-cell experiments and it was found that the catalysts supported on CNF-ON have high ORR activity. The CNF-ON electrodes can change the ORR from the two-electron pathway to the four-electron pathway. Pt/CNFs have been tested in hybrid fuel cell and compared with Pt/C.