Carbon nanotube as catalyst support for proton exchange membrane fuel cell

As a potential candidate for an environmentally benign and a highly efficient electric power generation technology, proton exchange membrane fuel cells (PEMFC) are now attracting enormous interest for various applications such as low/zero-emission vehicles, distributed home power generators, and power sources for small portable electronics. The major issue in commercialization is through the cost and durability of PEMFCs. Pt catalyst is a major cost component for PEMFCs. Though there have been several efforts to find a cheap alternative, Pt is still the best catalyst for PEMFC reactions to date. In order to lower the cost of PEMFC stacks, a number of efforts are being made in the last decade to reduce the cost by increasing the efficiency of PEMFCs further and to lower the Pt catalyst loading in the electrodes by increasing the Pt utilization efficiency and specific power density output. In state of art PEMFCs Pt supported on carbon black is used as the electrocatalyst. The specific surface area and dispersion of Pt catalyst strongly depends on support surface area and morphology. Catalyst support also plays an important role in deciding electrical properties of the catalyst layer and the structure of catalyst layer. The durability of Pt electrocatalyst and the catalyst layer structure strongly depends on catalyst support stability. Carbon support corrosion is one of the most important factors affecting the durability of Pt electrocatalyst in PEMFCs. In the present thesis work carbon nanotubes (CNTs) have been proposed as catalysts support for Pt electrocatalyst for PEMFCs in place of carbon black. The advantages of using CNTs as catalyst support are discussed in 3 important aspects pertaining to the catalyst layer. (1) Pt catalyst utilization efficiency; (2) Mass transfer properties of catalyst layer; (3) Durability of catalyst layer CNTs due to their elongated morphology and good electronic properties are shown to improve the Pt catalyst utilization in PEMFCs. In addition the elongated morphology is shown to improve the mass transfer properties of the catalyst layer which is a significant factor for performance loss at higher current densities. Also apart from their good thermal and mechanical properties, CNTs are shown to be resistant to electrochemical corrosion in PEMFC environment. This is very significant for the durability of PEMFC electrodes. Though presently cost of CNTs is a major concern for their use in a commercial PEMFC technology, an alternative cheaper option of cup stacked carbon nanotubes (CSCNTs) is proposed for the catalyst support. Most of the work presented here is focused on multiwalled carbon nanotubes (MWNTs) and cup stacked carbon nanotubes (CSCNTs) types of CNTs.