Durable Catalysts for High Temperature Proton Exchange Membrane Fuel Cells

Durability of proton exchange membrane fuel cells (PEMFCs) is recognized as one of the most important issues to be addressed before the commercialization. The failure mechanisms are not well understood, however, degradation of carbon supported noble metal catalysts is identified as a major failure mode of PEMFCs.

Under idle, load-cycling or start-up/shutdown modes of operation, which are prerequisite for automobile applications, the cathode will experience significantly higher potentials and therefore suffer from serious carbon corrosion, especially at the presence of platinum. The carbon corrosion, in turn, triggers the agglomeration of platinum particles resulting in reduction of the active surface area and catalytic activity.

This is a major mechanism of the catalyst degradation and a key challenge to the PEMFC long-term durability. High temperature PEMFC, on the other hand, has attached significant attention in recent years because of its potential advantages such as high CO tolerance, easy cooling, better heat utilization and possible integration with fuel processing units.

However, the high temperature obviously aggravates the carbon corrosion and catalyst degradation. Based on thermally treated carbon black and structurally designed carbon nanotubes (CNTs) as support, highly dispersed and adhered platinum nanoparticles were prepared in this work. Surface functionalization and activation of the support materials were found to be able to boost the catalyst activity and improve the selectivity for platinum loading.

Fuel cell durability tests in term of performance degradation were performed with acid doped polybenzimidazole membrane fuel cells at temperatures of up to 160°C. The tests were focused on catalyst degradation by means of a potential cycling protocol. The electrochemical active area of the electrode, hydrogen permeability of the membrane and the area specific resistance of the cell were also measured during the tests.

Compared with active carbon black supported catalysts, significant improvement in the catalyst durability was achieved.