Instability of Pt∕C Electrocatalysts in Proton Exchange Membrane Fuel Cells

Abstract

Equilibrium concentrations of dissolved platinum species from a Pt/C electrocatalyst sample in 0.5 M H 2 SO 4 at 80°C were found to increase with applied potential from 0.9 to 1.1 V vs reversible hydrogen electrode. In addition, platinum surface area loss for a short-stack of proton exchange membrane fuel cells ͑PEMFCs͒ operated at open-circuit voltage ͑ϳ0.95 V͒ was shown to be higher than another operated under load ͑ϳ0.75 V͒. Both findings suggest that the formation of soluble platinum species ͑such as Pt 2+ ͒ plays an important role in platinum surface loss in PEMFC electrodes. As accelerated platinum surface area loss in the cathode ͑from 63 to 23 m 2 /g Pt in ϳ100 h͒ was observed upon potential cycling, a cycled membrane electrode assembly ͑MEA͒ cathode was examined in detail by incidence angle X-ray diffraction and transmission electron microscopy ͑TEM͒ to reveal processes responsible for observed platinum loss. In this study, TEM data and analyses of Pt/C catalyst and cross-sectional MEA cathode samples unambiguously confirmed that coarsening of platinum particles occurred via two different processes: ͑i͒ Ostwald ripening on carbon at the nanometer scale, which is responsible for platinum particle coarsening from ϳ3 to ϳ6 nm on carbon, and ͑ii͒ migration of soluble platinum species in the ionomer phase at the micrometer scale, chemical reduction of these species by crossover H 2 molecules, and precipitation of platinum particles in the cathode ionomer phase, which reduces the weight of platinum on carbon. It was estimated that each process contributed to ϳ50% of the overall platinum area loss of the potential cycled electrode.

A Highly Stable Anode, Carbon‐Free, Catalyst Support Based on Tungsten Trioxide Nanoclusters for Proton‐Exchange Membrane Fuel Cells

“…Moreover, the existence of Pt particles could also accelerate carbon corrosion. [10,11] These effects would result in a rapid degradation of the Pt catalyst and thus shorten the lifetime of the PEMFC. Therefore, more robust, carbon-free support materials, such as conducting metal oxides, have been studied as potential supports with high corrosion-resistant properties.…”

High temperature (HT) polymer electrolyte membrane fuel cells (PEMFC) – A review

“…There are three main mechanisms that are widely accepted as being the methods of degradations: (i) the carbon supports corrode [83]; (ii) the platinum particles dissolve, leading to particle growth via Ostwald ripening, when the platinum is deposited [84]; (iii) the platinum particles agglomerate and sinter together on the carbon support via passive diffusion processes [85]. Novel methods for LT-PEMFC catalyst layer fabrication to increase active platinum surface area and thus decrease overall platinum levels are demonstrated by Curnick et al [86].…”

Highly stable Pt monolayer on PdAu nanoparticle electrocatalysts for the oxygen reduction reaction

“…O ne critical problem facing the proton electrolyte membrane fuel cells (PEMFCs) is the deterioration of activity during operating conditions, mainly caused by the dissolution and loss of platinum (Pt) nanoparticles at the cathode [1][2][3][4][5] . The durability of existing Pt catalysts is unsatisfactory for realizing the commercialization of PEMFCs for automotive applications.…”