Electrochemical Performance and Durability of Carbon Supported Pt Catalyst in Contact with Aqueous and Polymeric Proton Conductors

Abstract

Significant differences in catalyst performance and durability are often observed between the use of a liquid electrolyte (e.g., sulfuric acid), and a solid polymer electrolyte (e.g., Nafion). To understand this phenomenon, we studied the electrochemical behavior of a commercially available carbon supported platinum catalyst in four different electrode structures: catalyst powder (CP), catalyst ionomer electrode (CIE), half membrane electrode assembly (HMEA), and full membrane electrode assembly (FMEA) in both ex situ and in situ experiments under a simulated start/stop cycle. We found that the catalyst performance and stability are very much influenced by the presence of the Nafion ionomers. The proton conducting phase provided by the ionomer and the self-assembled electrode structure render the catalysts a higher utilization and better stability. This is probably due to an enhanced dispersion, an improved proton-catalyst interface, the restriction of catalyst particle aggregation, and the improved stability of the ionomer phase especially after the lamination. Therefore, an innovative electrode HMEA design for ex-situ catalyst characterization is proposed. The electrode structure is identical to the one used in a real fuel cell, where the protons transport takes place solely through solid state proton conducting phase.

X-ray photoelectron spectroscopy investigation on electrochemical degradation of proton exchange membrane fuel cell electrodes

“…This is probably due to the dissolution and migration of the platinum catalyst from the electrode and its transport through the hydrophilic domain of the membrane. This agrees well with the detection of platinum in the aqueous electrolyte by atomic adsorption spectroscopy, as confirmed earlier [19]. The interface between catalyst layer and conducting carbon layer (MEA-I) shows reduced influence by the electrochemical stress.…”

“…The electrode structure change reflected by the XPS study can be schematically illustrated in Fig. 5 (Pt particle growth was earlier confirmed by XRD [19]). …”

“…In our previous work [19], identical catalyst was found to possess significantly different electrochemical performance, especially with respect to the durability when the catalyst is in contact or not in contact with the ionomers. The reduction in the platinum catalyst performance (reduction of hydrogen adsorption/desorption ability in cyclic voltammetry) was due to the platinum degradation (detachment, dissolution and coalescence), carbon corrosion and ionomer degradation and change in the associated pore morphology and surface properties.…”

Niobium disulphide (NbS2)-based (heterogeneous) electrocatalysts for an efficient hydrogen evolution reaction

“…Noteworthily, these results have been achieved without using any binder, such as Naon, which could prospectively improve further the mechanical stability of the electrodes during H 2 evolution. 140,141 In fact, although the gas evolution, causing the nanostructuring of the electrodes, has been correlated with the self-optimization behaviour of catalytic group-5 MX 2 in acidic media, 54,55,57,77 it may imply a loss of catalytic materials, which should be controlled for practical purposes. In this context, the Li-TFSI-treated electrodes perform similarly to the electrochemically cycled electrodes, but do not require in operando pre-conditioning of the electrodes.…”

An opinion on catalyst degradation mechanisms during catalyst support focused accelerated stress test (AST) for proton exchange membrane fuel cells (PEMFCs)

“…Development of durable catalyst support materials for PEMFC applications requires fast evaluation of durability through accelerated stress test (AST) under predefined protocols based on the performance study either in an operating FC or in a liquid electrolyte electrochemical cell [15][16][17][18][19][20].…”