Understanding a Degradation Mechanism of Direct Methanol Fuel Cell Using TOF-SIMS and XPS

Abstract

The catalyst layers, which were obtained from the aged membrane electrode assemblies (MEAs) showing performance loss, 17%, 37%, 45% as compared with that from the pristine MEA were investigated using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) to understand the degradation mechanism of single-cell performance in direct methanol fuel cell. The metallic components in the PtRu anode catalyst layer was decreased significantly with the performance drop revealed from the change of the valance bands. It has been found that ruthenium and platinum were driven to the cathode by the gradient of electric field during the durability test. From the mass-resolved imaging technique of TOF-SIMS combined with a peel-off method, it was indicated that the traveled ruthenium from anode to cathode was not uniformly distributed within the cathode catalyst layer, but more accumulated at the surface of the catalyst layer, that is, the interface with the gas diffusion layer. XPS and TOF-SIMS results suggested that the ruthenium ions are electro-deposited to RuO x rather than metallic Ru, which seems to more closely correlate with the degradation of performance.

Enhanced activity and stability of Pt/C fuel cell anodes by the modification with ruthenium-oxide nanosheets

“…However, the CO tolerance of RuO 2 ns(1.0)-Pt/C is comparable to PtRu/C at elevated temperatures, where PtRu/C stability may become a major issue. The instability of Ru under the fuel cell operation conditions has been reported [20][21][22]. The amount of Ru loss due to dissolution should increase with increasing cell temperature.…”

“…It has been reported that metallic Ru in the PtRu alloy catalyst dissolves as Ru n+ and deposits at the cathode under fuel cell operating conditions, leading to catalyst degradation [20][21][22]. Thus, the stability of RuO 2 ns(0.5)-Pt/C was considered by an accelerated stability test (potential cycling between 0.05-1.2 V vs. RHE in 0.5 M H 2 SO 4 (60°C) at 50 mV s -1 for 1,000 cycles).…”

“…In terms of catalyst stability, Ru has been reported to be vulnerable to dissolution under longterm fuel cell operation, especially by voltage fluctuation due to repeated start up and shut down [19][20][21][22]. It is well known that crystalline RuO 2 has high electrochemical stability within the hydrogen and oxygen evolution region [23][24][25][26][27][28][29][30].…”

X‐Ray Photoelectron Spectroscopy in Analysis of SurfacesUpdate based on the original article by Steffen Oswald,Encyclopedia of Analytical Chemistry, © 2000, John Wiley & Sons, Ltd.

“…In addition, the surface properties of the mostly C-based membrane electrodes (229) and its degradation (230,231) during use are of interest. Often special electrochemical cells are used to avoid influence from atmosphere.…”

Durable Transition‐Metal‐Carbide‐Supported Pt–Ru Anodes for Direct Methanol Fuel Cells

“…Ru cations in the polymer electrolyte membrane affect its characteristic features, for example, an increase in the number of Ru ions per sulfonic acid group in the membrane decreases the water uptake of the membrane and increases the microviscosity of the fluidic regions possibly due to a change in the free volume of the membrane. Furthermore, Ru ions present in the membrane affect its proton conductivity, and accelerate membrane degradation [6][7][8]. Recently, the effects of catalyst-carbon support on proton conduction have been studied in detail by Liu et al [9].…”