Methodology for Evaluation of Contributions of Ostwald Ripening and Particle Agglomeration to Growth of Catalyst Particles in PEM Fuel Cells

Abstract

The degradation of the catalyst layer represents one of the main limiting factors in a wider adoption of fuel cells. The identification of the contributions of different mechanisms of catalyst degradation, namely the Ostwald ripening and particle agglomeration, is an important step in the development of mitigation strategies for increasing fuel cell reliability and prolonging its life time. In this paper, the degradation phenomena in high temperature polymer electrolyte membrane fuel cell (HT‐PEMFC) are analyzed using a physically‐based model of fuel cell operation and catalyst degradation, describing carbon corrosion, platinum dissolution and consequent growth of catalyst particles. The model results indicate significantly different time dependence of catalyst particle growth resulting from different mechanisms: linear growth in the case of particle agglomeration and root‐like time dependence for the Ostwald ripening. Based on these results, a new analytic method is proposed, performed by the fitting of a test root‐function to the time profile of the particle size growth and using best‐fit parameters to identify the prevailing growth mechanism. Using this method on a particle growth time trace deduced from in situ cyclic voltammetry measurement during HT‐PEMFC degradation, we are able to identify the agglomeration as the main mechanism of catalyst particle grow.

Tracking the Catalyst Layer Depth-Dependent Electrochemical Degradation of a Bimodal Pt/C Fuel Cell Catalyst: A Combined Operando Small- and Wide-Angle X-Ray Scattering Study

“…Stronger support-particle interaction of the larger particles due to the larger contact area with the support, as compared to smaller ones, could lead to less detachment of larger NPs from the support. 56 However, the support-particle interaction is also determined by other factors, e.g., by the degree of graphitization of the carbon support that is difficult to rationalize for commercial catalysts. 18,57 In the following, we now concentrate on the effect of the AST treatment on the catalyst, which is analyzed first at a depth close to the electrolyte-catalyst interface.…”

Challenges and Opportunities in Understanding Proton Exchange Membrane Fuel Cell Materials Degradation Using In‐Situ Electrochemical Liquid Cell Transmission Electron Microscopy

“…The PSD of Ostwald ripening is characterized by a uniformly broader histogram with an increase in its mean particle size, while the PSD histogram of agglomeration is also characterized by an increase in mean particles size, but with a broadened tail toward larger particles and a no/little broadening of the tail toward small particle. [ 153 ] 4)Detachment of catalyst particles from the carbon support is another pathway for the Pt degradation. Corrosion of the carbon support, which is accelerated in the presence of the catalyst material, leads to the detachment of Pt particles from the support ( Figure ).…”

“…Finally, the detachment of Pt and its agglomeration leads to significant decrease of ECSA and the performance of the cell. [ 153 ] Carbon corrosion can be mitigated by using corrosion‐resistive graphitized carbon supports and avoiding high cathode potentials in the range of 0.80–0.85 V versus RHE. [ 106 ] 5)The final mechanism of degradation, reaction site deactivation, is the process of contaminating the Pt catalysts’ surface with species originating from either the feeding gas or the cell assembly, such as sealing gaskets, bipolar plates, the membrane, or cooling systems.…”

“…However, it should be noted that the occurrence of dissolution/redeposition processes suggests the involvement of Ostwald ripening as the major degradation mechanism. Therefore, further study, using the high resolution images, is needed to perform the PSD analysis [ 153 ] and clarify the extent of involvement of the Ostwald ripening, or other mechanisms, in the degradation of the catalyst.…”

Tracking the Catalyst Layer Depth-Dependent Electrochemical Degradation of a Bimodal Pt/C Fuel Cell Catalyst: A Combined Operando Small- and Wide-Angle X-Ray Scattering Study

“…Stronger support-particle interaction of the larger particles due to the larger contact area with the support, as compared to smaller ones, could indicate that larger particles interact more strongly with the support and might migrate and detach less. 46 However, the support-particle interaction is determined by other factors, e.g., by the degree of graphitization of the carbon support. 47 The observed preferential particle detachment of larger NPs indicates a degradation scenario based on the support-particle interaction being a combination of both the nature of particles and support.…”