Mitigating Metal Dissolution and Redeposition of Pt-Co Catalysts in PEM Fuel Cells: Impacts of Structural Ordering and Particle Size

Abstract

Metal dissolution and redeposition are considered to be the most important degradation mechanism for Pt-based fuel cell electrocatalysts. Understanding key factors mitigating the dissolution and migration under realistic proton-exchange-membrane (PEM) fuel cells is crucial for improving their performance and durability. Using ordered and disordered PtCo electrocatalysts, we address how structural ordering and particle size can affect the dissolution of Co/Pt and their redeposition into the membrane upon catalyst accelerated durability test in PEM fuel cells by statistical scanning transmission electron microscopy (STEM) and spectroscopic analysis. Consistent with the improved performance and durability, we observe that both Co and Pt dissolution were mitigated in the ordered PtCo catalyst compared to the disordered one. The suppressed Pt dissolution was evidenced from the relieved particle coarsening and significantly suppressed Pt redeposition/migration in the membrane after the durability test. Moreover, we reveal an optimum particle size range between 2–5 nm for ordered PtCo catalysts, which favors the highest structural ordering degree and hence the highest retention of Co. These results provide a rationale for implementing ordered Pt intermetallic electrocatalysts in PEM fuel cells and further particle size optimization for improved durability.

Resolving the nanoparticles' structure-property relationships at the atomic level: a study of Pt-based electrocatalysts

“…In the literature, intermetallic alloys have already caught much attention due to their promising ORR performance ( Gamler et al., 2018 ; Hodnik et al., 2014 ; Li and Sun, 2019 ; Pavlišič et al., 2016 ; Rößner and Armbrüster, 2019 ; Zhang et al., 2020 ). However, although we can find many reports on intermetallic alloys of Pt-Cu ( Bele et al., 2014 ; Gatalo et al, 2019a , 2019b , 2019c , 2019d ; Hodnik et al., 2012a , 2014 ; Pavlišič et al., 2016 ) and Pt-Fe ( Liu et al., 2019 ; Wang et al., 2019b ; Wittig et al., 2017 ), the reports on intermetallic phases of more industrially relevant Pt-Co ( Cui et al., 2020 ; Xiong et al., 2019 ) and even more so Pt-Ni alloys ( Lu et al., 2009 ) are still very scarce ( Leonard et al., 2011 ; Zou et al., 2015 ). Careful examination of the XRD spectra also reveals the presence of pure M phases in Pt-M/C electrocatalysts containing Fe, Ni, and Co ( Figure 3 D; as pointed by the arrows).…”

“…Firstly, any issues related to carbon solubility and encapsulation seem to be much less detrimental as in the case of Ni, showing much more similar behavior to that of Pt-Cu. Furthermore, the formation of intermetallic structures is possible ( Kongkananad, 2020 ; Cui et al., 2020 ; Xiong et al., 2019 ), whereas the behavior of Co 2+ ion as an impurity in the PEMFC currently also points toward similar impacts as that of Ni 2+ ( Braaten et al., 2017 , 2019 ). Similarly again to Ni, it also does not block the Pt surface.…”

Alloying–realloying enabled high durability for Pt–Pd-3d-transition metal nanoparticle fuel cell catalysts

“…Such catalysts, and intermetallic alloy catalysts as well 4 , are perhaps the predominant pathway for making most of the state-of-the-art alloy catalysts. Electrochemical dealloying approach to catalyst preparation, which dates back more than a decade ago without breakthroughs in commercializing alloy catalysts in terms of cost and stability, has shown limited success for operation in fuel cells 2 , 19 , 20 . Many of the reported ultrahigh-activity alloy catalysts contain high atomic percentages of PGM (e.g., 75 at% Pt) or toxic elements (e.g., Pb) in the as-synthesized state, feature large particle sizes (10–20 nm), or do not survive long-term durability test, and almost all perform poorly in real fuel cells 15 .…”

A Review of Recent Developments and Advanced Applications of High-Temperature Polymer Electrolyte Membranes for PEM Fuel Cells

“…In the acidic environment of HT-PEM fuel cells, the dissolved platinum at the nano-and atomic-scale can precipitate in the membrane by reducing platinum ions [196]. This phenomenon can be confirmed by TEM analysis (Figure 7a,b) [197]. The attachment of platinum particles on the carbon support surface is weakened by increasing the operating temperature [26,196].…”