Abstract
The initial performance and decay trends of polymer electrolyte membrane fuel cells (PEMFC) cathodes with Pt3Co catalysts of three mean particle sizes (4.9 nm, 8.1 nm, and 14.8 nm) with identical Pt loadings are compared. Even though the cathode based on 4.9 nm catalyst exhibited the highest initial electrochemical surface area (ECA) and mass activity, the cathode based on 8.1 nm catalyst showed better initial performance at high currents. Owing to the low mass activity of the large particles, the initial performance of the 14.8 nm Pt3Co-based electrode was the lowest. The performance decay rate of the electrodes with the smallest Pt3Co particle size was the highest and that of the largest Pt3Co particle size was lowest. Interestingly, with increasing number of decay cycles (0.6 to 1.0 V, 50 mV/s), the relative improvement in performance of the cathode based on 8.1 nm Pt3Co over the 4.9 nm Pt3Co increased, owing to better stability of the 8.1 nm catalyst. The electron microprobe analysis (EMPA) of the decayed membrane-electrode assembly (MEA) showed that the amount of Co in the membrane was lower for the larger particles, and the platinum loss into the membrane also decreased with increasing particle size. This suggests that the higher initial performance at high currents with 8.1 nm Pt3Co could be due to lower contamination of the ionomer in the electrode. Furthermore, lower loss of Co from the catalyst with increased particle size could be one of the factors contributing to the stability of ECA and mass activity of electrodes with larger cathode catalyst particles. To delineate the impact of particle size and alloy effects, these results are compared with prior work from our research group on size effects of pure platinum catalysts. The impact of PEMFC operating conditions, including upper potential, relative humidity, and temperature on the alloy catalyst decay trends, along with the EMPA analysis of the decayed MEAs, are reported.
Highlights
To reduce the electrocatalyst cost for polymer electrolyte membrane fuel cells (PEMFCs), platinum alloys with higher oxygen reduction reaction (ORR) mass activity are being developed
The focus of this paper is to report a similar systematic analysis of Pt3Co catalysts that have nearly identical metal ratio but different mean particle sizes, and contrast these with Pt catalysts to delineate the impact of alloying and particle size
Pt3Co catalysts with nearly identical Pt:Co:carbon ratio but different mean particle sizes were prepared by heat treatment, in order to distinguish the effects of composition from particle size on the initial performance and stability
Summary
To reduce the electrocatalyst cost for polymer electrolyte membrane fuel cells (PEMFCs), platinum alloys with higher oxygen reduction reaction (ORR) mass activity are being developed. Chen et al showed that the acid treated PtxCo resulted in Co dissolution, which increased the thickness of the Pt-enriched surface layer This structural change was identified as a contributor to the reduction in the specific activity of PtxCo nanoparticles after potential cycling [18]. Min et al showed that the particle size and alloying effects are the two most important factors affecting the catalytic activity towards ORR, with lowered Pt–Pt bond distance resulting in favorable adsorption of oxygen [13]. The impact of Pt3Co particle size with nearly identical metal ratio is needed to delineate the effects of composition and particle size on the initial performance and stability The catalyst structures, such as the core-shell type, offer the benefits of low platinum content in the electrodes and high activity [31,32,33,34]. The focus of this paper is to report a similar systematic analysis of Pt3Co catalysts that have nearly identical metal ratio but different mean particle sizes, and contrast these with Pt catalysts to delineate the impact of alloying and particle size
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
