Understanding the Crucial Significance of the Temperature and Potential Window on the Stability of Carbon Supported Pt-Alloy Nanoparticles as Oxygen Reduction Reaction Electrocatalysts

Abstract

The present research provides a study of carbon-supported intermetallic Pt-alloy electrocatalysts and assesses their stability against metal dissolution in relation to the operating temperature and the potential window using two advanced electrochemical methodologies: (i) the in-house designed high-temperature disk electrode (HT-DE) methodology as well as (ii) a modification of the electrochemical flow cell coupled to an inductively coupled plasma mass spectrometer (EFC-ICP-MS) methodology, allowing for highly sensitive time- and potential-resolved measurements of metal dissolution. While the rate of carbon corrosion follows the Arrhenius law and increases exponentially with temperature, the findings of the present study contradict the generally accepted hypothesis that the kinetics of Pt and subsequently the less noble metal dissolution are supposed to be for the most part unaffected by temperature. On the contrary, clear evidence is presented that in addition to the importance of the voltage/potential window, the temperature is one of the most critical parameters governing the stability of Pt and thus, in the case of Pt-alloy electrocatalysts, also the ability of the nanoparticles (NPs) to retain the less noble metal. Lastly, but also very importantly, results indicate that the rate of Pt redeposition significantly increases with temperature, which has been the main reason why mechanistic interpretation of the temperature-dependent kinetics related to the stability of Pt remained highly speculative until now.

The Importance of Chemical Activation and the Effect of Low Operation Voltage on the Performance of Pt-alloy Fuel Cell Electrocatalysts

“…While A2' Cu (Figures 2g-h) remains stable a bit further even in the metallic form due to its 2h-g) 30,31,41 . Nevertheless, the A1' Cu dissolution in the case of Pt-Cu alloy is still significantly higher than that of Pt-Ni alloy, which is in accordance to our prior work 41,74 .…”

“…Consequently, at the same LVL, a higher fraction of Pt-oxide gets reduced with increasing temperature, leading to a lower protection of the less noble metal towards the dissolution and thus, a higher voltage loss. Both the effects of the voltage window as well as the temperature are in line with our recent liquid electrolyte follow-up study 74 .…”

Alternative and facile production pathway towards obtaining high surface area PtCo/C intermetallic catalysts for improved PEM fuel cell performance

“…In the present study, we take advantage of the promising catalytic activity for the ORR and the high ECSA of the Pt-alloy catalyst based on double passivation galvanic displacement. [23][24][25] We confirm the significantly narrower particle size distribution of the novel PtCo/C catalysts compared to commercial PtCo/C catalysts via transmission scanning electron microscopy (TEM) image analysis and X-ray powder diffraction (XRD). In addition, the effect of the significantly narrowed particle size distribution obtained by the optimized synthesis route on the performance is demonstrated with thin-film rotating disk electrodes (TF-RDEs) and in single-cell MEA validation.…”

“…Double passivation with galvanic displacement -In the first step (Scheme 1a-b), Pt NPs were deposited onto the carbon support (Ketjen Black EC300J) via previously reported double passivation galvanic displacement method. [23][24][25] Briefly, the Pt deposition step consists of oxide passivation of Co followed by carbon monoxide (CO) capping of Pt-based NPs formed by galvanic displacement of Co after Pt-salt addition. To achieve that, multigrams of propriatery Co+CoO/C composite, prepared using the pulse combustion method reported elsewhere, 24 were suspended in an aqueous solution.…”

“…Oxygen reduction reaction (ORR) polarization curves and carbon monoxide (CO) electrooxidation cyclic voltammetry (CV) were measured in a thin-film rotating disk electrode (TF-RDE), of which the setup was described in the previous works. 25,28 As a reference electrode (RE), the reversible hydrogen electrode (RHE; HydroFlex, Gaskatel) was used, while the graphite rode electrode was used as a counter electrode. The working electrode (WE) was a 0.196 cm² glassy carbon disc embedded in Teflon (Pine Instruments).…”