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 comprehensive 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), allowing for highly sensitive time- and potential-resolved measurements of metal dissolution. The findings contradict the generally accepted hypothesis that in contrast to the rate of carbon corrosion, which follows the Arrhenius law and increases exponentially with temperature, 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.

Electrochemical Valorization of Glycerol via Electrocatalytic Reduction into Biofuels: A Review

“…Plus, higher temperature might positively impact the exophilic nature of the electrocatalysts used. [50,51] However, a thorough study to explain this significant influence is needed, since Faraday's first law of electrolysis has theoretically neglected the dependent towards electrolysis temperature.…”

“…This equation shows that as T increases or E a decreases (as electrocatalysts are equipped), the rate constant (K) will be increased which is directly proportional to the rate of the chemical reaction and hence, making it useful for calculating the rate law parameters. Yet, from authors' knowledge, there is still wide knowledge gap that exist related to the synergistic effect between the operating temperature with the nature of electrocatalysts (its E a and structural changes), [50,51] within glycerol ECR.…”

Adjusting the Operational Potential Window as a Tool for Prolonging the Durability of Carbon-supported Pt-alloy Nanoparticles as Oxygen Reduction Reaction Electrocatalysts

“…Namely, it has been clear for some time that an increase in UPL strongly affects the stability of carbon-supported Pt-nanoalloys, both in terms of carbon support corrosion 47 and metal dissolution. 23,39,[57][58][59][60] Moreover, in terms of metal dissolution, in our recent work 42 it has been shown that at a constant high temperature (75 o C),…”

“…Specifically, the fuel cell electrocatalysts are exposed to very aggressive conditions, including a corrosive environment, high temperatures, humidity, frequent stops and starts, fluctuations in the operational voltage, and so forth. 9 These non-intrinsic operational conditions, together with the intrinsic properties of the electrocatalyst (choice of M, 23 order/disorder, 22 de-alloying/activation, 36 type of carbon/degree of graphitization 37 ), lead to a spectrum of very complex and interconnected degradation mechanisms: (i) electrochemically induced (transient) dissolution of Pt, which is defined by thermodynamic tendency of Pt to the formation/reduction of the Pt-oxide, [38][39][40][41] resulting in Ostwald ripening 42,43 and/or formation of metallic Pt-bands in the membrane, [44][45][46] (ii) dissolution of M 23,42 and (iii) electrochemical and chemical carbon support corrosion, [47][48][49] leading to the agglomeration and/or detachment of whole Pt NPs. These complex instability phenomena are of crucial importance for the longevity of the PEMFCs in the case of their application in both light-duty vehicles (LDVs) beside heavyduty vehicles (HDVs).…”

“…Furthermore, the dependence of the stability of carbon-supported Pt-based nanoalloys not only on intrinsic but also on non-intrinsic factors, should be addressed in both RDE and MEA. For instance, in addition to the effect of temperature, 42,47,56 the impact of the potential window on the stability of carbon-supported Pt-based nanoalloy electrocatalysts has also recently been shown and extensively described. Namely, it has been clear for some time that an increase in UPL strongly affects the stability of carbon-supported Pt-nanoalloys, both in terms of carbon support corrosion 47 and metal dissolution.…”