Comparison of Oxygen Adsorption and Platinum Dissolution in Acid and Alkaline Solutions Using Electrochemical Quartz Crystal Microbalance

Abstract

Platinum (Pt) is a widely used electrocatalyst material in fuel cells and electrolysers. Proton exchange membrane (PEM) fuel cells and electrolysis operate under highly acidic conditions whereas the more recently developed anion exchange membrane (AEM) processes take place under alkaline conditions. Pt dissolution and Pt oxidation during operation and varying potentials has been studied mainly for the acidic PEM and less for the alkaline AEM. This study presents a comparison of Pt dissolution and Pt oxidation in 0.5 M H2SO4 and 1 M KOH using electrochemical quartz crystal microbalance (EQCM) on Pt thin films. Physical characterisation using electron microscopy and atomic force microscopy (AFM) revealed small, yet significant differences in the Pt film surface structure, which is related to differences in measured electrochemical surface area (ECSA). The mass increase from adsorption of oxygenated species and Pt oxidation is higher in alkaline conditions compared to in acid while dissolution of Pt is similar.

Anodic and Cathodic Platinum Dissolution Processes Involve Different Oxide Species

“…However, we cannot rule out a weak influence of the anion species on the slower oxidation kinetics which occurs on the timescale of minutes after the initial fast oxidation [26,45,46] . The influence of both electrolyte solutions on Pt dissolution has been compared on polycrystalline Pt samples [47,48] . No or negligible influence of the anion species in the electrolyte was found.…”

Anodic and Cathodic Platinum Dissolution Processes Involve Different Oxide Species

“…However, we cannot rule out a weak influence of the anion species on the slower oxidation kinetics which occurs on the timescale of minutes after the initial fast oxidation [26,45,46] . The influence of both electrolyte solutions on Pt dissolution has been compared on polycrystalline Pt samples [47,48] . No or negligible influence of the anion species in the electrolyte was found.…”

“…[26,45,46] The influence of both electrolyte solutions on Pt dissolution has been compared on polycrystalline Pt samples. [47,48] No or negligible influence of the anion species in the electrolyte was found. Although an influence cannot be ruled out for single crystal samples without an explicit experiment, these results suggest that the influence of these anion species on Pt dissolution is weak.…”

Fundamental insight into enhanced activity of Pd/CeO2thin films in hydrogen oxidation reaction in alkaline media

“…A complementary study comparing E-QCM measurements with varying inversion potentials would give further insight into the effect of Pd distribution and oxidation states on stability, but is beyond the scope of this work. 28 It should be noted here that the control sample made of 2 nm of Pd on a 20 nm Ti film (without CeO 2 ) were not stable and degraded during CV, making a comparison impossible.…”

“…27 It is also a powerful method to investigate and quantify mass changes occurring on surfaces due to phenomena of dissolution, adsorption, absorption, physisorption and desorption, while the reaction is occurring. 28 Using E-QCM, we provide fundamental understanding of the adsorption, absorption and desorption phenomena occurring on Pd/CeO 2 thin films during HOR. We show that on pure Pd thin films, mass changes are dominated by the absorption of hydrogen while on Pd/CeO 2 they are dominated by the oxidation/reduction of ceria and adsorption of hydroxyl groups.…”