Monometallic Palladium for Oxygen Reduction in PEM Fuel Cells: Particle-Size Effect, Reaction Mechanism, and Voltage Cycling Stability

Abstract

In this experimental study, we determine the size dependent activity as well as accelerated voltage cycling stability of various carbon supported palladium electrocatalysts for the oxygen reduction in acidic medium. Furthermore, ex-situ transmission electron microscopy studies before and after accelerated voltage cycling provide a deeper understanding regarding particle stability during voltage cycling. Regarding oxygen reduction, a particle size effect on the specific activity is observed, with bulky Pd-black (≈4 m 2 g −1 Pd ) exhibiting ≈x6 times higher activity than Pd supported on Vulcan carbon (≈190 m 2 g −1 Pd ). Mass activities, however, exhibit a strong correlation with catalyst surface area at small electrochemically active surface area (ECSA) values, but are observed to be nearly constant between ≈50−200 m 2 g −1 Pd . As stability tests during voltage cycling reveal a benefit for smaller surface areas, i.e. bigger particles, a limited gain in stability can be achieved by increasing catalyst particle size at a negligible cost of electrocatalytic mass-based activity. Moreover, we provide a deeper insight regarding the oxygen reduction reaction mechanism and show significant hints that a sequential two-plus-two electron reduction mechanism via intermediate hydrogen peroxide is likely to occur on carbon supported Pd catalysts.

CO as a Probe Molecule to Study Surface Adsorbates during Electrochemical Oxidation of Propene

“…CVs performed after CO and propene adsorption show suppression of H upd features in the potential region of 0.0-0.4 V vs. RHE, due to poisoning from adsorbed species, consistent with expectations. [21][22][23] The oxidation features observed for CO stripping and propene stripping are also consistent with those described previously under similar conditions. [2,23] We see that CO is anodically stripped with a sharp oxidative peak observed at ca.…”

Janus electrocatalytic flow-through membrane enables highly selective singlet oxygen production

“…4e , thick lines). As the Pd cathode favors the formation of H 2 O 2 and H 2 O via a serial two-plus-two-electron transfer in ORR, its generation of O 2 •− intermediates from the one-electron transfer is minor 63 , 64 . This proposed analysis is also verified by tuning the electrofiltration modes.…”

Electrocatalysis of Oxygen Reduction Reaction on Shape-Controlled Pt and Pd Nanoparticles—Importance of Surface Cleanliness and Reconstruction

“…Pd is considered to be a promising alternative to Pt, perhaps because of their similar crystal structure (face centered cubic) and electronic configuration (d-transition metals) (Mittermeier et al, 2017). Most importantly, Pd is situated at the peak of the volcano plot of ORR activity, adjacent to Pt (Nørskov et al, 2004).…”