Structure effects on electrocatalysts. Oxygen reduction on Te-modified Pt(111) surfaces: Site-blocking vs electronic effects

Abstract

In this work, the oxygen reduction reaction (ORR) on tellurium-modified Pt(111) surfaces has been studied. Adsorption of Te adatoms on Pt(111) progressively shifts toward less positive values of both the ORR reaction onset and the half-wave potential in 0.1M HClO 4 for 0 < θ Te < 0.25. However, at θ Te > 0.25, the ORR activity increases relative to the one at θ Te < 0.25, but remains lower than that on clean Pt(111). Results were analyzed in light of simulations of kinetic currents as a function of θ Te , calculated by employing a simple mean field model including both site blocking and electronic effects. Inside this framework, experimental data are best explained by considering that oxygenated Te species inhibit the ORR by either negatively modifying adsorption energies of reaction intermediates or combined site-blocking and electronic effects. A redox ORR catalysis due to redox properties of Te adatoms is discarded. Contrarily, in 0.05M H 2 SO 4 , a positive catalytic effect has been found, interpreted in terms of a competitive adsorption-desorption mechanism involving the replacement of adsorbed sulfate by Te adatoms. On the other hand, despite the strong site-blocking effect on H ads and OH ads adsorption by Te adatoms, it appears that the reduced Te-Pt(111) adlayer does not inhibit the reaction, suggesting different active sites for H ads and OH ads adsorption and for the rate-determining step of the ORR mechanism.

Electrocatalysis of Oxygen Reduction on Te-Modified Platinum Stepped Crystal Surfaces

“…Furthermore, a new peak at ca. 0.93–0.95 V appears, corresponding to the redox process on Te adatoms (eq ) previously reported: …”

“…Te adatoms in the oxidized state act only as spectators, that is, third-body effect, which blocks active sites and reduces the ORR activity. 58 However, a sharp increase in the ORR current can be observed at the peak potential for the redox process of Te on the Te-modified Pt(111) electrode (Figure S2b). Conversely, Te adatoms in the reduced state catalyze the ORR activity.…”

“…, Moreover, information gained through modification has been successfully employed for the rational design of nanocatalysts with improved reactivity for electrochemical energy substance conversion devices including PEMFCs. − Recently, studies have reported that the oxygen reduction reaction activity on platinum single-crystal electrodes and nanoparticles can be substantially improved by the adsorption of metals, ,, amines, , hydrophobic cations, ionic liquids, and melamine. , Nevertheless, studies on the modification of Pt­( hkl ) by oxygen group elements (VIA group) such as tellurium and their ORR performance are rare. A preliminary study by Feliu and co-workers found that Te modification of Pt(111) hampered the ORR performance . To gain a comprehensive understanding of how Te modification changes the electrode surface properties, this study extends the research of the ORR behavior to Te-modified Pt(100) and a series of platinum stepped surfaces (Pt­(S)-[ n (111) × (100)]).…”

The role of adsorbates in electrocatalytic systems: An analysis of model systems with single crystals

“…Gomez-Marin et.al. [12] showed a higher ORR activity on Pt(111) modified by a submonolayer of Te adatoms in 0.05M H 2 SO 4 electrolyte when compared to bare Pt(111). The intriguing result is discussed in terms of the chemical nature of the adsorbing anion and not its adsorption strength, since the Te adatoms also inhibit the ORR kinetics.…”

“…Different adatoms have been used to decorate platinum single crystal electrodes for several reactions, e.g. nitrate reduction reaction [14,[38][39][40][41][42][43][44][45], ORR [12,46], organic molecules oxidation [47][48][49][50][51][52][53][54][55], among others. The influence of adatoms depends on the substrate, the adatom and the studied reaction and straightforward conclusion can be made from the available results.…”