Role of surface defect sites: from Pt model surfaces to shape-controlled nanoparticles

Abstract

In the present paper, preferentially oriented (111) Pt nanoparticles (mostly octahedral and tetrahedral, namely {111}Pt nanoparticles) have been characterized and compared with a Pt(554) single-crystal electrode as their voltammetric features are quite similar in 0.5 M H 2 SO 4 . The anion and Bi adsorption behaviours suggest that the {111}Pt nanoparticles contain relatively wide hexagonal domains and also isolated sites which could adsorb solely hydrogen. Bi step decoration has been successfully extended to modify the defects of {111}Pt nanoparticles without blocking terrace sites. CO charge displacement has been applied to determine the potential of zero total charge (pztc) of non-decorated and Bi decorated surfaces. It has found that the positive shift of pztc on defect-decorated {111}Pt nanoparticles is not so significant in comparison with that of Pt(554) due to the relative short mean length of (111) domains on the {111}Pt nanoparticles. CO stripping demonstrates that {111}Pt nanoparticles exhibit higher reactivity toward CO oxidation. This reflects the role of the defect sites in nanoparticles, evidenced by the disappearance of the ''pre-wave'' in the stripping voltammogram once the defects were blocked by Bi. The stripping peaks shift to higher potential on Bi decorated surfaces, indicating the active role of both steps and defects for CO oxidation. By comparing the CO stripping charge and the change in hydrogen adsorption charge of surfaces with and without Bi decoration, including reasonable deconvolution, the local CO coverage on defect and terrace sites were obtained for the first time for the {111}Pt nanoparticles, and the results are in good agreement with those obtained on Pt(554). Chronoamperometry studies show tailing in all current-time transients of CO oxidation on all surfaces studied. The kinetics of CO oxidation can be satisfactorily simulated by a modified LangmuirHinshelwood model, demonstrating that CO oxidation on all studied surfaces follows the same mechanism.

On the behavior of CO oxidation on shape-controlled Pt nanoparticles in alkaline medium

“…Taking into account the remarkable structure sensitivity of CO electro-oxidation reaction on Pt electrodes, it would be expected a similar trend with shape-controlled Pt nanoparticles for which their surface structure and particularly their preferential (100) or (111) terrace contributions are similar to the single crystal surfaces [23]. In acidic medium, CO oxidation reaction on these shape-controlled Pt nanoparticles showed a clear CO oxidation peak multiplicity that was attributed to CO oxidation from ordered (100) and (111) domains as well as from disordered surface domains [23][24][25][26].…”

“…In acidic medium, CO oxidation reaction on these shape-controlled Pt nanoparticles showed a clear CO oxidation peak multiplicity that was attributed to CO oxidation from ordered (100) and (111) domains as well as from disordered surface domains [23][24][25][26]. As found on Pt single crystal electrodes, the sharp CO oxidation peak at high potentials was assigned to the CO oxidation on two-dimensional (100) terraces because this contribution well correlates with the amount and quality of the (100) domains present at the surface of the nanoparticles.…”

“…The supporting electrolytes, 0.5 M H2SO4 (Merck KGaA 96%) and 0.1 M NaOH (Merck KGaA, 99.99 %) were prepared in ultrapure water (Millipore Milli-Q 18.2 MΩ cm). In H2SO4 solution, the active surface area of the different Pt nanoparticles was determined by the charge involved in the socalled hydrogen UPD (Under Potential Deposition) region until 0.63 V assuming 230 µC cm -2 for the total charge after the subtraction of the double layer charging contribution as previously discussed [23]. In alkaline solution, the total charge measured between 0.06 and 0.90 V (without any double layer correction) was normalized to 390 µC cm -2 as recently proposed by VidalIglesias et al [29].…”

Synthesis and Electrocatalytic Properties of H2SO4‐Induced (100) Pt Nanoparticles Prepared in Water‐in‐Oil Microemulsion

“…The active surface area of the Pt NPs was determined by the charge involved in the so-called hydrogen UPD region (between 0.06 V and 0.6 V) after the subtraction of the double layer charging contribution and assuming the calibration ratio (UPD charge)/(Pt surface area) as 0.23 mC cm -2 . [38] 0. …”

Pt catalysts modified with Bi: Enhancement of the catalytic activity for alcohol oxidation in alkaline media

“…In acidic conditions, the presence of Bi in the catalyst caused a negative shift (higher potentials) on the potential onset for the reaction. This effects was explained by the change on the electronic properties of the surface with consequent stabilization of the adsorbed CO molecule [26,37] through the increase the electronic back donation phenomena (Bi donates electrons to Pt, causing an increase in the extent of dπPt⇓2π * CO [38]). However, in the present case, in addition to the current increase there is a positive effect on the onset potential and the oxidation reaction starts more than 0.1 V earlier suggesting some other effect in addition to the third body (that is responsible for the increase of the oxidation currents and hysteresis).…”