Recovery of Active Surface Sites of Shape-Controlled Platinum Nanoparticles Contaminated with Halide Ions and Its Effect on Surface-Structure

Abstract

The interaction of halide ions (I − , Br − , Cl − ) with well-cleaned faceted platinum (nanocube, cuboctahedral) nanoparticles and platinum polycrystalline is investigated in 0.5 M H 2 SO 4 electrolyte. Under electrochemical conditions, the Pt surface gets poisoned with halide ad-atoms and it causes the attenuation of both hydrogen adsorption/desorption in the lower potential region (0.06-0.4 V) and electroxidation of Pt nanoparticles in the higher potential region (0.6-1.2 V). Above certain concentration (5 × 10 −6 M), the strongly adsorbing I − ions mask the H upd features. On the other hand, Br − and Cl − ions alter the peak features in the H upd region, those are characteristic of different Pt surface sites. On excursion to higher potentials (∼>1.2 V), concurrent halogen evolution, Pt oxidation, and oxygen evolution are observed; the increase in peak intensity in the H upd region reflects the reconstruction of the Pt surface. To remove the adsorbed halide ions from the Pt surface, an in-situ potentiostatic method is employed, which involves holding the working electrode at ∼0.03 V in 0.1 M NaOH solution. The cleanliness and retention of surface-structure are confirmed from the voltammograms recorded in the test electrolyte and the recovery of oxygen reduction reaction (ORR) activity after cleaning the Br − ion-contaminated Pt surface supports this conjecture. Anions specifically adsorbed on precious metal surfaces adversely impact several electrochemical reactions including oxidation/ reduction, metal deposition, corrosion and dissolution.1-6 Catalyst poisoning by the adsorbed anions (halides, sulfates and others) is a well-known phenomenon and it decreases the activity of electrocatalysts; for example, in fuel-cell, batteries and electrolyzers. 7,8 Especially platinum, a material for catalyzing a variety of electrochemical reactions, is prone to get poisoned in the presence of adatoms/adsorbates/solution anions under electrochemical conditions. Thus, oxygen reduction reaction (ORR) in fuel cells is affected by the adsorbed species or impurities and it is highly dependent on the cleanliness and surface structure of the catalyst. [9][10][11][12][13] In hydrogen-bromine fuel cells, bromides and bromine species migrate across the membrane and poison the hydrogen-electrode catalyst; moreover, Pt dissolves in Br − ion-containing solutions. 22-35 Most of the available surface sensitive techniques were used to elucidate adsorbate coverage and structure. Such techniques, including auger electron spectroscopy (AES), low energy electron diffraction (LEED), second harmonic generation (SHG), surface X-ray scattering (SXS), electrochemical scanning tunneling microscope (ESTM) 31,34 and electrochemical quartz crystal microbalance (EQCM), used to investigate anion adsorption have offered significant insight on the dependence of adsorption process on exposed single crystal orientations. Thus, AES/LEED studies revealed that Cl − ion adsorption occurs on Pt(100) surface at lower potential than that with Pt(111) surfaces, indi...

Charge Transfer Improvement after Solvent-Induced Phase Change in Type-I Cs4PbBr6@CsPbBr3 Core–Shell Perovskites

“…The suppression of this peak after the addition and stirring of PbBr 2 salt on the electrochemical cell (Figure S9) was also observed, supporting the defect attribution, since this salt could act to passivate the deep defects of the PNCs surface. The later reduction peak (0.55 V) is assigned to the probable adsorption of CsBr onto the platinum electrode surface after the plausible phase change reaction, as seen in other similar works: − …”

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

“…In the process of translating the understanding of fundamental studies carried out at single crystal surfaces to the nanoparticle surfaces, the effect of halide ions (I − , Br − , Cl − ) on H ads/des and reconstruction of shape-controlled Pt nanoparticles (Pt-NCs and Pt-COs) and Pt-PCs were investigated in 0.5 M H 2 SO 4 electrolyte (Devivaraprasad et al, 2017). Characteristic facet-dependent I − , Br − , Cl − adsorption/desorption features were observed and the adsorption strength of halides was in the order of I − > Br − > Cl − ; thus, the H upd area of Pt decreased significantly with the addition of I − ions to 0.5 M H 2 SO 4 electrolyte.…”

“…As discussed in section Stability of Metal Nanoparticles Under Electrochemical Conditions on the effect of potential cycling in pure electrolytes, it is observed that the shape-controlled Pt nanoparticles undergo reconstruction in the presence of halide ions as well. Thus, potential cycling in the range of 0.06–1.4 or 1.6 V causes the conversion of ordered terraces to disordered sites, resulting in eventual Pt-PC voltammetric features (Devivaraprasad et al, 2017).…”

“…ORR polarization curves with Pt-CO in oxygen-saturated 0.5 M H 2 SO 4 in relation to that intentionally contaminated with 10 −3 M Br − ions. Reproduced with permission (Devivaraprasad et al, 2017). Copyright 2017, Journal of the Electrochemical Society (ECS).…”

Controllable Surfactant‐free Synthesis of Colloidal Platinum Nanocuboids Enabled by Bromide Ions and Carbon Monoxide

“…Besides, the addition of foreign metal ions is also effective. [9][10] However, either organic capping agents or metal ions may remain on the particle surface or in the bulk structure which would have significant impacts on catalytic performance. Therefore, developing a surfactant-free strategy is required for synthesizing surface-clean Pt cuboids.…”