Oxygen and Hydrogen Peroxide Reduction on Polycrystalline Platinum in Acid Electrolytes: Effects of Bromide Adsorption

Abstract

Changes in the electrocatalytic activity of Pt for the oxygen and hydrogen peroxide reduction reactions (ORR and HPRR, respectively) in an aqueous acidic electrolyte induced by the adsorption of bromide, as a model impurity, have been investigated using chronoamperometric techniques under forced convection. Experiments were carried out using a polycrystalline Pt|Pt rotating ring-disk electrode in O 2 -saturated 0.1 M HClO 4 containing 10 μM KBr (800 ppb). Potential steps were applied to the Pt disk from E o , at which Br − is fully desorbed, to more positive values, E step , at which Br − undergoes adsorption. During this period, the currents both at the disk, i disk , and at the ring, i ring , were monitored, with the ring polarized at a potential at which H 2 O 2 (aq) oxidation proceeds under diffusion-limited conditions. The results obtained, assuming the ORR does not interfere with Br − adsorption, made it possible to correlate i disk and i ring with the coverage of adsorbed Br − , θ Br − , and E step . As evidenced from the data collected, significant drops in the diffusion-limited currents for O 2 reduction induced by the presence of 10 μM KBr could only be observed for θ Br − > 0.25 regardless of E step . Similar measurements involving the same Pt(poly) rotating disk electrode performed in 1 mM H 2 O 2 in deaerated 0.1 M HClO 4 devoid of O 2 displayed a similar trend. This behavior was found to be consistent with a simple blockage of surface-active sites by adsorbed bromide, as predicted by the attenuation model proposed by Levart. shielded i ring using the method reported originally by Markovic et al. 1,7,16 This information made it possible to correlate the disk current, i disk and i ring , associated, respectively, with the ORR and the oxidation of H 2 O 2 (aq) under diffusion-limited conditions, with θ Br − in O 2 -saturated solutions. Also to be

Temporally-Resolved Ultrafast Hydrogen Adsorption and Evolution on Single Platinum Nanoparticles

“…As Scherson and Tolmachev have described, the surface of a nanometer-scale electrode or particle can be quickly contaminated when exposed to even trace amounts of organic impurities. 45 Jerkiewicz et al has also reported that trace halides may foul Pt surfaces 46 and mitigate HER kinetic rates. 47 Figure 1B shows an example of a i−t trace recorded at −400 mV on a 5 μm CFE in 25 mM HClO 4 using the microjet system.…”

Derivative-Extremum Analysis Principle for Irreversible Electrode Reactions: Feature Parameter Extractions from Polarization Curves

“…22 In this case, the derivative-extremum analysis can be applied to the subprocess, and so, efforts should be made to calculate or measure the polarization curve of the subprocess. Second, for the reactions interfered by side processes, such as the electromigration in the electrolyte of low ionic strength, 33,34 and the specific adsorptions of ions, 35,36 the extracted E 1/2 and PV may deviate from the derived equations. In this case, the E 1/2 and PV can serve to qualitatively investigate the interference effect on the potential and activation features, whereas quantitative estimations of the parameters are not applicable.…”

Electrochemical Oxidative Rearrangement of Tetrahydro-β-carbolines in Zero-gap Flow Cell

“…Away from the double layer enters the diffusion layer, where we desire the rapid transport of the halide towards the electrode for an adequate local concentration of RHS necessary for the rearrangement, while avoiding concentration polarization that may result in side reactions. 32,33 At last, the electrons from the anode must be consumed at the cathode through a sustainable reaction, preferably water splitting without decomposing the reactant or the product from the anode. In our work, we address the challenge with LiBr as the mediator in a zero-gap, high-rate divided flow cell.…”

“…A change of the anode from the carbon paper to Pt mesh (entry 5) diminished the yield and FE drastically, due to side reactions catalyzed by Pt such as the C1 oxidation/ring-opening and/or OER. 39 We also examined other halides (Cland I -) (entries 7,8), but they were not effective mediators. We suspected that the oxidation potential of the chloride ion might be higher than the nonselective indole oxidation.…”