Bisulfate anion adsorption

The supporting electrolyte type and concentration of formic acid impact the observed overpotentials. The two most commonly used supporting electrolytes are either H2SO4 or HCIO4. Specific bisulfate anion adsorption onto Pt surface sites from H2SO4 adversely increases the onset potential of formic acid electrooxidation. The top of Fig. 3.8 shows an unfavorable increase in the onset potential for OHads in the anodic cycle by 0.1 V on a Pt ( 2.3 nm)/C catalyst in the presence of 0.1 M H2SO4 versus 0.1 M HCIO4 [65]. In the presence of 0.5 M formic acid, the initial response in the forward anodic sweep at potentials below 0.4 V versus SCE is... 

Atomic layer epitaxy, 117 Atomic level studies of CdTe(lOO), electrochemical digital etching, 115-123 Auger electron spectrometers, 106 Auger electron spectroscopy bisulfate anion adsorption on Au(l 11), Pt(l 11), and Rh(l 11) surfaces, 126-138 to monitor composition of acidified water surfaces, 106-114 underpotential deposition of lead on Cu(lOO) and Cu(lll), 142-154 use for bisulfate anion adsorption, 127... 

Many authors have been discussing the surface structure dependence of Pt toward the ORR under different conditions. Markovic et al (1995) found that the activity for ORR in 0.1 M HCIO4 decreases in the sequence of the Pt low-index planes (110) > (111) > (100), whereas the reactivity in H2 SO4 increased in the sequence (111) < (100) <(110). These differences in the sequence are ascribed to the strong bisulfate anion adsorption on the highly coordinated surfaces. Therefore, it is important to consider the strength of the anion adsorption and its surface-structure-dependent adsorption properties to understand the oxygen reduction reaction (Rabis et al, 2012). 

Figure 9.5 Anion adsorption on Pt in several electiolytes bisulfates and TFMSA as determined by radiotracers (RT), and OH and H as reflected in A/r, the ampUtiide of the XANES peak. The effect of 6 M TFMSA suppressing OH formation can be seen. (Reproduced with permission from Teliska et al. [2007].)...

The specific adsorption of bisulfate anions is observed in H2SO4 in both EXAFS and XANES data and, in agreement with voltammetry, is seen to impede oxygen adsorption. Significant specific anion adsorption was found in 6 M TFMSA, but not in 1 M TFMSA [Teliska et al., 2007]. As mentioned above, this specific anion adsorption suppresses OH adsorption (particularly the formation of subsurface O), causes the Pt nanoparticle to become more round, and weakens the Pt-Pt bonding at the smface. The specific anion adsorption becomes site-specific only after lateral interactions from other chemisorbed species such as OH force the anions to adsorb into specific sites. 

In this contribution, we present new results of a cychc voltanunetiy study of the influence of (CeHglads on Hypo and on anion adsorption at the Pt(l 11) electrode in aqueous HCIO4 and H2SO4, and relate them to analogous studies at Pt(110) and Pt(lOO) electrodes in aqueous H2SO4. Perchlorate anions are known to be less strongly adsorbed on Pt than bisulfate or sulfate anions thus, the cychc voltanunetiy behavior in the two electrolytes is expected to reveal important differences. 

Wifckowski and coworkers [37] have reported adsorption of bisulfate anions on Au(lll), Pt(lll), and Rh(lll) electrodes in sulfuric acid solution using electrochemical and several nonelectrochemical techniques. It was concluded from the low-energy electron-diffraction data that the structure of bisulfate on gold is different from that on Pt(lll) and Rh(lll). Adsorption of bisulfate on Au(lll) is associated with a charge transfer from the electrode to the adsorbate. However, the formation of this particular bond does... 

The adsorption of anions on solid surfaces is of considerable interest, mainly because of its effect on the kinetics of electrochemical reactions. Several in-situ techniques have been applied toward this purpose. Infrared measurements were used to identify adsorbed species, estimate anion adsorption isotherms, and to gain information on anion interaction with electrode surfaces. " Sulfuric acid anions are possibly the conunonest anion adsorbates because of their specific adsorption on metal surfaces. Depending on the metal, its surface orientation, and the concentration of anion, either sulfate or bisulfate can be specifically adsorbed on the surface. Identifying the predominant adsorbate on platinum-group metals has engendered some controversy. While STM studies show that... 

Figure 6b also reveals that the positive lobe of the bipolar band around 1280 cm decreases at potentials above 0.45 V this decline coincides with the onset of the surface oxidation in the voltammetry of Ru(OOOl) (c.f., Fig. 2). Adsorption of the OH species is followed by the desorption of bisulfate and a concurrent increase in the bisulfate species in the double layer. This effect becomes visible in the IR spectrum by the appearance of the positive-going solution-phase bands for the bisulfate anion at 1051 and 1200 cm at potentials equal to, or higher than 0.55 V. The most pronounced feature in the IR spectra above 0.55 V is the negative lobe of the bipolar band centered at 1248 cm , which represents adsorbed bisulfate at the reference potential.

The potential dependence of the surface relaxation and the stabihty of the Pd film was probed by XRV measurements [32]. Desorption of Hupd caused a slight Pt-Pd contraction, but the surface became expanded again ( 2.5%) after the adsorption of bisulfate anions. At positive potentials, i.e. in the potential region of OH adsorption, there was a significant (but reversible) change in the Pd structure associated with oxide formation. Importantly, if the Pt(lll) monometallic surface had been cycled up to this potential, then a Pt oxide would be formed that would lead to irreversible roughening (which is the precursor to Pt dissolution) of the surface upon reduction. 

Finally, combined Ap XANES and EXAFS studies have recently been reported on other more complex electrocatalysts, including RuS," "" RhSe, Au/SnOx, Pt/NbOx, " and Pt/TPPTP/C (TPPTP = triphenyl phosphine triphosphate) " catalysts. The Ap XANES has also been used to study the effects of anion adsorption on Pt including bisulfate " and Cl,"" differentiate the various oxidation states of S dming the electrochemical oxidation of S on Pt ", and identify acetaldehyde-like intermediates during ethanol oxidation on Pt. In all of these studies, unprecedented new details on the coverage and binding sites of adsorbates in situ have been revealed. Further, similar XAS studies in gas phase cat-... 

We report on adsorption of bisulfate anion on the Au(lll), Pt(lll), and Rh(lll) electrodes in sulfuric acid media using electrochemistry. 

Our AES, LEED and CEELS data indicate that bisulfate anion is undergoing specific adsorption on these three (111) surfaces, but the coverage and the adsorption potential vary considerably among these substrates. For Au(l 11), the maximum is only 1/5 ML, both from the quantitative AES, chronocoulometric and radiochemical studies. For Pt(l 11) and Rh(l 11), the coverage is close to 1/3 ML. The latter coverage is typical of the Me(lll)(V3 X V3) R30° surface structure which we confirmed by electron diffraction. On gold, the (V3 x V3)-type structure is poorly developed and we... 

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