Polycrystalline Platinum Electrodes

Poly crystalline silver layer electrodeposited on a polycrystalline platinum electrode. 

Santos MC, Machado SAS (2004) Microgravimetric, rotating ring-disc and voltammetric studies of the underpotential deposition of selenium on polycrystalline platinum electrodes. J Electroanal Chem 567 203-210... 

More than a decade ago, Hamond and Winograd used XPS for the study of UPD Ag and Cu on polycrystalline platinum electrodes [11,12]. This study revealed a clear correlation between the amount of UPD metal on the electrode surface after emersion and in the electrolyte under controlled potential before emersion. Thereby, it was demonstrated that ex situ measurements on electrode surfaces provide relevant information about the electrochemical interface, (see Section 2.7). In view of the importance of UPD for electrocatalysis and metal deposition [132,133], knowledge of the oxidation state of the adatom in terms of chemical shifts, of the influence of the adatom on local work functions and knowledge of the distribution of electronic states in the valence band is highly desirable. The results of XPS and UPS studies on UPD metal layers will be discussed in the following chapter. Finally the poisoning effect of UPD on the H2 evolution reaction will be briefly mentioned. 

Methanol Oxidation at a Smooth Polished Polycrystalline Platinum Electrode d 3.3—The Electrochemical Reduction of CO[sub(2)]... 

Methanol oxidation at a smooth polished polycrystalline platinum electrode... 

Figure 2. Diagram of electrode in adsorption position and "squeezed" position for adsorbate measurement (1) smooth, polycrystalline platinum electrode (2) polished glass scintillator detector (3) Macor ceramic disk, which forms cell bottom ( )) resin (5) electrode shaft.

Figure 5. The corrected current (a) and the second harmonic signal (b) obtained during cathodic sweep (10 mV s 1 scan rate) from a polycrystalline platinum electrode in a 0.35M HCIO4 aqueous solution.

The polycrystalline platinum electrode was mounted in Kel>F resin and polished with a scries of alumina powders down to 0.05, resulting mirror finish. The apparent surface area was 1.85 cm. The electrode was washed with fuming sulfuric add and rinsed with ultra pure water prior to each measurement. 

Fig. 3-30 In situ infrared spectra of polycrystalline platinum electrode in 3 M H2S04 wi 0.1 M CH3OH. Reference state 100mV.

It was found that changes in the voltam-metric response of polycrystalline platinum electrodes in the direction expected for preferred oriented surface electrodes can be achieved using a fast repetitive potential perturbation. 

Table 6.13 shows the calculated values of entropy of adsorption for different models of the adsorption reaction of bisulfate on polycrystalline platinum electrodes, as well as its comparison with the experimental value. The conditions that best describe the experiments are those shown on line 4. This means that in solution the bisulfate... 

D KIEs proved439 that in the oxidation of formaldehyde on a polycrystalline platinum electrode modified with Pb atoms and on pure platinum electrode, the cleavage of both OH and CH bonds and the abstraction of the hydrogen atom from an OH bond in hydrated formaldehyde are rate-determining on the Pt/Pb and on the Pt electrode, respectively. The ku/ku for the oxidation of formaldehyde at copper electrode (at pH 13, at 25 °C) depends on the electrode potential and reaches the highest value of 7 at low potentials and drops to about 2.5 at higher positive potentials440. 

Fig. 18.4. SNIFTIRS spectrum observed between 0.05 V and 0.45 V on a polycrystalline platinum electrode in 0.01 M MeOH/0.5 M H2S04. [From K. Kunimatsu Ber. Buns. Phys.

The hydrogen reaction on a platinum electrode is among the most widely studied electrochemical reactions [46]. Early kinetic studies of the HE/OR were carried out either on a polycrystalline platinum electrode [47] or on platinum single crystals that had poorly defined surface structures [48]. The first measurements of the kinetics of the HER on well-ordered, platinum single-crystal electrodes [49] reported that even... 

Early studies at platinum electrodes have shown that the formation of adsorbed CO2 requires the presence of adsorbed hydrogen, thus, a reduction takes place leading to the surface species denoted as reduced CO2. According to recent in situ spectroscopic studies, both linearly bonded and multibonded CO molecules are the main adsorbates formed as a result of CO2 reduction at polycrystalline platinum electrodes. 

Most of the earlier studies were carried out on polycrystalline platinum electrodes in aqueous solutions. During the last decade extensive studies have been undertaken with platinum single-crystal surfaces in order to establish the influence of the surface structure on the reaction of the oxidation of methanol. 

It follows from in situ FTIR and DBMS investigations of species adsorbed on a polycrystalline platinum electrodes " in acid medium that a great variety of strongly adsorbed residues of the original molecules could be anchored to the surface of the electrode. These residues are sensitive to oxidative and/or reductive attacks. 

Fig. 5.19. Electroreflectance spectra of a polycrystalline platinum electrode in contact with a solution of 0.5 M Na2S04 -h 5 x 10 M / -nitroaniline, Fmse = 440 mV, AE = 100 mV, (based on data in [101])...

Any species showing infrared active vibrational modes adsorbed on a reflecting surface can be studied with infrared spectroscopy. The beam of light will interact absorptively with the species when passing through the adsorbate layer before and after the point of reflection. This enables studies of all kinds of adsorbates on many surfaces. Of particular interest in electrochemistry are surfaces of metals and semiconductors employed as electrodes. Thus the following text deals only with reflection at these surfaces other surface and interfaces are not treated. Attempts to record infrared spectra of emersed electrodes (i.e. ex situ measurements) have been reported infrequently in studies of adsorption of hydroquinone and benzoquinone on a polycrystalline platinum electrode [174-177]. Further development of this approach has... 

Further reported examples include electrocatalytic processes and their intermediates [313, 314]. Formate could be identified as an active intermediate of methanol electrooxidation at a polycrystalline platinum electrode [315]. Water molecules coadsorbed during methanol adsorption on platinum were identified as those species that react subsequently with COad that was formed as a result of methanol chemisorption [316]. The high sensitivity of SEIRAS allows mapping of two-dimensional spectra (for selected examples, see [285]). Finally, two-dimensional correlation analysis of electrochemical reactions becomes possible [317]. 

Fig. 5.77. SR spectra of an electrochemically roughened polycrystalline platinum electrode in contact with an aqueous solution of 0.5 M sulfuric acid and 0.244 mM Sn(S04)2, Frhe = 1.191 V, nitrogen saturated, Aq = 488 nm, P = 40 mW, resolution =10 cm (based on data in [472])...

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