Platinum Electrode In Acid Medium Research Articles

Impact of Electrolyte Composition on Bulk Electrolysis of Furfural over Platinum Electrodes**

AbstractPartial oxidation of furanic biomass derivatives such as furfural is of interest for the sustainable production of chemicals including furoic acid, maleic acid, and 2,5‐furandicarboxylic acid (FDCA). The oxidative bulk electrolysis of furfural is here investigated on platinum electrodes in acidic media. The effects of potential, concentration, pH, and supporting anion are studied, and selectivity trends are coupled with attenuated total reflectance surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS) to illuminate adsorbate structures that influence the catalysis. Increasing potential is found to shift selectivity from primarily C5 products to C4 products, coincident with oxidation of the Pt surface. Selectivity changes are also observed moving from pH 1 to pH 4, with an increase in C5 products at higher pH. Changing from the weakly adsorbing perchlorate anion to the specifically‐adsorbing phosphate anion results in a number of changes that manifest differently depending on potential and pH. Selectivity to furoic acid is found to be highest above the pKa of phosphoric acid due to the strongly adsorbed phosphate ions suppressing flat‐lying configurations of furfural that lead to C−C cleavage. These results point toward opportunities to use electrolyte engineering to tune selectivity and optimize surface conditions to disfavor binding of inhibitory products.

Comparative Evaluation of Dimethylsulfoxide and Dimethylsulfone Adsorption on a Smooth Platinum Electrode in Acidic Environment

a comparative assessment of dimethylsulfoxide and dimethylsulfone adsorption on a smooth platinum electrode in acidic medium in the region of anode potentials is presented. The adsorption isotherms in the “hydrogen” potential range, depending on the dimethylsulfoxide and dimethylsulfone concentration, are S-shaped. At the adsorbate concentrations in the solution exceeding 0.1 M, the surface coverage with dimethylsulfoxide and dimethylsulfone is nearly the same and changes but slightly. A significant difference in the adsorption characteristics of dimethylsulfoxide and dimethylsulfone in the potential region of oxygen adsorption is found. According to the Pt-electrode surface coverage with oxygen in the presence of the test substances, it was concluded that the value of the dimethylsulfoxide and dimethylsulfone adsorption is maximal only when their bulk concentration is higher than 0.1 M, here the oxygen surface coverage in the presence of dimethylsulfone exceeds that in the background solution.

Comparative study of γ-hidroxybutiric acid (GHB) and other derivative compounds by spectroelectrochemistry raman (SERS) on platinum surface

The electrochemical behaviour of gamma-hydroxybutyric acid (GHB), the cyclic lactone derivative (GBL), 1-butanol, butyric acid and succinic acid on a platinum electrode in acidic medium has been studied by means of Raman spectro-electrochemistry using the SERS effect. Only GHB and 1-butanol were found to be electroactive substances that can form the acid product mainly and other species in minor proportion through the electro-catalytic oxidation reaction of alcohol group. The interaction of all these molecules with the platinum and platinum oxides, generated during the electrodic process has been investigated in a wide interval of potentials. Succinic acid was found to play the role of both intermediate (to produce the conjugate derivative) and product in GHB electrocatalytic oxidation. Likewise, the electro-oxidation of 1-butanol produced butyric acid predominantly. The carbon (CH2) and the ring skeletons presented a predominant interaction with the platinum oxide surface for 1-butanol and GBL, respectively.

Study of the electro-oxidation of a recreational drug GHB (gamma hydroxybutyric acid) on a platinum catalyst-type electrode through chronoamperometry and spectro-electrochemistry

The electro-oxidation of gamma-hydroxybutyric acid (GHB) on a polycrystalline platinum electrode in acidic medium has been studied using chronoamperometry and spectroelectrochemistry. The study has been performed in a wide interval of potentials and at different concentrations.It was found that at longer times the density currents reached stationary values over 0.3V whereas it is zero to potentials below the above mentioned. These characteristics in the j–t curves suggest a different mechanism for the electro-oxidation of GHB, potential dependent, with a catalytic process and an adsorption process controlled by mass transport in the respective potential regions indicated.The change in the stationary current obtained at +0.9V with variable GHB concentrations also suggests an oxidation mechanism catalysed by the platinum surface with platinum hydroxides acting as reaction intermediates to make the final oxidation product for GHB. The results obtained using chronoamperometry are in good agreement with those obtained using cyclic voltammetry where the alcohol group is oxidized at different potentials.In situ surface enhanced Raman scattering (SERS) spectra corresponding to GHB intermediates and water adsorbed species being formed/consumed at the potential-dependent adsorption processes have been analysed using spectro-electrochemistry. A peak at 1590cm−1, corresponding to the asymmetric stretching of carboxylic group in a bridge configuration, increases with the potential. This supports the hypothesis of a mechanism of formation of the succinic acid on the platinum surface as reaction product under the experimental conditions studied.

Electrochemical derivatization‐capillary electrophoresis‐contactless conductivity detection: A versatile strategy for simultaneous determination of cationic, anionic, and neutral analytes

The simultaneous determination of cationic, anionic, and neutral analytes in a real sample was demonstrated by coupling electrochemical (EC) derivatization with counter-EOF CE-C(4) D. An EC flow cell was used to oxidize alcohols from an antiseptic mouthwash sample into carboxylic acids at a platinum electrode in acid medium. The carboxylates formed in the derivatization process and other sample ingredients, such as benzoate, saccharinate, and sodium ions, were separated in counter-flow mode and detected in one run in Tris-HCl buffer, pH 8.6. Fewer than 5 min were needed to complete each analysis with the automated flow system comprising solenoid pumps for the management of solutions. Insights into the electrochemistry of benzoic acid, present in the sample matrix, were also gained by EC-CE-C(4) D; more specifically, by applying potentials higher than 1.47 V to the platinum electrode, some formiate and minute amounts of salicylate were detected.

Spectroscopic elucidation of reaction pathways of acetaldehyde on platinum and palladium in acidic media

The electrochemical behavior of acetaldehyde on palladium and platinum electrodes in acidic media was comparatively studied by means of differential electrochemical mass spectrometry (DEMS) and in situ Fourier transform infrared spectroscopy (FTIRS) combined with cyclic voltammetry. It was observed that acetaldehyde decomposition depends on the catalyst material, applied potential, and reactant concentration. Additionally, it was detected that acetaldehyde adsorbs and dissociates at potentials lower than 0.60 V vs RHE, producing methane and adsorbed CO on Pd; while C2-species, CHx and COad are formed on Pt. Besides carbon dioxide, acetic acid and adsorbed acetate were observed at E > 0.6 V, and their contribution increased with acetaldehyde concentration. Differences between Pt and Pd in potential dependence of the products and intermediates were established. Calibration of the mass spectrometer, together with the use of labeled acetaldehyde and IR spectra, allows establishment of the nature of adsorbed species and products for both Pt and Pd at different potentials, elucidating global reaction pathways for acetaldehyde on these two noble metals.

Electrochemical behaviour of gamma hydroxybutyric acid at a platinum electrode in acidic medium

The electrooxidation of gamma hydroxybutyric acid (GHB) on a polycrystalline platinum electrode is studied by cyclic voltammetry in acidic medium. Two oxidation peaks, A and B, are obtained in the positive scan within the potential range of the double layer region and of the platinum oxide region, respectively. In the negative going potential sweep an inverted oxidation peak with an onset partially overlapping with the tail of the cathodic peak for the reduction of the platinum oxide formed during the anodic scan is obtained (peak C). This inverted peak can be observed at a potential close to +0.2V (vs Ag/AgCl at pH 2) and separated 0.4 and 0.8V from the two other oxidation peaks obtained during the anodic scan and in such conditions that the surface is particularly activated to favour this electrochemical process. The response obtained in the electronic current for the different peaks when GHB concentration and scan rate were changed to allows inferring that these are the result of a potential dependent mechanism. The behaviour observed is according with the oxidation of the alcohol group to the corresponding aldehyde and carboxylic acid (succinic acid) as main products.

Effect of Cs + ions on the electrochemical nanogravimetric response of platinum electrode in acid media

Platinum electrodes have been investigated in sulfuric acid solutions in the presence and absence of Cs + ions by electrochemical quartz crystal nanobalance (EQCN). An unusual potential dependence of the quartz crystal frequency response has been observed in the presence of Cs + ions. The frequency decrease is more pronounced in the region of the underpotential deposition of hydrogen, and the frequency decrease in the double layer region diminishes as the concentration ratio of Cs + and H + ions increases. After immersion in Cs 2SO 4 solutions the frequency change was higher than that expected taking into account the density and viscosity. The effects observed can be explained by the specific adsorption of Cs + ions on the Pt surface, which competes with the hydrogen adsorption. At more positive potentials than the potential of zero charge (pzc) a desorption of the Cs + ions starts. In this potential region both Cs + and HSO 4 − ions are adsorbed at the platinum surface. In the double layer region the mass change caused by the desorption of Cs + ions and the starting adsorption of sulfate ions compensates each other.

Electrocopolymerization of a Binary Mixture of 2-chloroaniline and 2-amino-4-(4-methoxyphenyl) thiazole

Electropolymerization of a binary mixture of 2-chloroaniline and 2-amino-4-(4-methoxyphenyl) thiazole on platinum electrode in acid medium was carried out under varying reaction conditions as temperature, current density, hydrochloric acid, and monomer concentrations with duration time. The initial rate of the electrocopolymerization reaction was small and the rate law was RP = K2[D]0.92[HCl]0.98[M]1.93. The apparent activation energy (Ea) was found to be 57.34 kJ mol−1. The obtained copolymer films were characterized by 1HNMR, elemental analysis, GPC, IR, UV-visible, and cyclic voltammetry compared with those of the two homopolymers. The mechanism of the electrocopolymerization reaction had been also discussed. The monomer reactivity ratio (r1 and r2) was calculated. The thermogravimetric analysis (TGA) was used to confirm the proposed structure and determination of the number of water molecules in the copolymeric chain unit. X-ray and scanning electron microscopic analysis were used to investigate the surface morphology.

Electropolymerization of 2-Methoxyaniline: Kinetic Studies, Mechanism, Characterization of the Polymer and Applications as Corrosion Protection for Mild Steel in Acid Medium

Electropolymerization of 2-methoxyaniline on platinum electrode in acid medium was carried out under different reaction conditions as temperature, current density, hydrochloric acid, and monomer concentrations with reaction duration time. The initial rate of the electropolymerization reaction is small and the orders are found to be 1.18, 1.25, and 0.88 with respect to current density, HCl, and monomer concentrations, respectively. The apparent activation energy (Ea) is found to be 56.87 kJ/mol. The obtained polymer films are characterized by 1H-NMR, elemental analysis, and IR spectroscopic studies. The mechanism of the electropolymerization reaction has also been discussed. The thermogravimetric analysis (TGA) was used to confirm the proposed structure and determination of the number of water molecules associated with each polymeric chain unit. X-ray and scanning electron microscopic analysis were used to investigate the surface morphology. The corrosion behavior of uncoated and coated mild steel electrode with poly (2-Methoxyaniline) in 1 M HCl at 25°C was investigated potentiodynamically. The various electrochemical parameters (Icorr, Ecorr, and P%) were calculated from Tafel plots for uncoated and coated electrodes. The influence of some coating conditions as duration time, current density of the electropolymerization, and monomer concentrations were investigated. The data reveal that the presence of coated polymer films on the electrode surface increase the cathodic and anodic polarization compared to the uncoated sample.

Understanding CO-stripping mechanism from Ni UPD/Pt(1 1 0) in view of the measured nickel formal partial charge number upon underpotential deposition on platinum surfaces in sulphate media

We recently showed nickel-underpotential deposition (Ni-UPD) occurs on polycrystalline or single crystal platinum electrodes in acidic media. Whereas the decoupling of the nickel and hydrogen adsorption/desorption peaks is difficult for low pH, these processes can be better separated for higher pH values, typically pH > 3. However, even for platinum single crystals, high pH solutions do not enable to sufficiently separate nickel from hydrogen phenomena. As a result, electrochemistry alone cannot yield important information about Ni-UPD, such as the formal partial charge number (valency of electrosorption) and the role of the sulphate or hydrogen sulphate anions. So, we decided to couple cyclic voltammetry to electrochemical quartz crystal microbalance (EQCM). EQCM measurements enable to decorrelate the simultaneous hydrogen and nickel adsorption/desorption peaks, which we could not attempt solely with electrochemistry. The coupling between gravimetric and electrochemical measurements allows us to detect the contribution of the anions and thus to isolate that of nickel: nickel coverage can then be determined. Nearly 4/5 Ni UPD monolayer ( θ Ni ≈ 0.8) over platinum is reached at nickel equilibrium potential for high pH solutions (5.5). The QCM and electrochemistry coupling further allows the determination of nickel formal partial charge number: ι Ni,EQCM = 1.3 ± 0.13. Direct electrochemistry measurements (Swathirajan and Bruckenstein method) yield: ι Ni,Pt(poly) = 1.5 ± 0.17. These two values are close, which validates the electrochemical method for the nickel/platinum system. In consequence, we used Swathirajan and Bruckenstein method for Pt(1 1 0)-(1 × 2) crystal and found: ι Ni,Pt(1 1 0) ≈ 1.4 ± 0.1. Whatever the system (Ni UPD/Pt(poly) or Ni UPD/Pt(1 1 0)-(1 × 2)) or the experimental technique, nickel formal partial charge number is lower than nickel cation charge: ι Ni < z Ni = 2. In consequence, upon underpotential deposition on platinum surfaces, nickel cations discharge and then undergo additional charge exchange processes, such as anion (or water) adsorption, resulting in apparent partial nickel cation discharge. Moreover, Ni UPD/Pt(1 1 0) surface displays high activity towards CO ad oxidation reaction. We explain such positive effect by the possible existence of a bifunctional mechanism in which oxygenated-species-covered Ni UPD adatoms provide the oxygen atom to CO ad⋯Pt species, enabling its facile oxidation.

Electrocopolymerization of a binary mixture of pyrrole and 2‐amino‐4‐phenylthiazole: Kinetic studies, copolymer structure, and applications as corrosion protection for mild steel in acid medium

AbstractElectrochemical copolymerization of a binary mixture of pyrrole and 2‐amino‐4‐phenylthiazole on platinum electrode in acid medium was carried out. The kinetic parameters were calculated using ex situ microgravimetric and electrochemical data. The experimentally obtained kinetic equations were RP,W = kW [acid]1.16 [monomer]1.85 from microgravimetric data and RP,E = kE [acid]1.1 [monomer]1.9 from the values of the anodic current density using cyclic voltammetry technique. The apparent activation energy was calculated by the two techniques and is found to be 32.55 and 29.6 kJ/mol from microgravimetric and electrochemical data respectively. The monomer reactivity ratios (r1 and r2) were calculated according to Fineman–Ross method and the copolymer structure was determined from the obtained data, which is found to be a block copolymer structure. The applications of the prepared copolymer as corrosion protection of mild steel in acid medium are studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 4047–4058, 2007

Electrochemical Polymerization of 2,6-Dichloroaniline and Characterization of the Obtained Polymer

ABSTRACT Electropolymerization of 2,6-dichloroaniline on platinum electrode in acid medium was carried out under different reaction conditions as temperature, current density hydrochloric acid, and monomer concentrations with reaction during time. The initial rate of the electro-polymerization reaction is small and the orders are found to be 0.94, 1.13, and 1.26 with respect to current density, acid, and monomer concentrations, respectively. The apparent activation energy (Ea) is found to be 65.1 kJ mol−1. The rate law is Rp = K2[D]0.94[HCl]1.13[M]1.26. The obtained polymer films are characterized by 1H-NMR, elemental analysis, IR, and cyclic voltammetry. The mechanism of the electro-polymerization reaction has also been discussed. The thermogravimetric analysis is used to confirm the proposed structure and determination of the number of water molecules associated with each polymeric chain unit. X-ray and scanning electron microscopic analyses are used to investigate the surface morphology.

Electrochemical Polymerization of 3-Methoxyaniline and Characterization of the Obtained Polymer

ABSTRACT Electropolymerization of 3-methoxyaniline on platinum electrode in acid medium was carried out under different reaction conditions such as temperature, current density, hydrochloric acid, and monomer concentrations with duration time. The initial rate of the electropolymerization reaction is small and the orders are found to be 0.99, 0.98, and 0.97 with respect to current density, acid, and monomer concentrations, respectively. The apparent activation energy (Ea) is found to be 59.673 KJ mol−1. The rate law is RP = K2[D]0.99 [HCl]0.98 [M]0.97. The obtained polymer films were characterized by 1H-NMR, elemental analysis, IR, and cyclic voltammetry. The mechanism of the electropolymerization reaction has also been discussed. The thermogravimetric analysis (TGA) was used to confirm the proposed structure and determination of the number of water molecules in the polymeric chain unit. X-ray and scanning electron microscopic analysis were used to investigate the surface morphology.

Mechanism of di(methyl)ether (DME) electrooxidation at platinum electrodes in acid medium

The electrooxidation of DME was studied at a bulk platinum electrode. It was shown that the DME adsorption was a slow step in the overall oxidation reaction. The DME adsorption is potential dependent in the hydrogen region of platinum and independent in the double layer region. From low potential scan rate voltammetry and DME stripping experiments, it was shown that the DME oxidation mechanism occurred via several reaction paths. At low potentials, DME oxidation leads to the existence of a positive current plateau. “In situ” Infrared Reflectance Spectroscopy experiments were carried out to identify the intermediate and reaction products of DME adsorption and oxidation at different potentials. COL (linearly bonded CO), COB (bridge bonded CO), adsorbed COOH species and CO2 were detected. From these electrochemical and spectro-electrochemical results, it was proposed that some adsorbed DME was hydrolysed and directly oxidized to CO2 or HCOOH species and some partially blocked platinum sites at the surface forming Pt–CHO and/or Pt–CO. Then, as soon as platinum becomes able to activate water, a bifunctionnal mechanism occurs to form either HCOOH or CO2 again following two different reaction paths.

Electrochemical Polymerization of 2-Chloroaniline and Characterization of the Obtained Polymer Films

ABSTRACT Electrochemical polymerization of 2-chloroaniline on platinum electrode in acid medium was carried out under various reaction conditions, altering temperature, current density, hydrochloric acid, and monomer concentrations and time duration. The initial rate of the electropolymerization reaction is small and the orders are found to be 1.00, 1.06, and 0.96 with respect to current density, acid, and monomer concentrations, respectively. The apparent activation energy (Ea) is found to be 44.336 kJ mol−1. The rate law is RP = K 2[D]1.00[HCl]1.06[M]0.96. The obtained polymer films are characterized by 1H-NMR, elemental analysis, IR, and cyclic voltammetry. The mechanism of the electropolymerization reaction is also discussed. The thermogravimetric analysis (TGA) is used to confirm the proposed structure and determination of the number of water molecules in the polymeric chain unit. X-ray and scanning electron microscopic analysis are used to investigate the surface morphology.

Electrocopolymerization kinetics of a binary mixture of 3‐chloroaniline 2‐amino‐4‐phenylthiazole and characterization of the obtained block copolymer films

AbstractElectrocopolymerization of a binary mixture of 3‐chloroaniline and 2‐amino‐4‐phenylthiazole on platinum electrode in acid medium was carried out under different reaction conditions such as temperature, current density, hydrochloric acid, and monomer concentrations with duration time. The initial rate of the electrocopolymerization reaction on platinum electrode is small and the rate law is Rp = K2 [D]1.29[HCl]0.97[M]1.94. The apparent activation energy is found to be 38.87 kJ/mol. The obtained copolymer film is characterized by 1H‐NMR, elemental analysis, GPC IR, UV‐visible, and cyclic voltammetry and compared with those of the two homopolymers. The mechanism of the electrocopolymerization reaction is also discussed and the monomer reactivity ratio (r1and r2) is calculated. The thermogravimetric analysis (TGA) is used to confirm the proposed structure and determination of the number of water molecules in the polymeric chain unit. X‐ray and scanning electron microscopic analysis are used to investigate the surface morphology. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2076–2087, 2005

ELECTROPOLYMERIZATION OF 2-AMINO-4-PHENYLTHIAZOLE AND CHARACTERIZATION OF THE OBTAINED POLYMER FILMS

Electrochemical oxidative polymerization of 2-amino-4-phenylthiazole on platinum electrode in acid medium was carried out. Different reaction parameters were investigated such as current density, acid concentration, monomer concentration, and temperature with duration of time. The orders of the electropolymerization reaction were found to be 1.06, 1.10, 1.16 with respect to current density, acid concentration, and monomer concentration, respectively. The apparent activation energy (Ea) was found to be 61.04 kJ mol−1. The obtained polymer films were characterized by IR, UV, 1H-NMR, elemental analysis, thermogravimetric analysis, and cyclic voltammetry. The mechanism of the electrochemical polymerization reaction has been also discussed. Surface morphology of the obtained polymer film was characterized by X-ray diffraction and scanning electron microscopy.

Hydroxylamine Electrochemistry at Low-Index Single-Crystal Platinum Electrodes in Acidic Media

The electrochemistry of hydroxylamine at low-index single-crystal platinum electrodes in acidic media has been studied by voltammetry and in-situ FTIRRAS. Hydroxylamine (HAM) reactivity at platinum is largely controlled by interaction of the other components of the solution or products of the HAM partial oxidation with the electrode surface. Reduction of HAM is a structure-sensitive reaction, at least through the structure sensitivity of the hydrogen adsorption on platinum. No formation of gaseous products was detected in the potential region corresponding to the Hupd region on Pt(111) and Pt(110). Voltammetric and spectroscopic data point to adsorbed nitric oxide (NO) as the main stable intermediate of the HAM oxidation. Being electrochemically stable in a wide potential region between ca. 0.5 and 0.8 V, adsorbed NO acts as a poison for further oxidation of HAM. The HAM oxidation to NO appears to be a structure-insensitive process, though somewhat affected by the anion coadsorption. The Tafel slope analy...

Spectroelectrochemical study of the oxidation of aminophenols on platinum electrode in acid medium

The electrochemical oxidation of para-, meta- and ortho-aminophenols was carried out using a platinum electrode in aqueous acid medium. The spectroscopic results indicate that p-aminophenol suffers hydrolysis giving the formation of hydroquinone/ p-benzoquinone. CO 2 has been detected by in situ FTIR spectroscopy as the main soluble oxidation product. The m-aminophenol oxidation produces a blocking polymeric film on the platinum surface. The main oxidation products detected by in situ infrared spectroscopy were CO 2 and quinone. Cyclic voltammetry and in situ FTIR spectroscopy were combined to study the redox processes of the conducting polymer obtained in the o-aminophenol oxidation. The spectroscopic results indicate that phenoxazine units are produced during the oxidation/reduction of poly( o-aminophenol).