Polycrystalline Platinum Electrode Research Articles

The Influence of Acetone on the Kinetics of Water Electrolysis Examined at Polycrystalline Pt Electrode in Alkaline Solution

This study investigated the impact of acetone on the electrochemical behavior of polycrystalline platinum electrodes in 0.1 M NaOH solution, with respect to the kinetics of hydrogen and oxygen evolution reactions (HER and OER) and indirectly to the underpotential deposition of hydrogen (UPDH). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were employed to analyze these processes for acetone concentrations ranging from 1.0 × 10−6 to 1.0 × 10−3 M. The addition of (CH3)2C=O enhanced the catalytic efficiency of alkaline water splitting, which was believed to be a result of a significant reduction in the surface tension phenomenon (due to mutual interaction of acetone and water molecules), thus considerably facilitating hydrogen bubble detachment from the Pt electrode. Key findings in this work are described with respect to facilitation of both the HER and the OER reactions’ kinetics by the presence of acetone (also undergoing Pt electroreduction over the potential range for UPDH) in the working solution, without an electrode surface poisoning effect. The latter implies significant opportunities for traces of organic additives into alkaline electrolyte to improve the industrial alkaline water electrolysis process.

The role of cations in hydrogen evolution reaction on a platinum electrode in mildly acidic media

In this work, we study the influence of cation concentration and identity on the hydrogen evolution reaction (HER) on polycrystalline platinum (Pt) electrode in pH 3 electrolytes. Our observations indicate that cations in the electrolyte do not affect proton reduction at low potentials. However, an increase in cation concentration significantly enhances water reduction. Simultaneously, we identify a non-negligible migration current under mass transport limited conditions in electrolytes with low cation concentration. To separate migration effects from specific cation-promotion effects on HER, we carried out further experiments with electrolytes with mixtures of Li+ and K+ cations. Our results show that, adding strongly hydrated cations (Li+) to a K+-containing electrolyte leads to a less negative onset potential of water reduction. Interfacial pH measurements reveal a same interfacial pH at the platinum electrode in pH 3 in the presence of 80 mM LiClO4 and KClO4, respectively, at potentials where water reduction occurs. Based on these results, we suggest that under the current conditions, the strongly hydrated cations (Li+) promote water dissociation on the Pt electrode more favorably in comparison with the more weakly hydrated cations (K+), and that this promotion is not related to a local pH effect.

Determination of dopamine in blood serum and urine samples by differential pulse voltammetry at an iodine-coated platinum electrode

While platinum electrode shows hyperactivity towards adsorption and surface processes, iodine-coated platinum electrode offers remarkable inertness toward them. Therefore, iodine-coated platinum electrodes lend themselves to probe chemical species in the bulk solution without intervention from adsorption and surface processes. The current work presents utilization of iodine-coated polycrystalline platinum electrode as a voltammetric sensor for determination of dopamine in serum and urine samples. Differential pulse voltammetry (DPV) at iodine coated polycrystalline platinum electrode is the technique of choice whenever higher sensitivity is sought. DPV with a scan rate of 5 mV/s was applied for determination of dopamine in PBS at pH 7. The anodic peak related to dopamine oxidation in the above-mentioned solution was centered at ~0.1V vs. Ag/AgCl quasi reference electrode. The linear range for the developed method was between 1.0 and 100 µM. The anodic peak current showed excellent linearity with dopamine concentration (R2 =0.9977) over the above-mentioned range. The limit of detection (LOD) and limit of quantitation (LOQ) were 0.29 µM and 0.96 µM respectively which attests to the high sensitivity of the developed method. The proposed method was successfully applied to the analysis of dopamine in serum and urine samples. The percent recovery values ranged from 94.4 to 104.5% attesting to the accuracy of the developed method and absence of determinate errors.

Electrochemistry and Mass Transport of Ytterbium(III) in Bis(trifluoromethylsulfonyl)imide-Based Room-Temperature Ionic Liquids: Effects of Temperature, Viscosity, and Electrode Materials

Cyclic staircase voltammetry, rotating disk electrode voltammetry, controlled potential coulometry, and electrochemical impedance spectroscopy were used to probe the electrochemistry and mass transport of Yb3+ in the six room temperature ionic liquids based on the bis(trifluoromethylsulfonyl)imide (Tf2N−) anion with, 1-(1-butyl)−3-methylimidazolium (BuMeIm+), 1-(1-butyl)−1-methylpyrrolidinium (BuMePyro+), 1-(1-butyl)pyridinium (BuPy+), 1-butyltrimethylammonium (BuMe3N+), 1-ethyl-3-methylimidazolium (EtMeIm+), and tri(1-butyl)methylammonium (Bu3MeN+) cations. These investigations were carried out at glassy carbon as well as polycrystalline gold, platinum, and tungsten electrodes. The heterogeneous electron transfer rate of the quasireversible Yb3+/2+ redox couple was found to depend strongly on the electrode materials with the fastest rate observed at gold and the slowest rate found at tungsten, but was independent of the physicochemical properties of the various ionic liquids, in particular, the absolute viscosity. However, the mass transport of Yb3+ was dependent on the viscosity, and the temperature dependence of the diffusion coefficients was well represented by a Vogel-Tammann-Fulcher type expression for glass-forming ionic liquids. Analysis of the diffusion coefficient data with the Stokes-Einstein equation indicated that the solvodynamic radius of the diffusing Yb3+ was constant and independent of the structure and properties of the ionic liquid cations. The solvodynamic radius of Yb3+ was estimated from the “stick model” for the Stokes-Einstein equation. Application of the Random Closest Packing (RCP) model for spheres in consideration of the solvodynamic radius of the diffusing Yb3+ and the ionic radii of Yb3+ and Tf2N−, indicated that the former must diffuse in association with ∼5–6 of the anions.

Influence of Chlorine Oxyacid on the Electrooxidation of Methanol in Strong Acid

An electrochemical oxidation of methanol in a strong acid solution was investigated at a polycrystalline platinum electrode in the presence of different concentrations of hypochlorite. The addition of a slight amount of hypochlorite brought about drastic increase in the oxidation current of methanol, because the presence of hypochlorite inhibited the formation of a platinum oxide film on platinum electrodes. However, the oxidation current of methanol decreased with increasing the concentration of coexisting hypochlorite. The result may be due to i) the enhancement of the methanol adsorption to the surface of platinum electrodes by the inhibition of the formation of oxide film, and ii) the inhibition of methanol adsorption on platinum electrodes by higher concentration of NaClO and chemical compounds generated by the chemical reaction between methanol and increased hypochlorite.

Impact of toluene contamination on the oxygen reduction at polycrystalline platinum electrode: Poisoning and mitigation

Cyclic and hydrodynamic voltammetric measurements have been used to examine mechanistically the oxygen reduction reaction (ORR) at toluene-poisoned polycrystalline platinum (poly-Pt) electrode to explore the effect of poisoning with toluene, as a hydrocarbon model, on the electrochemical behavior of ORR at poly-Pt electrode. For this purpose, ORR is used as a marker reaction for the poisoning extent and for the ease of the in-situ mitigation of the poly-Pt electrode activity. The in-situ recovery at various scenarios is examined as it is crucial for the development of proton-exchange membrane fuel cells (PEMFs). Rotating ring-disk electrode voltammetry proved that the toluene-poisoning of poly-Pt electrode results in the change in ORR mechanism from the direct reduction of O2 to H2O to the reduction of O2 to H2O2 followed by further reduction to H2O. Voltammetric studies shows a preferential adsorption of toluene on the various facets of poly-Pt electrode. Recovery scenario in which the potential of the electrode was scanned in the range −0.2 to 1.3 V was found to be remedial in complete recovery of the poisoned electrode. Using RRDE, it has been shown that the limiting current in 100 ppm toluene contaminated H2SO4 at the previously reduced and oxidized electrodes to decrease to 60% and 20% of the value obtained in the absence of toluene.

The influence of platinum surface oxidation on the performance of a polymer electrolyte membrane fuel cell—probing changes of catalytically active surface sites on a polycrystalline platinum electrode for the oxygen reduction reaction

AbstractTo obtain fundamental insights into the performance of polymer electrolyte membrane (PEM) fuel cells, we perform a parallel investigation of the influence of platinum surface oxide (PtO) formation on the electrocatalytic activity toward the oxygen reduction reaction (ORR) for a polycrystalline platinum electrode in comparison with a commercial PEM fuel cell. PtO is formed by holding both systems at a constant potential for a given period of time. Conditioning potentials between 0.5 and 1.0 V versus SHE and conditioning times from 5 s up to 10 h are explored, respectively. We find that the voltage difference of the ORR between the oxidized and oxide‐free states depends on both the conditioning potential as well as the conditioning time at a given potential and furthermore increases with the applied target current. The change of the voltage loss over time, the so‐called voltage loss rate α, shows a maximum at potentials between 0.85 and 0.9 V and increases with increasing current density. We discuss various hypotheses to explain these findings obtained by linear voltammetry, Tafel slope analysis, Auger electron spectroscopy, and atomic force microscopy experiments. Finally, we conclude that the voltage loss rate is influenced by changes in the relative electrocatalytic activity of different crystal facets for the ORR as the oxide coverage varies.

Influence of experimental conditions on the electrochemical window. Case study on bis(trifluoromethylsulfonyl)imide-based ionic liquids

Ionic liquids (ILs) are often selected as electrolytes in various devices, such as batteries, capacitors and sensors, because of their chemical stability, non-flammability, low volatility, high electrical conductivity, low melting point, high thermal stability, and wide electrochemical window (EW). The width of the EW of an IL depends on the cation type, the water content, the electrode material, and the chosen specific current density used to measure it. In this work, the EWs of four ILs containing the common and stable bis(trifluoromethylsulfonyl)imide anion and triethylsulfonium, 1-(2-hydroxyethyl)-3-methylimidazolium, 1-methyl-1-propylpiperidinium and 1-butyl-1-methylpiperidinium cations were investigated by linear sweep voltammetry in order to analyze their electrochemical stability toward reduction and oxidation at polycrystalline platinum, gold and glassy carbon disc electrodes under anhydrous conditions. Specific current densities of 0.1 mA·cm−2 or 1 mA·cm−2 or the linear fitting method were used for the systematic comparison of the EWs obtained from each dataset. The results indicate the dependence of the EW width of each IL on the electrode material and, more importantly, on the chosen specific current density. In this paper, we present new insight into some of the difficulties encountered during determination of the EW for ILs.

Voltammetric Determination of Ascorbic Acid in Pharmaceutical Formulations Using Modified Iodine-Coated Platinum Electrode

Background: Despite the high reactivity of the platinum electrode, the iodine-coated platinum electrode shows obvious inertness toward adsorption and surface processes. For that, iodine-coated platinum electrodes accommodate themselves to interesting voltammetric applications. Objectives: This study reports using the modified iodine-coated polycrystalline platinum electrode as a voltammetric sensor for ascorbic acid determination in pharmaceutical formulations. Methods: The developed voltammetric method based on recording cyclic voltammograms of ascorbic acid at iodine-coated electrode The optimized experimental parameters for the determination of ascorbic acid were using 0.1 M KCl as a supporting electrolyte with a scan rate of 50mV/s. Results: The anodic peak related to ascorbic acid oxidation was centered at nearly 0.28V. An excellent and extended linear dependence of the oxidative peak current on the concentration of ascorbic acid was observed in the range 2.84x10-3 - 5.68 mM. The limit of detection (LOD) and limit of quantitation (LOQ) were 1.0 µM and 3.01 µM, respectively, attesting to the method’s sensitivity. The investigation for the effect of potential interference from multivitamin tablet ingredients (vitamins B1, B6, B12, folic acid, citric acid, sucrose, glucose, and zinc) indicated specific selectivity toward ascorbic acid and the absence of any electrochemical response toward these components. Recovery results in the range 98.93±2.78 - 99.98±5.20 for spiked standard ascorbic acid in pharmaceutical formulations further confirmed the potential applicability of the developed method for the determination of ascorbic acid in real samples. Conclusions: The developed method was successfully applied to the analysis of ascorbic acid (vitamin C), and the obtained results were in good agreement with the labeled values; besides, the statistical tests indicated no significant difference at p=0.05 with a 95% confidence level.

Oxygen Reduction Reaction Kinetics on Pt in Mixtures of Proton-Conducting Ionic Liquids and Water: The Influence of Cation Acidity

The aim of this study is to investigate the effect of the acidity of proton-conducting ionic liquids (PILs) on the oxygen reduction reaction (ORR) kinetics at polycrystalline platinum electrodes. T...

Anodic Stripping Voltammetric Determination Of Copper In Multivitamin-Mineral Formulations Using Iodine-Coated Platinum Electrode

In this work, the utilization of the modified iodine-coated polycrystalline platinum electrode as a voltammetric sensor for copper determination in pharmaceutical formulations was reported. The optimized experimental parameters for the determination of copper were using 0.1M KCl as a supporting electrolyte with a scan rate of 50 mV/s, deposition potential of - 0.2 V, and a deposition time of 2 minutes. The anodic peak related to Copper oxidation is centered at about + 0.05 V. The extended detected linear range for the developed method was between 1 ppm and 100 ppm. The anodic current showed excellent linearity with R2 = 0.9986. The limit of detection (LOD) and limit of quantitation (LOQ) were 0.115 ppm and 0.346 ppm, respectively, which attests to the sensitivity of the method. The investigation for the effect of potential interferences from multivitamins tablet ingredients indicated a specific selectivity toward copper and the absence of any electrochemical response toward these components. The developed method was successfully applied to analyze copper and the obtained results were in good agreement with the labeled values, besides that, the statistical tests indicated no significant difference at p = 0.05 with 95 % confidence level.

Voltammetric Determination of Paracetamol in Pharmaceutical Formulations at Iodine-Coated Polycrystalline Platinum Electrode

In this work the modified iodine-coated polycrystalline platinum electrode was used to develope a voltammetric sensor for paracetamol determination in pharmaceutical formulations. The optimized experimental parameters for the determination of paracetamol were using 0.5 M H2SO4 as a supporting electrolyte with a scan rate of 50 mV/s. The anodic peak related to paracetamol oxidation was centered at about +0.60 V. The extended calibration graph was constructed between 1 ppm and 500 ppm. The anodic current showed excellent linearity with R2 = 0.9985. The limit of detection (LOD) and limit of quantitation (LOQ) were 0.046 and 0.139 ppm, respectively, which attests to the sensitivity of the method. The investigation for the effect of potential interferences from the content of tablet matrices indicated a specific selectivity toward paracetamol and the absence of any electrochemical response toward these components. The developed method was successfully applied to analysis paracetamol in three brands of pharmaceutical formulations and the obtained results were in good agreement with the labeled values, besides that, the statistical tests indicated no significant difference at p = 0.05 with a 95 % confidence level.

Pré-Tratamento Químico e Eletroquímico para Eletrodos de Platina Policristalina e Análise de Substâncias Interferentes

Pré-Tratamento Químico e Eletroquímico para Eletrodos de Platina Policristalina e Análise de Substâncias Interferentes

Comparative Oscillatory Electro-Oxidation of Formic Acid on Palladium and on Platinum

The electro-oxidation of formic acid has been extensively studied, mainly because of two reasons. From the applied perspective, formic acid has been pointed out as one of the most promising molecules to be used in fuel cells. On the other hand, from the fundamental perspective, it has been used as a model system to study the electro-oxidation of other small organic molecules [1,2]. Despite the large amount of studies concerning the electro-oxidation of formic acid, some mechanistic issues remain to be well understood. In this work, we report a comparative study of the electro-oxidation of formic acid on polycrystalline platinum and palladium electrodes under oscillatory regime. The experiments were performed under potential control mode, with an external resistance coupled between the working electrode and the potentiostat. All results are shown in terms of Phi potential, that is, the electrode potential compensated by the external resistance. On platinum, the oscillations develop between ~0.58 and ~0.80 V, with an oscillatory frequency in the range of 0.78 – 1.49 Hz. As a general trend, the potential slowly increases from ~0.58 to ~0.62 V, followed by a sudden increase to ~0.80 V. On palladium, a very different behavior was observed in oscillation’s waveforms and frequencies. The oscillations develop between ~0.25 and ~0.55 V, with an oscillatory frequency in the range of 0.17 – 0.20 Hz. At the beginning, there is an abrupt increase in the electrode potential from ~0.25 to ~0.38 V. After that, the potential slowly increases until ~0.55 V, when it falls abruptly to ~0.25 V, and the process restart. Overall, the results suggest that the surface chemistry underlying the dynamics of formic acid electro-oxidation on palladium and on platinum is considerably different, particularly under oscillatory regime. Results suggest that the surface poisoning due carbon monoxide adsorption on palladium system is different when compared to platinum, even though the reaction steps for oxidation is similar in both systems. The low frequency oscillations observed on palladium indicates a slower poisoning process on its surface. Consequently, provide us perspectives on mechanistic aspect of this system, not yet treated in much detail. Thus, a broad discussion about the mechanistic issues of those systems will be presented.

Unraveling the reaction mechanism of co-reactant free in-situ cathodic solid state ECL of Ru(bpy)32+ molecule immobilized on Nafion coated nanoporous gold electrode

The electrochemiluminescence (ECL) of Ru(bpy)32+ molecule which is immobilized on Nafion coated nanoporous gold electrode (Ru(bpy)32+/Nafion/NPG) is investigated without involving any additional co-reactant in 0.1 M phosphate buffer solution (PBS) at pH 7.4 and the observed results are compared with Ru(bpy)32+ molecule immobilized on Nafion coated polycrystalline gold (Ru(bpy)32+/Nafion/pc-Au). Because of high surface area volume ratio and more active sites on NPG, the obtained co-reactant free unusual cathodic ECL signal at less cathodic potentials (0.1 V vs Ag/AgCl) showed 40 times higher intensity on Ru(bpy)32+/Nafion/NPG when compared with Ru(bpy)32+/Nafion/pc-Au in PBS (pH 7.4). Interestingly, this kind of ECL signal is not observed in the case of Ru(bpy)32+ molecule which is immobilized on Nafion coated glassy carbon (GC) and polycrystalline platinum (pc-Pt) electrodes. Based on the detailed experiments on effect of different pH, various direction of scanning potential and in-situ spectroelectrochemical studies, we proposed a new reaction mechanism for the unusual cathodic ECL on Ru(bpy)32+/Nafion/NPG. Upon electrochemical oxidation on Ru(bpy)32+/Nafion/NPG at higher potential, the stored Ru(bpy)32+ is converted into Ru(bpy)33+ at the same time generated reactive intermediate species like OH radical from the conversion of Au(OH)3 to Au0 during the reduction process leads energetic electron transfer reaction to proceed the excited state of Ru(bpy)32+ and then emits light. Unlike the conventional ECL system, this kind of co-reactant free in-situ generated solid state ECL approach offers to the scope in various bio analytical applications.

The mechanism of Li2O2-film formation and reoxidation – Influence of electrode roughness and single crystal surface structure

In this work, the role of the electrode surface structure on oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in lithium ion containing dimethyl sulfoxide (DMSO) was elucidated for Pt single crystal electrodes and deliberately roughened polycrystalline gold and platinum electrodes. Both rotating ring disk electrode (RRDE) measurements and results obtained by differential electrochemical mass spectrometry (DEMS) show that the amount of insoluble Li 2 O 2 formed is proportional to the roughness factor and corresponds to one or two monolayers if referenced to the true surface area. The amount of soluble LiO 2 is independent of roughness, although the formation of the passivating Li 2 O 2 layer takes longer. On gold electrodes less side products are formed as compared to platinum electrodes. It was furthermore found that ORR on single crystalline Pt(100) leads to two monolayers of Li 2 O 2 , while in case of Pt(111)/Pt(pc) only one monolayer was reoxidized. The shape of the reoxidation peaks in the anodic potential scan is independent of roughness, but it depends not only on the electrode material (Au or Pt) but also on the atomic surface structure. Since Tafelslopes cannot be determined directly by usual methods for such surface confined reactions, we used ac voltammetry to determine the apparent transfer coefficient ( α′ ) and gain some insight into the reoxidation mechanism; the obtained α ′ of 0.3 hints to a rate determining first charge transfer. This agrees well with the detection of superoxide during oxidation of Li 2 O 2 on the surface. • Strong effect of electrode surface structure on electrochemistry in Li + -containing DMSO. • Superoxide as intermediate during lithium peroxide oxidation in DMSO. • Apparent transfer coefficient of lithium peroxide oxidation in Li + -containing DMSO. • Direct correlation of lithium peroxide formation and surface roughness.

The Influence of Solution pH on the Kinetics of Resorcinol Electrooxidation (Degradation) on Polycrystalline Platinum.

Electrochemical oxidation of resorcinol on a polycrystalline platinum electrode was investigated in five different solutions, namely 0.5 and 0.1 M H2SO4, 0.5 M Na2SO4, 0.5 and 0.1 M NaOH. The rates of electrochemical degradation of resorcinol were determined based on the obtained reaction parameters, such as resistance, capacitance and current-density. The electrochemical analyses (cyclic voltammetry and a.c. impedance spectroscopy) were carried-out by means of a three-compartment, Pyrex glass cell. These results showed that the electrochemical oxidation of resorcinol is strongly pH-dependent. In addition, the energy dispersive X-ray (EDX) spectroscopy technique was employed for Pt electrode surface characterization. Additionally, the quantitative determination of resorcinol removal was performed by means of instrumental high-performance liquid chromatography/mass spectrometry (HPLC/MS) methodology.

Effect of mass transfer process on hydrogen adsorption on polycrystalline platinum electrode in sulfuric acid solution

The underpotential adsorption of hydrogen (HUPD) is one of the most attractive fields in surface electrochemistry and electrocatalysis. In this work, the hydrogen adsorption on polycrystalline platinum electrode experimentally as well as on single crystal Pt(110) and Pt(100) electrode theoretically were studied. The effect of forced convection on the adsorption and desorption process of hydrogen was studied through adjusting the sampling rate of the microporous sampler closing to the surface of the platinum electrode immersed in dilute sulfuric acid solution. The relationship between HUPD and surface structure sensitivity was built quantitively. The DFT simulation shows that the adsorption strength of hydrogen on Pt(100), due to the lower adsorption energy, is weaker than that on Pt(110). Moreover, the bridged position of hydrogen on Pt(100) and the short-range bridged position on Pt(110) were found to be the optimal adsorption sites. The study of forced convection on the electrode surface promotes the HUPD research from static process to a convective mode and also provides a new strategy to investigate the hydrogen adsorption in solution.

Tuning the Hydrogen Evolution Reaction on Metals by Lithium Salt

Tuning the electrode–electrolyte interfaces transiently for controlling the kinetics of hydrogen evolution reaction (HER) on metals will be highly intriguing in energetics. Here, the inherent HER activities of polycrystalline platinum (Pt) and gold (Au) electrodes are altered by different lithium salts. The HER activity of Pt is shown to be suppressed by increasing the Li+ ion concentration while inverse effect is observed in Au, and this is verified in different pH (2–13) conditions and also with different counterions (Li+, Na+, ClO4–, Cl–, and bis(trifluoromethanesulfonyl)imide) ion. A mechanistic insight is provided for this observed phenomenon, which has paramount importance in other electrocatalytic processes as well, such as carbon dioxide reduction and nitrogen reduction reactions.

Molecular-Scale Structure of Electrode-Electrolyte Interfaces: The Case of Platinum in Aqueous Sulfuric Acid.

Knowledge of the molecular composition and electronic structure of electrified solid-liquid interfaces is key to understanding elemental processes in heterogeneous reactions. Using X-ray absorption spectroscopy in the interface-sensitive electron yield mode (EY-XAS), first-principles electronic structure calculations, and multiscale simulations, we determined the chemical composition of the interfacial region of a polycrystalline platinum electrode in contact with aqueous sulfuric acid solution at potentials between the hydrogen and oxygen evolution reactions. We found that between 0.7 and 1.3 V vs Ag/AgCl the electrical double layer (EDL) region comprises adsorbed sulfate ions with hydrated hydronium ions in the next layer. No evidence was found for bisulfate or Pt-O/Pt-OH species, which have very distinctive spectral signatures. In addition to resolving the long-standing issue of the EDL structure, our work establishes interface- and element-sensitive EY-XAS as a powerful spectroscopic tool for studying condensed phase, buried solid-liquid interfaces relevant to various electrochemical processes and devices.