Pt Electrodes In Alkaline Solution 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.

Ni3P-Ni heterostructure electrocatalyst for alkaline hydrogen evolution

Highly active and stable electrocatalysts at low cost for hydrogen evolution reaction are essential for large scale hydrogen production. The Ni3P-Ni heterostructure confined in 3D networks of carbon nanotube (CNT) has been successfully prepared as the hydrogen evolution reaction (HER) electrode. The morphology and phase composition of Ni3P-Ni heterostructure are tunable by varying the acid pickling time. The Ni3P-Ni/CNT composite electrode with optimized Ni:Ni3P ratio of 22.29 wt% demonstrate high catalytic activity and excellent stability for HER. It demonstrates a comparable HER activity to the standard Pt electrode in alkaline solution, i.e., overpotentials of 116 vs 67 mV at 10 mA·cm−2 and Tafel slops of 59 vs 37 mV·dec−1. No degradation is observed after 1000 cyclic voltammetry (CV) cycles or 50 h operation under constant 0.3 V overpotential.

Glycerol Oxidation Reaction Mechanism on Ag-Modified Pt Electrode in Alkaline Medium

Introduction Recently, biodiesel fuel (BDF) attracts attention due to the progress of global warming. Glycerol as a byproduct is produced with BDF, and practically used for pharmaceuticals, cosmetics, food additives and so on. With the mass production of BDF, new applications of the glycerol byproduct need to be found. The application of glycerol as anode for direct alcohol fuel cells (DAFCs) can be an important solution because it has low toxicity and high specific energy (5.0 kWh kg-1). However, glycerol has two C-C bonds and three OH groups, so the mechanism for glycerol oxidation reaction (GOR) is complex,1 and the rate for GOR is so slow that the complete oxidation to CO2 is very difficult. Palladium is known to be one of active materials for GOR. We have found the alloy nanoparticles of Pd with Ag or Au improved the GOR activity and tolerance to the poisoning species on Pd nanoparticle in alkaline medium due to the electronic and bi-functional effects.2 Meanwhile, the Pt electrode had higher GOR activity than the Pd electrode in terms of the onset potential of GOR current, and Ag would improve the GOR activity of Pt. In this study, the effect of the modification with Ag on the GOR activity of a Pt substrate was evaluated by cyclic voltammetry (CV). Moreover, the mechanism for GOR on the Ag-modified Pt (Ag/Pt) electrode was discussed based on in situ infrared reflection absorption spectra at different potentials. Experimental The Ag/Pt electrode was prepared by underpotential deposition of Cu (Cu-upd) on a Pt substrate and the following galvanic replacement with Ag. The coverage of Ag (θ Ag) on the Pt substrate were calculated from the charge for H desorption before and after the Ag modification. The Ag/Pt electrodes with θ Ag = 0.8 and 0.5 were used in this study, which are denoted as Ag(0.8)/Pt and Ag(0.5)/Pt, respectively. The electrolytes were 1 M KOH or (1 M KOH + 0.5 M glycerol) solutions. Pt plate (1 cm × 1 cm) and a Hg/HgO electrode were used as counter and reference electrodes, respectively. In situ infrared reflection-absorption spectroscopy (IRAS) was used to qualitatively analyze the products of GOR on the Pt, Ag(0.8)/Pt and Ag(0.5)/Pt electrodes in alkaline solution. All electrochemical measurements were performed at room temperature. Results and Discussion The GOR activity for the Pt, Ag(0.8)/Pt and Ag(0.5)/Pt electrodes in alkaline medium was evaluated by CV (Fig. 1). Both Ag(0.8)/Pt and Ag(0.5)/Pt electrodes had twice higher current density and about 150 mV lower onset potential than the Pt substrate. This means that the enhancement of the GOR activity is caused by the modification of Ag atomic layers. Moreover, as θ Ag increased, a GOR wave was separated into two. The durability for GOR was evaluated by potentiostatic electrolysis for 60 min at -0.1 V and -0.3 V (vs. Hg/HgO). At -0.1 V, the durability for GOR was decreased in the order of Ag(0.5)/Pt > Pt > Ag(0.8)/Pt. On the other hand, at -0.3 V, the Ag(0.5)/Pt electrode still showed the best tolerance to the poisoning species, but the durability for GOR of Ag(0.5)/Pt was poorer than that of Pt. These results indicated that the modification of Ag on Pt improved the GOR activity and durability. IRAS gives us the information on the GOR mechanism. In the case of the Pt electrode, the mainly absorption band are observed at 1310 cm-1, 1335 cm-1, 1350 cm-1, 1385 cm-1 and 1575 cm-1 which can be attributed to glyceraldehyde or glycerate, dihydroxyacetone, hydroxypyruvate, symmetric and symmetric O-C-O stretching of carboxylate, respectively. At higher potentials, the absorption band at 1310 cm-1 was obviously observed. On the other hand, in the case of both Ag(0.8)/Pt and Ag(0.5)/Pt electrodes, the absorption band at 1335 cm-1 due to dihydroxyacetone was more obviously observed at -0.4 to -0.2 V, whereas at -0.2 to 0.1 V, the absorption band at 1310 and 1350 cm-1 was strengthen. This results indicate that the oxidation of primary and secondary OH groups depends on potential, and the secondary OH (-0.4 to -0.2 V) and the primary OH ( -0.1 V) are preferentially oxidized on the Ag modified Pt electrodes. Acknowledgement This work was partially supported by JSPS KAKENHI Grant Number 15H04162. References 1) M. Simoes et al., Appl. Catal. B: Environ., 93, 354 (2010).2) B. T. X. Lam et al., J. Power Sources, 297, 149 (2015). Figure 1

H–D kinetic isotope effects of alcohol electrooxidation on Au, Pd and Pt electrodes in alkaline solutions

The identification of rate-determining step (RDS) is vital for understanding reaction mechanisms and designing advanced catalysts. Here, we systemically studied the H–D kinetic isotope effects (KIEs) on electrooxidation of ethanol, isopropanol, and ethylene glycol (EG) on Au, Pd and Pt electrodes in alkaline solution by combining cyclic voltammetry and in situ FTIR spectroscopy. Large primary KIEs are observed on Au electrode: 8.4 for ethanol, 6.2 for EG and 7.9 for isopropanol when α-H of alcohols are substituted by deuterium, but much lower KIEs (<3.2) were observed on Pt, and the values on Pd are between Au and Pt. According to the criteria (KIEs=6–10) for CH (D) breaking/forming as RDS, we conclude that the cleavage of the α-H from CH bond is the RDS for alcohol electrooxidation on Au, but not on Pt. On Pd, the RDS depends on the structure of alcohols. The difference can be rationally correlated with the binding affinity of hydrogen on precious metal surfaces.

The electro-oxidation of formate ions at a polycrystalline Pt electrode in alkaline solution: an in situ FTIR study

This paper reports in situ FTIR studies on the oxidation of formate at polycrystalline Pt in aqueous KOH. Data are presented which show that hydroxyl species play a major role in the electro-oxidation of small organic molecules under alkaline conditions at polycrystalline Pt, and that a number of possible mechanistic pathways are possible. Small changes in experimental conditions appear to be able to cause the reaction to flick between these pathways; for example, the presence of oxygen has a marked effect upon the observed electrochemistry. In contrast to acid solution, our postulated model includes the formation of intermediates bonded through O atoms, rather than C, as being an important option in alkaline solution. Finally, the pH distribution across the reflective electrode in external reflectance IR is modelled and significant variations in pH across the electrode surface in FTIR cells predicted and confirmed experimentally.

Hydrogen Oxidation and Evolution Reaction Kinetics on Platinum: Acid vs Alkaline Electrolytes

The kinetics of the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) on polycrystalline platinum [Pt(pc)] and high surface area carbon-supported platinum nanoparticles (Pt/C) were studied in 0.1 M KOH using rotating disk electrode (RDE) measurements. After corrections of noncompensated solution resistance from ac impedance spectroscopy and of hydrogen mass transport in the HOR branch, the kinetic current densities were fitted to the Butler–Volmer equation using a transfer coefficient of , from which HOR/HER exchange current densities on Pt(pc) and Pt/C were obtained, and the HOR/HER mechanisms in alkaline solution were discussed. Unlike the HOR/HER rates on Pt electrodes in alkaline solution, the HOR/HER rates on a Pt electrode in 0.1 M were limited entirely by hydrogen diffusion, which renders the quantification of the HOR/HER kinetics impossible by conventional RDE measurements. The simulation of the hydrogen anode performance based on the specific exchange current densities of the HOR/HER at illustrates that in addition to the oxygen reduction reaction cell voltage loss on the cathode, the slow HOR kinetics are projected to cause significant anode potential losses in alkaline fuel cells for low platinum loadings ( at and ), contrary to what is reported for proton exchange membrane fuel cells.

Analysis of the Impact of Individual Glass Constituents on Electrocatalysis on Pt Electrodes in Alkaline Solution

In our previous paper [ Journal of the Electrochemical Society , 155 , P1 (2008) ] we reported on the impact of glass corrosion on establishing the electrocatalytic activity of fuel cell catalysts. It was shown that the leaching of glass constituents into the electrolyte is responsible for insufficiently reproducible measurements of the oxygen reduction reaction as well as the hydrogen oxidation reaction on polycrystalline platinum. In the present report we elucidate which glass constituents are leached into the electrolyte through the analysis of alkaline electrolytes in contact with Duran glass by inductively coupled plasma optical emission spectroscopy. By adding these constituents, i.e., silicates, borates, aluminates, and lead, separately to the electrolyte, we evaluate their individual impact on electrocatalytic measurements. The results presented in this study help to explain the effects seen in measurements in alkaline electrolyte with glass cells.

Superoxide Anion is the Intermediate in the Oxygen Reduction Reaction on Platinum Electrodes

We identified the superoxide anion as the intermediate in the oxygen (O2) reduction reaction on a platinum (Pt) electrode in alkaline solution (pH = 11) using a surface-enhanced infrared spectroscopy technique with an attenuated total reflection mode. Spectral and voltammetry data, together with the vibrational frequencies calculated using the density functional theory, provide evidence for the formation of O2-. The supporting evidence includes similar spectra that we obtained for O2 reduction on Pt in acetonitrile solutions and a lack of spectra in the absence of O2 or its reduction. The appearance of O2- means that the series reaction pathway operates during O2 reduction on Pt electrodes in alkaline solutions and very likely also in acid solutions. This finding opens up the possibility of formulating a detailed reaction mechanism on surfaces supporting a four-electron reduction, which is critical in completely understanding the kinetics of O2 reduction, thus resolving dilemmas in the theoretical treatment of its kinetics and the design of new electrocatalysts.

Anodic Oxidation of Polyhydric Alcohols on a Pt Electrode in Alkaline Solution

The electrochemical oxidation of various polyhydric alcohols, ethylene glycol, glycerol, meso-erythoritol, and xylitol, on a platinum electrode was investigated systemematically in acidic H2SO4, and in alkaline KOH and K2CO3 solutions to evaluate the potential of these polyhydric alcohols as fuels in micro-fuel cells for portable electronic devices. All polyhydric alcohols tested in the present study showed high reactivities in both alkaline solutions. Ethylene glycol showed the highest reactivity. Although the reactivity of ethylene glycol was lower in K2CO3 than in KOH, the carbonate solution is a potential candidate as an electrolyte solution due to its resistance to solution carbonation. Furthermore, ethylene glycol showed much less significant electrode poisoning by adsorbed CO upon oxidation in alkaline solution.

Electropolymerization of chlorinated phenols on a Pt electrode in alkaline solution. Part IV: A gas chromatography mass spectrometry study

The electropolymerization of phenol and chlorinated phenols (monochlorophenols, dichlorophenols, 2,3,6-, 2,4,6-, 2,4,5-trichlorophenols and pentachlorophenol) was studied on a platinum electrode at 0.78 V vs SHE in alkaline 1 M NaOH aqueous solutions containing 0.1 M of the phenols. The low molecular weight reaction products were investigated by means of gas chromatography mass spectrometry (GCMS). Product analyses show that oligomers (dimers, trimers and tetramers) are present in the polymer mixtures formed. The MS spectra reveal the ether-linked nature of the oligomers formed during the electrooxidation-electropolymerization of the phenolic compounds. The mass spectra of the low molecular weight substances formed suggest that the oxidation–polymerization of phenols proceeds following two different mechanisms: (i) through the quinol-ether route (without chlorine elimination) and (ii) via the nucleophilic-radical substitution (SRN1) route (with some elimination of chlorine from ortho and/or para positions).

Electropolymerization of chlorinated phenols on a Pt electrode in alkaline solution. Part II: An electrochemical quartz crystal microbalance study

Electropolymerization of phenol and mono-, di-, tri-, pentachlorophenols was studied using EQCM on a Pt electrode at 0.78 V (SHE) in 1 M NaOH solution containing 0.1 M of the corresponding phenol. The highest electropolymerization rate was found for ortho-substituted chlorophenols indicating a weak fouling of the electrode. Low electropolymerization rates for para-substituted chlorophenols suggest a low permeability of the polymer film, resulting in rapid electrode fouling. The EQCM data suggest that electropolymerization of chlorophenols occurs without Cl-elimination for the monomers with unsubstituted ortho and para positions. Dechlorination is most pronounced for electropolymerization of para-substituted isomers. The mechanism of electropolymerization of chlorophenols is discussed.

Oxidation of chlorophenols on Pt electrode in alkaline solution studied by cyclic voltammetry, galvanostatic electrolysis, and gas chromatography­mass spectrometry

Abstract Potentiodynamic investigations on a platinum electrode show that oxidation of phenol, monochlorophenols, dichlorophenols, 2,3,6-, 2,4,5-, 2,4,6-trichlorophenols, and pentachlorophenol in 1 M NaOH solution, containing 1 mM of phenols, proceeds in the potential region of Pt oxide formation. The oxidation rate of phenols decreases with the increase in the number of chlorine atoms in the benzene ring in the row: phenol &gt; monochlorophenols &gt; dichlorophenols &gt; trichlorophenols &gt; pentachlorophenol. The electrochemical stability of phenols, as studied using a cyclic voltammetry, depends on their chlorination degree and isomerism. Galvanostatic oxidation of 1 M NaOH solutions containing 1 mM of phenol, monochlorophenols, dichlorophenols, 2,3,6-, 2,4,5-, 2,4,6-trichlorophenols, and pentachlorophenol were carried out on a platinum electrode using 30 mA cm­2 current density. The electrolysis of the solutions was performed in the course of 10 h, and concentration of phenols in the anolytes was monitored during oxidation. The concentration of phenolic compounds diminishes from 1 mM to 10­50 mM during 4­5 h of electrooxidation and does not change during further galvanostatic oxidation. A decrease in concentration of phenols during galvanostatic electrolysis weakly depends on the isomerism and a chlorination degree of the compounds. A rapid decrease in concentration of studied phenols during the first 4­5 h of electrolysis and a nonselective oxidation of different chlorophenols suggest that the oxidation proceeds via electrochemically generated oxidants. Further decrease in concentration of phenols is rather small due to deactivation of the electrode as a result of polymerization of corresponding phenols and diffusion limitations.

Behaviour of a hydride phase formed in the hydrogen evolution reaction at a rotating Pt electrode: analysis of potential relaxation transients from a kinetic approach

The behaviour of overpotential-deposited (OPD) H species in the hydrogen evolution reaction (HER) in acid and alkaline solutions at a rotating-disc Pt electrode (RDE) was investigated by analysing open-circuit potential relaxation curves using a kinetic approach, i.e. fitting potential-decay transients by a set of rate constants k for various reaction mechanisms. Previous indications of a hydride phase, involving a number of equivalent monolayers of OPD H in the near-surface region of the Pt interface, were confirmed in the present study for the HER on Pt in acid solution. The highest electrocatalytic activity of activated Pt in acid solution, among the three systems studied, is determined not only by large j 0 (or large k values) but also by much lower Tafel slopes at low overpotentials η because of the predominance of the recombination pathway for the HER at such surfaces. It seems that the recombination step is a preferred pathway for the HER on the active Pt surface at which a hydride phase is formed in the near surface region. However, for a deactivated Pt electrode in alkaline solution, the polarization current at η = −0.1 V is a factor of 10 4 smaller than for the same activated Pt in acid solution, corresponding to an OPD H yield about a factor of 10 3 less under the former conditions. The comparison was made in terms of the steady-state pseudocapacitance Cω calculated using best-fit rate constants and an apparent charge q 1 for H accommodation, and the “operational” pseudocapacitance C b derived in previous studies.

Electron transfer through thin anodic films in oxygen evolution at Pt electrodes in alkaline solutions

Oxygen evolution reaction at Pt electrodes in alkaline solutions is characterized by two linear E-log i relationships. At low current densities (cd), the Tafel slope is close to 60 mV, whereas at high cd, it is close to 120 mV. The rates at high cd are strongly affected by the presence of an anodic oxide film over electrodes. They decrease exponentially with the film thickness. In contrast, the rates at low cd are unaffected by the film thickness. The reaction order with respect to OH − is 3/2 at high, and 2 at low cd. The mechanism of the reaction involves electron tunneling through the oxide film. The first electron transfer step is rate determining (rd) at high cd. The major factor affecting the rates is the probability for successful transfer of electrons through the potential energy barrier. The dependence of the rates on electrode potential is, however, controlled principally by the distribution of the occupied electron energy levels in solution. At low cd, a chemical step following the first electron transfer step is rd. The observed pH dependences cannot be accounted for in terms of any customary approach to electrode kinetics. They are accounted for in terms of the quasi-equilibrium that exists across the outer Helmholtz layer.

Electro-oxidation of methanol on graphite-supported perovskite-modified Pt electrodes in alkaline solution

Graphite-supported perovskite-modified Pt electrodes exhibited much higher electrocatalytic activities than smooth Pt or graphite-supported Pt electrodes towards methanol electro-oxidation in 1 M NaOH solution at 25°C, showing zero-current potential as low as 200 mV versus the reversible hydrogen electrode. For CO oxidation the modified electrodes exhibited less positive zero-current potentials (120 and 110 mV in the case of Co- and Mn-type perovskites respectively) than the smooth Pt electrode (230 mV) or the graphite-supported Pt electrode (220 mV). The catalytic activities of the modified electrodes were found to be very stable and to remain unaffected towards the poisoning effect of CO. Rather, they could oxidize both CO and methanol simultaneously, or the methanol oxidation was enhanced by the presence of CO at highly positive potentials.

Oxygen Evolution at Platinum Electrodes in Alkaline Solutions: II . Mechanism of the Reaction

Kinetic data of the oxygen evolution reaction at Pt electrodes in alkaline solutions have shown two types of behavior, a Tafel slope of 60 mV/decade of current density at low applied current densities and a slope of 120 mV/decade at high current densities. At low current densities, and rate of the reaction was found to be independent of the thickness of the underlying Pt oxide film, while the electrode potential has a −120 mV dependence on solution pH. At high current densities, the rate is strongly dependent on film thickness and exhibits a −180 mV dependence on pH. A mechanism of the oxygen evolution reaction which is consistent with this data is presented. It involves a rate‐determining first electron transfer step at high current densities. At low current densities, the chemical step following the now rapid first electron transfer step is rate limiting. The −180 mV pH dependence observed at high current densities implies a fractional reaction order of with respect to the OH− ion. This has been explained in terms of a dual barrier model of the metal oxide film/solution interface. According to this model, the rates across each barrier are pH dependent. The fractional reaction order is due to the existence of these two dependences and is primarily related to the dependence of the potential difference across the outer Helmholtz layer on pH.