Electrochemical Oxidation Of Formic Acid Research Articles

Facile Synthesis and Electrochemical Properties of Intermetallic PtPb Nanodendrites

We report on a facile and environment-friendly route to synthesize intermetallic PtPb nanodendrites with controllable compositions. This involves a hydrothermal-assisted coreduction of Pt and Pb inorganic precursors by formic acid in aqueous solutions without the use of any surfactant or polymer. Our systematic structural characterization and in situ electrochemical infrared spectroscopic studies of the formed PtPb nanodendrites reveal that the underlying morphogenesis, resulting from the intermetallic phase evolution from a Pt-based face-centered cubic to a PtPb hexagonal type, is responsible for the significant improvement of electrocatalytic activities toward the electrochemical oxidation of formic acid. A foreign-particles-induced growth mechanism is proposed to account for the underlying dendritic growth process. The facile approach described in this study is further demonstrated to be universal for growing a variety of intermetallic nanodendrites, thus opening a door to develop and study novel nanod...

Probing anodic reaction kinetics and interfacial mass transport of a direct formic acid fuel cell using a nanostructured palladium–gold alloy microelectrode

The anodic reaction kinetics and interfacial mass transport of a direct polymer electrolyte membrane formic acid fuel cell have been investigated in an all solid-state electrochemical cell using a highly active nanostructured palladium–gold alloy microelectrode as an in situ probe. Well-defined “S-shaped” steady-state cyclic voltammograms exhibiting current-rising region at lower overpotentials and limiting current region at higher overpotentials have been first obtained for the electrochemical oxidation of formic acid at varying temperature. The “S-shaped” steady state polarization curves and chronoamperometric curves enable convenient measurements of the anodic reaction kinetics and interfacial mass transport of formic acid under real polymer electrolyte membrane conditions. It is encouragingly found that formic acid can be directly oxidized to CO 2 with the first electron transfer being the likely rate-determining step and the formation of surface poison can be neglected. The exchange current density for the electrooxidation of formic acid is on the order of magnitude of 10 −7 A cm −2 in the temperature range of 20–60 °C. The permeability and diffusion coefficient of formic acid through a Nafion ® 117 membrane are of the order of magnitude of 10 −9 mol cm −1 s −1 and 10 −6 cm 2 s −1, respectively. The combination of a nanostructured microelectrode and an all solid-state electrochemical cell offers a versatile approach to evaluate potential electrocatalysts for fuel cells and electrochemical sensors employing polymer electrolyte membranes.

Hydrogen production by electrochemical decomposition of formic acid via solid polymer electrolyte

The aim of this work is to investigate the feasibility of simultaneous hydrogen production by electrochemical decomposition of formic acid via solid polymer electrolyte (SPE) in an electrochemical reactor. Titanium oxide coated with iridium oxide as anode and carbon fibre with Pt catalyst as cathode were used in the experiments. Effects of applied current density, flow rates and temperature of formic acid solution, concentration of supporting electrolyte and pH of the solution on performance of the process have been investigated. The effect of membrane thickness has also been examined. The results suggest that electrolysis using SPE is a promising method for the treatment of organic pollutants. Hydrogen with purity of 99.999% at ambient temperature by using carbon fibre cathode with Pt catalyst can be produced simultaneously and COD removal efficiency of 95% has been achieved not requiring any chemical addition and temperature increase. Also complete electrochemical oxidation of formic acid at the original pH to CO 2 and H 2O without production of intermediate has been proved by HPLC analysis.

Structural effects on the oxidation of formic acid on the high index planes of palladium

Electrochemical oxidation of formic acid has been studied on the stepped and kinked-stepped surfaces of Pd in 0.1 M HClO 4 containing 0.1 M formic acid with the use of voltammetry. The surfaces examined are Pd(S)-[ n(1 0 0) × (1 1 0)], Pd(S)-[ n(1 1 1) × (1 0 0)] and Pd(S)-[ n(1 1 1) × (1 1 1)] series ( n = 2–9). The results are compared with those of Pd(S)-[ n(1 0 0) × (1 1 1)] series reported previously. All the electrodes give maximum currents of formic acid oxidation j P between 0.5 and 0.8 V (RHE). The values of j P plotted against the density of step (kink) atoms d S depend on the surface structure remarkably. Pd(S)-[ n(1 1 1) × (1 0 0)] surfaces provide maximum of j P at n = 5, whereas Pd(S)-[ n(1 0 0) × (1 1 0)] and Pd(S)-[ n(1 1 1) × (1 1 1)] do not give maximum of j P. The values of j P have the following order: Pd(S)-[ n(1 1 1) × (1 1 1)] < Pd(S)-[ n(1 1 1) × (1 0 0)] < Pd(S)-[ n(1 0 0) × (1 1 0)] < Pd(S)-[ n(1 0 0) × (1 1 1)]. The anodic current at more negative potential 0.20 V (RHE) shows different activity series: Pd(1 1 1) and Pd(1 1 0) have the highest rate for formic acid oxidation at 0.20 V (RHE).

Activity of a PtBi alloy in the electrochemical oxidation of formic acid

Formic acid oxidation in acid solution was examined on a PtBi alloy characterized by X-ray photoelectron spectroscopy. Three chemical states of Bi, i.e., PtBi or Bi(0), Bi 2O 3 and BiO(OH) were found. Electrochemical characterization revealed that PtBi follows the behavior of its constituents, as well as that Bi is not stable in the PtBi alloy. It was established that the activity of PtBi is highly dependent of the reduction/oxidation of Bi species. Oxidation of formic acid does not occur on Bi covered PtBi. Rotated PtBi showed impressive activity relative to polycrystalline Pt, with the onset potential shifted by 0.25 V towards more negative potentials, and attained steady state current densities at 0.05 V, higher by two and half orders of magnitude. The activity of PtBi is caused by UPD phenomena of Bi on Pt, which was electrochemically detected. In addition, based on XPS analysis, it is proposed that the activity of PtBi could also be caused by the bifunctional action of hydroxylated Bi species.

An Experimental and Theoretical Study of Interactions between Unlike Surface Anions and Increases in the Rate of Electrochemical Reactions

Experimental and theoretical results are presented on increases in the rate of electrochemical reactions, which are achieved by replacing a small fraction of the original anions in solution with more inhibiting ones. The rate of the electrochemical oxidation of formic acid was substantially increased by replacing a small amount of the supporting electrolyte, perchloric acid, with either sulfuric acid or tetrafluoroboric acid. The largest increases were achieved by substituting mixtures of the last two acids. A theoretical analysis of an electrochemical reaction coupled to anion adsorption is presented. The analysis reveals that, if repulsive forces of appropriate strength form between unlike surface anions, replacing a fraction of the original anions in solution with one or two kinds of more inhibiting anions can increase the rate of reaction.

Spectroelectrochemical Evaluation of Rh Microparticles as Electrocatalyst for Carbon Monoxide and Formic Acid Oxidation

Electrooxidation of carbon monoxide and formic acid was performed on Rh microparticles deposited on both, Glassy Carbon (Rh/GC) and polyaniline films (Rh/PANI), to evaluate the electrocatalytic activity of those electrodes. The deposit of Rh microparticles on those substrates provides a higher surface and exhibits a better electrocatalytic activity compared with that shown by smooth Rh for the electrochemical oxidation of formic acid in sulphuric acid. The oxidation of CO and HCOOH on Rh/GC and Rh/PANI was followed using in situ Multi-Step FTIR Spectroscopy (MS-FTIRS). Either linear or bridge bonded adsorbed CO (COl, COb), has been observed by FTIRS as the main species. In comparison to the adsorption of CO on smooth Rh surface, the IR features of CO adsorbed on Rh/GC and Rh/PANI electrodes showed an anomalous behaviour.

Improvements in the Efficiency of the Oxidation of Formic Acid Obtained by Increasing the Overall Anion Adsorption Strength

Measurements are reported on changes in the efficiency of the electrochemical oxidation of formic acid that were caused by varying the overall “anion adsorption strength”. The adsorption strength w...

Quantification of CO 2 from electrochemical oxidation reactions with a strategy based on transmission infrared spectroscopy

The use of a micro-volume infrared transmission flow cell for quantitative determinations of CO 2 dissolved in solutions following electrochemical oxidation reactions is described. Results are compared with previous in situ infrared measurements as a step toward evaluating the performance of infrared spectroelectrochemical cells under conditions where non-ideal optical effects can become important. The electrochemical oxidation of formic acid on platinum is investigated as a model.

Two-parameter stochastic resonance in a model of electrochemical oxidation of formic acid on Pt

Stochastic resonance (SR) is shown in a two-parameter system, a model of electrochemical oxidation of formic acid on Pt. The driving current and the saturation coverage for carbon monoxide are two control parameters in this model. Modulation of an excitable focal stable state close to a Hopf bifurcation by a weak periodic signal in one parameter and noise in the other parameter is found to give rise to SR. The results indicate that the noise can enlarge a weak periodic signal and lead the system to be ordered. The scenario and novel aspects of SR in this system are discussed.

Detection of Intermediates and Products of Electrochemical Processes-a DEMS Study

The presentation describes an on-line connection of electrochemical cell and mass spectrometer used for detection, identification and observation in time of volatile and semivolatile species during electrochemical polarisation of working electrode (DEMS - Differential Electrochemical Mass Spectrometry). DEMS is a type of experimental technique, which makes possible an investigation of electrosorption, electrooxidation and electrohydrogenation processes of molecules like aromatic hydrocarbons, some other small organic molecules and reaction intermediates. The experimental set-up consists of a mass spectrometer connected with an electrochemical cell separated by hydrophobic membrane. Standard three-electrode electrochemical arrangement is applied. As test system we studied the process of electrochemical hydrogenation of naphthalene and benzene and processes of electrochemical oxidation of formic acid and dimethylformamide in 0,5 M H2SO4 on polycrystalline Pt electrode.

Investigation of the mechanism of the electrochemical oxidation of formic acid at a gold electrode in sulfuric acid solution

The oxidation of formic acid at the Au electrode in sulfuric acid solution was investigated using a programmed potential step procedure. The j– t curve of the direct reactive oxidation of formic acid suggested a two-stage mechanism of the electrode reaction. The oxidation current density peak on the chronoamperometric plot corresponded to the formation of a steady adsorptive layer of COOH ads through adsorption of HCOOH and the first electron transfer, while the steady current density corresponded to the further oxidation of the adsorptive layer of COOH ads formed. A data fitting program was developed for extracting kinetic parameters from the j to t transient experimental data. The adsorption rate constants ( k a) for formic acid, the reaction rate constants ( k 2) and the transfer coefficient ( β) for the further oxidation of COOH ads were obtained at various potentials. These results confirmed that the further oxidation of COOH ads was the rate-limiting step after the adsorption balance of COOH ads was achieved, and before that, the adsorption of formic acid was the rate-limiting step.

Enhancement of the electrochemical oxidation of formic acid. Effects of anion adsorption and variation of rotation rate

Results are presented from a study on the electrochemical oxidation of formic acid. Perturbing a HCOOH+HClO 4 solution by causing a small amount of any one of several different anions to be present dramatically changes observed nonlinear behavior in an apparently unique manner. Quantitative changes are also observed. In current-control experiments, the presence of fluoroborate ions causes a substantial increase in the value of the applied current density for which low valued stationary potentials remain stable. In potential-control experiments, the current density substantially increases at relevant potential values. Although most properties possessed by the fluoroborate anion exist among the other anions studied, the presence of any one of these other ions in solution yields inferior current–potential characteristics. Results from current-control experiments show that changes in rotation rates have no effect on the observed behavior regardless of anion composition or whether the limiting state is stationary or oscillating.

Oscillatory behavior in the electrochemical oxidation of formic acid on Pt(100): rotation and temperature effects

Abstract We investigated the oscillatory behavior in the kinetics of formic acid electrooxidation on Pt(100) in 1 mM HClO4 solution. We studied the effect of different experimental parameters on the oscillatory behavior, viz. defined HCOOH mass-transport to the electrode surface by using the rotating disk electrode technique, the temperature of the supporting electrolyte, and the nature of anions. We suggest that the interdependence of the reaction steps during HCOOH oxidation, the adsorption of anions and the competition for adsorption sites among the reaction partners and intermediates lead to complex non-linear kinetics. It was evident that once the individual reactions in the dual path mechanism reach steady state the oscillations vanish. These conditions can be reached either by enhanced formic acid reaction rates induced by electrode rotation or by increased temperature. Under specific conditions of anion and formic acid concentration, relaxational oscillations can be transformed into mixed-mode oscillations.

Increases in reaction rates and improvement of current–potential characteristics in the electrochemical oxidation of formic acid

In current-control experiments, perturbing an aqueous solution containing 0.10 M formic acid and 0.50 M HClO 4 by including a small amount of HBF 4 causes more than a 60% increase in the value of the applied current for which low-valued stationary potentials remain stable. The current increases by more than 50% at relevant potential values in potential-control experiments. Current–potential characteristics inferior to those of the HCOOH + HClO 4 solution are obtained with other solutions made by adding small amounts of a strong acid or salt. Properties that exist among the anions present in the latter solutions are possessed by BF 4 −. Nonlinear behavior exhibited by formic acid oxidation is changed drastically by the presence of a small amount of any one of the anions studied. These results and other arguments support the hypothesis that HBF 4 enhances current–potential characteristics by causing the formation of surface anion complexes possessing OH components at low potentials.

Differences in Oscillations and Sequences of Dynamical States Caused by Anion Adsorption in the Electrochemical Oxidation of Formic Acid

Effects of anions on the electrocatalyzed oxidation of formic acid at polycrystalline Pt under constant current conditions are studied by varying the electrolyte composition. A subcritical bifurcation and an apparently unique sequence of oscillatory states are observed when the supporting electrolyte is H2SO4. Different behaviors, including a different sequence of oscillatory states, are seen when HClO4 is used as the supporting electrolyte. Effects of increasing the overall anion “adsorption strength” are also investigated by examining changes in the dynamical response when small amounts of HCl are added to the solution containing formic acid and HClO4. When the concentration of HCl is increased beyond a small critical value, instabilities occur that are not observed when using either the HCl free HClO4 solution or the H2SO4 solution. All the stated differences are in contrast to previously reported differences in potential control experiments that were caused by switching electrolytes. The differences in the latter experiments are quantitative. They were interpreted in terms of adsorption and blockage of surface reaction sites by anions. It is argued that the results of the current control experiments imply that anions are also directly involved in the oxidation process. They affect the formation and, consequently, the reactivity of surface water, surface bonded hydroxyl radicals, and Pt oxides.

Nonlinear dynamical analysis of spike generation in electrochemical oxidation of formic acid on Pt

A nonlinear dynamical analysis is made for the generation of potential spikes in response to the change in the current in the electrochemical oxidation of formic acid on Pt, based on a mechanistic model. This model assumes the potential-dependent adsorption, desorption, and reaction of the adsorbed water and carbon monoxide. The model is found to reproduce the spikes observed experimentally in a previous report. The trajectory of the state point in the state space shows how and why the system generates spikes.

Effects of anions on chemical instabilities in the oxidation of formic acid

Results are presented from experiments conducted on the electrochemical oxidation of formic acid at polycrystalline Pt under constant current conditions. Sulfuric acid and perchloric acid with and without small amounts of HCl were used as supporting electrolytes. The onset of distinctive instabilities, not observed in the HCl-free perchloric acid solution, occurred when the concentration of HCl reached 5 × 10 6 M. For [HCl] = 1 × 10 6 M, the observed instabilities were essentially the same as those seen in the HCl-free solution. The result indicates that instabilities might be used for the detection of fairly small anion concentrations. Instabilities observed using the sulfuric acid solution and those observed using the perchloric acid solution were drastically different. A greater extent of adsorption of a given anion cannot be the only reason for the different behaviors. It is argued that anions are directly involved in the oxidation process.

Dynamics of potential oscillations in the electrochemical oxidation of formic acid on Pt

A mechanistic model for the galvanostatic potential oscillation in the electrochemical oxidation of formic acid on Pt (H. Okamoto, N. Tanaka and M. Naito, Chem. Phys. Lett., 1996, 248, 289) is analyzed here from the viewpoints of nonlinear dynamics and bifurcation. The model assumes the potential-dependent adsorption, desorption, and reaction of water and carbon monoxide. It is shown that the adiabatic elimination of the potential is warranted in the dynamics and so the essential variables for the dynamics are only chemical ones. The potential oscillation occurs in a certain range of the applied current due to a Hopf instability. The potential dependence of the adsorption and desorption of water to and from the electrode plays an essential role in the Hopf bifurcation. The current dependence of the stability of the system is also a result of the potential dependence of the amount of adsorbed water.

Remote triggering of waves in an electrochemical system

In the potentiostatic electrochemical oxidation of formic acid on a platinum ring electrode under bistable conditions, an appropriate perturbation at one location of the ring can cause the emergence of a wave on the opposite side (remote triggering). These findings can be rationalized in terms of the nonlocal coupling function of the system and are theoretically reproduced by solution of the corresponding reaction-migration equation.