pH-neutral Electrolyte Research Articles

Silver–tungsten carbide nanohybrid for efficient electrocatalysis of oxygen reduction reaction in microbial fuel cell

Microbial fuel cell (MFC) is able to produce electricity from organic compounds upon anodic electrochemically active microorganisms (negative electrode) and cathodic oxygen reduction reaction (ORR, positive electrode). The diminution in ORR activity associated with the pH-neutral electrolyte degrades the cathode performance of MFC. To optimize the thermodynamic process of ORR involving dissociative chemisorptions of molecular oxygen onto metal surface and subsequent electroreduction of oxides, we synthesize the carbon-supported nanometer silver/tungsten carbide hybrid (Ag–WC/C) using hydrothermal method and evaluate its electrochemical activity in pH-neutral phosphate buffer solution. Both the powder X-ray diffraction analysis and transmission electron microscopy observation suggest the formation of nanocrystalline structure of Ag (homogeneous particles of average 14 nm) and WC crystals that were uniformly dispersed on amorphous carbon support. Based on electrochemical measurements, the Ag–WC/C nanohybrids achieve catalysis of four-electron ORR with efficiency being comparable to commercial Pt/C catalyst. The promoted ORR activity should originate from the synergistic effect between WC and Ag nanoparticles. The inexpensive Ag–WC/C catalyst can produce a comparable magnitude of power density to commercial Pt/C catalyst in MFC. This study gives a demonstration of platinum-free high-efficiency and cost-effective ORR electrocatalyst for more sustainable electricity generation from biomass materials in MFC.

In-situ activation of hydrogen evolution in pH-neutral electrolytes by additions of multivalent cations

Activation of the hydrogen evolution reaction (HER) in close to pH-neutral electrolytes can be achieved by addition of trivalent cations. This activation has been investigated using steady state polarization, electrochemical impedance spectroscopy (EIS) and chemical analysis of cathode films for yttrium. Several multivalent cations were included in this study, such as Al(III), Mg(II), Y(III), Sm(III), La(III) and Sc(III). In general the more acidic the metal ions the larger is the activation. Metal hydroxide films formed in the alkaline diffusion layer at the cathode surface can have a negative impact on the magnitude of this activation, and therefore complicate the interpretation of the results. The activation corresponds to a transport of metal ion complexes to the electrode surface and the reduction of bound ligand water to form hydrogen.

In-situ activated hydrogen evolution by molybdate addition to neutral and alkaline electrolytes

Activation of the hydrogen evolution reaction (HER) by in-situ addition of Mo(VI) to the electrolyte has been studied in alkaline and pH neutral electrolytes, the latter with the chlorate process i ...

Folic acid Determination in neutral pH electrolyte by Adsorptive Stripping Voltammetry at the Mercury Film Electrode

A stripping method for the determination of folic acid at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation of folic acid at the hanging mercury drop electrode followed by differential pulse measurement of the adsorbate. The adsorptive stripping response was evaluated with respect to concentration dependence, accumulation time, accumulation potential, scan-rate, size of the mercury drop, pH, ionic strength, presence of possible interferences and other variables. Cyclic voltammograms at pH 7.1(0.2 mol.L -1 KH2PO4/ NaOH buffer solution) showed four cathodic peaks at 0.57, 0.75, -1.18 and -1.39 V. The second peak, (at –0.75 mV), was the most useful for analytical purposes (more sensitive, quasi reversible and well defined) and it was used for quantifying folic acid by differential pulse adsorptive stripping voltammetry in four types of pharmaceutical multivitamin preparations. Sequential determination of folic acid with ascorbic acid is also possible. The results obtained in analysing medicines having folic acid as active constituent were compared favourably with those obtained by HPLC with UV detection. The average content of folic acid found in these medicines by HPLC was 4.81±0.09mg and by voltammetry, 4.87±0.09mg. The proposed method is very simple, efficient and does not involve time-consuming separation steps. KeywordsAscorbic acid, differential pulse voltammetry, folic acid, pharmaceutical preparations, vitamins.

Electrochemical properties of ruthenium metallopolymer: Monolayer-protected gold cluster nanocomposites

Nanocomposite polymer films of [Ru(bpy) 2(PVP) 10] 2+ metallopolymer and gold monolayer-protected clusters (MPCs) have been formed. Cyclic voltammetry of the films has been performed in both acidic (0.1 M H 2SO 4) and neutral (0.1 M Na 2SO 4) pH electrolyte solution. In acidic electrolyte, the protecting monolayers is desorbed as the gold surface is oxidized. Transmission electron microscopy of the nanocomposite following electrochemical cycling reveals aggregates of “naked” MPCs. In sharp contrast, in neutral pH electrolyte, the MPCs are stable towards voltammetric cycling and no gold oxide formation is evident in the voltammetry. The homogeneous charge-transfer diffusion coefficient, D CT , was determined for a range of nanocomposite films as the MPC mole fraction is systematically varied. When acidic electrolyte is used, D CT decreases from 2.8 ± 0.5 × 10 −10 to 1.5 ± 0.1 × 10 −11 cm 2 s −1 as the MPC mole fraction is increased from 0 to 0.45. In contrast, the D CT determined in neutral electrolyte is universally lower than that determined in acidic electrolyte, it increases by over two orders of magnitude from 2.6 ± 0.9 × 10 −15 to 4.0 ± 0.5 × 10 −13 cm 2 s −1 as MPC mole fraction increases from 0.05 to 0.5.

Tungsten carbide as electrocatalyst for the hydrogen evolution reaction in pH neutral electrolyte solutions

In this communication we demonstrate that tungsten carbide, WC, is a promising electrocatalyst for the hydrogen evolution reaction in pH neutral electrolytes. In a systematic investigation of mixed catalysts containing different fractions of WC, W2C, W and WO2 we show that the performance of the catalyst is proportional to its WC content, whereas W2C, W and WO2 play only a minor role. The relationship between WC content and electrocatalytic activity indicates that hydrogen evolution and oxidation are related to similar surface sites preferentially formed on WC. In contrast to anodic conditions, the cathodic polarization diminishes corrosion processes and thus increases the long term stability.

Comparative study on the performance of pyrolyzed and plasma-treated iron(II) phthalocyanine-based catalysts for oxygen reduction in pH neutral electrolyte solutions

The performance of pyrolyzed and plasma-treated non-precious catalysts for the oxygen reduction is discussed in the light of their application in microbial fuel cells. An Ar-radio frequency (RF) plasma treatment is applied to enhance the electrochemical activity of iron(II) phthalocyanine (FePc)-based catalysts. The electrochemical properties of the catalysts are analyzed by galvanodynamic linear sweep voltammetry and chronoamperometric experiments. Surface elemental analysis of the catalysts is examined by means of X-ray photoelectron spectroscopy (XPS). The influence of plasma power and treatment time on the elemental surface concentration and performance of the catalysts is investigated. The electrochemical activity, expressed in terms of the current density at 0 V vs. Ag/AgCl, is up to 40% higher for the plasma-treated samples than for pyrolyzed ones. It is found that optimal treatment time was 30 min and optimal plasma power was 150 W for the best electroactivity of FePc-based catalysts. From the results of XPS data, it is revealed that Ar-plasma treatment of the catalysts leads to an increase in the oxygen and nitrogen concentration on the catalysts surface. A correlation is found between the activity and surface concentration of oxygen and nitrogen on the catalysts’ surface.

Investigation of the oxygen evolving electrode in pH-neutral electrolytes: Modelling and experiments of the RDE-cell

A model has been developed to illustrate the complex interplay between the acidifying electrode reactions for oxygen evolution, mass transport and homogeneous reactions in pH-neutral electrolytes. Modelled polarisation curves of the oxygen evolution reaction were verified by polarisation curves experimentally measured in 5 M NaClO 4 on a RDE of DSA material. The conditions in the simulations and in the experiments were similar to those in the chlorate process (high ionic strength, 70 °C, chromate-containing electrolyte, DSA electrode), in which the oxygen evolution reaction is one of the possible side reactions. The model predicted the concentration gradients of H +, OH −, CrO 4 2− and HCrO 4 − during oxygen evolution on the RDE. It was found that an important part of the chromate buffering effect at high current densities occurs in a thin (in the order of nanometers) reaction layer at the anode. From comparisons between the model and experiments, a buffering reaction has been proposed. The most likely reaction for the chromate buffering in the investigated system is CrO 4 2− reacting with water to HCrO 4 − and OH −. In the chlorate process, where chromate is a buffer and oxygen evolution is a side reaction, it is likely that chromate promotes oxygen evolution from OH −.

Studies on the particulation and percolation in ultrafine ceramic reinforced barrier layers

Discusses the particulation of organic barrier layers, based on laboratory‐bench data, obtained from the exposure of painted panels in low, high or neutral pHelectrolytes. It also discusses their compatibility with the succeeding and preceding layers and the galvanic interactions at the layer substrate interfaces. Aspects like substrate effect, leaching of the micaceous iron powder, role of high temperature and hydrodynamic disturbances and distribution of ultrafine particulates have been highlighted using potential versus time plot, AAS data, and galvanic current measurements and XRD analysis. Exposure tests conducted under ambient conditions and under very strong hydrodynamic disturbances, revealed superior properties of the SiC particulated epoxy based barrier layers.

Homogeneous and heterogenous charge transfer dynamics of [Os(bipy) 2(PVP) nCl]Cl films in neutral pH electrolytes

The homogeneous charge transport rate ( D CT), and heterogenous electron transfer rate ( k 0), for the Os(II/III) oxidation within [Os(bipy) 2(PVP) n Cl]Cl films [25 ≥ n ≥ 5; PVP = poly(4-vinylpyridine); bipy = 2,2′-bipyridyl] have been evaluated using cyclic voltammetry and chronamperometry as well as sampled current voltammetry. The effect of electrolyte concentration and redox site loading on these parameters is examined in both sodium chloride and lithium perchlorate supporting electrolytes. Thermodynamic parameters evaluated for the homogeneous charge transport process suggest that ion diffusion limits the rate of charge transport through these materials for low electrolyte/high redox site loading combinations. A linear correlation between D CT and k 0 is observed for all redox site loading/electrolyte concentration combinations. This behaviour is interpreted in terms of the influence of the physico-chemical properties of the polymer film on the coupled heterogenous and homogeneous charge transfer reactions.

A comment on the analysis of CO hydrogenation using the BOC-MP approach

The Ni3S2 bulk phase supports efficient oxygen reduction reaction (ORR) catalysis in pH neutral aqueous electrolytes. Here, we combine electrochemistry, surface spectroscopy, and high-resolution microscopy to show that Ni3S2 undergoes self-limiting oxidative surface restructuring under ORR conditions to form an amorphous surface film conformally coating the Ni3S2 crystallites. The surface film has a nominal NiS stoichiometry and is highly active for ORR catalysis. Density functional theory calculations suggest that, to a first approximation, the catalytic activity of nickel sulfides is determined by the Ni-S coordination numbers at surface-exposed sites through a simple geometric descriptor. In particular, Ni surface sites with three S nearest neighbors, formed via reconstruction of the Ni3S2 surface, provide an optimal energetic landscape for ORR catalysis. By providing a framework for understanding catalytic activity on reconstructed amorphous surface phases, the work enables the rational design of high-performance electrocatalysts based on kinetically labile, earth-abundant materials.

Studies on polyelectrolytes. III. Polyglucosamine hydrochloride

Summary The viscosity, conductivity, and the effect of pH and other neutral electrolytes on the physicochemical properties of polyglucosamine hydrochloride solutions have been measured. The similarity in behavior of polyglucosamine hydrochloride to those of other similarly constituted substances in which the polymer ion is oppositely charged, has been shown. All these properties can be explained by the folding-chain theory of Fuoss.