932 research outputs found
3D-printed porous electrodes for advanced electrochemical flow reactors: a Ni/stainless steel electrode and its mass transport characteristics
No full textPorous electrodes have shown high performance in industrial electrochemical processes and redox flow batteries for energy storage. These materials offer great advantages over planar electrodes in terms of larger surface area, superior space time yield and enhanced mass transport. In this work, a highly ordered porous stainless steel structure was manufactured by 3D-printing and coated with nickel from an acidic bath by electrodeposition in a divided rectangular channel flow cell. Following the electrodeposition, the volumetric mass transport coefficient of this electrode was determined by the electrochemical reduction of 1.0×10−3 mol dm−3 of ferricyanide ions by linear sweep voltammetry and chronoamperometry. The convection diffusion characteristics are compared with other geometries to demonstrate the novelty and the advantages of 3D-printed porous electrodes in electrochemical flow reactors. Robust porous electrodes with tailored surface area, composition, volumetric porosity and flow properties are possible
The 3D printing of a polymeric electrochemical cell body and its characterisation
No full textAn undivided flow cell was designed and constructed using additive manufacturing technology and its mass transport characteristics were evaluated using the reduction of ferricyanide, hexacyanoferrate (III) ions at a nickel surface. The dimensionless mass transfer correlation Sh = aRebScdLee was obtained using the convective-diffusion limiting current observed in linear sweep voltammetry; this correlation compared closely with that reported in the literature from traditionally machined plane parallel rectangular flow channel reactors. The ability of 3D printer technology, aided by computational graphics, to rapidly and conveniently design, manufacture and re-design the geometrical characteristics of the flow cell is highlighted
Flow influenced electrochemical corrosion of nickel aluminium bronze – Part I. Cathodic polarisation
No full textThe cathodic polarisation behaviour of CA 104 nickel aluminium bronze (NAB) has been examined in fully characterised seawaters (filtered and artificial) using the rotating disc electrode (RDE) and the rotating cylinder electrode (RCE). Linear sweep voltammetry and a potential step, current transient technique were used to examine the charge transfer and mass transfer controlled cathodic response as a function of both laminar and turbulent fluid flow. For freshly polished surfaces, the rate of irreversible charge transfer controlled oxygen reduction is controlled by the exchange of a single electron and hydrogen evolution is only significant at potentials more negative than approximately –1.0 V vs. the saturated calomel electrode (SCE)
Strategies for the determination of the convective-diffusion limiting current from steady state linear sweep voltammetry
No full textThe limiting current is an important parameter for the characterization of mass transport in electrochemical systems operating under convective-diffusion control. Four methods to determine the limiting current from current (I) vs. potential (E) plots are considered. Strategies to determine the limiting current values include: 1) direct measurement from I vs. E curves, 2) estimation from the current value at EL =DE/2 where DE is the length of the limiting current plateau), 3) evaluation of the first derivative dI/dE in the I vs. E curve and 4) from plots of E/I vs. I-1. The electrode reactions chosen to demonstrate the different strategies are: Cu(II) ? Cu(I) and Cu(I) ? Cu(0) in 1.5 mol dm-3 NaCl (pH 2) at a platinum rotating disc electrode and K3Fe(CN)6 ? K4Fe(CN)6 in 1 mol dm-3 NaOH at a 60 ppi reticulated vitreous carbon electrode (RVC)
The reduction of l-cystine hydrochloride at stationary and rotating disc mercury electrodes
No full textThe kinetics of l-cystine hydrochloride reduction have been studied at a mercury-plated copper rotating disc electrode (RDE) and at a stationary mercury disc electrode (SMDE) in 0.1 mol dm?3 HCl at 298 K. The reduction of the disulphide is irreversible and hydrogen evolution is the major side reaction. In contrast to steady state electrode kinetic studies at a mercury drop electrode (which shows a well-defined limiting current), the mercury-plated Cu RDE shows overlap between disulphide reduction and hydrogen evolution. These effects are attributable to strong reactant adsorption with a calculated surface coverage close to 100%. A Tafel slope of ?185 mV per decade is found with a cathodic transfer coefficient of 0.32 and a formal rate constant of 6.7 × 10?9 m s?1. The relative merits of steady state voltammetry at a mercury-plated copper RDE and linear sweep voltammetry at the SMDE are discussed, as is the mechanism of l-cysteine hydrochloride formation
Electrochemically deposited polypyrrole films and their characterization
No full textIonically conductive polypyrrole films have been deposited at 295 K from anhydrous acetonitrile, acetonitrile/H2O and NaBF4 aqueous solutions onto platinum, mild steel and stainless steel discs, using cyclic voltammetry, potentiostatic and galvanostatic techniques. Cyclic voltammetry of the polymer films has been studied as a function of water content of the acetonitrile solvent, polypyrrole concentration and potential sweep rate. Potentiostatic growth of thicker (<30 micron) films on stainless steel allowed free-standing polypyrrole membranes to be produced. Well adherent and conductive films were deposited at constant potential in stirred solutions from acetonitrile electrolytes containing 1% (v/v) of water. The membrane resistivity of the reduced films in 0.5 mol dm-3 KCl(aq) at 295 K was ? 1 x 106 ohm cm, while the resistivity of the oxidised membrane was 2700 ohm cm
FINANCING THE DISPOSAL OF UNWANTED AGRICULTURAL PESTICIDES
No full textThe disposal of accumulated agricultural pesticides is an expensive proposition due to the hazardous nature of these materials. States have inititated unwanted pesticide collection efforts based on several funding options. Through an evaluation of regulations, funding options and comparison of amounts of pesticides collected to expenditures for pesticides, our paper offers some recommendations for future state collection efforts. It may be advantageous to give greater weight to efficiency considerations for the disposal of existing unwanted pesticide stocks, while equity considerations may be emphasized for the disposal of anticipated future stocks.Environmental Economics and Policy,
The reduction of l-cystine hydrochloride at lead using static and rotating disc electrodes
No full textThe reduction of the disulphide, l-cystine hydrochloride to the l-cysteine hydrochloride thiol, in 0.1 mol dm?3 HCl at 298 K, has been studied at pre-treated, circular, 0.50 cm2 lead disc electrodes using steady state linear sweep voltammetry, non-steady state voltammetry and controlled potential coulometry. The diffusion coefficient for l-cystine hydrochloride was approximately 4.8 × 10?10 m2 s?1 from the three techniques. Reduction of the disulphide was irreversible and hydrogen evolution occurred as a competitive reaction at approximately ?1.35 V vs. SCE. Analysis of the mixed control kinetics, using a Koutecky–Levich approach, allowed the relative roles of charge transfer and mass transport to be resolved. Anomalously high Tafel slopes, of typically ?183 mV, were observed due to disulphide adsorption. The charge transfer kinetics are consistent with the first electron gain being rate determining while reaction orders are +1 with respect to both the disulphide and proton concentrations. The mechanism of l-cystine hydrochloride reduction has been critically discussed
The effect of surfactants on the kinetics of borohydride oxidation and hydrolysis in the DBFC
No full textThe kinetics of borohydride oxidation at gold in the presence of surfactants was analysed by cyclic voltammetry at a static disc and linear sweep voltammetry at a rotating disc electrode. The electrolytes contained 0.02 mol dm-3 NaBH4 in 3 mol dm-3 NaOH, at 23ºC, in the absence and in the presence of surfactants including alkoxylated ether non-ionic Triton X-100, sodium dodecyl sulphate (SDS) and FC4430. A rotating disc gold electrode of 0.125 cm2 geometrical area was used. Through these techniques, the value of the diffusion coefficient of the borohydride ion was found to be 0.98 × 10-5cm2s-1 and (0.33–1.63) × 10-5cm2s-1 in the absence and in the presence of surfactants, respectively. The presence of Triton X-100, and FC4430 surfactants inhibited borohydride oxidation while SDS increased the current density at concentrations lower than 0.001 wt. %. As promising results were obtained in the presence of SDS, the kinetic parameters such as the heterogeneous rate constant (at various potentials), the standard rate constant and the charge transfer coefficient were calculated in the presence of this surfactant at different concentrations
Electrodeposition of copper from mixed sulphate–chloride acidic electrolytes at rotating disc electrode
No full textThe effect of chloride ion on the deposition of copper from low metal concentrations in aqueous, acid sulphate solutions was investigated. The electrolytes contained 0·05 mol dm-3 CuSO4 and 0·5 mol dm-3 Na2SO4 at pH 2 and 296 K. The chloride ion concentration was varied in a wide range from 0·03 to 2·0 mol dm-3. Linear sweep voltammetry was carried out under well defined flow conditions at a smooth platinum rotating disc electrode. The progressive transition from a single, two-electron reaction for the reduction of Cu(II)?Cu(0) to two, single-electron reactions for the reduction sequence: Cu(II)→Cu(I)→Cu(0) was clearly evident as the chloride ion concentration increased. The charge transfer and mass transport characteristics of these reactions were evaluated. The formal potential for the Cu II) reduction to Cu(I), the shift in the potential region for complete mass transport controlled reduction of Cu(I) to Cu(0) and the potential for hydrogen evolution at the deposited copper were also studied. A semi-logarithmic relationship between exchange current density and half-wave potential for Cu(II)→Cu(I) with chloride ion was achieved when the Cl-/Cu(II) ratio in the electrolytes exceeded 2, due to the presence of the Cu(I) dichlorocuprous anion, CuCl2-
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