HBr electrolysis in the Ispara Mark 13A flue gas desulphurization process: electrolysis in a DEM cell

The potential application of a DEM cell for the electrolysis of hydrogen bromide in the Ispra Mark 13A process for flue gas desulphurization has been tested in a number of laboratory experiments and in long-duration tests in a bench-scale plant of the process. Satisfactory electrode materials have been found, i.e. Hastelloy C 276 for the cathode and a RuO₂ coating on titanium for the anode. Both electrode materials showed a good stability during a 1500 hours experiment. Cell voltage/current density relationships have been determined during bench-scale plant operation. A typical value is 1.5V at a current density of 2.5 kA m^–2. It has been shown that in an undivided cell a cathodic back reaction occurs which causes a decrease of the current efficiency. Under normal operation conditions current efficiencies of about 90% are obtained.A simplified flow model for the DEM cell was developed which is useful in understanding the phenomena which occur during scale-up of the cell. An industrial size installation for the production of 170 kg h^–1 of bromine at a current density of 2 kA m^–2 was constructed and has been in operation since August 1989.Nomenclature a _x thermodynamic activity of the constituentx (mol cm^–3) - C bromine concentration (mol l^–1) - e _z local current efficiency - e _ov overall cell efficiency - E _a ⁰ anodic standard potential (V) - E _c ⁰ cathodic standard potential (V) - E _a ^c equilibrium anode potential (V) - E _e ^c equilibrium cathode potential (V) - F Faraday number (C mol^–1) - g _a anodic overpotential (V) - g _c cathodic overpotential (V) - G electrolyte flow rate (l h^–1) - i current density (A m^–2) - K _c cathodic back reaction rate factor (l mol^–1) - L cell width (m) - n number of electrons involved (n=2) - R gas constant (J K^–1 mol^–1) - R _cell cell resistance (ohm m²) - R _c circuit resistance (ohm m²) - w _b local cathodic back reaction rate (mol m^–2 h^–1) - w _th local theoretical reaction rate (mol m^–2 h^–1) - W _th overall theoretical reaction rate (mol h^–1) - T temperature (K) - Z cell length (m)     

The effect of the type of electric current on the cathodic corrosion of aluminium

A comparative experimental study on the cathodic corrosion of aluminium in 0.52 M sodium chloride distilled water solutions is carried out. The electrolysis is conducted using a single half-cycle rectified, direct or industrial frequency current. Characteristic relationships concerning the cathodic corrosion are noted. Attention is drawn to the higher rates of cathodic corrosion observed on electrolysis with single half-cycle rectified current which is combined with lower energy costs.Nomenclature w _k1 cathodic corrosion rate for direct current electrolysis (g s^–1 m^–2) - w_k2 cathodic corrosion rate for single half-cycle rectified current electrolysis (g s^–1 m^–2) - w _a anodic dissolution rate (g s^–1 m^–2) - w _F theoretical Faradaic dissolution rate (g s^–1 m^–2) - w dissolution rate for alternating current electrolysis (g s^–1 m^–2) - j electric current density (A m^–2)     

Electrodeposition of catalytically active Co-Ni-Tl alloy powders from dilute sulphate baths

Cobalt-nickel-thallium alloy powders were electrodeposited from dilute metal sulphate baths of composition: 0.007–0.0245 mol l^–1 CoSO₄·7H₂O, 0.0245–0.007 mol l^–1 NiSO₄·6H₂O, 0.001 mol l^–1 TlCl, 0.5 mol l^–1 (NH₄)₂SO₄, 0.07 mol l^–1 Na₂SO₄·10H₂O and 0.4 mol l^–1 H₃BO₃. The cathodic polarization curves were traced during electrodeposition and utilized in the discussion of a reaction mechanism for the electrolytic powder deposition. The alloy composition and the cathodic current efficiency were influenced to a great extent by the bath composition (I) and slightly by the deposition current density (II). Irrespective of variables (I) and (II), the electrodeposition of the alloy belonged to the anomalous type. The surface morphology and the catalytic activity, towards the decomposition of 0.4% H₂O₂ solution, of the as-deposited alloy powders were affected predominantly by the percentage of cobalt in the alloy. X-ray diffraction studies showed that the alloys consisted mainly of the face-centred cubic nickel phase either alone or with minor proportions of face-centred cubic cobalt phase and hexagonal close-packed -cobalt phase. The occurrence of the latter phases was observed only in the alloys with a higher cobalt percentage than nickel.     

New electrodes for oxygen evolution in acidic solution

Conventional electrowinning of metals such as zine and copper from 1–1.5 kmol m^–3 H₂SO₄ electrolytes involves anodic oxygen evolution at Pb alloy/PbO₂ anodes operating at 200–800 A m^–2. The oxygen overpotential, estimated to be about 0.6 V, constitutes a significant proportion of the cell voltage (typically 2.5 V for Cu and 3.3 V for Zn). The objective of this work was to lower the anode overpotential and so decrease the process specific energy requirements, by devising new anode materials based on: (1) PTFE-bonded PbO₂ catalysts, supported on Pb–Ag alloys; (2) modification of the pore structure of porous electrodes to maximize the utilization of the available surface without the use of PTFE bonding. Both methods are shown to produce significant benefits in lowering oxygen overpotentials, though the latter technique has been tested only in alkaline electrolytes, as yet. However, with the former approach, substrate oxidation through the porous catalyst layer has been found to cause catalyst shedding after>60 h at 1 kA m^–2, though careful pre-oxidation of the anode substrate appears to extend the anode life.Paper presented at the 2nd International Symposium on Electrolytic Bubbles organized jointly by the Electrochemical Technology Group of the Society of Chemical Industry and the Electrochemistry Group of the Royal Society of Chemistry and held at Imperial College, London, 31st May and 1st June 1988.     

Modelling potentials, concentrations and current densities in porous electrodes for metal recovery from dilute aqueous effluents

One-dimensional steady-state models have been developed for the recovery of Pb(II) ions from lead–acid battery recycling plant effluent by simultaneous lead and lead dioxide deposition, including oxygen evolution/reduction and hydrogen evolution as loss reactions. Both monopolar and bipolar reactor with porous graphite electrodes were modelled, as a design aid for predicting spatial distributions of potentials, concentrations, current densities and efficiencies, as well as specific electrical energy consumptions and by-pass currents. Since the industrial effluent contains a large excess of supporting electrolyte (Na₂SO₄), the electrical migrational contribution to reactant transport rates was neglected and the current density–potential relationship was described by the Butler–Volmer equation, allowing for both kinetic and mass transport control. The models were implemented and the governing equations solved using commercial finite element software (FEMLAB). The effects were investigated of electrolyte velocity, applied cathode potential, dissolved oxygen concentration and inlet Pb(II) ion concentration on single-pass conversion, current efficiency and specific electrical energy consumptions. According to model predictions, de-oxygenation of the inlet process stream was found to be crucial to achieving acceptable (i.e. >0.8) current efficiencies. Bipolar porous electrodes were also determined to be inappropriate for the recovery of Pb(II) from effluents, as the low concentration involved resulted in the predicted fraction of current lost as by-pass current, i.e. current not flowing in and out of the bipolar electrode, to be greater than 90% for the ranges of the variables studied.     

Selective electrodeposition of PbO2 on anodised-polycrystalline titanium

Electrochemical experiments on titanium electrodes were coupled with electron backscattered diffraction (EBSD) experiments. The substrates were thermally treated and electropolished in order to have flat and reproducible polycrystalline surfaces, leading to EBSD orientation mapping. Afterwards, the samples were anodised by a galvanostatic procedure. It was shown that electrodeposition of PbO₂ from a 0.5 M Pb(NO₃)₂+2.5 M HNO₃ solution occurs selectively on the near {0 0 0 1} grains, whereas lead electrodeposition occurs on all the grains, whatever their orientation. These results are discussed, taking into account the fact that on {0 0 0 1} grains, the oxide layers are thinner than on other grains. It was concluded that electrodeposition is observed locally on Ti/TiO₂ electrodes for (i) cathodic electrodeposition of metals at low overvoltage; (ii) anodic electrodeposition of PbO₂, in potentiostatic or galvanostatic conditions.     

Electrochemical incineration of chloranilic acid using Ti/IrO2, Pb/PbO2 and Si/BDD electrodes

The electrochemical oxidation of chloranilic acid (CAA) has been studied in acidic media at Pb/PbO₂, boron-doped diamond (Si/BDD) and Ti/IrO₂ electrodes by bulk electrolysis experiments under galvanostatic control. The obtained results have clearly shown that the electrode material is an important parameter for the optimization of such processes, deciding of their mechanism and of the oxidation products. It has been observed that the oxidation of CAA generates several intermediates eventually leading to its complete mineralization. Different current efficiencies were obtained at Pb/PbO₂ and BDD, depending on the applied current density in the range from 6.3 to 50 mA cm⁻². Also the effect of the temperature on Pb/PbO₂ and BDD electrodes was studied.UV spectrometric measurements were carried out at all anodic materials, with applied current density of 25 and 50 mA cm⁻². These results showed a faster CAA elimination at the BDD electrode. Finally, a mechanism for the electrochemical oxidation of CAA has been proposed according to the results obtained with the HPLC technique.     

The behaviour of a trickle tower electrolytic cell for the production of cobalt(III) acetate from cobalt(II) acetate

The production of Co(III) acetate from Co(II) acetate using a bipolar trickle tower of graphite Raschig rings was investigated. Space time yields up to 18 kg m^–3 h^–1 were obtained, which showed no improvement over those achievable in a conventional plate and frame cell. A mathematical model of the system indicated that the electrode reactions occurred almost entirely at the opposing annular surfaces between consecutive layers of Raschig rings and that the unexpectedly low performance of the device was most probably due to the unfavourable mass transport conditions which existed in the intervening gaps.Nomenclature a annular cross sectional area of one Raschig ring (m²) - b _C kinetic exponential constant for reduction of Co(III) (V^–1) - b _A kinetic exponential constant for oxidation of Co(II) (V^–1) - b _H kinetic exponential constant for hydrogen evolution (V^–1) - b ₀ kinetic exponential constant for oxygen evolution (V^–1) - [Co(II)] concentration of Co(II) (mol m^–3) - [Co(III)] concentration of Co(III) (mol m^–3) - F Faraday constant (96 487 C mol^–1) - f fraction of total flow by-passing the annular gap between adjacent Raschig rings in a vertical row - I current per vertical column of rings (A) - k _C rate constant for reduction of Co(III) (A m mol^–1) - k _A rate constant for oxidation of Co(II) (A m mol^–1) - k _H rate constant for hydrogen evolution (A m^–2) - k _O rate constant for oxygen evolution (A m^–2) - k _L mass transfer coefficient (m s^–1) - Q flow rate per vertical row of Raschig rings (m³s^–1) - v volume of annular gap between adjacent Raschig rings in a vertical row (m³) - V superficial velocity of electrolyte (m s^–1) - _A anodic potential (V) - _C cathodic potential (V)     

The potentiodynamic response of polycrystalline nickel electrodes in 0.5mK2CO3

The electrochemical behaviour of nickel in 0.5 M K₂CO₃ is investigated by applying simple and combined potentiodynamic techniques in the potential regions of the Ni(OH)₂/Ni and Ni(III)/Ni(II) redox couples. The diffusion controlled hydrated NiCO₃ precipitation interferes with the electroformation of the Ni(OH)₂ prepassive layer. Both anodic and cathodic peak multiplicities are observed in the potential range of the Ni(III)/Ni(II) electrode. The presence of CO ₃ ^2– ions is tentatively associated with a change in the hydration of the composite Ni(OH)₂/NiOOH layer and eventually with HCOc ions coming out from the CO ₃ ^2– /HCO ₃ ^– equilibrium, which depends on the local change in pH produced during the corresponding anodic and cathodic reactions.     

An experimental study of mass transfer in pulse reversal plating

An experimental study has been made of the limiting pulse current density for a periodic pulse reversal plating of copper on a rotating disc electrode from an acidic copper sulfate bath containing 0.05m CuSO₄ and 0.5M H₂SO₄. The measurements were made over a range of the electrode rotational speeds of 400–2500 r.p.m., pulse periods of 1–100 ms, cathodic duty cycles of 0.25–0.9, and dimension-less anodic pulse reversal current densities of 0 to 50. The experimental limiting pulse current data were compared to the theoretical prediction of Chin's mass transfer model. A satisfactory agreement was obtained over the range of a dimensionless pulse period ofDT/ ²=0.001–1; the root mean square deviation between the theory and 128 experimental data points was ±8.5%.Notation C _b bulk concentration of the diffusing ion (mol cm^–3) - C _s surface concentration of the diffusing ion (mol cm^–3) - D diffusivity of the diffusing ion (cm² s^–1) - F Faraday's constant (96 500C equiv^–1) - i current density (A cm^–2) - i ₁ cathodic pulse current density (A cm^–2) - i ₃ anodic pulse reversal current density (A cm^–2) - i ₃ ^* dimensionless anodic pulse reversal density defined asi ₃/i _lim - i _lim cathodic d.c. limiting current density (A cm^–2) - i _{lim, a} anodic d.c. limiting current density (A cm^–2) - i _PL cathodic limiting pulse current density (A cm^–2) - i _PL ^* dimensionless limiting pulse current density defined asi _PL/i _lim - m dummy index in Equation 1 - n number of electrons transferred in the electrode reaction (equiv/mol) - l time (s) - t ₁ cathodic pulse time (s) - i ₃ anodic pulse reversal time (s) - T pulse period equal tot ₁+t ₃ (s) - T ^* pulse period defined asDT/ ² (dimensionless) Greek letters thickness of the steady-state Nernst diffusion layer (cm) - electrode potential (V) - _de time-averaged electrode potential (V) - _m eigenvalues given by Equation 2 (dimensionless) - ₁ cathodic duty cycle (dimensionless) - ₃ anodic duty cycle in pulse reversal plating (dimensionless) - kinematic viscosity (cm² s^–1) - electrode rotational speed (rad s^–1)     

Application of Combinatorial Methodologies to the Synthesis and Characterization of Electrolytic Manganese Dioxide

A combinatorial method has been used to investigate the effects of anodic current density, and Mn(II) and H₂SO₄ concentrations on the electrochemical synthesis and characterization of electrolytic manganese dioxide (EMD). The combinatorial method involved rapid parallel and series electrochemical deposition of EMD from electrolytes with various Mn(II)(0.15–1.82 M) and H₂SO₄(0.05–0.51 M) concentrations, at various anodic current densities (25–100 A m^–2), onto individual 1 mm² titanium electrodes, in an overall array consisting of 64 electrodes. Electrode characterization was then by average plating voltage (recorded during deposition), and open circuit voltage and chronoamperometric discharge in 9 M KOH. The applicability and benefit of the method was demonstrated by identifying the conditions of 0.59 M Mn(II), 0.17 M H₂SO₄ and 62.5 A m^–2 anodic current density as leading to the best performing EMD. These are comparable with existing knowledge regarding the synthesis and electrochemical performance of EMD, demonstrating clearly the capabilities of the combinatorial method, and providing a starting point for future experimentation. An added benefit of the method in this work was the considerable time saved during experimentation.     

Pitting corrosion of lead in sodium carbonate solutions containing NO3 ions

Pitting corrosion of Pb in Na₂CO₃ solutions (pH=10.8) containing NaNO₃ as a pitting corrosion agent has been studied using potentiodynamic anodic polarization, cyclic voltammetry and chronoamperometry techniques, complemented with scanning electron microscopy (SEM) examinations of the electrode surface. In the absence of NO₃⁻, the anodic voltammetric response exhibits three anodic peaks prior to oxygen evolution. The first anodic peak A₁ corresponds to the formation of PbCO₃ layer and soluble Pb²⁺ species in solution. The second anodic peak A₂ is due to the formation of PbO beneath the carbonate layer. Peak A₂ is followed by a wide passive region which extends up to the appearance of the third anodic peak A₃. The later is related to the formation of PbO₂. Addition of NO₃⁻ to the carbonate solution stimulates the anodic dissolution through peaks A₁ and A₂ and breaks down the dual passive layer prior to peak A₃. The breakdown potential decreases with an increase in nitrate concentration, temperature and electrode rotation rate, but increases with an increase in carbonate concentration and potential scan rate. Successive cycling leads to a progressive increase in breakdown potential. The current/time transients show that the incubation time for passivity breakdown decreases with increasing the applied anodic potential, nitrate concentration and temperature.     

Electrosynthesis of a manganese(iii) aminopolycarboxylate complex in alkaline media

Mn(iii)CyDTA [(trans-cyclohexane-1,2-diamine-N,N,N,N-tetraacetato) manganate(iii)] was generated electrochemically from Mn(ii)CyDTA (6–54 mm) in 0.1 m NaHCO₃ at pH 9.0 and 10.5, respectively, 25 °C, for two CyDTA/Mn molar ratios (1/1 and 2/1). A divided batch electrochemical reactor was employed with anode current densities from 2.6 to 102 A m^–2. Separate cyclic voltammetry experiments of Mn(iii)CyDTA in alkaline media showed a prepeak behaviour, indicating the adsorption of Mn(ii) species. The visible anodic deposit, formed during the electrosynthesis of Mn(iii)CyDTA at pH 10.5 and 1/1 CyDTA/Mn molar ratio on stainless steel and PbO₂/Pb, reduces the current efficiency for Mn(iii). For a Mn(ii) concentration of 18 mm and at 13 A m^–2, the graphite and platinized titanium anodes gave a current efficiency for Mn(iii) of 78% and 66%, respectively, without a visible deposit. A 2/1 CyDTA/Mn molar ratio, avoided a visible anodic deposit formation, but gave lower current efficiencies for Mn(iii) than in the case of a 1/1 ligand to metal ratio. The electrosynthesis of Mn(iii)CyDTA is recommended for routine preparation of the complex and is also suitable for in situ electrochemically mediated oxidations in alkaline media (up to pH 11).     

Kinetics of Sn electrodeposition from Sn(II)–citrate solutions

The influence of solution chemistry on the electrodeposition of Sn from Sn(II)–citrate solutions is studied. The distribution of various Sn(II)–citrate complexes and citrate ligands is calculated and the results presented as speciation diagrams. At a SnCl₂·H₂O concentration of 0.22 mol/L and citrate concentration from 0.30 mol/L to 0.66 mol/L, SnH₃L⁺ (where L represents the tetravalent citrate ligand) is the main species at pH below about 1.2 and SnHL⁻ is the main species at pH above about 4. Polarization studies and reduction potential calculations show that the Sn(II)–citrate complexes have similar reduction potentials at a given solution composition and pH. However, the Sn(II)–citrate complexes become more difficult to reduce with higher total citrate concentration and higher solution pH. Nevertheless, SnHL⁻ which forms at higher pH is a favored Sn(II)–citrate complex for Sn electrodeposition due to better plated film morphology, likely as a result of its slower electroplating kinetics. Precipitates are formed from the Sn(II)–citrate solutions after adding hydrochloric acid (to lower the pH). Compositional and structural analyses indicate that the precipitates may have the formula Sn₂L.     

Use of a rotating cylinder electrode in corrosion studies of a 90/10 Cu–Ni alloy in 0.5 mol L−1 H2SO4 media

The corrosion of 90/10 Cu–Ni alloy in deaerated 0.5 mol L^–1 H₂SO₄ containing Fe(III) ions as oxidant and benzotriazole as inhibitor was studied using a rotating cylinder electrode (RCE). Nonselective dissolution was observed in all experimental conditions investigated. In the absence of Fe(III) ions, the anodic process is diffusion controlled while cathodic process is charge transfer controlled. In contrast, with Fe(III) ions as oxidant, the cathodic process is controlled by diffusion and the anodic process is under charge transfer control. These conclusions were obtained from measurements of open circuit potential as a function of the RCE rotation rate as previously verified for the RDE. Inhibition efficiency evaluated from weight loss and calculated from polarization curves showed good agreement.     

The behaviour of PbO2 in concentrated sulphuric acid

Linear sweep experiments on Pb in H₂SO₄ at concentrations in excess of 5 mol dm^–3 have been conducted using computer controlled techniques. Measurements have indicated that the maximum charge in the PbO₂ reduction peak occurs at 5 mol dm^–3, the available capacity decreasing with the concentration of H₂SO₄.     

Hypochlorite electro-generation. I. A parametric study of a parallel plate electrode cell

A parametric study is described of a parallel plate Ti/PbO₂/x mol dm^–3 NaCl/Ti hypochlorite cell, for which the cell voltage, current efficiency, and energy yield (mol ClO^– kWh^–1) were examined as functions of current density, chloride concentration, and electrolyte flow rate, inlet temperature and pH.The cell was found to behave ohmically, with current efficiencies of 85–99% for 0.5 mol dm^–3 NaCl electrolyte, a typical chloride concentration for sea water. However, the hypochlorite energy decreased substantially with increased current density, reflecting the large contribution of the electrolyte ohmic potential drop to the cell voltage.The behaviour of the Ti/PbO₂ anode was found to be irreproducible, and low temperature (say 278K)/high current density operation was irreversibly detrimental both in terms of the anode potential/cell voltage and current efficiency.Nomenclature b polarization resistance (ohm m²) - d _min interelectrode spacing to minimize the cell voltage (m) - f(x) volume fraction of gas at levelx f - _av average volume fraction of gas - F Faraday constant (96487 C mol^–1) - h electrode length/height (m) - i(x) current density at positionx (A m^–2) - i _av average current density (A m^–2) - I cell current (A) - P pressure of gas evolved at electrodes (N m^–2) - R universal gas constant (8.314 J mol^–1K^–1 ) - R _eff total ohmic resistance of electrolyte and gas in cell (ohm) - s bubble rise rate (m s^–1) - chloride ion transport number - T electrolyte temperature (K) - w electrode width (m) - x distance from bottom of electrodes (m) - z number of Faradays per mole of gas evolved - (x) overpotential at positionx (V) - resistivity of gas free electrolyte (ohm m) - (x) resistivity at levelx of electrolyte containing bubbles (ohm m)     

Preparation and characterization of chromium deposits obtained from molten salts using pulsed currents

The electroplating of chromium from fused chloride electrolytes was investigated. The experimental conditions were defined taking into account the mechanisms of the electrochemical reduction of CrCl₂ and of the chromium nucleation and electrocrystallization phenomena. Chromium was plated on various substrates from concentrated LiCl–KCl–CrCl₂ (600 to 800 mol m^–3 CrCl₂) electrolyte. Direct or pulsed current electrolysis were carried out under a dry argon atmosphere in the 400 to 440 °C temperature range. The shape of the current signals was chosen, taking into account the chromium electrocrystallization phenomena onto a foreign substrate, so as to obtain well-defined structures for the chromium layers. The chromium deposits were characterized by SEM and EDX analysis, and by microhardness determination. Uniform chromium electroplates of high purity, high adherence with no cracks, were obtained by using pulsed current: signals with cathodic pulses and open-circuit periods preceded by cathodic pre-pulses. With this current shape, the mean rate of the chromium electroplating process remained lower than 10 m h^–1. However, using a repeated of periodic cathodic pre-pulse/cathodic pulse/anodic pulse/open circuit sequences, the growth rate of compact chromium layers increased to 100 m h^–1 or more.     

A feasibility study of mercury deposition in a lead fluidized bed electrode

Following previous work on the recovery of copper from very dilute solutions using a copper fluidized bed electrode, the behaviour of a lead fluidized bed electrode (FBE) is described, for the recovery of mercury from chloride solutions, as typified by chlor-alkali plant effluent.Injection of known quantities of Hg(II) into the FBE catholyte and integration of the current vs time response followed by chemical analysis, allowed mean current efficiencies for mercury deposition to be determined as a function of:feeder electrode potential, Hg(II) concentration, flow rate, bed depth, particle size range, and reservoir volume. By judicious choice of these experimental variables, particularly by limiting bed depths to 20 mm, (potentiostatic) current efficiencies for Hg(II) deposition of 99% could be achieved.Nomenclature a cross sectional area of FBE cell (1.26×10^–3 m²) - A area per unit volume of FBE electrode (m^–1) - c(x) concentration at distancex from feeder electrode (mol m^–3) - c ₀ inlet concentration (mol m^–3) - c _XL outlet concentration (mol m^–3) - D diffusion coefficient (m²s^–1) - I current density (A m^–2) - L static bed length (mm) - t time (s) - T catholyte temperature (K) - u electrolyte superficial linear velocity (mm s^–1) - V electrolyte volume (m³) - XL expanded bed length (mm) - diffusion layer thickness (m) - characteristic length (u/DA) (m) - (lead) density (11.4×10⁶ g m^–3)     

An in situ spectroelectrochemical Raman investigation of Au electrodeposition and electrodissolution in KAu(CN)2 solution

Spectroelectrochemical behaviour of CN^– on a Au electrode in a KAu(CN)₂ bath at pH 6.3 was studied by in situ confocal Raman spectroscopy. Internal (CN stretch) and external (Au–CN) CN^–-related frequencies were investigated under potentiostatic control in a potential interval spanning cathodic and anodic ranges (–1800 to +1200 mV vs Ag/AgCl). Electrochemical behaviour was assessed by cyclic voltammetry. Stark-shifted Au–NC^– species are the dominating ones under cathodic polarization. Above the hydrogen evolution potential a Au–H stretch band can also be observed. At open circuit Au–CN^– species tend to prevail, while anodic conditions relate to the enhanced formation of Au(CN)₂ ^– and OCN^–.