EQCM Study of Rhodium Anodic Dissolution in Sulfuric Acid

Rh anodic dissolution is studied in 0.5 M H₂SO₄ solution in the E range from 0.2 to 1.2 V (RHE) by means of EQCM, cyclic voltammetry, photometry, and XPS. Bright pure Rh electroplate 0.5 m thick on a gold sputtered quartz crystal electrode is used for electrochemical and microgravimetrical studies. It is found that the increase in Rh electrode weight during the anodic process is lesser than its decrease during the cathodic one. The difference is 120 ± 60 ng cm^–2. The electrode weight also decreases under open-circuit conditions, i.e. at E _{I = 0}. A linear relationship between the weight change and the charge exists for the anodic process. The presence of Rh(III) compounds in the solution and on the electrode surface is confirmed by a photometrical analysis and XPS measurements. It is assumed that the formation and reduction of Rh(OH)₃ phase on Rh electrode surface within E range investigated proceed according to equation Rh + 3H₂O [Rh(OH)₃]_s + 3H⁺ + 3e, where [Rh(OH)₃]_s is a surface layer of Rh(OH)₃ phase. is evaluated to be 0.6 V. Rh(OH)₃ partly dissolves in the electrolyte.     

Realization of Rhodium Metal‐Oxide Electrode in Indifferent Electrolytes

The pH‐dependence of the stationary open‐circuit potential E_i=0^st of rhodium electrode with a surface layer of anodically formed insoluble compounds has been studied in sulfate and phosphate solutions by means of cyclic voltammetry and chronopotentiometry. The range of potentials of the investigations performed has been confined to the region of rhodium electrochemical oxidation/reduction, i.e., 0.2<E<1.2 V (RHE) in order to prevent any possible interference of other reactions such as H₂ and O₂ evolution. It has been shown that rhodium electrode with a layer of surface compounds formed anodically at E<<1.23 V (RHE) behaves like a reversible metal‐oxide electrode within the range of pH values from ca. 1.0 to ca. 8.0. It has been presumed that the stationary potential of such electrode is determined by the equilibrium of the following electrochemical reaction: Rh+3H₂O??Rh(OH)₃+3H⁺+3e^?. The pH‐dependence of the reversible potential of Eequation/tex2gif-inf-6.gif electrode has been found to be: Eequation/tex2gif-inf-8.gif=E_i=0^st=0.69?0.059 pH, V. In acid solutions (pH<2.0) rhodium hydroxide dissolves into the electrolyte, therefore, to reach equilibrium, the solution must be saturated with Rh(OH)₃. This has been achieved by adding Rh³⁺ ions in the form of Rh₂(SO₄)₃. The solubility product of Rh(OH)₃, estimated from the experimental Eequation/tex2gif-inf-16.gif?pH dependence obtained, is ca. 1.0×10^?48, which is close to the value given in literature.     

Electrochemical properties of sulfur adsorbed on gold electrodes

The electrochemical properties of sulfur adsorbed on gold electrodes were studied in 10^?5M solutions of S^2? in 1 M NaOH. In general, ∵_S is less than a monolayer. At E=0.05 V only, a monolayer will be formed after long times. The sulfur layer is stable in the potential range between ?0.6 and +0.4 V. At lower potentials, sulfur can be desorbed cathodically (charge Q_red), but at higher potentials, where layers of gold oxide are formed, the sulfur is oxidized anodically (charge Q_ox). From the ratio Q_red·6/Q_ox=γ, the electrosorption valency γ=?2 is obtained. This means, that the sulfide ions are almost completely discharged during adsorption. The same layer can be formed by adsorption from polysulfide solutions, which can be explained by a break of the sulfur bond and adsorption of single sulfur atoms. The double layer capacity decreases during adsorption of sulfur indicating the formation of an insulating sulfur layer with a dielectric constant of about 2. The anodic adsorption of sulfide ions is limited by diffusion only. For longer polarisation times, the coverage is independent of time, i.e. place exchange reactions between Au and S can be excluded. The cathodic desorption as well as the anodic oxidation of the adsorbed sulfur are potential dependent charge transfer processes, as can be concluded from potentiodynamic measurements with various sweep rates.     

Quasi-reversible two-electron reduction of oxygen at gold electrodes modified with a self-assembled submonolayer of cysteine

The electrochemical reduction of molecular oxygen (O₂) has been performed at gold electrodes modified with a submonolayer of a self-assembly (sub-SAM/Au) of a thiol compound (typically cysteine (CYST)) in O₂-saturated 0.5 M KOH. At bare gold electrode O₂ reduction reaction proceeds irreversibly, while this reaction is totally hindered at gold electrodes with a compact structure of CYST over its surface. The partial reductive desorption of the compact CYST monolayer was achieved by controlling the potential of the CYST/Au electrode, leading to the formation of a submonolayer coverage of the thiol compound over the Au electrode surface (sub-SAM/Au), at which the CYST molecules selectively block the Au(1 0 0) and Au(1 1 0) fractions (the so-called rough domains) of the polycrystalline Au while the Au(1 1 1) component (the so-called smooth domains) remains bare (i.e., uncovered with CYST). This sub-SAM/Au electrode extraordinarily exhibits a quasi-reversible two-electron reduction of molecular oxygen (O₂) in alkaline medium with a peak separation (ΔE_p) between the cathodic and anodic peak potentials (E_p^c,E_p^a) of about 60 mV. The ratio of the anodic current to the cathodic one is close to unity. The formal potential (E^o′) of this reaction is found to equal −150 mV vs. Ag/AgCl/KCl(sat.).     

Iridium Anodic Oxidation to Ir(III) and Ir(IV) Hydrous Oxides

Iridium oxide films (IROFs) are known to have an enhanced or the so‐called super‐Nernstian (<59 mV/pH) pH‐sensitivity. The intention in the present study was to find out the reasons of such behavior and also to elucidate the nature of iridium anodic oxidation processes. The methods employed were combined cyclic voltammetry and chronopotentiometry. Iridium layers of 0.1 to 0.2 μm thickness, deposited thermally on titanium or gold‐plated titanium substrates, were used for investigations. IROFs on the surface of working electrodes were formed anodically by applying a constant potential in deaerated and oxygen‐containing solutions of 0.5 M H₂SO₄, 0.1 M KOH and 0.5 M H₃PO₄+KOH. Linear pH‐dependences of the stationary open‐circuit potential with the slopes close to 59 mV/pH were found for iridium electrode oxidized at 0.4 V–0.8 V (RHE) in deaerated and at 0.8 V–1.2 V (RHE) in O₂‐containing solutions. They were attributed to reversible Ir/Ir(OH)₃ and Ir/ IrO₂?nH₂O metal‐oxide electrodes, respectively. It has been suggested that the main current peaks seen in the voltammograms of iridium electrode in acid and alkaline solutions are of different nature. The difference between iridium electrode surface states in acid and alkaline solutions has been presumed to be the main reason of super‐Nernstian pH‐sensitivity of the IROFs. On the basis of the results obtained standard potential of Ir/Ir(OH)₃ electrode and the solubility product of Ir(OH)₃ have been evaluated: =0.78±0.02 V and K_sp=3.3×10^?64.     

Electrochemical behavior of phthaloyl peroxide in aqueous media

The electrochemical behavior of phthaloyl peroxide C₈H₄O₄ on an Au disk electrode in a 0.05 M aqueous solution of Na₂SO₄ was studied by cyclic voltammetry (CVA). It demonstrated a high activity in cathodic reduction with the formation of an irreversible peak on the CVA curve at E =–0.81 V. Additionally, during the anodic oxidation of C₈H₄O₄, the surface of the Au electrode became passivated by compounds which prevented its oxidation during the registration of repeated cycles. Apparently, these compounds are surface complexes of phthaloyl peroxide with a gold cation.     

EQCM Study of Ru and RuO2 Surface Electrochemistry

The present study represents comparative analysis of voltammetric and microgravimetric behavior of active ruthenium (Ru), electrochemically passivated ruthenium (Ru/RuO₂) and thermally formed RuO₂ electrodes in the solutions of 0.5 M H₂SO₄ and 0.1 M KOH. It has been found that cycling the potential of active Ru electrode within E ranges 0 V–0.8 V and 0 V–1.2 V in 0.5 M H₂SO₄ and 0.1 M KOH solutions, respectively, leads to continuous electrode mass increase, while mass changes observed in alkaline medium are considerably smaller than those in acidic one. Microgravimetric response of active Ru electrode in 0.5 M H₂SO₄ within 0.2 V–0.8 V has revealed reversible character of anodic and cathodic processes. The experimentally found anodic mass gain and cathodic mass loss within 0.2–0.8 V make 2.2–2.7 g F^?1, instead of 17 g F^?1, which is the theoretically predicted value for Ru(OH)₃ formation according to equation: Ru+3H₂O?Ru(OH)₃+3H⁺+3e^?. In the case of Ru/RuO₂ electrode relatively small changes in mass have been found to accompany the anodic and cathodic processes within E range between 0.4 V and 1.2 V in the solution of 0.5 M H₂SO₄. Meanwhile cycling the potential of thermally formed RuO₂ electrode under the same conditions has lead to continuous decrease in electrode mass, which has been attributed to irreversible dehydration of RuO₂ layer. On the basis of microgravimetric and voltammetric study as well as the coulometric analysis of the results conclusions are presented regarding the nature of surface processes taking place on Ru and RuO₂ electrodes.     

Photoelectrochemical studies on gold electrodes with surface oxide layers: Part I. Photocurrent measurement in the visible region

By illumination with visible light at wavelengths of 340–730 nm, anodic photocurrents were observed at a gold electrode in contact with a 0.2 M NaClO₄ aqueous solution (pH 6.0) in the potential range from +1.0 to +2.1 V vs. RHE. Based on the results of potentiodynamic and photocurrent measurements, the following three characteristic potential ranges have been distinguished: (1) +1.0–+1.4 V, where possibly low-coverage surface oxides (or chemisorbed OH) other than Au₂O₃ are present; (2) +1.5–+1.8V where the predominant surface oxide is Au₂O₃ up to ca. 1 nm in thickness; and (3) above +1.9 V, where a thicker surface layer, absorbing mainly in the UV wavelength range, is formed on the Au₂O₃ under-layer. The photocurrent quantum yield at the Au₂O₃ layer 0.3–0.8 nm thick was estimated to be on the order of 20% at 490 nm, assuming an absorption coefficient of 10⁵ cm^?1.     

Gold Dissolution Electrocatalysis in Thiourea Electrolytes in the Presence of Chemisorbed Sulfide Ions

Adding a microscopic quantity of sodium sulfide (～10^?5 M) into acid solutions of thiourea leads to a dramatic acceleration of anodic dissolution of gold. The acceleration effect is greater at larger thiourea concentrations (c) and longer times of the electrode contact with solution (Δt) before the beginning of measurements. The effect diminishes after a polarization curve passes through a maximum at E ? 0.5 V. Regularities of the gold dissolution in a solution containing 0.1 M thiourea and 0.5 M H₂SO₄ at given values of c and Δt are studied with use made of the technique of renewing the electrode surface by cutting off a thin surface layer of metal. The discovered regularities are given an explanation which is based on the assumption that the dissolution process is catalyzed by sulfide ions adsorbed on the electrode surface.     

Oxidation of the polycrystalline gold foil surface and XPS study of oxygen states in oxide layers

Gold oxide films obtained on the surface of polycrystalline gold foil upon oxidation by oxygen activated by a high-frequency discharge have been studied by X-ray photoelectron spectroscopy. High-frequency O₂ activation affords oxide films more than 3–5 nm thick. As follows from Au4f spectra, the surface gold atoms are oxidized to the oxidation state +3. The O1s spectra have a composite shape and are decomposed into four components that characterize nonequivalent states of oxygen in the resulting oxide films. It is assumed that the two major oxygen states (E _b(O1s) = 529.0 and 530.0 eV) correspond to the oxygen atoms in two-and three-dimensional gold oxide Au₂O₃, respectively. The oxygen states characterized by the higher binding energies (E _b(O1s) = 531.8 and 535.2 eV) likely correspond to molecular oxygen in peroxide and superoxide groups, respectively.     

Electrochemical and XPS measurements on thin oxide films on zirconium

The potentiodynamic growth of thin oxide films on zirconium electrodes was investigated by coulometric and simultaneous impedance measurements, as a function of the electrode potential (0 V ⩽ E ⩽ 9 V), the pH (0 ⩽ pH ⩽ 14) and the surface preparation (electropolishing, etching and mechanical polishing). The initial film thickness d₀ is at least 4–6 nm; with increasing potential, the oxide grows irreversibly by 2.6 nm/V (pH 0.3) up to 3.2 nm/V (pH 14). In Cl⁻- and ClO⁻₄-containing solutions the oxide growth is limited by localized corrosion. The oxide behaves like a typical insulator with a donor concentration N_D < 10¹⁹ cm⁻³ and a dielectric constant D = 31. Below −0.5 V (vs. SHE) only, th film behaves like an n-type semiconductor with N_D ≈ 3 × 10¹⁹ cm⁻³. From photoelectrochemical measurements a direct and an indirect transition with band gap energies of E_g = 5 eV and E_g = 2.8 eV could be derived. Anodic electron-transfer reactions (ETRs) are blocked at the homogeneous oxide surface, but cathodic ETRs are possible at larger overvoltages. Near the flatband potential E_fb ≈ −1.3 ± 0.2 V (vs. SHE) hydrogen evolution takes place with a simultaneous increase of the capacity which may be attributed to hydrogen incorporation. With XPS measurements the stoichiometry of the oxide film was determined as ZrO₂ at all the pH values examined, but a thin outer layer contained some hydroxide. Components of the forming electrolyte could not be detected (sulphate, borate and perchlorate < 1%), but etching in HF caused accumulation of F⁻ at the inner boundary.     

EQCM Study of Iridium Anodic Oxidation in H2SO4 and KOH Solutions

In the present study anodic oxidation of iridium layer formed thermally on a gold‐sputtered quartz crystal electrode has been investigated by electrochemical quartz crystal microgravimetry (EQCM) in the solutions of 0.5 M H₂SO₄ and 0.1 M KOH. The emphasis here has been put on the microgravimetric behavior of iridium as a metal, because a few previous EQCM studies reported in literature have been devoted to iridium oxide films (IROFs). The objective pursued here has been to elucidate the nature of the main voltammetric peaks, which occur at different ranges of potential in the solutions investigated. It has been found that anodic oxidation of iridium electrode in 0.5 M H₂SO₄ and 0.1 M KOH solutions is accompanied by irregular fluctuations of the electrode mass at 0.4 V<E<0.8 V followed by regular increase in mass at 0.8 V<E<1.2 V. The cathodic process initially, at 1.2 V>E>0.9 V, proceeds without any or with slight increase in electrode mass, whereas at E<0.8 V a regular decrease in mass is observed. It has been found that mass to charge ratio characterizing the processes of interest is 2 to 3 g F^?1in acidic medium, whereas in the case of alkaline one it is 4 to 6 g F^?1. The main pair of peaks seen in the voltammograms of Ir electrode in alkaline medium at E<0.8 V is attributable to redox transition Ir(0)→Ir(III), whereas those observed in the case of acidic medium at E>0.8 V should be related to the redox process Ir(0)→Ir(IV) going via intermediate stage of Ir(III) formation. As a consequence of these redox transitions, the gel‐like surface layer consisting of Ir(III) or Ir(IV) hydrous oxides forms on the electrode surface.     

Electrochemistry of a carotenoid self-assembled monolayer

A carotenoid self-assembled monolayer was prepared by dipping a gold electrode into a solution of 4^′-thioxo-β,β-caroten-4-one in acetonitrile. Electrochemistry of the surface layer was investigated by cyclic voltammetry in an aqueous solution. No electrochemical reaction was detected in the potential region between 0.5 and −0.6 V vs. SCE. The anodic reaction of adsorbed carotenoid occurs at 0.8 V, whereas the irreversible anodic desorption proceeds at 1.4 V in 0.01 M HClO₄. Formation of the surface layer resulted in a decrease of the charging current as well as in a strong inhibition of the electron transfer reaction for species such as Fe(CN)₆³⁻, Ru(NH₃)₆³⁺, and dissolved oxygen. Prolonged voltage cycling in the O₂ reduction range induced some changes in the surface layer characteristics that were tentatively accounted for by the cross-linking of adsorbed molecules under the effect of transient oxygen radicals.     

Coupled radiotracer and voltammetric study of the adsorption of 1-hydroxy-ethane-1,1-diphosphonic acid on polycrystalline gold

Coupled application of a version of the in-situ radiotracer ‘foil’ method and voltammetry provided information on the time-, potential-, concentration- and pH-dependent adsorption of 1-hydroxy-ethane-1,1-diphosphonic acid (HEDP) on a polycrystalline gold electrode, and on the effect of Zn²⁺ ions on the adsorption phenomena. Adsorption processes on the oxide-free surface of gold were observed to be potential-dependent in the potential range 0.05–1.00 V (versus RHE), while formation and irreversible accumulation of oxidation products of HEDP could be detected at E>1.00 V. The relative adsorption strength of HEDP (its dissociation and/or oxidation products) was found to be higher on an oxide-free gold surface than on an oxide-covered one. The surface excess of HEDP increased with increasing pH. Addition of Zn²⁺ ions to the solution exerted a substantial effect on the HEDP accumulation. Namely, significant differences in the surface coverage, as well as in the kinetics and mechanism of HEDP adsorption could be detected in the potential regions below and above E=0.2 V. Reduction of Zn(II) species at E≤0.1 V is probably coupled with the induced adsorption of HEDP on an Au electrode, leading to the formation of a polymolecular HEDP–Zn surface complex layer.     

Potential dependence of anodic current transients on the renewed gold surface in thallium-containing thiosulfate solutions

The effect of potential on the anodic current transient times τ_p, which were measured on the gold electrode surface renewed by cutting off a thin surface metal layer immediately in the thallium-containing thiosulfate solutions of compositions (M): 0.05 Na₂S₂O₃, 10^?5 to 10^?4 TlNO₃, and 0.25 K₂SO₄, is studied. It is shown that the logarithm of inverse transient times 1/τ_p linearly depends on the electrode potential. Using the microgravimetrical method, it is found that, in the studied potential range, the amount of chemisorbed thallium ions only slightly depends on the potential, and at E = 0.3 V, it is approximately 0.12 μg/cm². It is evidenced that the transients reaches a plateau, when an equilibrium surface concentration of catalyst is reached. The value 1/τ_p reflects the rate of electrochemical oxidation of preliminarily adsorbed thallium(I) ions with the formation of catalytically active thallium(III) ions, and the first electron transfer is the limiting stage of the process.     

Direct electrochemistry and electrocatalysis of hemoglobin on gold nanoparticle decorated carbon ionic liquid electrode

In this paper a carbon ionic liquid electrode (CILE) was fabricated by using ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM]EtOSO₃) as modifier and further gold nanoparticles were in situ electrodeposited on the surface of CILE. The fabricated Au/CILE was used as a new platform for the immobilization of hemoglobin (Hb) with the help of a Nafion film. Electrochemical experimental results indicated that direct electron transfer of Hb was realized on the surface of Au/CILE with a pair of well-defined quasi-reversible redox peaks appeared. The formal peak potential (E⁰′) was obtained as −0.210 V (vs. SCE) in pH 7.0 phosphate buffer solution (PBS), which was the characteristic of Hb heme Fe(III)/Fe(II) redox couple. The fabricated Nafion/Hb/Au/CILE showed excellent electrocatalytic activity to the reduction of trichloroacetic acid (TCA) and the reduction peak current was in proportional to TCA concentration in the range from 0.2 to 18.0 mmol/L with the detection limit as 0.16 mmol/L (S/N = 3). The proposed electrode showed good stability and reproducibility, and it had the potential application as a new third-generation electrochemical biosensor.     

The influence of the conditions of the anodic formation and the thickness of Ag(I) oxide nanofilm on its semiconductor properties

The anodic formation of Ag(I) oxide nanofilms on polycrystalline silver and Ag–Au alloys as well as on low-index single crystals of silver in 0.1?М KOH was examined. By the methods of photocurrent i _ph and photopotential E _ph measurements, the n-type conductivity of Ag₂O film was established. Since the film (6–120 nm) is thinner than the space charge region, the dependence of photocurrent and photopotential appears on the film thickness L: i _ph ~L and E _ph ~L ². The transition from polycrystalline silver to single crystals as well as the addition of a small amount of gold (X _Au?≤?4 at.%) into the silver lattice decreases the degree of deviation from the stoichiometric composition Ag₂O. The parameters of Ag₂O film (optical absorption coefficient α, donor defects concentration N _D, space charge region W, and Debye’s length of screening L _D) depend on the index of a crystal face of silver, volume concentration of gold X _Au in the alloy, and film-formation potential E. At Е?=?0.52 V, the sequences of variation of these parameters correlate with the reticular density sequence. The growth of the potential disturbs these sequences. The band gap in Ag₂O formed on Ag_poly, Ag_hkl, and Ag–Au is 2.32, 2.23, and 2.19 eV. Flat band potential in Ag(I) oxide, formed on Ag_poly in 0.5 M KOH is 0.37 V. The appearance of the clear dependence between the state of the oxide/metal interface and the structure-sensitive parameters of semiconductor Ag(I) oxide phase allows considering the anodic formation of Ag₂O on Ag as a result of the primary direct electrochemical reaction, not of the precipitation from the near-electrode layer.     

Étude de l'oxydation et de la réduction électrochimiques de l'or par ellipsométrie avec excitation de plasmons de surfaces (SEW)

We studied the variation of optical parameters of voltage-sweep oxidized films on gold electrodes (evaporated gold on glass; 0.5 M H₂SO₄; 0<V<1.8 V/ENH; dV/dt=0.03 V s^?1). By ellipsometry with surface plasmons, we can measure large variations of Δ and ψ with oxygen coverage (20° for Δ; 10° for ψ). By associating optical and coulometric data, and assuming different values for the thickness d_f⁰ of diatomic Au₂O₃ layer corresponding to V=1.6 V, θ=1.2 (2 Å<d_f⁰<10 Å) we calculate at each coverage, the complex dielectric constant ?~, during oxidation and reduction steps. Anodic sweep: if 1.3 V<V<1.45 V (0<θ<0.38), ε₂?0. Only chemisorbed oxygen is present on the surface. If 1.45<V<1.60 V (0.38<θ<1.2) ε₁ and ε₂ increase according to the generalized Lorenz-Lorentz equation applied to a model of lateral growth of Au₂O₃ nuclei. If V>1.6 V, ε₁ and ε₂ have very slight variations with θ. Cathodic sweep: the slight variation of ε₂ with coverage for θ≥0.6 is in agreement with a model of uniform reduction of oxidized film until the Au₂O₃ layer becomes monoatomic. Optical, crystallographic, and coulometric data make us consider d_f⁰=3.7 Å to be the most likely value.     

Dielectric properties of tetragonal tungsten bronze films deposited by RF magnetron sputtering

Tetragonal tungsten bronze (TTB) films have been synthesised on Pt(111)/TiO₂/SiO₂/Si substrates from Ba₂LnFeNb₄O₁₅ ceramics (Ln = La, Nd, Eu) by RF magnetron sputtering. X-ray diffraction measurements evidenced the multi-oriented nature of films with some degrees of preferential orientation along (111). The dependence of the dielectric properties on temperature and frequency has been investigated. The dielectric properties of the films are similar to those of the bulk, i.e., ε ∼150 and σ ∼10⁻⁶ Ω⁻¹ cm⁻¹ at 1 MHz and room temperature. The films exhibit two dielectric anomalies which are attributed to Maxwell Wagner polarization mechanism and relaxor behaviour. Both anomalies are sensitive to post-annealing under oxygen atmosphere and their activation energies are similar E_a ∼0.30 eV. They are explained in terms of electrically heterogeneous contributions in the films.     

Electrodeposited nanogold decorated graphene modified carbon ionic liquid electrode for the electrochemical myoglobin biosensor

In this paper, a carbon ionic liquid electrode (CILE) was fabricated using ionic liquid 1-hexylpyridinium hexafluorophosphate as modifier, which was further in situ electrodeposited with graphene (GR) and gold nanoparticles step by step to get an Au/GR nanocomposite modified CILE. Myoglobin (Mb) was further immobilized on the Au/GR/CILE surface with Nafion film to get the modified electrode denoted as Nafion/Mb/Au/GR/CILE. Cyclic voltammetric experiments indicated that a pair of well-defined quasi-reversible redox peaks appeared in pH 3.0 phosphate buffer solution with the formal potential (E ^0′) located at ?0.197 V (vs. saturated calomel electrode), which was the typical characteristics of Mb heme Fe(III)/Fe(II) redox couples. Thus, the direct electron transfer rate between Mb and the modified electrode was promoted due to the high conductivity and increased surface area of Au/GR nanocomposite present on electrode surface. Based on the cyclic voltammetric data, the electrochemical parameters of Mb on the modified electrode were calculated. The Mb-modified electrode showed excellent electrocatalytic activities towards the reduction of trichloroacetic acid and H₂O₂ with wider linear range and lower detection limit. Using GR and Au nanoparticles modified CILE, a new third-generation electrochemical Mb biosensor was constructed with good stability and reproducibility.