Diamond Thin Film Electrodes Research Articles

Heterogeneous electron-transfer rate constants for ferrocene and ferrocene carboxylic acid at boron-doped diamond electrodes in a room temperature ionic liquid

Heterogeneous electron-transfer rate constants were determined for ferrocene and ferrocene carboxylic acid (FCA) in the room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), at boron-doped microcrystalline diamond thin-film electrodes. Comparison data for FCA in 1M KCl were also obtained. The apparent heterogeneous electron-transfer rate constant, kapp0, for FCA was 10× lower in the RTIL 1.5 (±1.1)×10−3cms−1 as compared to KCl 4.6 (±1.3)×10−2cms−1. The kapp0 for ferrocene was also 10x lower in the RTIL 5.0 (±1.2)×10−3cms−1 as compared to a common organic electrolyte solution 5.5 (±1.2)×10−2cms−1. The diffusion coefficient for FCA (Dred) was determined by chronoamperometry to be 1.3×10−7cm2s−1, ca. 100× lower than the value (1.9×10−5cm2s−1) in KCl. The lower diffusion coefficient is consistent with the 100× greater viscosity of the RTIL. The lower kapp0 values for these outer-sphere redox systems is attributed, at least in part, to a reduced number of attempts to surmount the activation barrier (i.e., a reduced nuclear frequency factor, νn) due to the more viscous medium.

A coal desulfurization process via sodium metaborate electroreduction with pulse voltage using a boron-doped diamond thin film electrode

A preliminary study was conducted on the coal desulfurization process via NaBO2 electroreduction with pulse voltage using a boron-doped diamond (BDD) thin film electrode. It has been proved that NaBO2 was converted into NaBH4 by 11B NMR. The factors that influence the conversion rate of NaBO2 into NaBH4 and coal desulfurization efficiency were investigated. Under the conditions of −1.5 V forward pulse voltage, +0.5 V reverse pulse voltage, 0.2 mol L−1 NaBO2 concentration, 0.5 mol L−1 NaOH concentration, 2 s forward pulse duration, 1 s reverse pulse duration, 50 g L−1 coal concentration, 0.8 mmol L−1 NiCl2 concentration and 2.5 h electrolytic time, a higher desulfurization efficiency (64%) was obtained compared with the common electrochemical desulfurization (ECDS) process using a Pt electrode. By analyzing and comparing the coal samples and electrolytes before and after desulfurization it was indicated that the removed S from the coal sample in the form of gaseous H2S was mainly converted into Na2S and Na2Sx and boron (B) recycling was realized during coal desulfurization. Particularly, the combustion characteristics of coal were improved after desulfurization. Finally, the desulfurization mechanism was proposed. All these results indicated that the desulfurization process via NaBO2 electroreduction with pulse voltage using a BDD thin film electrode is effective and highly promising for coal desulfurization.

Complementary Mechanism Model for the Electrochemical Mineralization

Comninellis and his research group have elucidated a theoretical model that permits us to predict the chemical oxygen demand (COD) and instantaneous current efficiency (ICE), during the electrochemical oxidation of organic pollutants on a synthetic boron-doped diamond thin film electrodes (BDD) in a batch recirculation system under galvanostatic conditions. Several studies highlight the good correlation between theoretical predictions and empirical data, but it was noted that some data, from some experiments, were not in agreement with the theoretical model, since it achieved efficiencies above 100%. Recently, few studies have reported phenomena that occur in electrocatalytic systems which were not deducted in the first models. Thus, we emphasize that the mineralization of organic compounds on BDD electrodes involves not only hydroxyl radicals but also the molecular oxygen present in air, in saturated aqueous solutions or strong oxidants generated from simultaneous reactions. Therefore, this highlights summarizes the results reported by other electrochemists until nowadays to understand the electrochemical oxidation mechanisms. Keywords: Dissolved oxygen, Hydroxyl radicals, Complementary mechanism model, Strong oxidant species, electrochemical oxidation, galvanostatic, organic pollutants, anode, hydroxyl radicals, biodegradable

Application of a boron doped diamond (BDD) electrode as an anode for the electrolytic reduction of UO2 in Li2O–LiCl–KCl molten salt

A boron doped diamond thin film electrode was employed as an inert anode to replace a platinum electrode in a conventional electrolytic reduction process for UO2 reduction in Li2O–LiCl molten salt at 650°C. The molten salt was changed into Li2O–LiCl–KCl to decrease the operation temperature to 550°C at which the boron doped diamond was chemically stable. The potential for oxygen evolution on the boron doped diamond electrode was determined to be approximately 2.2V vs. a Li–Pb reference electrode whereas that for Li deposition was around −0.58V. The density of the anodic current was low compared to that of the cathodic current. Thus the potential of the cathode might not reach the potential for Li deposition if the surface area of the cathode is too wide compared to that of the anode. Therefore, the ratio of the surface areas of the cathode and anode should be precisely controlled. Because the reduction of UO2 is dependent on the reaction with Li, the deposition of Li is a prerequisite in the reduction process. In a consecutive reduction run, it was proved that the boron doped diamond could be employed as an inert anode.

Kinetic experiments of electrochemical oxidation of iohexol on BDD electrodes for wastewater treatment

Electrolysis of iohexol, an iodinated X-ray contrast medium, on synthetic boron-doped diamond (BDD) thin film electrodes was investigated for the first time. Kinetic experiments of electrochemical oxidation resulted in complete elimination of iohexol. Data from the kinetic experiments were compared against estimates by the kinetic model proposed previously by Comninellis et al. Excellent agreement between the experimental results and the kinetic model was observed. The results suggest that electrolysis on BDD electrodes is a promising method for the elimination of iohexol from wastewater.

Electrochemical treatment of wastewater containing chlorophenols using boron-doped diamond film electrodes

The electrochemical treatment of wastewater containing chlorophenols (2-monochlorophenol, 4-monochlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol) was carried out experimentally with synthetic boron-doped diamond (BDD) thin film electrodes. Current vs time curves under different cell voltages were measured. Removal rate of COD, instant current efficiency (ICE) and energy consumption were investigated under different current densities. The influence of supporting media is reported, which plays an important role in determining the global oxidation rate. The oxidative chloride is stronger than peroxodisulphate. The electrochemical characteristics of boron-doped diamond electrodes were investigated in comparison with active coating Ti substrate anode (ACT). The experimental results show that BDD is markedly superior to ACT due to its different absorption properties.

Dopamine Sensor Based on a Boron-Doped Diamond Electrode Modified with a Polyaniline/Au Nanocomposites in the Presence of Ascorbic Acid

A selective dopamine (DA) sensor was developed using gold nanoparticles (Au-NPs) dispersed overoxidized-polyaniline (PANI(ox)) based on a boron-doped diamond (BDD) thin-film electrode. The concentration of the DA was determined using voltammetry as a non-enzymatic sensor. BDD thin film has a high signal-to-noise ratio, a long-term stability, a high sensitivity, and a good reproducibility. PANI nanocomposites were directly synthesized on the BDD electrode and overoxidized using 0.5 M H(2)SO(4) solution. The overoxidized PANI film enhances selectivity and sensitivity toward DA. The Au-NPs were dispersed on the PANI nanocomposite by electrochemical deposition. The nanometer-sized Au-NPs favor the sensing of DA in the presence of ascorbic acid (AA). The combination of the PANI with the Au-NPs and the BDD electrode can create synergetic effects for the performance of the biosensor, such as a fast response time, a lower detection limit, a wider linear range, enhanced selectivity, and higher sensitivity for the determination of DA.

Electrochemical Treatment of Wastewater Containing Chlorophenols Using Boron-Doped Diamond Film Electrodes

The electrochemical treatment of wastewater containing 2, 4, 6-trichlorophenol has been carried out experimentally with synthetic boron-doped diamond (BDD) thin film electrodes. Removal rate of COD, instant current efficiency (ICE) and energy consumption were investigated under different current density. The influence of supporting media is reported, which plays an important role in determining the global oxidation rate. The oxidative chloride is stronger than peroxodisulphate. The electrochemical characteristics of boron-doped diamond electrodes were investigated in comparison with active coating Ti substrate anode (ACT). The experimental results show that BDD is markedly superior to ACT due to its different absorption properties.

Analytical Characteristics of Electrochemical Biosensor Using Pt‐Dispersed Graphene on Boron Doped Diamond Electrode

AbstractAn electrochemical biosensor was developed using Pt‐nanoparticles (Pt‐NPs) dispersed graphene based on a boron‐doped diamond thin film electrode. To compare its performances with those of other biosensors, glucose was used as a target analyte. This biosensor exhibited a wide linear range, a low detection limit and a higher sensitivity compared to other amperometric biosensors using graphene‐based electrodes. In addition, the biosensor promotes a direct electron transfer between the redox enzymes and the electrode surface and detects low concentration analytes. The excellent performance of the biosensor is attributed to the synergistic effect of the Pt‐NPs, graphene sheet and the BDD thin film. Therefore, it can be a promising application for electrochemical detection of analytes.

Electrolyte and Temperature Effects on the Electron Transfer Kinetics of Fe(CN)6–3/-4 at Boron-Doped Diamond Thin Film Electrodes

Cyclic and linear sweep voltammetry were used to investigate the effects of the electrolyte composition and temperature on the electron-transfer kinetics of Fe(CN)6–3/–4 at well-characterized, boron-doped diamond thin-film electrodes. Highly conductive films were employed, which were first cleaned of any adventitious nondiamond carbon impurity by a two-step chemical-oxidation, and subsequently hydrogenated in hydrogen microwave plasma. The apparent heterogeneous electron-transfer rate constant, k°app, depended on the electrolyte concentration and the electrolyte cation type, increasing in order of Li+ < Na+ < K+ < Cs+. However, the dependence of koapp on the electrolyte cation was less than the dependence observed for other electrodes, like glassy carbon and gold. For example, koapp at the 1.0 M concentration was only a factor of 1.6 greater in KCl than in LiCl for diamond. This is less than the factor of 5–10 seen for other electrodes, like glassy carbon and gold. The transfer coefficient for the oxidati...

Electrochemical Pretreatment of Wastewater from DDNP Production Using BDD Thin Film Electrode

The electrochemical oxidation of wastewater from DDNP production was investigated using a boron-doped diamond (BDD) thin film electrode. The effects of operating factors such as cell voltage, interelectrode distance and additive NaCl have been studied. This study showed that the chemical oxygen demand (COD) reduction is most influenced by the applied cell voltage. Higher current densities resulting from higher cell voltages increase the formation of oxidative reagents resulting in an increased COD removal rate. The maximum COD removal was 57% after 210 min, with an energy consumption of 14.90 KWh·kg-1COD when cell voltage was 12V, interelectrode distance was 3cm and additive NaCl concentration was 1g·L-1. The use of BDD thin film electrode for the treatment of DDNP production wastewater appears commercially feasible.

Electrochemical Behaviors of Chlorophenol Aqueous Solutions at Boron-Doped Diamond Electrode

The electrochemical behaviors of different chlorophenols at boron-doped diamond thin film electrode were investigated. Four chlorophenols, the 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6- TCP) and pentachlorophenol (PCP), with various number of chlorine atoms in the benzene rings, were studied by using cyclic voltammetry at different scan rates over the potential range of -1 V to 2.5 V (vs MSE). The results indicated that the reactions of the 2-CP, 2,4-DCP and 2,4,6-TCP at the diamond electrode are irreversible and controlled by diffusion, and the irreversible trend increases with the decrease of the chlorine atom number in the benzene ring. However, the activity of the boron-doped diamond film electrode does not depend on the number of the chlorine atom. Different from the three chlorophenols, fouling of the electrode occurs in PCP solutions. The possible electro-oxidation mechanisms are discussed for different chlorophenols.

Anodic oxidation of anthraquinone dye Alizarin Red S at Ti/BDD electrodes

The boron-doped diamond (BDD) thin-film electrode with high quality using industrially titanium plate (Ti/BDD) as substrate has been prepared and firstly used in the oxidation of anthraquinone dye Alizarin Red S (ARS) in wastewaters. The Ti/BDD electrodes are shown to have high concentration of sp 3-bonded carbon and wide electrochemical window. The results of the cyclic voltammetries show that BDD has unique properties such as high anodic stability and the production of active intermediates at the high potential. The oxidation regions of ARS and water are significantly separated at the Ti/BDD electrode, and the peak current increases linearly with increasing ARS concentration. The bulk electrolysis shows that removal of chemical oxygen demand (COD) and color can be completely reached and the electrooxidation of ARS behaves as a mass-transfer-controlled process at the Ti/BDD electrode. It is demonstrated that the performances of the Ti/BDD electrode for anodic oxidation ARS have been significantly improved with respect to the traditional electrodes.

Electrical Conducting Diamond Thin-Films: An Alternative Counter Electrode Material for Dye Sensitized Solar Cells

ABSTRACTCarbon is a favorable alternative as counter electrode material for dye sensitized solar cells (DSSC) as compared to Pt. Various carbon materials such as carbon nanotubes (CNT), activated carbon (AC) and carbon nanofibers have been investigated as counter electrodes for DSSC applications, based on their high electrochemical activity, high specific surface area, chemical inertness and high electrical conductivity. Among various phases of carbon, diamond is the most robust and chemical inert material that can be used for electrode application. It has band gap of 5.5 eV, high thermal conductivity. its electrical resistivity can be tuned by doping such as boron. In this work, we investigate boron doped diamond thin film electrode for DSSCs. The conductive diamond thin electrode films were grown using Blue Wave hot wire chemical vapor deposition (HWCVD) system. The electrical resistance in diamond thin films was tuned by controlling grow temperature, filament power, dopant concentration and sp3/sp2 ratio in the film, it thickness, and initial seeding process. Scanning electron microscopy, Raman spectroscopy and electrical resistivity measurement were used to characterize morphology, diamond quality and electrode conductivity, respectively. Diamond film electrodes with optimized surface morphology and electrical characteristics were used for DSSC fabrication. We used nanocrystalline TiO2 paste (P25 Degussa) with average particle size of 25nm as an active layer, the electrolyte comprised of a LiI/I2 electrolyte in acetonitrile (CH3CN), a Ru based metal complex dye [cis-diisothiocyanato-bis(2,2’-bipyridyl-4,4’-dicarboxylato) ruthenium(II) bis(tetrabutylammonium)] OR N719 was used as sensitizer. The photovoltaic performance was determined using J-V characteristics under standard illumination conditions and was compared to a reference DSSC with Pt counter electrode. Results are discussed in the context of diamond electrical and durability and chemical stability of diamond films against most commonly used family of iodine based electrolytes.

Cyclic Voltammograms of Chlorophenol Oxidation on Boron-Doped Diamond Electrode

The electrochemical behaviors of several chlorophenols were investigated on boron-doped diamond thin film electrode. 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol solutions were prepared as the electrolyte. Such four chlorophenols with various number of chlorine atoms in the benzene ring were studied by cyclic voltammetry at different scan rates between –1V to 2.5V (vs. MSE). The results indicated that the reactions of the 2-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol at the diamond electrode are irreversible and under diffusion control. The irreversible trend increases as the number of the chlorine atoms decreases. However, the activity of the boron-doped diamond film electrode is not affected by the number of the chlorine atom. Different from the three chlorophenols, fouling of the electrode appears in pentachlorophenol solutions.

The effect of CVD-diamond film thickness on the electrochemical properties of synthetic diamond thin-film electrodes

The electrochemical behavior of polycrystalline diamond films of different thickness (0.5–7 μm), grown by hot-filament CVD method, was studied by electrochemical impedance spectroscopy and cyclic voltammetry. The differential capacitance, background current, and potential window were measured in supporting electrolyte solution; the electrochemical kinetics, in [Fe(CN)6]3−/4− model redox system. With the increasing of the films thickness, the crystallite size increased; both the differential capacitance and background current in the indifferent electrolyte, as well as the transfer coefficients in the redox system, decreased; thus, the diamond electrode becomes as if less reversible. The effect of the films’ thickness is reduced to that of nondiamond (amorphous) carbon contribution from intercrystalline boundaries on the electrochemical behavior of the polycrystalline diamond electrodes.

Investigating the Nucleation and Growth of Electrodeposited Pt on Polycrystalline Diamond Electrodes

The nucleation and growth of electrochemically formed Pt adlayers on highly boron-doped, polycrystalline diamond thin-film electrodes were investigated using chronoamperometry. The experimental curves measured at different fixed potentials were analyzed and compared to theoretical curves for the two limiting cases of three-dimensional nucleation and growth, as described by Scharifker and Hills [ Electrochim. Acta , 28 , 879 (1983)] : instantaneous and progressive. Metal phase formation at short times proceeded via a more instantaneous nucleation mechanism at lower overpotentials on both microcrystalline and ultrananocrystalline diamonds. However, there was a transition on both diamond types to a progressive mechanism at higher overpotentials. Based on the results, apparently, there exists a relatively constant nucleation site density on these conducting polycrystalline films at lower overpotentials, with new nucleation sites developing over time at higher overpotentials. We suppose that the initial nucleation is strongly related to heterogeneities in the density of electronic states (DOS) across a film brought about by variations in the local boron and hydrogen content more so than variations in the physicochemical properties. The shift to a more progressive nucleation and growth mechanism is consistent with an increased DOS at more negative overpotentials. Some comparison measurements are reported for glassy carbon and highly oriented pyrolytic graphite.

Preparation of grain size controlled boron-doped diamond thin films and their applications in selective detection of glucose in basic solutions

Boron-doped diamond (BDD) thin films with different crystal grain sizes were prepared by controlling the reacting gas pressure using hot filament chemical vapor deposition (HFCVD). The morphologies and structures of the prepared diamond thin films were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. The electrochemical responses of K4Fe(CN)6 on different BDD electrodes were investigated. The results suggested that electron transfer was faster at the boron-doped nanocrystalline diamond (BDND) thin film electrodes in comparison with that at other BDD thin film electrodes. The prepared BDD thin film electrodes without any modification were used to directly detect glucose in the basic solution. The results showed that the as-prepared BDD thin film electrodes exhibited good selectivity for detecting glucose in the presence of ascorbic acid (AA) and uric acid (UA). The higher sensitivity was observed on the BDND thin film grown on the boron-doped microcrystalline diamond (BDMD) thin film surface, and the linear response range, sensitivity and the low detection limit were 0.25–10 mM, 189.1 μA mmo−1 cm−2 and 25 μM (S/N=3) for glucose in the presence of AA and UA, respectively.

Amperometric Determination of Aminobiphenyls Using HPLC‐ED with Boron‐Doped Diamond Electrode

AbstractAmino derivatives of biphenyl have been proven to be genotoxic and/or carcinogenic, thus they are widely monitored in the environment as well as in biological liquids. This study was devoted to HPLC determination of 2‐aminobiphenyl, 3‐aminobiphenyl, and 4‐aminobiphenyl in model drinking and river water samples using amperometric detection in a thin layer cell with boron doped diamond thin film electrode. Satisfactory separation of studied analytes was achieved at a ChiraDex column (Merck, Germany) with chemically bonded β‐cyclodextrin in a mobile phase aqueous buffer/acetonitrile/methanol (40/30/30, v/v/v) with total separation time of six minutes. The highest detector response with satisfactory repeatability (relative standard deviation &lt;2.9% for all aminobiphenyls) was obtained using 0.01 mol L−1 acetate buffer at pH 5.0 as an aqueous component of the mobile phase. For direct determination of aminobiphenyls in drinking and river water model samples limits of quantitation ca. 4×10−7 mol L−1 were achieved. Applying off‐line solid phase extraction using Lichrolut EN (Merck, Germany) cartridges and elution by diethyl ether, limits of quantitation were lowered down to the 10−9 mol L−1 concentration range.

Non-enzymatic glucose detection using as-prepared boron-doped diamond thin-film electrodes

Electrochemical oxidation of glucose in alkaline solution at as-prepared boron-doped microcrystalline diamond (BDMD) and nanocrystalline diamond (BDND) thin-film electrodes is investigated by cyclic voltammetry. The results demonstrate that glucose can be directly oxidized at as-prepared boron-doped diamond (BDD) thin-film electrodes and the curve of the negative scan traces onto the positive scan. The effect of sodium hydroxide concentration on the response of glucose is also studied in the range of 0.02-0.6 M and the optimum concentration of sodium hydroxide is found to be 0.1 M. The voltammetric signal of glucose and the mixture of ascorbic acid (AA) and uric acid (UA) can be observed well-separated at as-prepared BDD thin-film electrodes in 0.1 M sodium hydroxide solution. The peak current is proportional to the glucose concentration in the range 0.25-10 mM with a correlation coefficient of 0.9993 in the presence of AA and UA. Furthermore, the experiment results also show that the non-enzymatic glucose sensor based on as-prepared BDD thin-film electrodes has high sensitivity, good reproducibility and stability.