Boron-doped Diamond Thin-film Electrodes Research Articles

A Diamond/Graphene/Diamond Electrode for Waste Water Treatment

Boron-doped diamond (BDD) thin film electrodes have great application potential in water treatment. However, the high electrode energy consumption due to high resistance directly limits the application range of existing BDD electrodes. In this paper, the BDD/graphene/BDD (DGD) sandwich structure electrode was prepared, which effectively improved the conductivity of the electrode. Meanwhile, the sandwich electrode can effectively avoid the degradation of electrode performance caused by the large amount of non-diamond carbon introduced by heavy doping, such as the reduction of the electrochemical window and the decrease of physical and chemical stability. The microstructure and composition of the film were characterized by scanning electron microscope (SEM), atomic force microscopy (AFM), Raman spectroscopy, and transmission electron microscopy (TEM). Then, the degradation performance of citric acid (CA), catechol, and tetracycline hydrochloride (TCH) by DGD electrodes was systematically studied by total organic carbon (TOC) and Energy consumption per unit TOC removal (ECTOC). Compared with the single BDD electrode, the new DGD electrode improves the mobility of the electrode and reduces the mass transfer resistance by 1/3, showing better water treatment performance. In the process of dealing with Citric acid, the step current of the DGD electrode was 1.35 times that of the BDD electrode, and the energy utilization ratio of the DGD electrode was 2.4 times that of the BDD electrode. The energy consumption per unit TOC removal (ECTOC) of the DGD electrode was lower than that of BDD, especially Catechol, which was reduced to 66.9% of BDD. The DGD sandwich electrode, as a new electrode material, has good electrochemical degradation performance and can be used for high-efficiency electrocatalytic degradation of organic pollutants.

Electrochemical Determination of Chemical Oxygen Demand Based on Boron-Doped Diamond Electrode

A rapid and environment-friendly electrochemical sensor to determine the chemical oxygen demand (COD) has been developed. The boron-doped diamond (BDD) thin-film electrode is employed as the anode, which fully oxidizes organic pollutants and provides a current response in proportion to the COD values of the sample solution. The BDD-based amperometric COD sensor is optimized in terms of the applied potential and the solution pH. At the optimized conditions, the COD sensor exhibits a linear range of 0 to 80 mg/L and the detection limit of 1.1 mg/L. Using a set of model organic compounds, the electrochemical COD sensor is compared with the conventional dichromate COD method. The result shows an excellent correlation between the two methods.

Exploring the effect of surface chemistry and particle size of boron-doped diamond powder as catalyst and catalyst support for the oxygen reduction reaction

The interest for the electrodes based on conductive boron-doped diamond powder (BDDP) is increasing in recent years due to their excellent physical and chemical stability, the wide potential window in both aqueous and organic electrolytes, the relatively large specific surface area, and their versatility in comparison to boron-doped diamond thin film electrodes. These materials have been proposed as alternative cathode catalyst support due to their high corrosion resistance when subjected to the highly positive potentials originated during the start-stop operations in fuel cells, especially in automobiles. In this work, we present three BDDP supports with different particle sizes and different surface oxygen contents as supports of different iron species for oxygen reduction reaction in alkaline solution. BDDP supports were modified with carbon nitride (C3N4) or phthalocyanines (Pc) as anchoring points for iron. The different electrocatalytic performance observed confirmed the strong influence of the surface chemistry of the BDDP supports on the activity of the metallic sites for FePc samples while, for Fe-C3N4 samples, the determining effect was the particle size of the BDDP support. Additionally, DFT calculations were used to obtain some insights about the interaction of the FePc with the diamond surface.

Deuterium-Grown Highly-Oriented Boron-Doped Diamond Electrodes

Boron-doped diamond (BDD) have attracted increasing attention as a material for electrochemical sensors and biosensors due to its remarkable properties such as its chemical inertness, wide electrochemical potential window, low background current and biocompatibility. Diamond layers are synthesized mainly from a gas phase consisting of carbon, hydrogen, and a dopant source by microwave plasma-assisted chemical vapour deposition (MPACVD). The gas composition during the growth of diamond film has a significant influence on its surface morphology, crystallographic structure, dopant concentration, and superficial non-diamond carbon phases. Thus, the growth conditions of the diamond layer affect the electrochemical properties of the material.Herein we demonstrate the electrochemical and physicochemical studies of as-grown boron-doped diamond thin-film electrodes, synthesized in a deuterium-rich plasma (BDDD). It is the first report concerning the study of the effect of replacing hydrogen by deuterium during BDD growth. The substitution of hydrogen to deuterium in the gas phase is primarily responsible for the enhanced boron doping and significantly decrease of nondiamond sp2 phase in diamond films. Moreover, the crystallographic structure of BDDD layer is dominated by the (111) configuration while the texture of the BDDH electrode film is oriented along the (220) direction [1].The proposed boron-doped diamonds synthesized in the deuterium-rich plasma electrodes were revealed to have a higher activity towards [Fe(CN)6]3-/4- and [Ru(NH3)6]2+/3+ redox mediators than BDD electrode grown in hydrogen-rich plasma (BDDH). The peak-to-peak separation recorded on BDDD electrode reaches 60.6 mV, and 59.8 mV in [Fe(CN)6]3-/4- and [Ru(NH3)6]2+/3+ redox couples, respectively. Moreover, in Ru(NH3)6 2+/3+ solution, the apparent heterogeneous electron transfer rate constant k° app for the BDDD was equal to 5.84·10-3 cm s-1. The BDDD and BDDH electrodes were also used as an electrochemical sensor for the paracetamol detection. BDDD electrode exhibits better sensing performance towards PCM comparing to BDDH electrode. The value of limit of detectionfor the BDDD electrode was 765 nM, whereas for the BDDH was 2510 nM. The better electrocatalytic behavior of the BDDD electrodes may result from the higher amount of electroactive zones on deuterium-terminated diamond strictly related to (111) crystal facets.AcknowledgementThis work was supported by the Polish National Science Centre [2020/01/0/ST7/00104]. The DS funds of the Faculty of Electronics, Telecommunications, and Informatics of the Gdansk University of Technology are also acknowledged.Reference:[1] A. Dettlaff et al., Carbon [In press]. Doi: doi.org/10.1016/j.carbon.2020.11.096.

Effect of oxygen terminated surface of boron-doped diamond thin-film electrode on seawater salinity sensing

Tremendous demands for highly sensitive and stable seawater salinometers have motivated intensive research on advanced electrode materials. Boron-doped diamond (BDD) is attractive in terms of its high mechanical stability and chemical inertness, but is usually hindered by its low double-layer capacitance (Cdl) for seawater salinity detection. Here, inspired by the principle of oxygen-terminated BDD electrode endowing higher Cdl than hydrogen-terminated surface, we introduce the oxygen terminated surface by oxygen plasma or reactive ion etch (RIE), and the fabricated oxygen terminated BDD electrodes demonstrate high sensitivity and long-term stability in seawater salinity detection comparing with the hydrogen terminated BDD electrodes. Significantly, the as-fabricated O-BDD-RIE electrodes not only show remarkable enhanced response even better than the commercial platinum black electrodes but also display long-time stability which is weekly verified by continuous monitor for 90 days. The outstanding performance of the oxygen terminated BDD electrodes can be ascribed to the enhancement of C-O surface functional group on Cdl. In addition, a comprehensive analysis of effective electroactive surface area (EASA) and Cdl proves that the surface oxygen is the major factor for the improved Cdl. In summary, the excellent oxygen terminated BDD electrodes promise potential application in seawater salinity detection.

Effect of Surface Oxygen on the Wettability and Electrochemical Properties of Boron-Doped Nanocrystalline Diamond Electrodes in Room-Temperature Ionic Liquids.

This paper reports on how the surface chemistry of boron-doped nanocrystalline diamond (BDD) thin-film electrodes (H vs O) affects the wettability and electrochemical properties in two room-temperature ionic liquids (RTILs): [BMIM][PF6] and [HMIM][PF6]. Comparative measurements were made in 0.5 mol L-1 H2SO4. The BDD electrodes were modified by microwave or radio-frequency (RF) plasma treatment in H2 (H-BDD), Ar (Ar-BDD), or O2 (O-BDD). These modifications produced low-, medium-, and high-oxygen surface coverages. Atomic O/C ratios, as determined by X-ray photoelectron spectroscopy (XPS), were 0.01 for H-BDD, 0.08 for Ar-BDD, and 0.17 for O-BDD. The static contact angle of ultrapure water on the modified electrodes decreased from 110° (H-BDD) to 41° (O-BDD) with increasing surface oxygen coverage, as expected as the surface becomes more hydrophilic. Interestingly, the opposite trend was seen for both RTILs as the contact angle increased from 20° (H-BDD) to 50° (O-BDD) with increasing surface oxygen coverage. The cyclic voltammetric background current and potential-dependent capacitance in both RTILs were largest for BDD electrodes with the lowest O/C ratio (H-BDD) and smallest contact angle. Slightly larger voltammetric background currents and capacitance were observed in [HMIM][PF6] than in [BMIM][PF6]. Capacitance values ranged from 8 to 16 μF cm-2 over the potential range for H-BDD and from 4 to 6 μF cm-2 for O-BDD. The opposite trend was observed in H2SO4 as the voltammetric background current and capacitance were largest for BDD electrodes with the highest O/C ratio (O-BDD) and smallest contact angle. In summary, reducing the surface oxygen on BDD electrodes increases the wettability to two RTILs and this increases the voltammetric background current and capacitance.

Novel Electrochemical Flow Injection Procedure for Albendazole Determination using Boron-doped Diamond thin Film Electrode

The homemade electrochemical cell for electrochemical determination of albendazole using boron-doped diamond (BDD) thin film electrode is developed. Electrochemical activity of albendazole was investigated by cyclic voltammetry in 0.10 M phosphate buffer containing 20% (v/v) methanol at pH 2.5. Using the BDD electrode well-defined and highly reproducible cyclic voltammogram was obtained with current signal-to-background ratio of higher than those obtained from the glassy carbon electrode. Flow injection analysis system with amperometric detection using the homemade thin-layer electrochemical flow-through cell with BDD electrode was studied. The hydrodynamic voltammogram of the drug exhibited single well defined maximum oxidation peak at 0.95 V versus Ag/AgCl. A low detection limit of 2 ppm was obtained. The current–concentration relationship was rectilinear over the concentration range of 3.3‒150 ppm. The proposed method was applied to albendazole tablets with satisfactory results.

Enhancement of substrate-coating adherence of boron-doped diamond electrodes by nanosecond laser surface texturing pretreatment

To improve the substrate-coating adherence of Nb-based boron-doped diamond (BDD) electrodes, laser surface texturing (LST) pretreatment was investigated. Substrates were textured by a Nd:YAG laser (1.06 μm radiation, 20 ns) with several laser parameters such as single pulse energy and scanning spacing, then coated with a BDD film by hot filament chemical vapor deposition (HFCVD). Characteristics of the substrates and BDD thin film electrodes were investigated. The results revealed that periodic valley-like structures were fabricated on substrate surfaces. LST pretreatment can significantly enhance the substrate-coating adherence of BDD electrode samples, and the laser cleaning step can effectively remove the surface oxide layer generated by laser pretreatment. Single pulse energy is a crucial influencing factor, the proper pulse energy can provide the best adherence property, providing sufficient surface treatment effect, promoting nucleation, release residual stress and promote the mechanical interlock. Suitable scanning spacing can further improve the coating adherence, and the match of scanning spacing and single pulse spacing can effectively avoid the directional peeling.

HPLC−EC Analysis of Estrogenic Compounds: A Comparison of Diamond and Tetrahedral Amorphous Carbon Electrode Performance

AbstractHigh pressure liquid chromatography (HPLC) with amperometric detection was used to quantify estrogenic compounds in water samples. The main goal was to compare the detection figures of merit for boron‐doped diamond thin‐film (BDD) and nitrogen‐incorporated tetrahedral amorphous carbon (ta‐C : N) thin‐film electrodes. The target analytes were estrone, estradiol, and estriol. The BDD and ta‐C : N electrodes were investigated because of their excellent properties, which include a wide potential window, low background current, microstructural stability at high potentials, low limits of detection, weak molecular adsorption, fouling resistance and response reproducibility. ta‐C : N electrodes have not yet been investigated extensively in electroanalysis and are receiving increasing interest because they exhibit many of the excellent electrochemical properties of BDD electrodes and they can be deposited at room temperature by physical vapor deposition. The results reveal as low or lower background current and noise for the ta‐C : N electrode, as compared to the BDD electrode, and comparable or superior analytical detection figures of merit for all three emerging pollutants. The linear dynamic range for both electrodes was from 0.2 to 100 μmol L−1 for estriol, and 0.4 to 100 μmol L−1 for estradiol and estrone, and the sensitivity ranged from 9.1 to 11.2 mA mol L−1. For all three analytes, the limit of detection (S/N=3) ranged from 0.16–0.35 μmol L−1 (45‐95 ppb) for BDD and 0.20–0.34 μmol L−1 (58‐95 ppb) for ta‐C : N.

Boron-Doped Diamond Powder as a Durable Support for Platinum-Based Cathode Catalysts in Polymer Electrolyte Fuel Cells

Platinum nanoparticle-supported boron-doped diamond powder (Pt/BDDP) was prepared and investigated as a durable polymer electrolyte fuel cell (PEFC) cathode catalyst. The use of the nanocapsule method enabled dense deposition of Pt nanoparticles (2–5 nm in size) on a boron-doped diamond (BDD) powder <500 nm in size. The Pt/BDDP cathode catalyst showed oxygen reduction reaction activity comparable to Pt-supported carbon black (Pt/C), indicating sufficient conductivity of the BDDP as a catalyst support. Potential cycling in a highly positive potential region (+1.0–+1.5 V vs. NHE) that simulates the start–stop operations of the PEFC was performed to investigate the durability of the Pt/BDDP catalyst. Decreases in the electrochemically active surface area of the Pt/BDDP were suppressed compared to that of Pt/C. Corrosion resistance of BDD against potential cycling was demonstrated by testing a BDD thin-film electrode. The corrosion resistance should be responsible for the improved durability of the BDDP support, possibly by lowering the Pt nanoparticle association process (e.g., agglomeration).

Facet-Dependent Temporal and Spatial Changes in Boron-Doped Diamond Film Electrodes due to Anodic Corrosion

The progression of corrosion in polycrystalline boron-doped diamond (BDD) thin film electrode is explored as the electrode undergoes high-current density anodic treatments with organic compounds. Micro-Raman spectroscopy and spectral mapping indicate that anodic corrosion is initiated by the conversion of sp3 diamond to amorphous sp2 carbon at the surface, which are then removed after longer anodic treatment. Polarized Raman analysis reveals that corrosion-induced changes on the surface are specific to (100)-grain facets and (111)-grain edges. X-ray photoelectron spectroscopic measurements suggest that carbonyl groups consequently form on these specific sites and act as an intermediate toward the etching of the surface. This process exposes and subsequently removes the subsurface boron atoms, thus reducing the doping density. The observed crystal grain orientation dependence of the corrosion process provides new insights toward a better understanding of degradation in BDD electrodes.

Modeling and optimization of Reactive Green 19 oxidation on a BDD thin-film electrode

A membrane-free electrochemical reactor with a boron-doped diamond (BDD) anode was used to degrade Reactive Green 19 (RG19), an azo dye widely used in the textile industry. Oxidation experiments were carried out under galvanostatic conditions according to a central composite design. The factors investigated were current density (100–500 A/m2), pH (3–11), chloride concentration (0–0.5 M) and agitation rate (250–750 rpm), while the response variables were the efficiencies of color and TOC removal. Color removal was strongly affected by chloride concentration and, to a lesser extent, by current density and stirring rate. In contrast, current density was the factor with the greatest influence on TOC removal, followed by pH and chloride concentration. Under optimal degradation conditions, the efficiencies of color and TOC removal reached values close to 90% and 80%, respectively. Taken together, the results of this study suggest that the anodic oxidation of RG19 on a BDD thin-film electrode can be a suitable method to degrade this dye, once the optimum operating conditions have been established.

Local impedance imaging of boron-doped polycrystalline diamond thin films

Local impedance imaging (LII) was used to visualise surficial deviations of AC impedances in polycrystalline boron-doped diamond (BDD). The BDD thin film electrodes were deposited onto the highly doped silicon substrates via microwave plasma-enhanced CVD. The studied boron dopant concentrations, controlled by the [B]/[C] ratio in plasma, ranged from 1 × 1016 to 2 × 1021 atoms cm−3. The BDD films displayed microcrystalline structure, while the average size of crystallites decreased from 1 to 0.7 μm with increasing [B]/[C] ratios. The application of LII enabled a direct and high-resolution investigation of local distribution of impedance characteristics within the individual grains of BDD. Such an approach resulted in greater understanding of the microstructural control of properties at the grain level. We propose that the obtained surficial variation of impedance is correlated to the areas of high conductance which have been observed at the grain boundaries by using LII. We also postulate that the origin of high conductivity is due to either preferential boron accumulation, the presence of defects, or sp2 regions in the intragrain regions. The impedance modulus recorded by LII was in full agreement with the bulk impedance measurements. Both variables showed a decreasing trend with increasing [B]/[C] ratios, which is consistent with higher boron incorporation into BDD film.

Highly sensitive determination of mercury using copper enhancer by diamond electrode coupled with sequential injection–anodic stripping voltammetry

A highly sensitive determination of mercury in the presence of Cu(II) using a boron-doped diamond (BDD) thin film electrode coupled with sequential injection–anodic stripping voltammetry (SI–ASV) was proposed. The Cu(II) was simultaneously deposited with Hg(II) in a 0.5M HCl supporting electrolyte by electrodeposition. In presence of an excess of Cu(II), the sensitivity for the determination of Hg(II) was remarkably enhanced. Cu(II) and Hg(II) were on-line deposited onto the BDD electrode surface at −1.0V (vs. Ag/AgCl, 3M KCl) for 150s with a flow rate of 14μLs−1. An anodic stripping voltammogram was recorded from −0.4V to 0.25V using a frequency of 60Hz, an amplitude of 50mV, and a step potential of 10mV at a stopped flow. Under the optimal conditions, well-defined peaks of Cu(II) and Hg(II) were found at −0.25V and +0.05V (vs. Ag/AgCl, 3M KCl), respectively. The detection of Hg(II) showed two linear dynamic ranges (0.1–30.0ngmL−1 and 5.0–60.0ngmL−1). The limit of detection (S/N=3) obtained from the experiment was found to be 0.04ngmL−1. The precision values for 10 replicate determinations were 1.1, 2.1 and 2.9% RSD for 0.5, 10 and 20ngmL−1, respectively. The proposed method has been successfully applied for the determination of Hg(II) in seawater, salmon, squid, cockle and seaweed samples. A comparison between the proposed method and an inductively coupled plasma optical emission spectrometry (ICP-OES) standard method was performed on the samples, and the concentrations obtained via both methods were in agreement with the certified values of Hg(II), according to the paired t-test at a 95% confidence level.

Comparative study of electrochemical water treatment processes for a tannery wastewater effluent

Comparison of tannery wastewater treatment results of electrocoagulation (EC), electro-oxidation (EOx), electro-Fenton (EF) and photoelectro-Fenton (PEF) processes using two current densities was performed and employed no only to assess the best electrochemical approach but also to have elements to suggest a combined and cost effective process. In this way, iron plates were used as the anode and cathode in the EC tests. For the EOx process, a boron-doped diamond (BDD) thin-film electrode was used as the anode, and an iron plate was employed as the cathode. For the EF and PEF treatments, both electrodes were of BDD and H2O2 was produced by O2 reduction at the cathode surface. Electrolytic trials were carried out in stirred open tank reactors containing 250mL of wastewater applying either 65 or 111mAcm−2. In PEF trials, the wastewater was irradiated using a 6W UVA light source. The characterization of the sludge generated in the EC process showed that it was not dangerous for the environment. Total Organic Carbon (TOC) removal values were larger at the highest density. Higher mineralization on the other hand, was found in EF and PEF when the concentration of Fe2+ was 3.0 instead 1.0mM. Comparison of the methods revealed that their efficiency to remove the organic pollutant increased in the order EOx<EC∼EF<PEF after 180min of electrolysis. Furthermore, the information obtained from the study, also allowed designing a combined strategy aimed to produce an effluent suitable for discharge. The combination of EC followed by PEF was also studied. The results showed that the EC/PEF treatment gave higher organic removal than EC and was more economic than PEF, being able to yield 90% TOC reduction of the tannery wastewater.

Comparative electrochemical response of estrone at glassy-carbon, nitrogen-containing tetrahedral amorphous carbon and boron-doped diamond thin-film electrodes

The anodic oxidation of estrone was comparatively investigated at glassy carbon (GC), nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) and boron-doped diamond (BDD) electrodes. The ta-C:N and BDD electrodes are characterized by a wider working potential window and lower background current that for GC. The latter is because of a reduced level of pseudocapacitance on the former electrodes due to the absence of significant levels of redox-active surface carbon–oxygen functionalities. The irreversible oxidation of estrone was recorded at a similar potential for all three electrodes (0.9–0.95V) in 0.5molL−1 H2SO4. The voltammetric peak current decreased some for all the electrodes with potential cycling suggestive of some response attenuation by reaction product adsorption (or slow desorption). From the dependence of the oxidation peak potential and current with solution pH, it was possible to conclude that the electrooxidation of estrone involves the transfer of two electrons accompanied by the loss of two protons at pH<10. Voltammetric and chronocoulometric data indicated the oxidation reaction kinetics on all three electrodes were under mixed control by both diffusion and adsorption. This was most apparent for GC where estrone adsorption was greatest (145pmolcm−2). The greater adsorption on GC can be explained by electronic and or chemical effects associated with the graphitic edge plane sites. In contrast, the estrone adsorption on ta-C:N and BDD was significantly lower, about 1/10 of that on GC. This behavior is due to the differences in the types and density of functional groups and the absence of an extended π-electron system in both materials. In summary, the here-reported properties of the ta-C:N and BDD electrodes suggest that both could be excellent candidates for electroanalytical measurements involving the detection and/or determination of estrone and similar hormones.

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

A novel desulfurization process of gasoline was realized via sodium metaborate (NaBO2) electroreduction with pulse voltage using a boron-doped diamond (BDD) thin film electrode under mild conditions. The results of cyclic voltammetry and 11boron (B) nuclear magnetic resonance (NMR) confirmed that NaBO2 was converted into sodium borohydride (NaBH4) by electroreduction and the electroreduction voltage ranged from −1.2V to −1.8V. The factors that influenced desulfurization efficiency were investigated and the desulfurization efficiency reached more than 95% for model gasoline and more than 97% for real gasoline. The components of model gasolines before and after desulfurization were analyzed by gas chromatography/mass spectrometer (GC/MS) and the elements content of electrolytes and digestion solution of precipitate were determined by inductively coupled plasma (ICP). Results indicated that reductive desulfurization process mainly involved the cleavage of C–S bond and the hydrogenation of C–C double bond and B recycle was realized at the same time as desulfurization. Consequently, possible desulfurization mechanism was proposed. Desulfurization kinetics showed a pseudo-first-order toward thiophene or benzothiophene. All these results indicated that the gasoline desulfurization process via sodium metaborate electroreduction with pulse voltage using a BDD thin film electrode was feasible.

Mild Process for Reductive Desulfurization of Diesel Fuel Using Sodium Borohydride in Situ Generated via Sodium Metaborate Electroreduction

A novel integrated process was proposed for reductive desulfurization of diesel fuel, in which the reductant sodium borohydride (NaBH4) was in situ generated via sodium metaborate (NaBO2) electroreduction. In order to improve the conversion rate of BO2– into BH4–, NaBO2 electroreduction was fulfilled by applying pulse voltage and using a boron-doped diamond (BDD) thin film electrode. The NaBO2 electroreduction process was analyzed by cyclic voltammetry and 11boron nuclear magnetic resonance (11B NMR) and the factors that influenced desulfurization efficiency were investigated. Under the optimal conditions desulfurization efficiency reached more than 93% for model diesel fuel. The components of model diesel fuel after desulfurization were analyzed by gas chromatography/mass spectrometry (GC/MS) and the electrolyte and digestion solution of precipitate were analyzed by inductively coupled plasma (ICP). Results indicated that B recycle was realized at the same time as desulfurization. Finally, the desulfuriz...

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.