Graphite Rod Electrode Research Articles

Preparation of Graphite Nanoflakes and Supported Noble Metal/Alloy Nanoparticles by Paired Electrolysis with Graphite Electrodes

We report a paired electrolysis method to prepare graphite nanoflakes (GNFs) and their supported noble metal/alloy nanoparticles (NM NPs/GNFs), by applying an alternating voltage (AV) on two graphite rod electrodes in a NaOH solution without/with noble–metal ions. The synthesis of GNFs might be related to the anodic exfoliation of graphite surface via OH− intercalation, accompanying the dispersion effect of hydrogen/oxygen gases evolution. The preparation of NM NPs/GNFs should be resulted from repeated coupling processes, namely the cathodic deposition of NM NPs and the electrochemical exfoliation-dispersion of NM NPs-decorated graphite layer. The as-prepared products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-disperse X-ray spectra (EDX), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (AAS) and inductively coupled plasma (ICP). The GNFs and NM NPs/GNFs exhibited high electrocatalytic activities toward the redox of 4-nitrophenol and oxidation of formic acid, respectively.

Amperometric Glucose Biosensor Based on Glucose Oxidase, 1,10-Phenanthroline-5,6-dione and Carbon Nanotubes

A biosensor for glucose determination was fabricated by the immobilization of glucose oxidase (GOx) on carbon nanotubes (CNTs) and/or 1,10-phenanthroline-5,6-dione (PD) modified graphite rod electrodes (GOx/PD/CNTs/GR) and its amperometric response toward glucose was investigated under aerobic and anaerobic conditions. The sensitivity of the GOx/PD/CNTs/GR electrode was found to be higher compared to that of a PD-modified GR electrode without CNTs (GOx/PD/GR), implying that CNTs play an important role in the facilitation of electron transfer between the redox active site of GOx and the electrode surface. The GOx/PD/CNTs/GR biosensor exhibited a linear dependency on substrate concentration in a range from 0.0 until 50.0 mM of glucose with oxygen present and from 0.0 until 62.5 mM of glucose in the absence of oxygen. With oxygen present, the limit of detection (LOD) values were determined to be 5.4 and 8.0 mM, and the limit of quantitation values (LOQ) were calculated as 16.2 and 24 mM for GOx/PD/GR and GOx/PD/CNTs/GR, respectively. In the absence of oxygen, the LOD values were calculated as 4.2 and 10.7 mM, and the LOQ values were calculated as 12.6 and 32.1 mM for GOx/PD/GR and GOx/PD/CNTs/GR, respectively. When examining the interference effect of uric acid for GOx/PD/GR and GOx/PD/CNTs/GR electrodes, no significant changes in the amperometric response of the modified electrodes were observed up to 100.0 mM of uric acid.

Evaluation of the Redox Mediating Properties of 1,10-Phenanthroline-5,6-dione for Glucose Oxidase Modified Graphite Electrodes

1,10-Phenanthroline-5,6-dione and glucose oxidase modified and unmodified graphite rod electrodes (GRE) were investigated in buffer with 0.04 mol*L−1 of glucose by electrochemical impedance spectroscopy (EIS). The EIS was conducted under potentiostatic conditions and showed relatively good stability. The impedimetric results were evaluated using estimated equivalent circuit. The EIS based study demonstrated redox mediating properties of 1,10-phenanthroline-5,6-dione deposited on GRE. EIS characteristics observed in this study show that electrodes modified by both 1,10-phenanthroline-5,6-dione and glucose oxidase can be used as an impedimetric glucose biosensor.

Biofuel Cell Based on Anode and Cathode Modified by Glucose Oxidase

AbstractA single compartment biofuel cell (BFC) based on an anode and a cathode powered by the same fuel glucose is reported. Glucose oxidase (GOx) from Aspergillus niger was applied as a glucose consuming biocatalyst for both anode and cathode of the BFC. The 5‐amino‐1,10‐phenanthroline modified graphite rod electrode (GRE) with cross‐linked GOx was used as the bioanode, and the GRE with co‐immobilised horseradish peroxidase and GOx was exploited as the biocathode of the BFC. The open‐circuit voltage of the designed BFC exceeded 450 mV and a maximal power density of 3.5 µW/cm2 was registered at a cell voltage of 300 mV.

Single stage electrochemical exfoliation method for the production of few-layer graphene via intercalation of tetraalkylammonium cations

We present a non-oxidative production route to few layer graphene via the electrochemical intercalation of tetraalkylammonium cations into pristine graphite. Two forms of graphite have been studied as the source material with each yielding a slightly different result. Highly orientated pyrolytic graphite (HOPG) offers greater advantages in terms of the exfoliate size but the source electrode set up introduces difficulties to the procedure and requires the use of sonication. Using a graphite rod electrode, few layer graphene flakes (2nm thickness) are formed directly although the flake diameters from this source are typically small (ca. 100–200nm). Significantly, for a solvent based route, the graphite rod does not require ultrasonication or any secondary physical processing of the resulting dispersion. Flakes have been characterized using Raman spectroscopy, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS).

Performance of liter-scale microbial fuel cells with electrode arrays: Effect of array pattern

Scale-up of microbial fuel cells requires the application of compact structure with well-arranged multi-electrode. For better understanding of electrode design, two liter-scale microbial fuel cells with staggered array (MFC-S) and inline array (MFC-I) were constructed using graphite rod electrodes. The effects of electrode array pattern on MFC startup, power generation, anodic current distribution, COD removal and coulombic efficiency were evaluated. The results showed that MFC-S had a faster startup with higher voltage output compared with MFC-I. Moreover, the maximum power density (23.8 W/m3) of MFC-S was approximately one quarter higher than that of MFC-I (19.1 W/m3) due to the structure-induced better mass transfer of staggered array. No noticeable difference in anodic current maldistribution between the two MFCs was observed at a similar cell current. For a batch feeding mode, compared with MFC-I, MFC-S had a slightly higher COD removal efficiency (84.3%) but much higher coulombic efficiency (82.3%) with a nonuniform segment CE distribution.

Anodic current distribution in a liter-scale microbial fuel cell with electrode arrays

A liter-scale microbial fuel cell with graphite rod electrode arrays (MFC-EA) was constructed and its relative anodic current distribution was investigated with 9 groups of anode electrodes. Meanwhile, the influences of COD concentration and ionic strength of anolyte on anodic current distribution were discussed. It is demonstrated that the electrode spacing between the anode segment and cathode significantly influenced the ohmic resistance distribution and the biomass content of each segment, further affected the anodic current distribution. A significantly uneven current distribution was found in MFC-EA, especially at high currents. The further the anode segment was away from the cathode, the smaller the segment current generation contributed to the total current. Consequently, a suitable MFC structure with equidistant electrode spacing will be a necessary consideration for large-scale MFC design. Moreover, for MFC-EA, improvement on the uneven current distribution was achieved by feeding the anolyte with a COD concentration of 1000mg COD L−1 or with 0.2M KCl.

Charge Transport through Geobacter sulfurreducens Biofilms Grown on Graphite Rods

Biofilms of the electroactive bacterium Geobacter sulfurreducens were induced to grow on graphite-rod electrodes under a potential of 0 V (vs Ag/AgCl) in the presence of acetate as an electron donor. Increased anodic currents for bioelectrocatalytic oxidation of acetate were obtained when the electrodes were incubated for longer periods with periodic electron-donor feeding. The maximum current density for acetate oxidation increased 2.8-fold, and the biofilm thickness increased by 4.25-fold, over a time period of 83-147 h. Cyclic voltammetry in the presence of acetate supports a model of heterogeneous electron transfer, one electron at time, from biofilm to electrode through a dominant redox species centered at -0.41 V vs Ag/AgCl. Voltammetry performed under nonturnover conditions provided an estimate of the surface coverage of the redox species of 25 nmol/cm(2). This value was used to estimate a redox species concentration of 7.3 mM within the 34-μm-thick biofilm and a charge-transport diffusion coefficient of 3.6 × 10(-7) cm(2)/s. This value of diffusion coefficient is greater than that observed in traditional thin-film voltammetric studies with redox polymer films containing much higher surface concentrations of redox species and might be associated with proton transport to ensure electroneutrality within the biofilm upon electrolysis.

Electrodeposition of Pd catalyst layer on graphite rod electrodes for direct formic acid oxidation

An electrodeposition method for preparing the Pd catalyst layer on graphite rod electrodes for direct formic acid oxidation is proposed in this study. This method consists of a repeated procedure involving the electrodeposition of Pd catalyst onto the graphite rods, followed by Nafion coating (RENC). The structural features and electrocatalytic properties of the electrode were extensively investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results show that coating the electrode with Nafion during each electrodepositing step plays a crucial role on the morphology, particle size and crystallinity of the electrocatalysts. Although the commercial Pd catalyst has the smaller particle size and more uniform distribution than that prepared by RENC, the RENC electrode exhibits almost the same electrochemical surface area, a better performance and durability toward formic acid electro-oxidation. These results can be attributed to the improved catalyst utilization resulting from the multi-layer structure and the predominance of the highly active Pd (111) crystallite phase on the surface of the catalyst layer.

Enhanced direct electron transfer between laccase and hierarchical carbon microfibers/carbon nanotubes composite electrodes. Comparison of three enzyme immobilization methods

Three immobilization protocols were investigated with respect to direct electron transfer between hierarchical carbon microfibers/carbon nanotubes composite material on graphite rod electrodes and Trametes hirsuta laccase. Immobilization was done by covalent binding of laccase to aminophenyl-modified electrodes via amide-bond formation with carboxylic acid residues or imino-bond formation with aldehyde groups introduced by oxidation of sugar residues of the enzyme's glycosylation shell. Moreover, immobilization was achieved by adsorbing laccase to electrodes hydrophilized with pyrene-hexanoic acid. High current densities for biocatalytic oxygen reduction were obtained for all immobilization strategies. The formation of the imino bonds let to the binding of laccase in close to 100% direct electron transfer configuration and consequently to the highest oxygen reduction currents.

A biosensor based on the self-entrapment of glucose oxidase within biomimetic silica nanoparticles induced by a fusion enzyme

We constructed a fusion protein (GOx–R5) consisting of R5 (a polypeptide component of silaffin) and glucose oxidase (GOx) that was expressed in Pichia pastoris. Silaffin proteins are responsible for the formation of a silica-based cell matrix of diatoms, and synthetic variants of the R5 protein can perform silicification in vitro [1]. GOx secreted by P. pastoris was self-immobilized (biosilicification) in a pH 5 citric buffer using 0.1 M tetramethoxysilane as a silica source. This self-entrapment property of GOx–R5 was used to immobilize GOx on a graphite rod electrode. An electric cell designed as a biosensor was prepared to monitor the glucose concentrations. The electric cell consisted of an Ag/AgCl reference electrode, a platinum counter electrode, and a working electrode modified with poly(neutral red) (PNR)/GOx/Nafion. Glucose oxidase was immobilized by fused protein on poly(neutral red) and covered by Nafion to protect diffusion to the solution. The morphology of the resulting composite PNR/GOx/Nafion material was analyzed by scanning electron microscopy (SEM). This amperometric transducer was characterized electrochemically using cyclic voltammetry and amperometry in the presence of glucose. An image produced by scanning electron microscopy supported the formation of a PNR/GOx complex and the current was increased to 1.58 μA cm −1 by adding 1 mM glucose at an applied potential of −0.5 V. The current was detected by way of PNR-reduced hydrogen peroxide, a product of the glucose oxidation by GOx. The detection limit was 0.67 mM (S/N = 3). The biosensor containing the graphite rod/PNR/GOx/Nafion detected glucose at various concentrations in mixed samples, which contained interfering molecules. In this study, we report the first expression of R5 fused to glucose oxidase in eukaryotic cells and demonstrate an application of self-entrapped GOx to a glucose biosensor.

Evaluation of amperometric glucose biosensors based on glucose oxidase encapsulated within enzymatically synthesized polyaniline and polypyrrole

In this article potential and suitability of enzymatically synthesized conducting polymers polyaniline (PANI) and polypyrrole (PPY) for fabrication of enzymatic amperometric glucose biosensors were evaluated. The polymerisation of these polymers was induced by catalytic activity of glucose oxidase (GOx) from Penicillium vitale cross-linked by glutaraldehyde (GA) on the graphite rod electrode (GOx-electrode) surface. The main precursors for initiation of polymerisation reactions were hydrogen peroxide as an initiator of polymerisation reaction and β- d-gluconic acid as a medium, which reduced the pH towards acidic one is the most suitable for the formation of PANI and PPY. During the polymerisation reactions the immobilized GOx was self-encapsulated within formed PANI or PPY layers in order to form GOx/PANI- and GOx/PPY-modified electrodes (GOx/PANI-electrode and GOx/PPY-electrode, respectively). Kinetic properties of GOx, which is acting as a biocatalyst in GOx/PANI- and GOx/PPY-electrodes, were studied and results were compared with GOx-electrode. The results show that in both GOx/PANI- and GOx/PPY-electrodes self-encapsulated GOx exhibited different parameters of catalysed reaction kinetics due to increasing diffusion limitations if compared with that of the GOx-electrode and it allowed the detection of glucose in a wider concentration interval. Moreover, both GOx/PANI- and GOx/PPY-electrodes exhibited good operational stability and reproducibility of analytical signal. The electrochemical characteristics of formed PANI and PPY in the GOx/PANI- and GOx/PPY-electrodes were also determined. In addition, the influence of temperature, pH and common interfering compounds on the steady-state current response of modified electrodes were investigated and discussed.

1,10-Phenanthroline derivatives as mediators for glucose oxidase

This study is focused on possible application of some 1,10-phenanthroline derivatives (PDs) in the development of biosensors and biofuel cells. Differently from some other studies, the PDs that were not involved into structures of metal complexes were investigated. Five PDs [1,10-phenanthroline monohydrate (PMH); 5-nitro-1,10-phenanthroline (5NP); 5-amino-1,10-phenanthroline (5AP), 5-amino,6-nitro-1,10-phenanthroline (5A6NP) and 5,6-diamino-1,10-phenanthroline (56DAP)] were selected for this study. Bioelectrochemical responses of PDs and glucose oxidase (GOX)-modified graphite rod electrodes (GREs) were studied amperometrically and potentiometrically. The best redox mediators for GOX were found on PDs containing amino groups: 5AP and 56DAP. Amperometrical measurements have shown that 5NP derivative was also acting as a redox mediator but activity of 5NP was approximately four times lower than 5AP and three times lower than 56DAP. This study clearly illustrates that some PDs can be applied as redox mediators for oxidases and are suitable for the development of reagent-less biosensors and biofuel cells. Since amino groups can be very easily involved in the formation of chemical bounds, the amino-PDs are interesting compounds for the development of nanobiotechnological tools by bottom-up technique.

Glucose biosensor based on graphite electrodes modified with glucose oxidase and colloidal gold nanoparticles

The electrochemistry of glucose oxidase (GOx) immobilized on a graphite rod electrode modified by gold nanoparticles (Au-NPs) was studied. Two types of amperometric glucose sensors based on GOx immobilized and Au-NPs modified working electrode (Au-NPs/GOx/graphite and GOx/Au-NPs/graphite) were designed and tested in the presence and the absence of N-methylphenazonium methyl sulphate in different buffers. Results were compared to those obtained with similar electrodes not containing Au-NPs (GOx/graphite). This study shows that the application of Au-NPs increases the rate of mediated electron transfer. Major analytical characteristics of the amperometric biosensor based on GOx and 13 nm diameter Au-NPs were determined. The analytical signal was linearly related to glucose concentration in the range from 0.1 to 10 mmol L−1. The detection limit for glucose was found within 0.1 mmol L−1 and 0.08 mmol L−1 and the relative standard deviation in the range of 0.1–100 mol L−1 was 0.04–0.39%. The τ1/2 of Vmax characterizes the storage stability of sensors: this parameter for the developed GOx/graphite electrode was 49.3 days and for GOx/Au-NPs/graphite electrode was 19.5 days. The sensor might be suitable for determination of glucose in beverages and/or in food.

Towards a high potential biocathode based on direct bioelectrochemistry between horseradish peroxidase and hierarchically structured carbon nanotubes

Adsorption of horseradish peroxidase (HRP) on graphite rod electrodes sequentially modified with carbon microfibers (CMF) carrying carbon nanotubes in a hierarchically structured arrangement and finally pyrene hexanoic acid (PHA) for improving hydrophilicity of the electrode surface is the basis for the direct bioelectrocatalytic reduction of H(2)O(2) at potentials as high as about +600 mV. The high-potential direct bioelectrocatalytic reduction of H(2)O(2) is implying a direct bioelectrochemical communication between the Fe(IV)=O,P(+*) redox state known as compound I. The HRP loading was optimized leading to a current of 800 microA at a potential of 300 mV.

Nondestructive Evaluation of Multiply Connected Electrical Arc Furnace Graphite Rod Electrodes

The low quality of graphite electrodes in a small electrical arc furnace causes many problems on furnace operation. High temperature and erosion at the remote electrode tip, and defects in the electrode increase the probability of electrode failure due to ageing phenomena such as thermal stress cracking. Most measurement techniques cannot determine the electrode quality under such conditions as the high temperature is highly destructive to the device. Nondestructive sensing techniques such as ultrasonics can possibly be used. Experimental studies on the feasibility of using mechanically connected and chemically bonded graphite rod electrodes as a sensing medium for an ultrasonic signal are performed. Graphite rod porosity and defects are inspected using ultrasonic, infrared, and Real-Time Neutron Radiography nondestructive inspection techniques. The acoustic characteristics of the graphite rods are determined, and the soundwave velocity of the graphite rods is measured to be 2529.4 m/s. Ultrasonic frequencies from 60.0 kHz to 10.0 MHz are studied. The optimum ultrasonic frequency for propagation through graphite rods, hence quality inspection, are 500.0 kHz and 1.0 MHz. The effect of electrode length and the number of mechanical joints on the operating ultrasonic frequency are discussed in detail.

Synthesis and X-ray or NMR/DFT Structure Elucidation of Twenty-One New Trifluoromethyl Derivatives of Soluble Cage Isomers of C76, C78, C84, and C90

Adding 1% of the metallic elements cerium, lanthanum, and yttrium to graphite rod electrodes resulted in different amounts of the hollow higher fullerenes (HHFs) C76-D2(1), C78-C2v(2), and C78-C2v(3) in carbon-arc fullerene-containing soots. The reaction of trifluoroiodomethane with these and other soluble HHFs at 520-550 degrees C produced 21 new C76,78,84,90(CF3)n derivatives (n = 6, 8, 10, 12, 14). The reaction with C76-D2(1) produced an abundant isomer of C2-(C76-D2(1))(CF3)10 plus smaller amounts of an isomer of C1-(C76-D2(1))(CF3)6, two isomers of C1-(C76-D2(1))(CF3)8, four isomers of C1-(C76-D2(1))(CF3)10, and one isomer of C2-(C76-D2(1))(CF3)12. The reaction with a mixture of C78-D3(1), C78-C2v(2), and C78-C2v(3) produced the previously reported isomer C1-(C78-C2v(3))(CF3)12 (characterized by X-ray crystallography in this work) and the following new compounds: C2-(C78-C2v(3))(CF3)8; C2-(C78-D3(1))(CF3)10 and C(s)-(C78-C2v(2))(CF3)10 (both characterized by X-ray crystallography in this work); C2-(C78-C2v(2))(CF3)10; and C1-C78(CF3)14 (cage isomer unknown). The reaction of a mixture of soluble higher fullerenes including C84 and C90 produced the new compounds C1-C84(CF3)10 (cage isomer unknown), C1-(C84-C2(11))(CF3)12 (X-ray structure reported recently), D2-(C84-D2(22))(CF3)12, C2-(C84-D2(22))(CF3)12, C1-C84(CF3)14 (cage isomer unknown), C1-(C90-C1(32))(CF3)12, and another isomer of C1-C90(CF3)12 (cage isomer unknown). All compounds were studied by mass spectrometry, (19)F NMR spectroscopy, and DFT calculations. An analysis of the addition patterns of these compounds and three other HHF(X) n compounds with bulky X groups has led to the discovery of the following addition-pattern principle for HHFs: In general, the most pyramidal cage C(sp(2)) atoms in the parent HHF, which form the most electron-rich and therefore the most reactive cage C-C bonds as far as 1,2-additions are concerned, are not the cage C atoms to which bulky substituents are added. Instead, ribbons of edge-sharing p-C6(X)2 hexagons, with X groups on less pyramidal cage C atoms, are formed, and the otherwise "most reactive" fullerene double bonds remain intact.

A novel method to produce carbon nanotubes using EDM process

Carbon nanotubes (CNTs) have been used in various fields of research due to their unique properties. There are various methods such as arc discharge, laser ablation, chemical vapor deposition (CVD), template-directed synthesis and the use of the growth of CNTs in the presence of catalyst particles. Special ambient gas is required for the fabrication of CNTs, in order to prevent the oxidation of carbon at high temperature. In this study, we developed a simple, fast and low cost method in which CNTs can be fabrication by single-pulse discharge with low energy in air. The single-pulse discharge system was designed to adjust the peak current and pulse duration. A graphite rod electrode generated an electric arc between electrode and the substrate at a distance of 1 μm. A promising result was obtained by using single-pulse discharge with a pulse duration of 1000 μs and peak current of 2.5 A; that is, many CNTs grew on the substrate under these conditions. This method can overcome the limitations of the special ambient gas and enable the fabrication of CNTs at a selected location on the substrate.

Planar and three-dimensional microfluidic fuel cell architectures based on graphite rod electrodes

We propose new membraneless microfluidic fuel cell architectures employing graphite rod electrodes. Commonly employed as mechanical pencil refills, graphite rods are inexpensive and serve effectively as both electrode and current collector for combined all-vanadium fuel/oxidant systems. In contrast to film-deposited electrodes, the geometry and mechanical properties of graphite rods enable unique three-dimensional microfluidic fuel cell architectures. Planar microfluidic fuel cells employing graphite rod electrodes are presented here first. The planar geometry is typical of microfluidic fuel cells presented to date, and permits fuel cell performance comparisons and the evaluation of graphite rods as electrodes. The planar cells produce a peak power density of 35 mW cm −2 at 0.8 V using 2 M vanadium solutions, and provide steady operation at flow rates spanning four orders of magnitude. Numerical simulations and empirical scaling laws are developed to provide insight into the measured performance and graphite rods as fuel cell electrodes. We also present the first three-dimensional microfluidic fuel cell architecture with multiple electrodes. The proposed fuel cell architecture, consisting of a hexagonal array of graphite rods, enables scale-up/integration of microfluidic fuel cell technology as well as power conditioning flexibility beyond that of the traditional fuel cell stack. When provided the same flow rate as the planar cell, the array cell generated an order of magnitude higher power output. The array architecture also enabled unprecedented levels of single pass fuel utilization, up to 78%.

A New Sodium Ion Selective PVC-Coated Graphite Rod Electrode Based on 4-Amino-Benzo-15-Crown-5 Derivatives of Fullerenes

A New Sodium Ion Selective PVC-Coated Graphite Rod Electrode Based on 4-Amino-Benzo-15-Crown-5 Derivatives of Fullerenes