Plane Pyrolytic Graphite Electrode Research Articles

The Mediatorless Electroanalytical Sensing of Sulfide Utilizing Unmodified Graphitic Electrode Materials

The mediatorless electroanalytical sensing of sulfide is explored at a range of commercially available graphitic based electrodes namely, edge and basal plane pyrolytic graphite (EPPGE and BPPGE, respectively), boron-doped diamond (BDDE), glassy carbon (GCE) and screen-printed electrodes (SPE). The electrochemical performance is evaluated in terms of current density/analytical signal and oxidation potential, where the GCE and SPE are found to possess the optimal electrochemical responses. The electroanalytical performance of the GCE is explored towards the electrochemical sensing of sulfide and it is found that it is hampered by sulfide passivation, thus requiring pretreatment in the form of electrode polishing between each measurement. We demonstrate that SPEs provide a simple analytically comparable alternative, which, due to their scales of economy, create disposable, one-shot sensors that do not require any pretreatment of the electrode surface. To the best of our knowledge, this is the first report using mediatorless SPEs (bare/unmodified) towards the sensing of sulfide. In addition, the electroanalytical efficacy of the SPEs is also explored towards the detection of sulfide within model aqueous solutions and real drinking water samples presenting good apparent recoveries, justifying the plausibility of this graphitic mediatorless screen-printed platform.

The Oxygen Reduction Reaction at Graphene Modified Electrodes

AbstractThe oxygen reduction reaction (ORR) is studied in acidic media utilising various graphene modified carbon electrodes including pristine graphene, Graphene Oxide (GO) and Q‐Graphene which are compared and contrasted against unmodified edge‐ and basal‐ plane pyrolytic graphite electrodes (EPPG and BPPG, respectively). The ORR is found to be highly dependent upon the material’s characteristics where a range of activities are observed; in terms of the smallest (least negative) reduction potential, the relative reactivities are ordered as follows: GO>Q‐Graphene>EPPG>BPPG>Pristine graphene. This phenomenon is discussed in terms of two parameters: i) the density of oxygenated species present and their composition; and ii) the density of edge plane‐like sites. Electrochemical analysis reveals that despite the observed variation in peak potentials from the modification with various graphenes, the underlying ORR mechanism in acidic media proceeds via the 2 electron process forming hydrogen peroxide. Insights from this work are highly important as it allows researchers to understand the electrochemistry of graphene in the ORR which has importance in energy generation and where graphene is used per se and also as fuel cell catalyst supports.

Enhanced Electrocatalytic Reduction of Oxygen at Electrodes Coated with a Multi-Metallic Co(II)/Pt(II) Porphyrin

Edge plane pyrolytic graphite (EPG) electrodes coated with the Co(II)/Pt(II)2 analog of 5,15-bis-(4-pyridyl)-10,20-bis-(3-methoxy-4-hydroxyphenyl)porphyrin undergo an electrochemical-chemical-electrochemical (ECE) reaction when anodically scanned in 1.0 M sulfuric acid. The new redox couple formed from this anodic conditioning of the coated electrode is dependent on the pH of the solution. Roughened EPG electrodes coated with the Co(II)/Pt(II)2 trimetallic porphyrin show a catalytic shift of 400 mV for the reduction of O2 when compared to the reduction of O2 at a bare EPG electrode. An additional catalytic shift of ca. 150 mV is observed for O2 reduction at an EPG electrode coated with the Co(II)/Pt(II)2 porphyrin which has been oxidized in 1.0 M sulfuric acid. In addition to the added electrocatalysis, a significant percentage of O2 reduced at the oxidized Co(II)/Pt(II)2 EPG electrode is converted to H2O as determined by rotating disk electrode measurements.

The electrochemical performance of graphene modified electrodes: An analytical perspective

We explore the use of graphene modified electrodes towards the electroanalytical sensing of various analytes, namely dopamine hydrochloride, uric acid, acetaminophen and p-benzoquinone via cyclic voltammetry. In line with literature methodologies and to investigate the full-implications of employing graphene in this electrochemical context, we modify electrode substrates that exhibit either fast or slow electron transfer kinetics (edge- or basal- plane pyrolytic graphite electrodes respectively) with well characterised commercially available graphene that has not been chemically treated, is free from surfactants and as a result of its fabrication has an extremely low oxygen content, allowing the true electroanalytical applicability of graphene to be properly de-convoluted and determined. In comparison to the unmodified underlying electrode substrates (constructed from graphite), we find that graphene exhibits a reduced analytical performance in terms of sensitivity, linearity and observed detection limits towards each of the various analytes studied within. Owing to graphene's structural composition, low proportion of edge plane sites and consequent slow heterogeneous electron transfer rates, there appears to be no advantages, for the analytes studied here, of employing graphene in this electroanalytical context.

Sensitive voltammetric sensor for determination of flumethasone pivalate, abused for doping by athletes

The voltammetric reduction of flumethasone pivalate has been studied at fullerene-C 60-modified edge plane pyrolytic graphite electrode (PGE) and two well defined peaks are obtained with a peak potential of ∼−1220 mV and ∼−1351 mV respectively. The modified electrode showed a better response in comparison to a bare basal plane PGE and bare edge plane PGE. Linear calibration curves are obtained with sensitivity of 0.685 μA μM −1 and 0.570 μA μM −1 and the corresponding limits of detection at both the peaks have been found to be 13.81 × 10 −8 M and 27.5 × 10 −8 M. The recovery studies for flumethasone pivalate in biological samples were also investigated.

Composite Films of Surfactants, Nafion, and Proteins with Electrochemical and Enzyme Activity

Stable, functional composite films were made from the ionomer Nafion, water-insoluble surfactants, and heme proteins or the enzyme alcohol dehydrogenase. Rates of electron transfer between myoglobin (Mb) and hemoglobin (Hb) and edge plane pyrolytic graphite (PG) electrodes in these composite films were much larger than those for Hb and Mb in solution on Nafion-coated or bare PG electrodes. Films containing Nafion, didodecydimethylammonium bromide (DDAB), and hemoglobin or myoglobin retained about 90% of the initial redox activity during 4 weeks of storage at 4 °C. DDAB is arranged in lamellar liquid crystal bilayers in these films at 25 °C, which were more stable than films of the proteins and DDAB alone. Films of Nafion−lecithin−Cyt c on edge plane PG also had good electrochemical properties but were much less stable. Electronic and vibrational spectra indicate that the heme proteins are not denatured in the composite films, but conformational differences from the native state may exist. Linear dichroism...