A new view of electrochemistry at highly oriented pyrolytic graphite

Major new insights on electrochemical processes at graphite electrodes are reported, following extensive investigations of two of the most studied redox couples, Fe(CN)64–/3– and Ru(NH3)63+/2+. Experiments have been carried out on five different grades of highly oriented pyrolytic graphite (HOPG) that vary in step-edge height and surface coverage. Significantly, the same electrochemical characteristic is observed on all surfaces, independent of surface quality: initial cyclic voltammetry (CV) is close to reversible on freshly cleaved surfaces (>400 measurements for Fe(CN)64–/3– and >100 for Ru(NH3)63+/2+), in marked contrast to previous studies that have found very slow electron transfer (ET) kinetics, with an interpretation that ET only occurs at step edges. Significantly, high spatial resolution electrochemical imaging with scanning electrochemical cell microscopy, on the highest quality mechanically cleaved HOPG, demonstrates definitively that the pristine basal surface supports fast ET, and that ET is not confined to step edges. However, the history of the HOPG surface strongly influences the electrochemical behavior. Thus, Fe(CN)64–/3– shows markedly diminished ET kinetics with either extended exposure of the HOPG surface to the ambient environment or repeated CV measurements. In situ atomic force microscopy (AFM) reveals that the deterioration in apparent ET kinetics is coupled with the deposition of material on the HOPG electrode, while conducting-AFM highlights that, after cleaving, the local surface conductivity of HOPG deteriorates significantly with time. These observations and new insights are not only important for graphite, but have significant implications for electrochemistry at related carbon materials such as graphene and carbon nanotubes

The improved electrochemical performance of cross-linked 3D graphene nanoribbon monolith electrodes

Technical advancement in the field of ultra-small sensors and devices demands the development of novel micro- or nano-based architectures. Here we report the design and assembly of cross-linked three dimensional graphene nanoribbons (3D GNRs) using solution based covalent binding of individual 2D GNRs and demonstrate its electrochemical application as a 3D electrode. The enhanced performance of 3D GNRs over individual 2D GNRs is established using standard redox probes – [Ru(NH3)6]3+/2+, [Fe(CN)6]3−/4− and important bio-analytes – dopamine and ascorbic acid. 3D GNRs are found to have high double layer capacitance (2482 μF cm−2) and faster electron transfer kinetics; their exceptional electrocatalytic activity towards the oxygen reduction reaction is indicative of their potential over a wide range of electrochemical applications. Moreover, this study opens a new platform for the design of novel point-of-care devices and electrodes for energy device

Selective and efficient electrochemical biosensing of ultrathin molybdenum disulfide sheets

Atomically thin molybdenum disulfide (MoS2) sheets were synthesized and isolated via solventassisted chemical exfoliation. The charge-dependent electrochemical activities of these MoS2 sheets were studied using positively charged hexamine ruthenium (III) chloride and negatively charged ferricyanide/ferrocyanide redox probes. Ultrathin MoS2 sheet-based electrodes were employed for the electrochemical detection of an important neurotransmitter, namely dopamine (DA), in the presence of ascorbic acid (AA). MoS2 electrodes were identified as being capable of distinguishing the coexistence of the DA and the AA with an excellent stability. Moreover, the enzymatic detection of the glucose was studied by immobilizing glucose oxidase on the MoS2. This study opens enzymatic and non-enzymatic electrochemical biosensing applications of atomic MoS2 sheets, which will supplement their established electronic application

Adsorption of C.I Direct brown 2: A bisazo dye from different base electrolytes

ElectrocapiJlary curves for 1 M solutions of NaCl, aNO) and . a2S04 in the presence of different concentrations of C.I. Direct Brown 2 show that the organic compound adsorbs on the positively cbarged mercury surface. The extent of adsorption from these base electrolytes follows the order Na2S04 > NaNO) > NaC!. Thermodynamic parameters like-eharge on the metal surface (qil'\ the surface excess of organic molecule adsorbed (rorg)' surface coverage (8) and free energy of adsorption (-tJ.Go) are evaluated. The adsorption of this compound is found to obey Langmuir's adsorption isotherm in all the cases, irrespective of the nature of the base electrolyte used

Tdsorption of C.1. Direct red 73 on the mercury electrode from different base electrolytes

The adsorption of C.I. direct red 73, a bisazo direct dye at the mercury/solution interface from 1 M solutions of NaCl, NaNOJ and NazS04 has been investigated using capillary electrometer. Thermodynamic parameters like charge on the metal surface (qM), the surface excess of organk molecule adsorbed (foil)' surface coverage (8) and free energy of adsorption (-AG) are evaluated and presented. The adsorption of C.I. direct red 73 obeys Langmuir's adsorption isotherm in all the three base electrolytes

Chitosan-graphene biosensors and methods for their use

Provided herein is a method for detecting mutations in polynucleotide sequences through the use of a glassy carbon electrode (GCE) coated with a chitosan-graphene nanosheet material (also referred to herein as a “CMG electrode.”) It is a surprising finding of the present invention that the CMG electrodes can be used to detect non-hybridization of capture and target polynucleotides using voltammetry, wherein non-hybridization indicates a mutation or difference in the target polynucleotide as compared to a control

Non-Precious Metal/Metal Oxides & Nitrogen Doped Reduced Graphene Oxide based Alkaline Water Electrolysis Cell

Development of strategies for water electrolysis half-cell reaction catalysts without the use of precious metals/metal oxides and the synergistic compilation of catalysts for the full cell fabrication are receiving tremendous scientific attention. Here, alkaline water electrolysis full cells are developed with novel spongy catalysts for both anode and cathode reactions - such as Co3O4-nitrogen doped reduced graphene oxide (Co3O4/NrGO) composite sponge for Oxygen Evolution Reaction (OER) and nickel-nitrogen doped reduced graphene oxide (NiNrGO) for hydrogen evolution reaction (HER). The performance of OER catalyst developed - Co3O4/NrGO, is compared with the commercial one (IrO2) in alkaline medium with a common benchmark cathode catalyst (Pt) and an augmented full cell performance is shown from this novel combination (320 mAcm-2 at an operating voltage of 1.9 V for Co3O4/NrGO, while 199 mA/cm-2 for IrO2). A water electrolysis full cell is developed without the use of HER catalyst Pt rather using a porous spongy catalyst - NiNrGO,having a low operating potential with a high stability (270 mAcm-2 at an operating voltage of 1.9 V with a stability tested for more than 9 hours), and this works opens up the possibilities of designing lightweight water electrolysis cells without the use of commercial benchmark precious catalysts