Boron-Doped Diamond Dual-Plate Deep-Microtrench Device for Generator-Collector Sulfide Sensing

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.A BDD-BDD dual-plate microtrench electrode with 6μm inter-electrode spacing is investigated using generator-collector electrochemistry and shown to give microtrench depth-dependent sulfide detection down to the μM levels. The effect of the microtrench depth is compared for a "shallow" 44 μm and a "deep" 180μm microtrench and linked to the reduction of oxygen to hydrogen peroxide which interferes with sulfide redox cycling. With a deeper microtrench and a fixed collector potential at -1.4V vs. SCE, two distinct redox cycling potential domains are observed at 0.0V vs. SCE (2-electron) and at 1.1V vs. SCE (6-electron).F. M. and A. J. G. thank EPSRC for financial support (EP/I028706/1)

A cobalt complex redox shuttle for dye-sensitized solar cells with high open-circuit potentials

Dye-sensitized solar cells are a promising alternative to traditional inorganic semiconductor-based solar cells. Here we report an open-circuit voltage of over 1,000 mV in mesoscopic dye-sensitized solar cells incorporating a molecularly engineered cobalt complex as redox mediator. Cobalt complexes have negligible absorption in the visible region of the solar spectrum, and their redox properties can be tuned in a controlled fashion by selecting suitable donor/acceptor substituents on the ligand. This approach offers an attractive alternate to the traditional I3−/I− redox shuttle used in dye-sensitized solar cells. A cobalt complex using tridendate ligands [Co(bpy-pz)2]3+/2+(PF6)3/2 as redox mediator in combination with a cyclopentadithiophene-bridged donor-acceptor dye (Y123), adsorbed on TiO2, yielded a power conversion efficiency of over 10% at 100 mW cm−2. This result indicates that the molecularly engineered cobalt redox shuttle is a legitimate alternative to the commonly used I3−/I− redox shuttle

Spontaneous grafting of nitrophenyl groups to planar glassy carbon substrates : evidence for two mechanisms

The covalent grafting of nitrophenyl functionalities to planar carbon substrates by reaction with 4-nitrobenezene diazonium salt at open circuit potential has been studied in aqueous acid and acetonitrile solutions. Atomic force microscopy and electrochemical measurements reveal that the reaction proceeds through two distinct mechanisms. Rapid film growth occurs via reduction of the 4-nitrobenezene diazonium cation by the substrate, giving an aryl radical that couples to the surface. Film growth by this mechanism ceases once the film has reached a thickness at which electron transfer through the passivating film is no longer possible. Slow film growth via a secondary, potential-independent mechanism continues even after the substrate-dependent reaction has ceased. We tentatively propose that slow film growth involves grafting of an aryl cation originating from thermal heterolytic decomposition of the diazonium cation

Microcontact printing using the spontaneous reduction of aryldiazonium salts

Patterning of aryl derivatives on graphitic carbon surfaces by printing with poly(dimethylsiloxane) stamps is described. The printing ink contained aryldiazonium salts which react spontaneously with the carbon substrate (pyrolyzed photoresist film) resulting in covalently attached modifiers. Printed surfaces were characterized using electrochemistry and scanning electron microscopy, and by generating water condensation figures. The method is very simple and versatile:  both aqueous acid and DMF were shown to be suitable ink solvents and the diazonium salt could be printed directly from its synthesis solution. Surfaces patterned with nitrophenyl, aminophenyl, and caboxyphenyl groups were successfully prepared. Extension of the method to patterning other conducting and semiconducting substrates should be straightforward

Formation of thick aminophenyl films from aminobenzenediazonium ion in the absence of a reduction source

Aminophenyl films, electrografted to conducting substrates from a solution of the corresponding diazonium ion, are a useful platform for building up functional surfaces. In our hands, reproducible preparation of aminophenyl films via electrografting is difficult, suggesting competing grafting pathways. To investigate the grafting process without the possibility of reduction of the diazonium ion by the substrate, we have used a spin-coated and cured SU-8 substrate that is nonconducting and very smooth (rms surface roughness 0.43 nm). After in situ formation of the aminobenzenediazonium ion (50 mM) in acidic solution, the substrate was added to the solution in the presence and absence of reducing agents (hypophosphorous acid and iron powder). At short reaction times, the films prepared with and without reducing agent have the same thickness and composition (as revealed by X-ray photoelectron spectroscopy). However, in the presence of a reducing agent, films reach a limiting thickness of 7–8 nm after 10 min, whereas, in the absence of a reducing agent, strong film growth continues, giving a film thickness of 14 nm after 120 min. This behavior contrasts with that of other diazonium ions which, in the absence of an applied potential, a reducing agent, or a reducing substrate, give only very thin films after long reaction times

Dependence of catalytic activity and long-term stability of enzyme hydrogel films on curing time

Enzyme hydrogels were prepared on carbon film electrodes using glucose oxidase and an epoxide crosslinking agent. The catalytic activity of the gels was found to depend strongly on curing time. The competing effects of increased mechanical stability and decreased enzyme activity as curing time increases resulted in the highest catalytic activity for films cured for 24 h at 25 °C. Weekly electrochemical measurements established that the long-term stabilities of all hydrogels cured for 24–72 h were similar, with close to half of the initial catalytic activity being retained after immersion for 3 months in agitated phosphate buffer solution at 25 °C