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The fabrication of ultramicroelectrodes (UMEs) for analytical electrochemical applications has been explored, using boron-doped diamond as the active electrode material in an insulating coating formed by deposition of electrophoretic paint. Because of the rough nature of the diamond film, the property of such coatings that is normally exploited in the fabrication of UMEs, namely the tendency to retract automatically from sharp protrusions, cannot be used in the present instance. Instead focused ion beam (FIB) sputtering was employed to controllably produce UMEs with well-defined geometry, critical dimension of a few micrometers, and very thin insulating coatings. If the FIB machining is carried out at normal incidence to the diamond electrode surface, significant ion beam damage reduces the yield of successful electrodes. However, if a parallel machining geometry is employed, high yields of ultramicroelectrodes with a flat disk geometry can be obtained very reliably. The electrochemical properties of diamond UMEs are characterized. They show much lower background currents than the equivalent Pt or carbon fiber electrodes but more varied electrochemical response than macroscopic diamond electrodes.

Boron-doped diamond (BDD) ultramicroelectrode (UME) tips were fabricated by the growth of BDD films by chemical vapor deposition onto sharpened tungsten wires. Both nanocrystalline and microcrystalline forms of diamond coatings were examined. The diamond-coated wires were selectively insulated with nail varnish, electrophoretic paint, or fast-setting epoxy to form UME tips of critical dimensions of 1-25 [micro]m. The geometry of the exposed electrode area was disk or hemispherical in most cases. Cyclic voltammetry and chronoamperometry were used to assess exposed electrode area and integrity of the insulation. BDD UMEs were used to obtain SECM approach curves to an insulating and a conducting subslrate, which were fitted to the theory appropriate for the observed tip geometry. The tips were used to obtain SECM images of immobilized respiring E. coli, illustrating the suitability of BDD UMEs for electrochemical imaging in biological media.

Electrochemical techniques were used to study the behavior of Escherichia coli on the addition of less than or equal to 10 MuM AgNO3. Scanning electrochemical microscopy was used to follow the uptake of 1 Mum Ag(super +) by living and dead Escherichia coli on a glass side coated with poly-L-lysine.

The pattern of conductivity and electrochemical activity at the surfaces of hydrogen-terminated boron-doped diamond electrodes is calculated using conductive probe atomic force microscopy (CP-AFM) and scanning electrochemical microscopy (SECM). CP-AFM indicates that the surface is predominantly insulating, with discrete conducting areas of less than two macrometer in diameter and nonuniformly distributed on the surface.

The use of an ultramicroelectrode tip as a basis for a Clark membrane electrode allows the sensing of oxygen concentration using the oxygen reduction signal and the application of scanning electrochemical microscopy (SECM) to pure gas-phase measurements. A 25-[micro]m-diameter Pt wire was sealed in glass and the glass coated with silver paint near the tip to produce a Ag ring, Pt disk electrode. A drop of electrolyte provided the contact between the Pt cathode indicator electrode and the Ag anode counter/reference electrode, while the liquid phase was maintained by a high-density polyethylene membrane pulled over the tip and fastened with an O-ring. The membrane isolated the electrode both electrically and chemically from the sample environment. The electrode was tested with both solution- and gas-phase samples, and SECM approach curves were recorded. The presence of a membrane caused a deviation in electrode behavior from theory in both solution and gas phases, due in part to an increase in the electrode response time. However, the approach curves obtained could be used to determine the distance of the membrane from a surface and the thickness of the electrolyte layer within the membrane. SECM images in the gas phase, of oxygen flux through an array of 100-[micro]m-diameter holes in a silicon wafer, were obtained by measuring the reduction current of oxygen while scanning in the x-y plane over the surface.

Electrocatalytic nitrogen reduction reaction (NRR) and hydrogen evolution reaction (HER) are intriguing approaches to nitrogen fixation and hydrogen production under ambient conditions, given the need to discover efficient and stable catalysts to light up the "green chemistry" future. However, bottlenecks are often found during N2/H2O activation, the very first step of NRR/HER, due to energetic electron injection from the surface of electrocatalysts. It is reported that the bottlenecks for both NRR and HER can be tackled by engineering the energy level via low‐valent transition‐metal doping, simultaneously, where rhenium disulfide (ReS2) is employed as a model platform to prove the concept. The doped low‐valent transition‐metal domains (e.g., Fe, Co, Ni, Cu, Zn) in ReS2 provide more active sites for N2/H2O chemisorption and electron transfer, not only weakening the NN/OH bonds for easier dissociation through proton coupling, but also elevating d‐band center toward the Fermi level with more electron energy for N2/H2O reduction. As a result, it is found that iron‐doped ReS2 nanosheets wrapped nitrogen‐doped carbon nanofiber (Fe‐ReS2@N‐CNF) catalyst exhibits superior electrochemical activity with eightfold higher ammonia production yield of 80.4 µg h−1 mg−1cat., and lower onset overpotential of 146 mV and Tafel slope of 63 mV dec−1, when comparing with the pristine ReS2. [ABSTRACT FROM AUTHOR]

A series of ethane‐dithiolate (edt = S(CH2)2S) complexes [Fe2(CO)5(EPh3)(µ‐edt)] and [Fe2(CO)4(EPh3)2(µ‐edt)] (E = P, As, Sb), biomimics of the core of [FeFe]‐hydrogenases, have been prepared and structurally characterised. The introduced ligand(s) occupies apical sites lying trans to the iron‐iron bond. NMR studies reveal that while in the mono‐substituted complexes the Fe(CO)3 moiety undergoes facile trigonal rotation, the Fe(CO)2(PPh3) centres do not rotate on the NMR timescale. The reductive chemistry has been examined by cyclic voltammetry both in the presence and absence of CO and the observed behavior is found to be dependent upon the nature of the substituents. With L = CO or SbPh3 potential inversion is seen leading to a two‐electron reduction, while for others (L = PPh3, AsPh3) a quasi‐reversible one‐electron reduction is observed. Protonation studies reveal that [Fe2(CO)5(PPh3)(µ‐edt)] is only partially protonated by excess HBF4·Et2O, thus ruling complexes [Fe2(CO)5(EPh3)(µ‐edt)(µ‐H)]+ out as a catalytic intermediates, but [Fe2(CO)4(PPh3)2(µ‐edt)] reacts readily with HBF4·Et2O to produce [Fe2(CO)4(PPh3)2(µ‐edt)(µ‐H)]+. While all new complexes are catalysts for the reduction of protons in MeCN, their poor stability and relatively high reduction potentials does not make them attractive in this respect. [ABSTRACT FROM AUTHOR]

Several experiments are conducted to explain the electrochemical response of an electrode-immobilized layer that is formed by the undoped diamond nanoparticles. The potentials of the various surface states of the layer are shown to be highly pH-dependent.

A series of diiron bis(2-diphenylphosphinoethyl)phenylphosphine (triphos) complexes Fe2(CO)3(μ-dithiolate)(μ,κ1,κ2-triphos) (1–4) [dithiolate = 1 pdt; 2 edt; 3 adt (R = Bz), 4 (SMe)2] have been prepared and investigated as biomimics of the diiron site of [FeFe]-hydrogenases. The triphos ligand bridges the diiron vector whilst also chelating to one iron and 1–3 exist as a mixture of basal–basal–apical (bba) and basal–basal–basal (bbb) isomers which differ in the mode of chelation. In solution the bba and bbb forms do not interconvert on the NMR time scale, but the bba isomers are fluxional, and at low temperature four forms of 1bba are seen as the conformations for the pdt ring and triphos methylene groups are frozen. Crystallographic studies have established bba (pdt) and bbb (adt) ground state conformations and in both there is a significant deviation away from the expected eclipsed conformation (Lap–Fe–Fe–Lap torsion angle 0°) by 49.4 and 24.9° respectively, suggesting that introduction of triphos leads to significant strain and DFT calculations have been used to understand the relative energies of isomers. The electron rich nature of the diiron centre in 1–4 would suggest rapid protonation, but while bridging hydride complexes such as [Fe2(CO)3(μ-pdt)(μ,κ1,κ2-triphos)(μ-H)][BF4] (1H+) can be formed the process is slow. This behavior is likely a result of the high energy barrier in forming the initial (not observed) terminal hydride which requires a significant conformational change in triphos coordination. CV studies show that all starting compounds oxidize at low potentials and the addition of [Cp2Fe][PF6] to 1 affords [Fe2(CO)3(μ-pdt)(μ,κ1,κ2-triphos)][PF6] (1+) which has been characterised by IR spectroscopy. DFT studies suggest a ground state for 1+ with a partially rotated Fe(CO)2P moiety that yields a weak semi-bridging carbonyl with the adjacent Fe(CO)P2 group. No reduction peaks are seen for 1–4 within the solvent window but 1H+ undergoes reduction at −1.7 V. All complexes act as proton-reduction catalysts in the presence of HBF4·Et2O. For 1, three separate processes are observed and their dependence on acid concentration has been probed, and a mechanistic scheme is proposed based on formation via a CECE process of 1(μ-H)H which can either slowly release H2 or undergo further reduction. Relative contributions of the three processes to the total current were found to be highly dependent upon the background electrolyte, being attributed to their relative abilities to facilitate proton transfer processes. While 2 and 4 show similar proton reduction behaviour, the adt complex 3 is quite different being attributed to facile protonation of nitrogen which is followed by addition of a second proton at the diiron centre. [ABSTRACT FROM AUTHOR]