Electrochemical studies of decamethylferrocene in supercritical carbon dioxide mixtures

Journal of Electroanalytical Chemistry

Cook

2015

Electrochemical impedance measurements were made in the single supercritical phase of CO 2 with 11 wt % acetonitrile as the co-solvent at temperatures and pressures between 306 and 316 K and 15.5 and 20.2 MPa over the potential range from -0.45 to +0.75 V vs. Pt. Gold, platinum and glassy carbon electrodes were studied together with the effects of electrolyte concentration for [ ], were also studied. We find that the impedance data can be described by a simple RC equivalent circuit where the uncompensated solution resistance is independent of the electrode potential and is consistent with earlier measurements for the electrolyte conductivity. The results for the double layer capacitance can be described by a simple Helmholtz layer model and are very similar to those found for similar electrolytes in non-aqueous solvents such as propylene carbonate. For glassy carbon the double layer capacitances show a parabolic like potential dependence which we attribute to the lower density of states near the Fermi level.

Section: Double Layer Capacitance At Au and Ptsupporting

confidence: 80%

Measurements of the double layer capacitance for electrodes in supercritical CO2/acetonitrile electrolytes

Journal of Electroanalytical Chemistry

Cook

2015

“…In addition the density of a supercritical fluid is strongly dependent on temperature and pressure near the critical point and inhomogeneities in the temperature distribution in the heated high pressure cell may also contribute to driving convection. The results seen here for scR32, for the effects of convection, are similar to those seen in previous work [29] in scCO 2 /CH 3 CN. Figure 4 shows a comparison of the voltammetry of 0.2 mM DMFc in scCO 2 /CH 3 CN and scR32 at a 49 m electrode recorded in the same design of high pressure cell.…”

Section: Electrochemistry Of Decamethylferrocene In Scr32 At Microelesupporting

confidence: 80%

“…In this paper we describe the results of experiments performed using DMFc as a model redox system in supercritical difluoromethane (scR32) at both micro and macro electrodes and compare the results to those of our earlier work in scCO 2 /MeCN [29]. We also report preliminary results for the electrochemistry of cobaltocene and decamethylcobaltocene in scR32.…”

Section: Introductionmentioning

confidence: 77%

See 1 more Smart Citation

The voltammetry of decamethylferrocene and coboltacene in supercritical difluoromethane (R32)

Journal of Electroanalytical Chemistry

Branch

2016

The voltammetry of decamethylferrocene, cobaltocene and decamethylcobaltocene at micro and macro disc electrodes in supercritical difluoromethane at 360 K and 17.6 MPa has been studied. In all cases the voltammetry is distorted to some degree by the effects of random convection but these can . Finally we have briefly investigated the voltammetry of cobaltocene and decamethylcobaltocene in supercritical difluoromethane under the same conditions. We find that reduction of the cobaltocenium cation leads to fouling of the Pt microdisc electrode which limits its use as a model redox system and that reduction of the decamethylcobaltocenium cation was not observed before electrolyte reduction at around -1.6 V vs. Pt.

“…27,33 Using this value and Equation 1 we get an estimate for the peak current density, j p , of 12 mA cm −2 at 100 mV s −1 . This is significantly larger than the observed current in Figure 1ai of ∼2 mA cm −2 and, taken together with the fact that the current density does not show any fluctuations caused by turbulent mixing in the low viscosity supercritical solution, 34 indicates that the reaction is kinetically controlled by a potential independent chemical step, possibly ligand substitution. The charge recorded for the first cycle (removing the background current) is 6.4 mC cm −2 which corresponds to ∼4.5 nm thick film (for a 100% efficient faradaic process).…”

Section: Resultsmentioning

confidence: 60%

Supercritical Fluid Electrodeposition of Elemental Germanium onto Titanium Nitride Substrates

Cummings

Pugh

et al. 2015

J. Electrochem. Soc.

Self Cite

We report the electrodeposition of germanium from supercritical difluoromethane (sc-CH 2 F 2 ) at 19 MPa and 358 K using [N n Bu 4 ] [GeCl 3 ]. Voltammetry shows a classic nucleation loop on the first anodic scan with a high nucleation overpotential for germanium on TiN. In all cases the deposition appears to be kinetically limited by a coupled, potential independent, chemical step. Films of germanium were deposited at a range of potentials. At high overpotentials the films were dendritic and poorly adherent. At lower overpotentials, below −2 V vs. Ag|LaF 3 , the films are smoother and more homogeneous. Analysis of the films by energy dispersive X-ray (EDX) spectroscopy shows the presence of germanium with some chloride impurity. Raman spectroscopy confirms the deposition of amorphous germanium. Plating by pulsing to −1.9 V vs. Ag|LaF 3 for 100 ms and then growth at −1.5 V vs. Ag|LaF 3 , was found to produce the best films. On annealing at 700 • C under an Ar atmosphere for 1 hour the as-deposited amorphous germanium film is converted into crystalline germanium, as determined by X-ray diffraction (XRD) and Raman spectroscopy. Since the discovery of semiconductor effects in crystalline germanium over half a century ago, 1 germanium based thin films and structures have received considerable interest. These include a number of advanced applications from doping in optics components 2 to high speed electronics, 3 and from Li-ion batteries 4 to third generation photovoltaics. 5Thin films of germanium are typically formed via vacuum processes such as chemical vapor deposition 6,7 or molecular beam epitaxy. 8 In comparison, the non-aqueous electrodeposition of germanium thin films is an attractive alternative as it has the advantages of high material efficiency, directly templated growth and fine control over the evolving structure. 9Over the previous decade Endres and his colleagues have pioneered the electrodeposition of germanium thin films from ionic liquids. [10][11][12][13][14] In this context ionic liquids have a number of advantages over conventional aqueous based solvents; they are chemically stable, they can be purified to remove impurities such as oxygen and water which can decompose the germanium precursors, and they have a wide electrochemical potential window. Initial work in ionic liquids focused on electrodeposition from the Ge(IV) reagent GeI 4 . The electrodeposition was investigated using in situ scanning tunnelling microscopy (STM) and the plated films were shown to be extremely thin (of the order of 12-16 nm) and the plating rate very slow. This self-limiting electrodeposition was attributed to the low conductivity of the deposited germanium film and complex germanium surface chemistry, possibly involving formation of a hydride, fluoride, iodide or hydroxide surface state.12 Germanium thin films have also been electrodeposited from the corresponding chloride and bromide precursors GeX 4 (X = Cl 11 or Br 10 ) in ionic liquids. Again plating rates were low and only very thin films were produced. A re...