Simplest Prussian-blue deposition from ferric ferricyanide solution by a reducing Ag spot put onto an ITO substrate

Prussian-blue (PB) film for electro-chromism can be electro-deposited on to an electrode (usually tin-doped indium oxide/glass) either directly from a PB colloid or from ferric ferricyanide in a two-electrode electro-chemical cell by applying a reductive potential. Alternatively, a “sacrificial” electron-producing silver flag electrode in the solution, when connected to the PB-receiving electrode, can effect the required reductive deposition. A silver spot, here innovatively applied as silver paint directly onto the deposition electrode, produces PB film on immersion in the iron(III)(III) solution, obviating the separate counter-electrode method

The direct electrochemistry of ferritin compared with the direct electrochemistry of nanoparticulate hydrous ferric oxide

Horse spleen ferritin is a naturally occurring iron storage protein, consisting of a protein shell encapsulating a hydrous ferric oxide core about 8 nm in diameter. It is known from prior work that the protein can be adsorbed onto the surface of tin-doped indium oxide (ITO) electrodes, where it undergoes voltammetric reduction at about –0.6 V vs Ag/AgCl. This is accompanied by dissolution of Fe(II) through channels in the protein shell. In the present work, it is demonstrated that a pre-wave at about –0.4 V vs Ag/AgCl is due to the reduction of FePO4 also present inside the protein shell. In order to prove that the pre-wave was due to the reduction of FePO4, it was first necessary to prepare 8 nm diameter hydrous ferric oxide nanoparticles without protein shells, adsorb them onto ITO electrodes, and then study their electrochemistry. Having achieved that, it was then necessary to establish that their behaviour was analogous to that of ferritin. This was achieved in several ways, but principally by noting that the same electrochemical reduction reactions occurred at negative potentials, accompanied by the dissolution of Fe(II). Finally, by switching to aqueous phosphate buffer, the pre-wave could be unambiguously identified as the reduction of FePO4 present as a thin layer on the hydrous ferric oxide nanoparticle surfaces. Although the bare and protein-coated hydrous ferric oxide nanoparticles were found to behave identically toward electrochemical reduction, they nevertheless reacted very differently towards H2O2. The bare nanoparticles acted as potent electrocatalysts for both the oxidation and the reduction of H2O2, whereas the horse spleen ferritin had a much lesser effect. It seems likely therefore that the protein shell in ferritin blocks the formation of key intermediates in hydrogen peroxide decomposition

Electrochemical reactivity of TiO2 nanoparticles adsorbed onto boron-doped diamond

TiO2 (anatase) nanoparticles of ca. 6–10 nm diameter are adsorbed from acidic aqueous solution onto polycrystalline industrially polished boron-doped diamond electrode surfaces. After immobilisation at the electrode surface, TiO2 nanoparticles are imaged in vacuum by electron microscopy (FEGSEM) and when immersed in a liquid film of aqueous 12 M LiCl by in situ scanning tunnelling microscopy (STM). Mono-layer films of TiO2 particles are studied voltammetrically in different electrolyte media. Boron-doped diamond as an inert substrate material allows the reduction of TiO2 particles in phosphate buffer solution to be studied and two distinct steps in the reduction–protonation process are identified: (i) a broad reduction signal associated with the binding of an outer layer of protons and (ii) a sharper second reduction signal associated with the binding of an inner (or deeper) layer of protons. Voltammetric experiments in aqueous 0.1 M NaClO4 with variable amounts of HClO4 suggest that the reduction of TiO2 particles is consistent with the formation of Ti(III) surface sites and accompanied by the adsorption of protons. Saturation occurs and the total amount of surface sites can be determined. Preliminary data for electron transfer processes at the reduced TiO2 surface such as the dihydrogen evolution process and the two-electron–two-proton reduction of maleic acid to succinic acid are discussed

Underpotential surface reduction of mesoporous CeO2 nanoparticle films

The formation of variable-thickness CeO2 nanoparticle mesoporous films from a colloidal nanoparticle solution (approximately 1–3-nm-diameter CeO2) is demonstrated using a layer-by-layer deposition process with small organic binder molecules such as cyclohexanehexacarboxylate and phytate. Film growth is characterised by scanning and transmission electron microscopies, X-ray scattering and quartz crystal microbalance techniques. The surface electrochemistry of CeO2 films before and after calcination at 500 °C in air is investigated. A well-defined Ce(IV/III) redox process confined to the oxide surface is observed. Beyond a threshold potential, a new phosphate phase, presumably CePO4, is formed during electrochemical reduction of CeO2 in aqueous phosphate buffer solution. The voltammetric signal is sensitive to (1) thermal pre-treatment, (2) film thickness, (3) phosphate concentration and (4) pH. The reversible ‘underpotential reduction’ of CeO2 is demonstrated at potentials positive of the threshold. A transition occurs from the reversible ‘underpotential region’ in which no phosphate phase is formed to the irreversible ‘overpotential region’ in which the formation of the cerium(III) phosphate phase is observed. The experimental results are rationalised based on surface reactivity and nucleation effects

Aerosol-assisted CVD of bismuth vanadate thin films and their photoelectrochemical properties

Thin film bismuth vanadate (BiVO4) photoelectrodes are prepared by aerosol-assisted (AA)CVD for the first time on fluorine-doped tin oxide (FTO) glass substrates. The BiVO4 photoelectrodes are characterised by X-ray diffraction (XRD), Raman spectroscopy (RS), and energy-dispersive X-ray (EDX) spectroscopy and are found to consist of phase-pure monoclinic BiVO4. Scanning electron microscopy (SEM) analysis shows that the thin film is uniform with a porous structure, and consists of particles approximately 75-125nm in diameter. The photoelectrochemical (PEC) properties of the BiVO4 photoelectrodes are studied in aqueous 1M Na2SO4 and show photocurrent densities of 0.4mAcm-2, and a maximum incident-photon-to-electron conversion efficiency (IPCE) of 19% at 1.23V vs. the reversible hydrogen electrode (RHE). BiVO4 photoelectrodes prepared by this method are thus highly promising for use in PEC water-splitting cells. Thin film bismuth vanadate (BiVO4) photoelectrodes are prepared by AACVD for the first time on fluorine-doped tin oxide (FTO) glass substrates. The photoelectrochemical (PEC) properties of the BiVO4 photoelectrodes are studied in aqueous 1M Na2SO4 and show photocurrent densities of 0.4mAcm-2 and a maximum incident-photon-to-electron conversion efficiency (IPCE) of 19% at 1.23V vs. RHE. BiVO4 photoelectrodes prepared by this method are highly promising for use in PEC water-splitting cells

Detection and Characterization of Liquid|Solid and Liquid|Liquid|Solid Interfacial Gradients of Water Nanodroplets in Wet <i>N</i>‑Octyl-2-Pyrrolidone

We report on the rotational diffusion dynamics and fluorescence lifetime of lissamine rhodamine B sulfonyl chloride (LRSC) in two thin-film experimental configurations. These are liquid|solid interfaces, where <i>N</i>-octyl-2-pyrrolidone (NOP) containing water and ethylene glycol (EG) thin films are each supported on glass, and a liquid|liquid|solid interface where thin films of water and NOP, both supported on glass, are in contact with one another, forming an NOP|water interface. The reorientation dynamics and fluorescence lifetime of LRSC are measured as a function of distance from the NOP|glass and EG|glass interfaces and from the NOP|water and NOP|glass interfaces in the liquid|liquid|solid experimental configuration. Fluorescence anisotropy decay data from the liquid|solid systems reveal a liquid film depth-dependent gradient spanning tens of micrometers from the NOP|glass interface into the wet NOP phase, while this gradient is absent in EG. We interpret these findings in the context of a compositional gradient in the NOP phase. The spatially resolved fluorescence lifetime and anisotropy decay data for an NOP|water|glass interfacial structure exhibits the absence of a gradient in the anisotropy decay profile normal to the NOP|water interface and the presence of a fluorescence lifetime gradient as a function of distance from the NOP|water interface. The compositional heterogeneity for both interfacial systems is in the form of water nanodroplets in the NOP phase. We understand this compositional gradient in the context of the relative surface energies of the water, NOP, and glass components

Xylose- and Nucleoside-Based Polymers via Thiol–ene Polymerization toward Sugar-Derived Solid Polymer Electrolytes

A series of copolymers have been prepared via thiol–ene polymerization of bioderived α,ω-unsaturated diene monomers with dithiols toward application as solid polymer electrolytes (SPEs) for Li+-ion conduction. Amorphous polyesters and polyethers with low Tg’s (−31 to −11 °C) were first prepared from xylose-based monomers (with varying lengths of fatty acid moiety) and 2,2′-(ethylenedioxy)diethanethiol (EDT). Cross-linking by incorporation of a trifunctional monomer also produced a series of SPEs with ionic conductivities up to 2.2 × 10–5 S cm–1 at 60 °C and electrochemical stability up to 5.08 V, a significant improvement over previous xylose-derived materials. Furthermore, a series of copolymers bearing nucleoside moieties were prepared to exploit the complementary base-pairing interaction of nucleobases. Flexible, transparent, and reprocessable SPE films were thus prepared with improved ionic conductivity (up to 1.5 × 10–4 S cm–1 at 60 °C), hydrolytic degradability, and potential self-healing capabilities

Xylose- and Nucleoside-Based Polymers via Thiol–ene Polymerization toward Sugar-Derived Solid Polymer Electrolytes

A series of copolymers have been prepared via thiol–ene polymerization of bioderived α,ω-unsaturated diene monomers with dithiols toward application as solid polymer electrolytes (SPEs) for Li+-ion conduction. Amorphous polyesters and polyethers with low Tg’s (−31 to −11 °C) were first prepared from xylose-based monomers (with varying lengths of fatty acid moiety) and 2,2′-(ethylenedioxy)diethanethiol (EDT). Cross-linking by incorporation of a trifunctional monomer also produced a series of SPEs with ionic conductivities up to 2.2 × 10–5 S cm–1 at 60 °C and electrochemical stability up to 5.08 V, a significant improvement over previous xylose-derived materials. Furthermore, a series of copolymers bearing nucleoside moieties were prepared to exploit the complementary base-pairing interaction of nucleobases. Flexible, transparent, and reprocessable SPE films were thus prepared with improved ionic conductivity (up to 1.5 × 10–4 S cm–1 at 60 °C), hydrolytic degradability, and potential self-healing capabilities

Mesoporous TiO2 carboxymethyl-gamma-cyclodextrate multi-layer host films: effects on adsorption and electrochemistry of 1,1 '-ferrocenedimethanol

TiO2 (anatase) nanoparticles are readily deposited layer-by-layer in the form of thin films with a carboxymethyl-γ-cyclodextrate binder. Electron microscopy, voltammetric, and quartz crystal microbalance data demonstrate that the film grows homogeneously and is electrically connected to the ITO electrode surface. 1,1'-Ferrocenedimethanol is employed as an adsorbing redox system to study the voltammetric characteristics of the mesoporous host film. The binding constants for the homogeneous complexation of 1,1'-ferrocenedimethanol with carboxymethyl-γ-cyclodextrin at pH 7, Kred = 1300 ± 200 M–1, and at pH 2, Kred = 1000 ± 200 M–1, are determined assuming 1 : 1 complex formation. In the presence of the TiO2 carboxymethyl-γ-cyclodextrate films, solution phase voltammetric responses are affected due to a lower rate of diffusion of 1,1'-ferrocenedimethanol across the film (possibly due to binding to receptor sites) and due to slow electron transfer at pH 7 but not at pH 2. The TiO2 carboxymethyl-γ-cyclodextrate modified electrode, when dipped into 1,1'-ferrocenedimethanol containing solution, rinsed, and transferred into clean buffer solution, shows characteristic signals for adsorbed 1,1'-ferrocenedimethanol, consistent with weak binding and fast release upon oxidation. There is evidence for two distinct binding sites for 1,1'-ferrocenedimethanol both at pH 7 and at pH 2

Electrochemical properties of core-shell TiC–TiO2 nanoparticle films immobilized at ITO electrode surfaces

Titanium carbide (TiC) nanoparticles are readily deposited onto tin-doped indium oxide (ITO) electrodes in the form of thin porous films. The nanoparticle deposits are electrically highly conducting and electrochemically active. In aqueous media (at pH 7) and at applied potentials positive of 0.3 V vs. SCE partial anodic surface oxidation and formation (at least in part) of novel core-shell TiC-TiO2 nanoparticles is observed. Significant thermal oxidation of TiC nanoparticles by heating in air occurs at a temperature of 250 oC and is leading first to core-shell TiC-TiO2 nanoparticles, next at ca. 350 oC to TiO2 (anatase), and finally at temperature higher than 750 oC to TiO2 (rutile). Electrochemically and thermally partially oxidized TiC nanoparticles still remain very active and for some redox systems electrocatalytically active. Scanning and transmission electron microscopy (SEM and TEM), temperature dependent XRD, quartz crystal microbalance, and voltammetric measurements are reported. The electrocatalytic properties of the core-shell TiC-TiO2 nanoparticulate films are surveyed for the oxidation of hydroquinone, ascorbic acid, and dopamine in aqueous buffer media. In TiC-TiO2 core-shell nanoparticle films TiO2 surface reactivity can be combined with TiC conductivity