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In this work we demonstrate the preparation of highly catalytically active Pt formed by the galvanic replacement of the copper adlayer on Au substrates, modified by the self-assembly of fourth generation amine terminated PAMAM dendrimer (G4NH2). The copper adlayer was formed on the dendrimer-modified gold substrate by chemical preconcentration of copper ions followed by electrochemical reduction. The Pt overlayer was characterized by SEM, XPS and by cyclic voltammetry. The catalytic efficiency of the modified film thus prepared through soft route was evaluated by the electro catalytic oxidation of methanol using cyclic voltammetry, chronoamperometry and AC impedance techniques. This work also demonstrates that the copper adlayer formed on the dendrimer-modified electrode can undergo galvanic replacement by nobler metals like Au and Ag, besides Pt. An elegant soft route involving a new three-step protocol to build the concentration of active Pt on the Au surface has been developed. Concentration of the same metal (Pt) or two different metals (Pt–Au) can be built at the interface in a stepwise manner at ambient temperature.

We report here the synthesis of palladium (Pd) nanoparticles incorporated poly-(3,4)ethylenedioxythiophene (PEDOT) matrix in aqueous medium and its catalytic performance towards 4-nitrophenol reduction. This simple one-pot synthesis involving a redox reaction between 3,4-ethylenedioxythiophene and palladium chloride (PdCl2) precursor, leads to the formation of Pd nanoparticles supported on particulate PEDOT. Pd nanoparticles of size 1–9 nm were found to distribute uniformly over the PEDOT matrix. Morphology of the Pd–PEDOT nanocomposite was characterized by field emission-scanning electron microscopy and transmission electron microscopy and the crystallographic details obtained using X-ray diffraction. The chemical nature of the PEDOT support matrix was analyzed using Fourier transform-infra red (FT-IR) spectroscopy. The catalytic activity of the composite was demonstrated using a model reaction, i.e., reduction of 4-nitrophenol to 4-aminophenol. The value of the apparent rate constant, ca. 65.8 × 10−3 s−1 obtained using UV visible spectroscopy of the reduction of 4-nitrophenol at the Pd–PEDOT nanocomposite is comparable to those reported for other catalytic systems.

Palladium (Pd) incorporated poly (3,4-ethylenedioxythiophene) (PEDOT) films were synthesized through an electrochemical route and characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electrochemical study showed catalytic oxidation of dopamine (DA) with optimum loading of Pd. DA and uric acid (UA) were detected using differential pulse voltammetry (DPV). In the presence of ascorbic acid (AA), DA-AA showed peak potential separation of 0.19 V while 0.32 V between UA-AA on Pd-incorporated PEDOT. These peak separations are large enough for sensing DA and UA in the presence of AA. DA and UA exhibited linear calibration plots and the minimum detection limits are 0.5 and 7 µM respectively. On Pd-PEDOT, the reversibility of DA oxidation was found to increase compared to bare glassy carbon electrode (GCE) and PEDOT modified GCE. Fouling effects were also found to be minimal making Pd-PEDOT composite suitable for electroanalysis.

In this communication, we report a strategy for the preparation of Pt nanoparticles encapsulated in Generation 4.5 (Polyamido amine) PAMAM dendrimer and subsequent chemical linking of the nanocomposite to the gold electrode through a self assembled cystamine monolayer. The modification resulted in the formation of a robust electrochemically active thin film with very high surface area, reflected by the enhanced hydrogen adsorption coverage. Interestingly, TEM images revealed self-assembly of Pt nanoparticles and the SAED (Selected Area Electron Diffraction) patterns showed the presence of Pt single crystals (111). The Pt-dendrimer nanocomposite film obtained using the novel modification procedure exhibited high electrocatalytic activity for the oxidation of organic fuels like methanol, ethanol and ethylene glycol. The film did not suffer from degradation even after repeated use in solution-phase voltammetry. It is however observed that the intermediate SAM layer and the bulky PAMAM dendrimer (generation 4.5) have slowed down the electron transfer kinetics which is reflected by a relatively high overpotential for methanol oxidation. Nevertheless this shortcoming is more than compensated by the existence of Pt(111) planes, which alleviate CO poisoning.

Polyol mediated synthesis for the preparation of tungsten trioxide and titanium doped tungsten trioxide has been reported. The reaction was carried out using chlorides of tungsten and titanium in diethylene glycol medium and water as the reagent for hydrolysis at 190 deg. C. Formation of a blue coloured dimensionally stable suspension of the precursor materials was observed during the course of the reaction. The particle sizes of the precursor materials were observed to be around 100 nm. The precursor materials were annealed to give tungsten trioxide and titanium doped tungsten trioxide. The precursor materials were characterised using TGA/DTA, FT-IR, optical spectra, SEM, TEM and powder XRD methods. It was observed that the doping of titanium could be effected at least up to 10% of Ti in WO{sub 3}. The TGA/DTA studies indicated that WO{sub 3-x}.H{sub 2}O is the dominant material that formed during the polyol mediated synthesis. The XRD data of the annealed samples revealed that the crystalline phase could be manipulated by varying the extent of titanium doping in the tungsten trioxide matrix.

There is a growing interest in devising wet chemical alternatives for physical deposition methods for applications involving thin films, e.g., catalysis. Deposition of platinum on thin gold films is often a problem leading to incomplete coverage and improper adhesion to solid surfaces. Gold substrates often need pre-activation for achieving complete coverage. We demonstrate here that dendrimers with proper functionalities and size work as well-defined nucleating agents and adhesion promoters. This feature is demonstrated using an amine-terminated dendrimer of generation 4.0. This approach allows one to obtain adherent nanoparticulate films of platinum on gold. Unlike other nucleating agents and adhesion promoting compounds, dendrimers have a well-defined ordered structure in terms of their space filling ability. The stability of the films obtained with adsorbed dendrimers is demonstrated using the electrocatalytic reactions of fuels like methanol. The films formed without dendrimers cannot sustain the electro-oxidation currents due to the instability of the films while the films formed with dendrimers can sustain currents for longer duration and for several cycles. The dendrimer-derived Pt films exhibit higher catalytic activity compared to other methods

In this work, we examine the electrocatalytic activity of electrodeposited Platinum (Pt)-Nickel (Ni) alloy layers on an inert substrate electrode for methanol oxidation reaction. Analyses using energy-dispersive fluorescent X-ray analysis and powder X-ray diffractometry confirm alloying of Pt with Ni in a range of compositions. Steady-state polarisation measurements in 0.5 M methanol+0.5 M H2SO4 solutions clearly show that the onset of electro-oxidation shifts to less anodic potential values (approximately 160 mV), while also exhibiting current enhancements up to ~15 times the currents obtained for the pure Pt electrodeposit. A linear relationship between the cyclic voltammetric peak (oxidation) current and [MeOH] is observed at a scan rate of 50 mVs−1, thus indicating reduced influence of adsorbed CO (COads) surface poison. A critical composition, Pt (92%)/Ni (8%) [denoted Pt-Ni(3) alloy] is found to exhibit maximum electrocatalytic activity, beyond which the activity drops, whereas pure Ni does not catalyse the reaction. While the promotion of electro-oxidation is understood to be largely due to the alloy catalyst, surface redox species of Ni oxide formed during the electro-oxidation process may also contribute to the oxygenation of COads, thereby enhancing the oxidation current. Plausible mechanisms of methanol oxidation on Pt/ transition metal alloy electrocatalysts are discussed in terms of electron transfer (in the alloy) and the role of Ni oxide species.

The formation of metal monolayers through underpotential deposition (UPD) depends on the interactions between the electrode surface and the depositing species. Other adsorbable species, if present in the solution, will influence the formation of UPD metal films through their adsorption on the electrode surface, taking place simultaneously. Copper UPD formation on polycrystalline gold surfaces has been investigated in the presence of small amounts of urea, thiourea (TU) and N-substituted thioureas using cyclic voltammetry. The results show that the UPD of copper on gold is significantly influenced by the presence of thiourea in solution. The charge corresponding to the stripping peak obtained in the presence of both Cu2+ and TU in solution is always larger than the sum of the charges resulting when either of them is present alone. Again, the charge observed during stripping in the presence of both Cu2+ and TU is believed to arise from (i) stripping of the UPD Cu, (ii) adsorption–desorption of TU and (iii) oxidation of Cu(TU)n+ complexes. The addition of N-substituted TUs is found to influence the UPD of Cu to different extents. This is tentatively explained in terms of the structure of the organic molecules.

Simultaneous underpotential deposition of lead and thallium from a tartrate medium on a polycrystalline silver electrode is reported. Results of cyclic voltammetric investigations of the effects of concentration and sweep rate on the codeposition behaviour are discussed. Further investigations of the codeposition behaviour through voltammetric experiments using programmed potential inputs are described and discussed in terms of formation of a two-dimensional alloy. Finally, the validity of the existing models of electrochemical phase formation has been investigated under the codeposition conditions.

Phosphosilicate molecular precursor for the synthesis of NASICON, natrium super ionic conductor, Na1+xZr2SixP3−xO12 (x = 1 and 2) has been devised and prepared by the hydrolysis of tetraethoxysilane (TEOS) employing sodium phosphate solution. The molecular precursor was reacted with Zr(OC3H7)4 in ethanol under solvolytic condition to yield nano precursor material of NASICON. This material was annealed at high temperature to yield phase-pure NASICON. The molecular precursor was characterized using 31P NMR, FTIR spectral data, powder XRD pattern and TG/DTA studies. The structure of the molecular precursor was deduced from the powder XRD data, which indicates the presence of edge sharing tetrahedral arrangement of −O−Si−O−P−O−Si− chain. The NASICON precursor material was characterized using TG/DTA, FTIR, TEM, SEM, MAS 31P NMR and XRD. The conductivity of the synthesized NASICON material was measured using the pellet annealed at 900 °C and was found to be 5.5 x10−3 S cm−1. The details on the preliminary inves...

The oxidation behaviour of methanol on platinum at room temperature in a low concentration of phosphoric acid (≈ 5%) has been studied. Voltammetric behaviour in phosphoric acid medium is compared with that in perchloric acid. The effect of a bismuth underpotential deposition (upd) layer on the oxidation of methanol is also reported.

The codeposition of lead and thallium UPD's on polycrystalline silver has been investigated. Studies on the effect of deposition time on the formation of the codeposit suggest the codeposit to be a solid solution resulting from underpotentially deposited mono/submono layers of lead and thallium with the stoichiometric ratio of 1 : 2 (Pb : T1).

Simultaneous deposition of lead and thallium UPD s on polycrystalline silver has been investigated under cyclic voltammetric conditions. Voltammetric data, resulting from systematic variation of potential sweep rates and concentration of metal ions, are presented and discussed. The experimental results for composite lead and thallium UPD s, obtained from mixed as well as single metal UPD s, obtained from single salt solutions under comparable conditions, have been analyzed in terms of the empirical models proposed for the growth mechanism based on adsorption/nucleation phenomena.

A gold electrode surface has been modified with a monolayer of 3,3'-thiodipropionic acid (TPA) by self-assembly. The pH-sensitive TPA monolayer is further derivatized to form a monolayer of nickel hexacyanoferrate. This electrode shows molecular discrimination between potassium and sodium ions and exhibits a near-Nernstian response, with a slope of 55 mV/decade to potassium ions in the range from 10 -2 to 1 M.

The formation of self-assembled monolayers (SAM) of 5,5'-dithiobis (2-nitrobenzoic acid), DNBA on gold has enabled further derivatization of the electrode surface with functional moieties anchored to the surface bound molecules. A SAM of DNBA was formed on the Au surface. Nickel ions tethered to the SAM-covered Au surface, were subsequently derivatized electrochemically to yield nickel hydroxide overlayers, thereby showing the possibility of preparing ultra-thin films of metal oxides through solution chemistry. The nickel hydroxide surface coverage obtained on bare and SAM-covered electrodes was estimated from voltammetric peaks and it varied from one monolayer to about 300 monolayers. The formation of a monolayer of nickel hydroxide has been achieved for the first time by electrochemical modification. Further, the modified electrodes were subjected to SERS and XPS studies to understand their surface characteristics. Modified electrodes provide a catalytic pathway involving nickel hydroxide for the electro-oxidation of glucose in alkaline solutions.