Electrode processes during Fe-Pt electrodeposition studied by electrochemical quartz crystal microbalance

An electrochemical quartz crystal microbalance study has been performed in order to understand the alloy electrodeposition process and especially the mechanism of oxygen incorporation during Fe-Pt electrodeposition. It reveals that the presence of Pt leads to an enhanced hydrogen evolution reaction. In comparison to the single metal depositions, an additional current and an anomalous mass increase are observed when depositing from the complete electrolyte. The corresponding films exhibit a high O content and a needle-like morphology. These characteristics are altered by nitrogen gas stirring. Fe hydroxide formation due to a pH rise at the cathode and underpotential deposition of Fe deposition due to Fe-Pt alloy formation are discussed to interpret the results.     

Potential dependence of composition and structure of electrodeposited Fe-Pt films

Composition and structure of electrodeposited Fe-Pt-O films are investigated in dependence on deposition potential. At potentials positive to the hydrogen evolution, a solid solution of Pt with some Fe is present that can be explained by underpotential deposition of Fe. In the potential region where hydrogen evolution by proton reduction is a side reaction, oxygen is detected in the films. The O content scales with the Fe content and at least part of the Fe is oxidized. When applying more cathodic potentials, the fraction of Fe and O increases, grain size is reduced and an amorphous/nanocrystalline phase forms. The Fe content is pH dependent in this potential region. At even more cathodic potentials, overpotential deposition of Fe in the bcc structure sets in, the O content is reduced. The results are discussed with respect to thermodynamics in the Fe-Pt-(O) system. The concepts of underpotential deposition of Fe during Fe-Pt alloy deposition and of hydroxide formation due to a pH rise at the cathode are evaluated. These simple models can only partially describe the deposition process in agreement with the compositional and structural information obtained and a coupled mechanism is proposed.     

Improving electrochromic behavior of spray pyrolised WO3 thin solid films by Mo doping

The effects of molybdenum [Mo] doping on the electrochromic behavior of spray pyrolised tungsten trioxide [WO₃] thin films have been studied. It has been observed that the color-bleaching kinetics, coloration efficiency, and stability of electrochromic WO₃ films are closely related to molybdenum doping concentration, apart from their microstructure and crystallinity. While a nominal 6.0 at.% molybdenum doping produces best electrochromic response in WO₃ films, the electrochemical stability is highest when the nominal concentration of molybdenum is about 2.0 at.%. The improved electrochromic behavior of the Mo doped WO₃ films has been explained from the improved H⁺ ion diffusion coefficient in the films during coloration and decoloration process.     

Adsorption behavior of Eu(III) on partially Fe(III)- or Ti(IV)-coated silica

The adsorption behavior of Eu(III) onto silica surface, which was partially coated with Fe(III) or Ti(IV), was investigated to determine Fe(III) or Ti(IV) effects on the surface reaction of lanthanides on mineral surfaces in groundwater. Compared with a parallel uncoated silica, the Fe(III)-coated silica did not enhance the adsorption of Eu(III). However, enhanced adsorption of Eu(III) on the Ti(IV)-coated silica was observed by increasing the amount of Ti(IV) on the silica surface.     

Optimization studies of HgSe thin film deposition by electrochemical atomic layer epitaxy (EC-ALE)

Studies of the optimization of HgSe thin film deposition using electrochemical atomic layer epitaxy (EC-ALE) are reported. Cyclic voltammetry was used to obtain approximate deposition potentials for each element. These potentials were then coupled with their respective solutions to deposit atomic layers of the elements, in a cycle. The cycle, used with an automated flow deposition system, was then repeated to form thin films, the number of cycles performed determining the thickness of the deposit. In the formation of HgSe, the effect of Hg and Se deposition potentials, and a Se stripping potential, were adjusted to optimize the deposition program. Electron probe microanalysis (EPMA) of 100 cycle deposits, grown using the optimized program, showed a Se/Hg ratio of 1.08. Ellipsometric measurements of the deposit indicated a thickness of 19 nm, where 35 nm was expected. X-ray diffraction displayed a pattern consistent with the formation of a zinc blende structure, with a strong (1 1 1) preferred orientation. Glancing angle fourier transform infrared spectroscopy (FTIR) absorption measurements of the deposit suggested a negative gap of 0.60 eV.     

Initial stages of Pt deposition on Au(111) and Au(100)

The deposition of Pt onto unreconstructed Au(111) and Au(100) was studied with cyclic voltammetry and in-situ STM. The latter revealed that in [PtCl₄]²⁻ containing electrolytes, both surfaces are covered by an ordered adlayer of the complex. For the adsorbed [PtCl₄]²⁻ a slightly compressed (√7×√7) R19.1°-structure was assumed for Au(111) and a (3×√10) for Au(100). In both cases, a rather high overpotential for Pt deposition was observed, most probably due to the high stability of the [PtCl₄]²⁻ complex. Nucleation of Pt starts mainly at defects like step edges for low deposition rates and three-dimensional clusters are formed. Due to the high overpotential, some nuclei appear also on terraces at random sites. Higher coverages of Pt lead to a cauliflower like appearance. It is not possible to dissolve the platinum clusters at positive potentials without severely roughening the gold surface. The [PtCl₄]²⁻ complex is oxidized to the [PtCl₆]²⁻ complex at about 0.7 V, when metallic Pt is on the surface.     

The Fe(CO)5 catalyzed pyrolysis of pentane: carbon nanotube and carbon nanoball formation

The Fe(CO)₅ catalyzed pyrolysis of pentane was investigated. The study, performed in a quartz tube, revealed that a range of carbonaceous materials could be formed with products determined by the temperature profile in the tube, the Fe(CO)₅ content in pentane, the carrier gas flow rate, the pyrolysis temperature and the pyrolysis time. The distribution of carbonaceous products also depends on the competition of the pyrolysis of Fe(CO)₅ and pentane in the different regions of the reactor. Carbonaceous materials produced included graphite film, carbon nanotubes and carbon nanoballs. The formation of carbon nanotubes takes place in a region in the quartz tube where both the pyrolysis of both Fe(CO)₅ and pentane occur, with carbon nanotubes formed by the pyrolysis of pentane. Alignment of carbon nanotubes was found when a high Fe(CO)₅ concentration was used.     

Metal-carbonate formation from ammonia solution by addition of metal salts—An effective method for CO2 capture from landfill gas (LFG)

The absorption of CO₂ from LFG in different weight concentration ammonia solution and metal salts (Zinc and Barium) is investigated in this study. Addition of metal salts results in useful metal carbonates when LFG is passed through the solution. Barium salts show a better potential of removing CO₂ as compared to Zinc salts. Addition of Barium salts to ammonia solution results in a new absorbent as no study has been focused on it till date. Also metal salts are added to alkaline wastewater which not only decreases the pH of the wastewater but also useful metal carbonates are obtained from wastewater when LFG is passed through it. Different parameters like CO₂ loading, reaction rate and change in pH are investigated. Formation of carbonates is proved by using SEM and XRD analysis. Raman spectroscopy was performed on the discarded liquid after removal of carbonates to understand the formation of bicarbonates, carbonates and carbamates.     

Unusual iron-mediated C–N bond formation and synthesis of the Fe(III) complex of a polypyridine ligand with one carboxamide group

A high-spin iron(III) chloro complex [(PaPPy₃)Fe(Cl)](ClO₄) (1, where =N,N-bis(2-pyridylmethyl)amine-N-propyl-2-pyridine-2-carboxamide) has been synthesized via the “template effect” and structurally characterized. The template reaction leads to the formation of a new carbon–nitrogen bond from coupling of a primary alkyl chloride with a secondary amine.     

Alloy formation during the electrochemical growth of a Ag-Cd ultrathin film on Au(1 1 1)

The electrodeposition of a Ag/Cd ultrathin film on a Au(1 1 1) surface and the formation of a surface alloy during this process have been studied using classical electrochemical techniques and in situ Scanning Tunneling Microscopy (STM). The films were obtained from separate electrolytes containing Ag⁺ or Cd²⁺ ions and from a multicomponent solution containing both ions. First, the polarization conditions were adjusted in order to form a Ag film by overpotential deposition. Afterwards, a Cd monolayer was formed onto this Au(1 1 1)/Ag modified surface by underpotential deposition. The voltammetric behavior of the Cd UPD and the in situ STM images indicated that the ultrathin Ag films were uniformly deposited and epitaxially oriented with respect to the Au(1 1 1) surface. Long time polarization experiments showed that a significant Ag-Cd surface alloying accompanied the formation of the Cd monolayer on the Au(1 1 1)/Ag modified surface, independent of the Ag film thickness. In the case of an extremely thin Ag layer (1 Ag ML) the STM images and long time polarization experiments revealed a solid state diffusion process of Cd, Ag, and Au atoms which can be responsible for the formation of different Ag-Cd or Au-Ag-Cd alloy phases.     

The Effect of Nickel on the Conversion of Amorphous Iron(III) Hydroxide into more Crystalline Iron Oxides in Alkaline Media

The effect of nickel (Ni) on the transformation of amorphous iron(III) hydroxide into more crystalline iron oxides has been followed using X-ray powder diffraction and chemical analysis. One aim of this study was to determine the fate of Ni that had been co-precipitated with amorphous iron(III) hydroxide as the amorphous phase recrystallised. Ni/amorphous iron(III) hydroxide co-precipitates transformed into Ni substituted α-FeOOH or α-Fe₂O₃, NiFe₂O₄ and α-3Ni(OH)₂.2H₂O in alkaline media. The type of reaction products formed depended on the concentration of Ni in the system and on the pH. Ni retarded the crystallisation of amorphous iron(III) hydroxide by stabilising the co-precipitate both against dissolution leading to α-FeOOH and against the internal rearrangement process which leads to α-Fe₂O₃. Chemical analysis showed that Ni was incorporated into the structure of α-FeOOH to a maximum level of 5.5 mol% and into the structure of α-Fe₂O₃ to up to 7 mol%. Excess Ni was adsorbed on the surface of the iron oxide or taken up by NiFe₂O₄ or the pure Ni phase. The b₀ dimension of the unit cell increased from 0.9960 nm for α-FeOOH to 0.9965 nm for α-FeOOH with 5.5 mol% Ni substitution. The same maximum level of Ni could be incorporated in the α-FeOOH structure in the presence of either Mn (up to 8 mol%) or Co (up to 7 mol%).     

Quantitative study of pH change during LaNi5−xAlx (x = 0, 0.3) discharge process by SECM

Oxygen reduction reaction (ORR) on Pt microelectrode was used for developing a micro pH sensor for scanning electrochemical microscopy (SECM) study in this work. When the potential of Pt microelectrode was held constant in ORR region, the ORR current (cathodic current) increased with decreasing solution pH and vice versa. The response time of the ORR current to pH changes was measured to be ca. 30 ms which implies that the pH response is fast enough for monitoring the temporal pH changes. Furthermore, a fine linear relationship was found to exist between the half wave potential of ORR (E_1/2) and the solution pH value, and the slope is −46 mV/pH. The Pt micro pH sensor was located 1 μm above the LaNi_5−xAl_x (x = 0, 0.3) substrate electrode surface in pH = 9 KOH solution to perform the tip-substrate voltammetry of SECM. In tip voltammogram, the ORR tip current qualitatively reflects the transit solution pH changes during LaNi_5−xAl_x discharge reaction. Also, the minimum values of the solution pH near LaNi₅ and LaNi_4.7Al_0.3 surface during the discharge reaction were quantitatively detected; they were 7.17 and 7.57, respectively. The result indicates that Al partial substitution for Ni degrades the maximum discharge ability of the alloy and decreases the hydrogen diffusion coefficient in alloy bulk.     

Combustion synthesis of (Ti1−xNbx)2AlC solid solutions from elemental and Nb2O5/Al4C3-containing powder compacts

Preparation of the (Ti_1−xNb_x)₂AlC solid solution (formed from the M_n+1AX_n or MAX carbides, where n = 1, 2, or 3, M is an early transition metal, A is an A-group element, and X is C) with x = 0.2-0.8 was investigated by self-propagating high-temperature synthesis (SHS). Nearly single-phase (Ti,Nb)₂AlC was produced through direct combustion of constituent elements. Due to the decrease of reaction exothermicity, the combustion temperature and reaction front velocity decreased with increasing Nb content of (Ti_1−xNb_x)₂AlC formed from the elemental powder compacts. In addition, the samples composed of Ti, Al, Nb₂O₅, and Al₄C₃ were adopted for the in situ formation of Al₂O₃-added (Ti,Nb)₂AlC. The SHS process of the Nb₂O₅/Al₄C₃-containing sample involved aluminothermic reduction of Nb₂O₅, which not only enhanced the reaction exothermicity but also facilitated the evolution of (Ti,Nb)₂AlC. Based upon the XRD analysis, two intermediates, TiC and Nb₂Al, were detected in the (Ti,Nb)₂AlC/Al₂O₃ composite and their amounts were reduced by increasing the extent of thermite reduction involved in the SHS process. The laminated microstructure characteristic of the MAX carbide was observed for both monolithic and Al₂O₃-added (Ti,Nb)₂AlC solid solutions synthesized in this study.