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Enhanced electrocatalytic performance of interconnected Rh nano-chains towards formic acid oxidation
No full textA chain-like assembly of rhodium nanoparticles (5–7 nm mean diameter) has been synthesized from rhodium chloride with the help of polydentate molecules like tartaric and ascorbic acids (1 : 3 in mM scale) as capping agents at room temperature. Subsequent characterization using transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy reveals a unique inter-connected network like features, while their electrochemical behavior using cyclic voltammetry and current–time transient suggests potential applications as electrocatalysts in fuel cells. A significant negative shift in
the onset potential as well as higher anodic peak current density for formic acid oxidation on Rh-
tartaric acid (Rh-TA) as compared to that of bulk Rh metal confirms their higher electrocatalytic
activity. Interestingly, the enhancement factor (R) with respect to that of bulk metallic Rh towards
formic acid oxidation ranges up to 2000% for Rh-TA and 1200% for Rh-AA (Rh-ascorbic acid)
respectively. The composition of Rh nano-chains has been further analyzed with thermogravimetry and
Fourier transform infra-red spectroscopy to demonstrate the importance of controlling the chain
topology using polyfunctional organic molecules. These findings open up new possibilities for tailoring
nanostructured electrodes with potential benefits since the development of a better electrocatalysts for
many fuel cell reactions continues to be an important challenge
Hydrous RuO2–carbon nanofiber electrodes with high mass and electrode-specific capacitance for efficient energy storage
No full textWe demonstrate a new strategy for the fabrication of supercapacitor electrodes possessing high mass and area-specific capacitance for efficient charge storage, which can be extremely useful for the development of light, compact and high performance supercapacitors for a variety of high power demanding applications. High mass and electrode area specific capacitances were attained by using
Hydrous Ruthenium Oxide (HRO)–Carbon Nanofiber (CNF) hybrid electrodes prepared by the deposition of HRO (~31% Ru content) on both the outer and inner surfaces of a cylindrical hollow CNF having open tips. Electrochemical studies of the uniformly deposited HRO nanoparticles on the
CNF surface showed a mass specific capacitance of 645 F/g and an electrode specific capacitance of 1.29 F/(cm.cm) with a HRO–CNF material loading of 2 mg /(cm.cm) in the supercapacitor electrodes. The mass specific capacitance of pure HRO is 301 F/g, whereas the mass specific capacitance of HRO in the HRO–CNF electrode is ~1300 F/g1, which is very close to the theoretical capacitance of HRO. This enhanced charge storage ability, high rate capability, better cyclic stability and low ESR of the HRO–CNF will be useful for the development of high performance supercapacitors
Photoluminescent studies on porous silicon/tin oxide heterostructures
No full textPorous silicon (PSi) structure was formed at different current densities in the range of 5–60mA/cm2 by the electrochemical anodization of PSi wafers etching in HF for 30 min. The PSi was characterized by X-ray diffraction studies. The PSi samples prepared at current densities above and below 30mA/cm2 show PL spectra with asymmetric and overlapped peaks. On the top surface as well as inside the pores of this PSi structures the precursor sol–gel was incorporated by the spin coating technique and SnO2 was formed by heating at 400 ◦C in air. Peaks pertaining to PSi along with those corresponding to SnO2 were observed,
which confirmed SnO2 formation as thin film on the PSi surface. The PL spectra of SnO2/PSi structure aged
for two months indicated a reduction in PL intensity but remained constant afterwards. SnO2 not only modifies the nature of silicon nanopores but also is expected to influence the interface states in SnO2/PSi junctio
Microemulsion-mediated sol–gel synthesis of mesoporous rutile TiO2 nanoneedles and its performance as anode material for Li-ion batteries
No full textMesoporous rutile TiO2 nanoneedles have been successfully synthesized using a reverse microemulsionmediated
sol–gel method at room temperature. The materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and the Bruauner–Emmet–Teller (BET) adsorption method, and their electrochemical properties were investigated by galvanostatic charge and discharge tests. XRD observations revealed the formation of a pure rutile TiO2 phase. Furthermore, TEM observation
revealed the presence of a highly porous needle-like morphology. The electrochemical measurements show that the nanoneedles deliver an initial capacity of 305 mA h g-1 as anode material for Li-ion batteries and sustain a capacity value of 128 mA h g-1 beyond 15 cycles. The reported synthesis is simple, mild, energy efficient, and without postcalcinatio
Solution combustion synthesis of layered LiNi0.5Mn0.5O2 and its characterization as cathode material for lithium-ion cells
No full textLiNi0.5Mn0.5O2, a promising cathode material for lithium-ion batteries, is synthesized by a novel solutioncombustion
procedure using acenaphthene as a fuel. The powder X-ray diffraction (XRD) pattern of the product shows a hexagonal cell with a = 2.8955 ˚A and c = 14.1484A˚ . Electron microscopy investigations indicate that the particles are of sub-micrometer size. The product delivers an initial discharge capacity of 161 mAh g−1 between 2.5 and 4.6 V at a 0.1 C rate and could be subjected to more than 50 cycles. The electrochemical activity is corroborated with cyclic voltammetric (CV) and electrochemical impedance data. The preparative procedure presents advantages such as a low cation mixing, sub-micron particles and phase purit
Microbiologically influenced corrosion on rails
No full textCorrosion of rails has been a cause of concern for the
Southern Railways. Out of many causes, corrosion due
to toilet droppings is more pronounced. In this study,
the role of bacteria, viz. heterotrophic bacteria, manganese
oxidizers, iron bacteria and ureolytic bacteria
on rails have been studied. The attachment of rod- and
cocci-shaped bacteria were noticed on the corroded
rail sample. A porous rust layer and fine cracks were
noticed on the steels. Twenty bacterial strains were
identified by molecular technique and most of the bacteria
were positive in citrate and urease test, where
85% species could tolerate high pH 9.0. X-ray photoelectron
spectroscopy revealed that FeOOH in the
bare steel was converted to ferric oxides and hydroxides
due to bacterial corrosion. When the rail sample was
tested at low AC perturbations, the biofilm provided
protection to the rails. However, at higher anodic
potentials, the biofilm was not able to protect the bare
material. It could be assumed that the ureolytic bacteria
and iron/manganese oxidizers may create differential
pH gradient on the metal surface which enhances
the electrochemical reaction of the metal surface
Enhanced electrocatalytic performance of functionalized carbon nanotube electrodes for oxygen reduction in proton exchange membrane fuel cells
No full textAlthough nitrogen doped CNTs (N-CNTs) are considered a promising alternative to platinized
carbon for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells
Q2 (PEMFCs), the origin of the enhanced ORR activity with N-CNTs is not clear at present. Among
several plausible reasons, the exposure of edge plane and creation of impurity band/surface states
near the Fermi level are considered as major causes behind the catalytic activity. However, CNTs
without nitrogen doping are not known to catalyze the ORR. In this work, we study the ORR
activity of functionalized carbon nanotubes with different functional groups, such as sulfonic acid
and phosphonic acid, in order to understand the role of surface functionalities in catalyzing the
reaction. Functionalized CNTs show significantly enhanced activity towards the ORR, while CNTs without such surface functional groups do not reveal any such special ORR activity. Linear sweep voltammetry experiments with different rotation rates show diffusion controlled limiting current values for functionalized CNTs, and the ‘n’ values derived from Koutecky-Levich plots are 3.3 and 1.7 for S-MWCNTs and P-MWCNTs, respectively. This work demonstrates the ORR activity of functionalized MWCNTs, which opens up new strategies for electrocatalyst
design in PEMFCs
A homogeneous redox catalytic process for the paired synthesis of l-cysteine and l-cysteic acid from l-cystine
No full textRedox catalytic process involved in the paired electrosynthesis of l-cysteine and l-cysteic acid from
l-cystine is investigated by cyclic voltammetric technique and also confirmed by preparative electrolysis. The cyclic voltammetric behaviour shows that in the catholyte, in situ deposited tin (Sn) surface acts as a redox catalyst for the electro-reduction of l-cystine to l-cysteine whereas in the anolyte, the electro-generated bromine acts as a homogeneous redox mediator to enhance the electro-oxidation of
l-cystine. l-Cysteine hydrochloride monohydrate (l-cysteine) and l-cysteic acid are prepared from lcystine by preparative electrolysis with high purity and high yield using graphite cathode and DSA anode. At optimum concentration of l-cystine with 1:1 concentration ratio (catholyte:anolyte), the material yield obtained for l-cysteine is above 80% and that for l-cysteic acid is close to 60% in the paired electrosynthesis process in the batch operation. Scope for further experiments in conversion efficiency is also discusse
Synthesis of tungstate doped polyaniline and its usefulness in corrosion protective coatings
No full textA study has been made on the corrosion protection performance of tungstate doped polyaniline containing
vinyl coating on steel. The tungstate doped polyaniline was chemically synthesized and characterized by FTIR, XRD, UV-VIS and TGA studies. The corrosion protection performance of vinyl coating containing tungstate doped polyaniline on steel was assessed in 3% NaCl by electrochemical impedance studies (EIS). The coating has been found to offer protection more than 60 days in salt spray and immersion in 3% NaCl. FTIR studies have shown that the formation of iron–tungstate complex along with the passive film on stee
Voltammetric investigations on the transition between dissolution, passivation and deposition characteristics of Ni, Cu and their alloys in fluorine based ionic liquid
No full textMultisweep cyclic voltammetric (CV) responses of nickel, copper, Monel and nickel–copper alloy had been extensively studied and compared in a variety of non-aqueous solvents such as acetonitrile (AN), propylene carbonate (PC) and sulfolane containing triethylamine trishydrogen fluoride (TEA·3HF) ionic liquid. The quantity of dissolution as well as surface morphological transformation on the electrode
surfaces as a result of anodic polarization were investigated using atomic absorption spectroscopy (AAS)
and scanning electron microscopy (SEM) respectively. The nature of crystallites formed on the polarized electrode was characterized using X-ray diffraction (XRD). The voltammetric study clearly indicates that Ni, Monel and Ni–Cu alloy are passive and stable in neat TEA·3HF medium in the recorded potential region of CV. Surface morphology of Ni after polarization, reveals the generation of pits, whereas the evolution of small crystallites of CuF2 are noted on the polarized alloy material, as evidenced by SEM
pictures. Copper electrode shows reversible voltammetric characteristics with high charge recovery ratio (qc/qa) suggesting that in this medium, Cu can certainly serve as reference electrode. Addition of water in TEA·3HF medium increases the solubility and stability of these metal fluoride film. In solvents such as PC, AN and sulfolane containing TEA·3HF, Ni and their alloys exhibit remarkable passivity and the charge recovery ratio decreases to some extent for Cu. In TEA·3HF/AN medium, the dissolution of Cu is very high. The present investigation suggests that the relative stability of all the four electrodes in neat TEA·3HF and solvents containing 0.1 M TEA·3HF decreases in the order: Ni > Monel > Ni–Cu alloy > Cu and relative
solubility of metal fluoride films in the three solvents increases in the order: PC < sulfolane < A