NiA and NiX zeolites as bifunctional electrocatalysts for water splitting in alkaline media

NiA and NiX zeolites were prepared and characterised using XRD, FTIR and SEM, and subsequently tested as electrodes for hydrogen (HER) and oxygen (OER) evolution reactions in alkaline media. Linear sweep voltammetry and chronoamperometry techniques showed that NiA has higher catalytic activity for these two reactions, as evidenced by higher current densities, which can be correlated with a higher weight fraction of Ni in this electrocatalyst than in the NiX and with its higher conductivity. HER and OER kinetic parameters, including Tafel slope, exchange current density and apparent activation energy were evaluated. Electrochemical impedance spectroscopy analysis yielded values of the resistance of the solution, charge transfer and mass transfer, as well as double layer capacitance and pseudo-capacitance of the working electrode, at different potentials and temperatures. Unlike the HER, during which the mass transfer resistance of the adsorbed intermediate is dominant in the case of NiA, the OER impedance response is controlled by the charge transfer process itself at the potentials of interest for these process. The overall resistance related to the HER is lower for NiA than for NiX. © 2018 Hydrogen Energy Publications LL

Electrochemical behavior of V2O5xerogel and V2O5xerogel / graphite composite in aqueous solution

The V2O5 xerogel and V2O5 xerogel /graphite composite were synthesized by sol-gel method. The obtained materials were characterized by X-ray diffractometry and simultaneous thermogravimetry and differential thermal analysis. The electrochemical behaviour was investigated by galvanostatic cycling in aqueous solutions of LiNO3. Better electrochemical performance was evidenced for composite V2O5 xerogel/graphite. Namely, the initial capacity of V2O5 xerogel/C was found to be 66 mAh g-1 against 40.4 mA h g-1 for V2O5, while capacity fade after 50 cycles was 10 % of initial capacity for V2O5 xerogel/ graphite, against 27% for V2O5.Physical chemistry 2012 : 11th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 201

In situ XRPD and DSC study of order-disorder phase transition in nanosize Li-ferrite

An order-disorder phase transition of nanosize Li-ferrite (Li0.50Fe2.50O4) was studied by DSC measurements and in situ XRPD technique. The phase transition temperature is found to be 762 °C (DSC) and (745±5) °C (XRPD).Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 200

NiA and NiX zeolites as electrocatalysts for water splitting in alkaline media

Water electrolysis represents a simple and clean method for production of hydrogen and oxygen. Nickel is a promising electrode material for large-scale application. Its activity could be improved by alloying it with other metals, non-metals or rare earth elements, or by fabrication in the form of foams or nanostructured composites, grafting onto a high surface area support, etc. In this study, Ni2+ cation-exchanged zeolites NiA and NiX were tested as electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) in alkaline media (1 M KOH). Conventional ion-exchange procedure was used to prepare Ni2+ cation-exchanged forms of NaA and NaX zeolites. The obtained materials, NiA and NiX, are described by formula Ni6(AlO2)12(SiO2)12 and Na23Ni32(AlO2)87(SiO2)105, respectively. XRD analysis generally confirmed the crystalline structure of the studied materials. In the case of NiA, broadening of diffraction peaks at 2θ angle of 11, 24 and 35o indicated partial distortion of the zeolite crystal lattice during ion-exchange process. Electrocatalitic activity of NiA and NiX for HER and OER was studied in 1 M KOH by recording polarization curves, chronoamperograms and electrochemical impedance spectra. For both reactions, NiA exhibited better catalytic activity than NiX, including higher current density and lower Tafel slope values. This could be correlated with higher Ni weight fraction in NiA than in NiX, and with higher electrical conductivity of NiA. Analysis of the electrochemical impedance spectra revealed that the HER is controlled by adsorption of the Hads intermediate, while the OER is controlled by the charge transfer at the potentials of interest for the process. Relatively good stability of both materials during HER and OER was deduced from the chronoamperometric curves

Electrochemical behavior of nanostructured MnO2/C (Vulcan®) composite in aqueous electrolyte LiNO3

The electrolytic solutions of contemporary Li-ion batteries are made exclusively with the organic solvents since anodic materials of these batteries have potentials with greater negativity than the potential of the water reduction, thus the organic electrolytes can withstand the voltages of 3-5 V that are characteristic for these batteries. Ever since it was discovered that some materials can electrochemically intercalate and deintercalate Li+ ions in aqueous solutions, numerous studies have been conducted with the aim of extending operational time of the aqueous Li-ion batteries. Manganese oxide has been studied as the electrode material in rechargeable lithium-ion batteries with organic electrolytes. In this paper its electrochemical behavior as an anode material in aqueous electrolyte solutions was examined. MnO2 as a component of nanodispersed MnO2/C (Vulcan®) composite was successfully synthesized hydrothermally. Electrochemical properties of this material were investigated in aqueous saturated LiNO3 solution by both cyclic voltammetry and galvanostatic charging/discharging (LiMn2O4 as cathode material) techniques. The obtained composite shows a relatively good initial discharge capacity of 96.5 mAh/g which, after 50th charging/discharging cycles, drops to the value of 57mAh/g. MnO2/C (Vulcan®) composite, in combination with LiMn2O4 as a cathode material, shows better discharge capacity compared to other anodic materials used in aqueous Li-ion batteries according to certain studies that have been conducted. Its good reversibility and cyclability, and the fact that hydrothermal method is simple and effective, makes MnO2/C(Vulcan®) composite a promising anodic material for aqueous Li-ion batteries

The LiFe(1-x)VxPO4/C Composite Synthesized by Gel-Combustion Method, with Improved Rate Capability and Cycle Life in Aerated Aqueous Solutions

The nitrate-(glycine + malonic acid)-assisted gel-combustion process, followed by a heat treatment at 750 °C under reductive atmosphere, was used as a fast and effective way to synthesize vanadium doped olivine incorporated in carbon matrix, of general formula LiFe(1−x)VxPO4/C. The two-phased Rietveld refinement confirmed that vanadium incorporation into olivine structure was complete. The heating under reduction atmosphere caused the formation of iron phosphide to some extent, the concentration was determined by Rietveld analysis. The capacity and rate capability of these composites were tested by both cyclic voltammetry and galvanostatic cycling. Specifically, the average discharging capacities of the composite with x = 0.055, determined in an saturated aqueous LiNO3 solution equilibrated with air, at the rates of 1, 10 and 100 C, amounted to 91, 73 and 35 mAh g−1, respectively, with no perceivable capacity fade

Post-treatment periapical status related to the quality of root canal fillings in adults living in Vojvodina

Background/Aim. Apical periodontitis (AP) is an acute or chronic inflammation of the periradicular tissue, usually caused by the presence of microbial irritants in the root canal system. The aim of the study was to radiographically assess the AP prevalence in root-filled teeth (RFT) in adults from an urban area of Vojvodina, Serbia. Methods. Randomly selected digital ortopantomographs of 616 subjects who visited the Clinic of Dentistry of Vojvodina, from January 2019 to December 2020 were examined. Periapical status, root canal filling (RCF) quality, type of coronal restorations, and their relationships were evaluated. The Chisquared (χ2) test was used for statistical analysis. Results. The total number of endodontically treated teeth was 965; 44.25% of them received an adequate RCF score, and 34.9% had AP, which was diagnosed i n 5 7.4% of inadequately s cored RFT. Posterior teeth had significantly worse RCF quality than anterior teeth (p < 0.001). The direct logistic regression results indicated that a technically well-performed RCF reduced the risk of AP almost 21-fold. The prevalence of AP in our cohort was not influenced by the type of restoration (direct or indirect), but statistically significantly, the highest prevalence of AP was found in RFT without any coronal restoration. Conclusion. The results of this study reaffirm that technically high-quality root canal treatment is crucial to ensure a more predictable root canal treatment outcome