Papers by Keyword: Oxygen Reduction

Abstract: The metal-air batteries, especially the Zinc-air batteries, are great solutions to the growing energy crisis with excellent rechargeable capacity. ORR is the key electro-chemical reaction in Zinc-air batteries, and the development of the ORR efficiency is being studied extensively. The doping of transition metal in Co₃O₄, with the basement of N-doped graphene have been confirmed to have catalytic activity which can be comparable to Pt/C. Herein, the Fe-doped Co₃O₄ supported by N-doped graphene is constructed as the catalyst of ORR, and that without Fe doping is also constructed as comparison. Through first-principle calculation, it shows that the adsorption energies to O₂ on the same site of each surface and on different sites on Fe-doped one. The partial density of state of the O₂ adsorption system shows the effects of electron transfer and orbital hybridization on catalysis, which provide evidence to the catalytic mechanism with Fe doping. The energy changes of each step in ORR on catalyst with Fe doping and without Fe doping show the shortcomings of the simulation, including the spin of Fe atoms. Thus the study confirms that the adding of Fe contributes to the catalystic capability compared to the pure Co₃O₄.

Abstract: The platinum (Pt) degradation, poisoning and carbon corrosion in acidic fuel cell has led to explore the research in alkaline fuel cell. However, the high cost of Pt has brought a lot of studies to find replacement for Pt catalyst. Due to that, silver metal is selected as non-Pt catalyst and supported by the nitrogen and phosphorus-doped on graphene for oxygen reduction reaction in alkaline medium. The adsorption energy and mechanism of the oxygen reduction reaction is studied by using density functional theory (DFT) calculation. The support catalyst of graphene is doped with three atom nitrogen and phosphorus namely as N3 and P3, respectively. The Ag supported on N3 and P3 are tested on O₂, OOH, O and OH species. There are two types adsorption of O2 on N3 and P3 which is side and end-on adsorption configuration. The N3-Ag has similar adsorption energy for both configurations, but P3-Ag has low adsorption energy by end-on adsorption configuration. The effect of doped atoms on graphene also have been tested on O₂, OOH, O and OH species. The result shows that increasing nitrogen doping atom has decreased the adsorption energy of O2 and vice versa on phosphorus atoms. A single phosphorus doping atom on graphene has shown the lowest adsorption energy, but the end-on configuration of P3-Ag has shown most stable adsorption. The schematic free energy profile shows that both N3-Ag and P3-Ag have high possibilities to be followed in oxygen reduction reaction mechanism but P3-Ag has advantage due to stable adsorption as non-Pt catalyst. The Ag metal supported on nitrogen and phosphorus-doped graphene show promising result to be a catalyst in alkaline fuel cell.

Abstract: This research is aimed to examine oxidation state of Copper (Cu) in both as-synthesized and reduced T’-Pr_2-xCe_xCuO₄ (T’-PCCO) with x = 0, 0.10, and 0.15 using Cu K-edge x-ray absorption near edge structure (XANES). The T‘-PCCO nanopowders were successfully synthesized by the chemically dissolved method with HNO₃ as a dissolving agent continued by calcination at 1000°C for 15 h. The reduced T’-PCCO nanopowders were obtained by reduction annealing process at 700°C for 5 h under Ar gas atmosphere. The analyses of XANES spectra show that oxidation states of the Cu ions in all of the T'-PCCO nanopowders have values between +1 and +2. This indicates the existence of electron doping in the CuO₂ planes, even in the undoped T’-structure. It is found that the oxidation states of the Cu ions change after reduction annealing depending on the existence of apical oxygen in the T'-structure. Based on the XANES analyses, it is revealed that the change of oxidation state is influenced by the presence of both electron and hole carriers in the two-carrier model of T’-structure.

Abstract: The thermoelectric properties of Sr_0.61Ba_0.39Nb₂O₆ ceramics, reduced in various conditions, were investigated in the temperature range from 323K to 1073K. Both the electrical resistivity and the absolute Seebeck coefficient decreased with the deepening degree of oxygen-reduction. However, the decrease of the electrical resistivity had a major influence on the thermoelectric power factor. Therefore, the more heavily reduced sample can gain the higher value of thermoelectric power factor. It has been observed that the thermal conductivity increased with the deepening degree of oxygen-reduction, which indicates that the scattering of the oxygen vacancies produced by reduction does not play a dominant role in the thermal conduction. In spite of the increase of the thermal conductivity, the oxygen-reduction still promoted the thermoelectric figure of merit via the increase of the thermoelectric power factor. And the most heavily reduced Sr_0.61Ba_0.39Nb₂O₆ ceramic has the highest thermoelectric figure of merit (~0.18 at 1073 K) among all the samples.

Abstract: Hydrogen peroxide production via cathodic reduction of oxygen on self-made gas diffusion electrode was investigated in an undivided electrochemical system. The effects of mass ratio between graphite and PTFE in cathode, the calcination temperature, current density, pH, and plate distance on hydrogen peroxide generation were discussed. The results showed that the self-made gas diffusion cathode had high catalyze capacity for production of hydrogen peroxide using cathodic oxygen-reducing reaction. The hydrogen peroxide concentration could reach 80.52 mg·L^{- 1} within 2 h. The optimal conditions for this system are as follows: mass ratio of graphite to PTFE in cathode, 21, calcination temperature, 300 °C, current density,4.69mA/cm^2, pH 13.0, and the distance between anode and cathode, 8cm. The high concentration of hydrogen peroxide generated gives a promising application of this novel gas diffusion electrode system in pulp bleaching and waste-water treatment.

Abstract: Electrochemical properties and possibilities of manufacturing the anodes based on water-soluble binders such as carboxymethylcellulose (CMC) have been investigated in order to create prerequisites for development of “green” technologies for recyclability of LIBs components.In this work an advanced anode was designed. A kind of nanosized carbon coated Si composite was synthesized. The charge/discharge test reveals that the advanced anode shows a reversible capacity of 600 mAh/g. The improved performance was ascribed to the carbon shell of Si and CMC binder. The binder CMC buffers the expansion of the Si and the improved electric contact between the active material and copper current collector.

Abstract: Acid-functionalized multiwalled carbon nanotube (AF-MWCNT)-supported tetranitro-copper phthalocyanine (TNCuPc) assemblies were prepared by solid phase synthesis method. The products were characterized by infrared spectroscopy, scanning electron microscopy and XRD. The electrocatalytic activity of the obtained AF-MWCNT-supported TNCuPc assemblies was measured by cyclic voltammetry (CV) and rotating disk electrode (RDE) techniques in an oxygen-saturated 0.1 M KOH. The results showed that the catalytic activity of TNCuPc/AF-MWCNTs towards oxygen reduction was a two-step, two-electron process for oxygen reduction.

Abstract: Iron tetrapyrazinoporphyrazine (FePTpz) and cobalt tetrapyrazinoporphyrazines (CoPTpz) supported on multiwalled carbon nanotubes (MWCNTs) are prepared by solid phase synthesis method. The products are characterized by scanning and transmission electron microscopy. The electrocatalytic activity of the obtained MWCNTs-supported FePTpz and CoPTpz assemblies (MPTpz/MWCNTs) is measured by cyclic voltammetry and rotating disk electrode techniques in an oxygen-saturated 0.1M KOH. The results show that MPTpz/MWCNTs are more efficient than reference MPTpz. FePTpz/MWCNTs are more efficient for O2 reduction than CoPTpz/MWCNTs, both of FePTpz/MWCNTs and CoPTpz/MWCNTs exhibit a one-step, four-electron pathway for ORR.

Abstract: A new composite electrocatalyst, well-dispersed TiO2/active carbon (AC), has been assessed with regard to its applicability for oxygen reduction in air electrodes. TiO2/AC powders were prepared by one-step vapor hydrolysis of TiCl4 with active carbon. The structure and composition of the powders were analyzed by means of XRD and FTIR, and the results showed that anatase titanium dioxide of particle size 16.5 nm was produced after calcination at 400 °C. The influences of the preparative parameters of the air electrode on its discharge performance were studied by polarization curve measurements. The terminal voltage of the air battery was maintained at above 1.05 V while the current density of the air electrodes reached 150 mA cm-2. These results show that the composite catalyst has high electrochemical activity for the oxygen reduction reaction.

Abstract: Two types of oxide nanosheet-based materials, a H3O+-exchanged layered titanate and restacked titania nanosheets (H3O+-RE) were synthesized by soft chemical methods, and their oxygen reduction reaction (ORR) activities were examined by semi-steady-state voltammetry with a rotating ring-disc electrode at 70°C in 0.05 M H2SO4. Both samples showed similar onset potentials of the ORR, ~ 0.50 vs. reversible hydrogen electrode, while the efficiencies (Eff4) of the 4-electron reduction of oxygen depended on their nanostructures, i.e. the stacking morphology of nanosheets, specific surface area and kinds of cation between the nanosheets. Both H3O+-form samples showed high Eff4 values are compared with Cs+-form layered titanate.and the H+-form restacked titania nanosheets. This reveals that the H3O+ions and the number of the active sites for ORR are related to the ORR activity. The H3O+-RE exhibited the best Eff4 value (> 90%), which is comparable to that of a conventional 20 mass% Pt/C catalyst.