Saturated Electrolyte Research Articles

Metal-Free Heterogeneous Nanoporous Carbon for CO2 electrochemical Reduction to CO and CH4 in Aqueous Solution

Recently, the electrochemical conversion of CO2 has gained a significant attention. It provides a potential solution for minimizing the CO2 concentration level in the environment and also offers an alternative way to convert it to renewable fuels. Various metals (Ag, Au, Cu, etc.) and metal complexes are used as heterogeneous catalysts for CO2 reduction. However, the limitations in their application are in the fact that many polycrystalline metals show a low product selectivity and high overpotential. Also, the rising cost of noble metals and a low stability of the catalysts are the main hindrance towards their practical applications. Therefore it is important to develop a new class of catalysts, which are less expensive than metals and show a sufficient performance in CO2reduction.Metal-free N-doped carbon nanofibers and N-doped carbon nanotubes (NCNTs) have been addressed in the literature as a catalysts for the reduction of CO2 to CO. Nanoporous carbons, which exhibit well-developed porosity combined with specific surface chemistry might be potential candidates for CO2 reduction catalysts. The previous research on nanoporous heteroatom doped (S- and N-) polymer-derived carbon indicated that the catalytic performance is governed by the positively charged sites in the carbon matrix. Pyridinic nitrogen was found as crucial since it brings positively charged sites to the carbon atoms, which stabilizes the CO2 · ¯ and COOH* intermediates for CO formation. The surface basicity and high volume of ultramicropores improved the CO2reduction process.In this research, various treatments were used to incorporate nitrogen groups to commercial wood-based activated carbon (BAX-1500, MeadWestvaco). The obtained carbons were studied for CO2 electrochemical reduction in KHCO3 electrolyte (0.1 M) saturated with CO2 (ultrapure). Testing was performed in an airtight three-electrode and two compartments cell. The electrocatalytic behavior of carbons were evaluated by Faradaic efficiency (FE). A chronoamperometry (CA) was run under a constant potential for 6h between -0.4 V and -1.2 V vs. RHE. During the CA run, the gas phase from the headspace of the cathodic compartment of the electrochemical cell was analyzed periodically (1h) using gas chromatography (GC) (model SRI 8610C, column Carboxen1000). The carbon treated with melamine and heat treated at 950 oC under N2 (BAX-M-950) showed the best electrochemical performance. The FE of 24.1% for CO and 0.9% for CH4 at -0.79 V vs. RHE were measured. The XPS results showed that nitrogen is mainly in pyridinic (36.3%), pyridonic (48.0%) and pyridine-N-oxides (15.7%) configurations. The obtained carbon has large surface area (1500 m2/g) with micro/mesoporous structure (Vmic/Vt~ 0.5). For BAX-M-950, the CO formation (Figure 1a) started at -0.49 V vs. RHE with a CO FE of approximately 6.3%. The maximum FE reached 24.1% at the reducing potential of -0.79 V vs. RHE for 4h. This voltage corresponds to an overpotential of 0.68 V as the CO2/CO dynamic equilibrium potential is -0.11 V vs. RHE. The FE decreased when reducing potential is more negative than -0.79V vs. RHE. Similar behavior has also been reported in the literature. The best Faradaic efficiency for CH4 formation is 0.71% and it is observed at -0.89 V vs. RHE. Stability of a catalyst is another main focus in this research. The results indicated that FE with respect to CO increased from 16.5% (at 0.5h) to 24.1% reaching it maximum at 4h (Figure 1c). That increase in FE with time could be either due to the increase in mass transport of CO2 to the carbon surface or due to the favorable change in surface chemistry during reduction. Thus the electrode was reduced for 4h performing chronoamperometry (CA) at -0.79V vs. RHE in N2 saturated electrolyte (It is referred to as CA pretreatment). When CO2was introduced to electrolyte the carbon showed the best FE for the CO formation reaching 39.9% and FE only increased 2.5% during first 3h reduction. The electrode after the CA pretreatment was studied by XPS. The results showed that the content of pyridinic N (~ 40 %) increased after 4h CA pretreatment compared to the initial material. This increase in the performance is linked to an increased contribution of this species on the surface. Figure: a) Faradaic efficiency for the CO formation of BAX-M-950 at different potentials; b) Faradaic efficiency for the CH4 formation of BAX-M-950 at different potentials; c) Carbon monoxide FE Comparison with and without CA pretreatment at -0.79V vs. RHE; d) Comparison of the FE after CA pretreatment for all carbon tested. (5 mg·cm-2 catalyst loading) Figure 1

High Performance and Biodegradable Skeleton Material Based on Soy Protein Isolate for Gel Polymer Electrolyte

A kind of biodegradable and well-sourced soy protein isolate (SPI)/poly(vinyl alcohol) (PVA) composite nanofiber membranes was fabricated via electrospinning and used as skeleton material in gel polymer electrolyte (GPE) of lithium-ion batteries. This study revealed that the proper material proportion, low crystallinity, sufficient porosity and good affinity between nanofiber and the electrode/electrolyte resulted in high saturated electrolyte uptake and conservation rate of the nanofiber membranes. The GPEs based on the SPI/PVA composite nanofiber membranes presented remarkable electrochemical performance, including high ionic conductivity, excellent compatibility with lithium electrode and good electrochemical stability. An ionic conductivity of 3.8 × 10–3 S cm–1 and interfacial resistance of 250 Ω for the GPEs can be obtained when the weight ratio of SPI to PVA in the spinning solution was 3:1, which was more superior to the existing biobased GPEs. In addition, the Li/GPE/LiCoO2 cells with GPEs based o...

Insights into the enhanced tolerance to carbon monoxide on model tungsten trioxide-decorated polycrystalline platinum electrode

Polycrystalline platinum decorated by WO3 nanoparticles (WO3/Ptpc) is used as a model electrode to gain insights into the enhanced tolerance to carbon monoxide (CO) observed on such composite materials. Bifunctional-type reactions involving WO3 and Pt active sites are observed, such as hydrogen spill-over or the electrooxidation of CO molecules adsorbed on Pt sites neighboring the WO3 nanoparticles. The resulting COad-free Pt sites are active for the hydrogen oxidation reaction (HOR), thereby enhancing the HOR activity for WO3/Ptpc electrode relatively to bare Ptpc in 300ppm CO/H2 saturated HClO4 electrolyte. However, this bifunctional effect occurs exclusively for CO molecules weakly adsorbed on Pt, i.e. only for a small fraction of the COad fully covering the Pt surface.

Linear behaviour in isothermal equilibria involving saturated electrolyte solutions: The H2O–Co(NO3)2–Ni(NO3)2 ternary system at low temperature

The solid–liquid equilibria of the H2O–Co(NO3)2–Ni(NO3)2 ternary system were studied at 248.15K and 258.15K, using a synthetic method based on conductivity measurements. The obtained results were complemented by chemical and powder X-ray diffraction analyses. The solid phases are ice and two large substitutional solid solutions: Co(1−σ)Niσ(NO3)2·6H2O, which has a monoclinic structure, and Ni(1−ω)Coω(NO3)2·6H2O, which has a triclinic structure. The formation of a Ni(1−ε)Coε(NO3)2·9H2O solid solution is also highly probable.The ice liquidus curves were modelled in a truly remarkable way, using the quasi-ideal model taking into account ionic dissociation and solvation. The liquidus of the solid solutions were analysed without regard to cation solvation, as a first approximation. Linear behaviour was observed in all cases. On the basis of simple, representative equations, the experimental values were evaluated critically, refined and extrapolated.

Conducting-Polymer-Supported Bacterial Biofilms As Active Matrices for Noble Metal and Molecular Catalytic Centers: Enhancement of Electroreduction of Oxygen and Carbon Dioxide

Hybrid matrices composed of porous conducting polymer - polyaniline (PANI) or poly(3,4- ethylenedioxythiophene) (PEDOT) - underlayer, robust bacterial biofilm and the multi-walled carbon nanotubes have been demonstarted to function as highly active supports for dispersed catalztic centers (both noble metal nanoparticles and molecular ligand complexes). We explore unique properties of biofilms, i.e. polymeric aggregates of microorganisms, in which cells adhere to each other on the electrode surfaces. Such systems are characterized by extracellular electron transfers involving c-type cytochromes (heme-containing proteins). Biofilms grown on inert carbon electrode substrates tend to exhibit electrocatalytic properties towards oxygen and hydrogen peroxide reductions in neutral media. The processes have been found to be further enhanced by introduction of multi-walled carbon nanotubes (MCNTs) that are modified with ultra-thin layers of organic (e.g. 4-(pyrrole-l-yl) benzoic acid. We expect here attractive electrostatic interactions between carboxyl-group containing anionic adsorbates and positively charged domains of the biofilm with c-type cytochrome enzymatic sites. Coexistence of the above components leads to synergistic effect that is evident from positive shift of the oxygen reduction voltammetric potentials and significant increase of voltammetric currents. Most likely, the reduction of oxygen has been initiated at the molecular (e.g. intentionally added cobalt porphyrin redox centers), whereas the undesirable hydrogen peroxide intermediate are further decomposed at the cytochrome sites. Among other important observations is the significant enhancement of activity of Pt nanoparticles toward electroreduction of carbon dioxide in the presence of such a robust bacterial biofilm as Y. enterocolitica. Although interactions between platinum and such a complex ecosystem as biofilm are difficult to describe precisely, it is reasonable to postulate some inhibition of the hydrogen evolution (competitive reaction) at platinum nanoparticles in presence of bacterial microcolonies in favor of enhancement of the CO2-reduction. It is also noteworthy that biofilms are highly hydrated, and existence of open water channels between the bacterial microcolonies facilitates flow of supporting electrolyte. Combination of the hydrophobic polymer (PANI) structures with hydrophilic bacterial aggregates seems to produce attractive hybrid supports for electrocatalysts operating in aqueous media. Based on numerous repetitive diagnostic experiments in both argon and carbon dioxide saturated electrolytes, it can be stated that, by growing and supporting the biofilm onto the PANI polymer underlayer, the overall stability of the biofilm-based system has been improved. Indeed, we have not effectively observed any degradation of the hybrid catalytic films (both in terms of electrocatalytic activity and physicochemical stability) during our prolonged diagnostic experiments. Because measurements have been performed in neutral (phosphate buffer at pH=6.1) rather than acid medium, the PANI films (regardless of the presence of some HSO4 - anions) are not expected to be very well conducting. Consequently, we have also introduced MWCNTs to the electrocatalytic interface to facilitate charge distribution there.

Electrochemical lithiation/delithiation kinetics and capacity of phosphate tungsten bronze and its chemically pre-lithiated derivatives in aqueous solutions

Monophosphate bronze (PW8O26, WPB) was synthesized by low-temperature (650 °C) heating of 12-tungstophosphoric acid (WPA). Its lithiated derivative with a low lithium content (Li3-WPB) was synthesized by heating lithium salt of WPA at 650 °C. Its lithiated derivative with a high lithium content was synthesized by mechanochemical lithiation of Li3WPB (Lin-WPB) (n > 3), followed by heat treatment at 650 °C. X-ray powder diffraction analysis confirmed that the bronze structure changed with the increase of the incorporated lithium content. These bronzes were investigated from the aspect of lithiation/delithiation kinetics in an aqueous saturated LiNO3 electrolyte solution. By cyclic voltammetry, both the kinetics of intercalation/deintercalation and the coulombic capacity were found to decrease with the increase of initial lithium content, in agreement with literature data for electrochemically lithiated tungstophosphate bronzes. Monoclinic lithium-free bronze PW8O26, as the most promising material, was subjected to a further detailed galvanostatic investigation coupled with the LiFe0.95V0.05PO4/C composite as a cathode material in an aqueous battery. In comparison to its behavior in an organic electrolyte, a considerably lower initial capacity of the bronze electrode was measured. However, its cyclic stability was much better in an aqueous than in an organic electrolyte.

Measurements of the complex permittivity of highly concentrated aqueous NaCl solutions and ferrofluid employing microwave cylindrical cavities

Few resonance cavities operating on different modes have been used for the accurate multi-frequency determination of the complex permittivity of highly concentrated aqueous NaCl solutions at a frequency range of 2.5 GHz to 24 GHz. It has been shown that the use of the perturbation method would lead to significant measurement uncertainties especially for lossy samples and should be avoided especially for TE0n1 mode cavities. At frequencies that are smaller than 15 GHz the imaginary part of the permittivity of NaCl solutions increases while at frequencies larger than 15 GHz it decreases, with the increasing conductivity of the electrolyte. In the last case the total dielectric losses for the saturated electrolyte are noticeably smaller than for pure water. The complex permittivity and complex permeability of ferrofluid, liquid that exhibits diamagnetic properties at microwave frequencies, were measured by employing two cylindrical cavities operating on complementary modes.

Radiation-crosslinked nanofiber membranes with well-designed core–shell structure for high performance of gel polymer electrolytes

The polymer nanofiber membranes with core (polyacrylonitrile, PAN)–shell (polyethylene oxide, PEO) structure were prepared by using coaxial electrospinning under different concentration of spinning solution. The polyporous nanofiber membranes were activated in liquid electrolytes and transformed into gel polymer electrolytes (GPEs). The microstructure, crystallization behavior and mechanical properties of nanofiber membranes were studied. Based on the proper collocation of polymer materials, desirable microstructure, appropriate crystallinity and moderate radiation-crosslinking, the high saturated electrolyte uptake, conservation rate and mechanical properties of polymer membranes were obtained. The electrochemical testing of the resulting GPEs revealed high ionic conductivities, good electrochemical stability and appropriate lithium-ion transference numbers, which are realized through choosing an optimal concentration of core/shell spinning solution. Moreover, the Li/GPE/LiCoO2 cells with GPEs based on the radiation-crosslinked nanofiber membranes with optimized core–shell structure showed excellent initial discharge capacities as well as remarkable cycle performance. Through the implementation of the proper collocation of two ordinary polymer materials and facile preparation techniques, comprehensive performance of the resulting GPEs was more superior to that of GPEs involved with pure PAN and commercial Celgard® 2500. The radiation-crosslinked nanofiber membranes with well-designed core–shell structure can be used as an ideal skeleton material in GPEs for lithium-ion batteries with high performance.

LiV3O8 nanowires with excellent stability for aqueous rechargeable lithium batteries

LiV3O8 nanowires have been successfully synthesized by a simple polyvinyl alcohol (PVA) assisted sol–gel method. The structure and morphology of LiV3O8 nanowires are characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. An aqueous rechargeable lithium battery with LiV3O8 nanowires anode, LiMn2O4 cathode, and saturated LiNO3 electrolyte is fabricated. The battery delivers 103.9 mAh·g−1 in the first cycle and remains at 86.5 mAh·g−1after 100 cycles at a current density of 150 mA g−1. LiV3O8 nanowires show excellent electrochemical stability as anode materials for aqueous rechargeable lithium batteries.

Formic Acid Electrooxidation on Au Electrode Studied By Potential Step and a Fast Scan ATR-FTIR Spectroscopy

The role of adsorbed formates in the electro-oxidation of formic acid on Pt electrodes was widely debated [1-3]; on a gold electrode formic acid oxidation was assumed to proceed via dimers of contiguously adsorbed bridge-bonded formates [4]. In the present work, formic acid oxidation on Au thin film electrode was studied by simultaneous in situ ATR-FTIRS and electrochemical measurements in both potentiodynamic and potential step mode with a fast IR spectra acquisition in a thin-layer flow cell configuration under well-defined mass transport conditions [2], to address the impact of adsorbed spectator species (perchlorate) and adsorbed bridge-bonded formate on the formic acid electrooxidation rate. 0.1 M HCOOH and DCOOH were used to i) assess the kinetic H/D isotope effect in formic acid oxidation on Au electrode; ii) identify the adsorbed species and follow their temporal development and the potential dependence. A thin (~30 nm) Au film was electrolessly deposited onto the top plane of a hemi-cylindrical Si prism, which was subsequently carefully annealed in a butane flame in nitrogen atmosphere to improve the adhesion and thus the stability of the Au film under enforced hydrodynamic conditions and large repetitive perturbations of the working electrode potential (from 0.0 up to 1.65 V vs. RHE). This gold thin film electrode exhibited an unprecedented sensitivity of DR/R ~ 0.03 for the linearly adsorbed CO band in CO saturated supporting electrolyte at 0.0 V (reference spectrum acquired in CO-free electrolyte at 0.0 V). The IR spectra were acquired applying p-polarized IR radiation at 0.025 s-1 time resolution, 16 cm-1 spectral resolution and 75 kHz frequency employing a Cary 680 FTIR spectrometer (Agilent Technologies) equipped with a step scan accessory, and operated in a dual scan / quad compute mode. A EG&G 273A (PAR) potentiostat was used for potentiodynamic (100 mV s-1) and multistep (from 0.0 V to desired oxidation potential) experiments. A base CV in 1M HClO4 supporting electrolyte revealed a clean Au film electrode as confirmed by in situ IR spectroscopy measurements, which exhibit only the potential dependent bipolar bands at 3610 / 3455 and 1654 / 1515 cm-1 related to adsorbed water, and a unipolar band at ca. 1125 cm-1 of adsorbed perchlorate. Formic acid oxidation starts at about 0.5 V, approaches a plateau from 0.9 to 1.2 V (HCOOH) and from 0.9 to 1.3 V (DCOOH), and then passes through a maximum at around 1.45 V, which is about three times higher for HCOOH than for DCOOH, due to kinetic isotope effects. The corresponding IR spectra show pronounced potential dependent HCOOad and DCOOad bands at 1326 and 1303 cm-1, respectively. Plots of the integrated adsorbed formate band intensity vs. the potential are qualitatively similar to those of the perchlorate band in supporting electrolyte. Perchlorate adsorption is suppressed by adsorbed formate, due to competitive adsorption of the more strongly adsorbing anion. When stepping the potential from 0.0 V to the respective oxidation potential, the integrated band intensities for both adsorbed bridge bonded formate and perchlorate increased instanta­neously (within 25 ms) and remained constant over the step duration (1 s). A similar behavior is observed for adsorbed perchlorate, a clear spectator species. The integrated intensity of adsorbed formate at constant potentials increases with the adsorption potential up to 1.0 V, similar to that of adsorbed perchlorate in pure supporting electrolyte. The development of adsorbed formate reduces the perchlorate adsorption at higher potentials, compared to pure supporting electrolyte, indicating a competitive adsorption of formate and perchlorate. Overall, the data reveal an adsorption behavior of the adsorbed bridge-bonded formate species, which is identical to that of other anions that are known to act as spectator species. Although the participation of adsorbed bridge-bonded formate as active intermediate in formic acid oxidation on a Au electrode [4] cannot be ruled out based on the present data, they are at least equally consistent with a model proposing reaction via coadsorbing formate anions and formic acid species [5]. Acknowledgement. This work was supported by the Deutsche Forschungsgemeinschaft (Research unit FOR 1376, JU 2781/2-2) [1] G. Samjeské, A. Miki, S. Ye, M. Osawa, J. Phys. Chem. B 110, 16559 (2006). [2] Y.X. Chen, M. Heinen, Z. Jusys, R.J. Behm, Angew. Chem. Int. Ed. 45, 981 (2006). [3] W. Gao, J.A. Keith, J. Anton, T. Jacob, J. Am. Chem. Soc. 132, 18378 (2010). [4] A. Cuesta, G. Cabello, F.W. Hartl, M. Escudero-Escribano, C. Vaz-Domínguez, L.A. Kibler, M. Osawa, C. Gutiérrez, Cat. Tod. 202, 79 (2013). [5] S. Brimaud, J. Solla-Gullón, I. Weber, J.M. Feliu, R.J. Behm, ChemElectroChem 1, 1075 (2014).

Electrochemical performances of (LiMn0.6Fe0.4PO4/C)//LiV3O8 in different aqueous solution electrolyte

The electrochemical performances of (LiMn0.6Fe0.4PO4/C)//LiV3O8 ARLB in different aqueous electrolyte, i.e. 0.5M Li2SO4, 2M Li2SO4, saturated Li2SO4 with pH value of 7, 2M LiNO3, 5M LiNO3, saturated LiNO3, saturated LiNO3 with pH value of 7, are studied. The results infer that (LiMn0.6Fe0.4PO4/C)//LiV3O8 ARLB in 5M LiNO3 or saturated LiNO3 aqueous electrolyte with pH value of 7 has favorable specific capacity and rate performance. According to the energy density calculations, the electrochemical performance of (LiMn0.6Fe0.4PO4/C)//LiV3O8 ARLB in the saturated LiNO3 with pH value of 7 is better than that in 5M LiNO3 solution.

A green strategy for the synthesis of graphene supported Mn3O4 nanocomposites from graphitized coal and their supercapacitor application

A by-product free strategy based on modified Hummers method was proposed to synthesize graphene/Mn3O4 composites without any additional manganese source. Coal-derived graphite (CDG) was used as carbon source instead of conventional natural graphite flakes and MnSO4 produced from the modified Hummers was in situ transformed into Mn3O4 by precipitation in air. After reduction with hydrazine, the reduced coal-derived graphene oxide/Mn3O4 (RCDGO/Mn3O4) was obtained and employed as the electrode material for the supercapacitors. In addition, K2SO4 produced from the modified Hummers was used as electrolyte, as a result, residual-free was achieved during the whole process, and the atom utilization was calculated as high as about 97%. A maximum specific capacitance of 260Fg−1 was achieved for RCDGO/Mn3O4 composite with 86% Mn3O4 in saturated K2SO4 electrolyte solution based on the synergetic effects between coal-derived graphene and attached Mn3O4 nanoparticles. Its specific energy density reached 8.7Whkg−1 at a current density of 50mAg−1 when used as a symmetrical supercapacitor. The good capacitance retention (92–94%) was also observed after 1000 continuous cycles of galvanostatic charge–discharge.

A Versatile Preparation of Highly Active ZIF-Based Non-PGM Catalysts through Solid State Synthesis

Current proton exchange membrane fuel cell uses precious metal such as platinum as the catalyst to promote electrochemical reactions at both electrodes, which presents a significant cost barrier for large scale fuel cell commercialization. To replace precious metal with other low cost, earth-abundant materials represents a critical yet incredible challenging area in future fuel cell research. To compete with the precious metal based catalyst, the non-platinum group metal (non-PGM) materials must have higher active site density and improved turn-over-frequency. In this report, we discuss a new method of preparing “support-free”, low-cost non-PGM catalysts produced by using “one-pot” synthesized metal-organic frameworks. The new approach led to the formation of catalysts with high-density of active site and high efficiency towards the oxygen reduction reaction in the acidic medium, measured by rotating disk electrode in oxygen saturated electrolyte and under single fuel cell operating condition.

Electrochemical and Physical Characterization of Ru Activated Carbon Supported Electrodes in Alkaline Solution

Polymer electrolyte fuel cells (PEMFC) are promising energy sources for stationary and portable fuel cell applications [1-3]. However, the slow oxygen reduction reaction (ORR) on different catalysts is one of the most limiting factors in the energy conversion efficiency of PEMFC. Improved cathode catalysts could have a dramatic impact on the fuel cell efficiency. Therefore platinum-ruthenium and other alloys deposited onto various carbon supports have been studied to find materials with higher ORR activity [2, 4-6].The following work examines the impact of ruthenium nanoparticles (20 wt%), deposited onto various carbon supports prepared from α-WC and Vulcan, on ORR kinetics in 0.1 M KOH aqueous solution. Experiments show that there is an important contribution of the nanoparticles to the electroreduction process of O2. Scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), high resolution transmission electron microscopy (HRTEM) and low temperature N2 adsorption experiments were carried out to characterize the structure of the prepared materials.EDX studies show that Ru nanoclusters have been deposited into/onto carbon support quite uniformly. A comparison of the N2 adsorption data (table) and SEM images show that ruthenium forms mesoporous clusters on the surface of the supporting material (figure). SEM images show also that small ruthenium nanoparticles were uniformly observed on the support material, which means that deposition doesn’t take place quite homogenously.Electrochemical measurements were carried out in a three-electrode electrochemical cell. Electrochemical characteristics for various Ru-modified micromesoporous carbons have been established by cyclic voltammetry (CV) and rotating disc electrode (RDE) methods. RDE data were measured at rotation rates from 0 to 3000 rpm (v=10 mV∙s-1) and in the region of potentials from +0.17 to -0.50 V vs. Hg|HgO|0.1 M KOH. CVs were measured at potential scan rates (v mV/s) 5, 10, 20, 30, 50, 70, 100, 150 and 200, in both Ar and O2 saturated solutions. The solutions were saturated with Ar or O2, respectively, between measuring of each voltammogram. A glassy carbon disk electrode (GCDE) was used as a catalyst support for electrochemical measurements. Catalyst ink was prepared by suspending the catalyst powders in isopropanol, Milli-Q+ water and Nafion dispersion solution (Aldrich) mixture (5 wt%) and pipetted onto GCDE.It was established that the ORR activity for 20%Ru-C(WC) is higher but comparable to 20%Ru-Vulcan. Ru-metal loadings play a dominant role in the kinetics of the ORR on both electrodes in alkaline solution. After correction for Ar saturated supporting electrolyte current densities, very nice diffusion current plateaus have been observed at E < -0.28 V vs. Hg|HgO|0.1 M KOH for 20%Ru-C(WC) and 20%Ru-Vulcan systems. CV data demonstrate that 20%Ru-C(WC) exhibits higher capacitance values than 20%Ru-Vulcan, which is in a good agreement with N2 adsorption data. Acknowledgements: This work was supported by the Estonian target research project SF0180002s08, the Estonian Centre of Excellence in Science Project TK117T "High-technology Materials for Sustainable Development", the Estonian Energy Technology Program project SLOKT10209T, the Materials Technology project SLOKT12180T.

Good discharge capacities of NaV6O15 material for an aqueous rechargeable lithium battery

NaV6O15 anode materials are prepared by the hydrothermal method and the precursor calcinations. The phase structure and the morphology of as-synthesized materials are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The cyclic voltammogram curves of NaV6O15 electrodes in the saturated LiNO3 electrolyte show that there exist three redox couples, which is in accordance with the charge-discharge voltage-capacity curves. The electrochemical cycle behaviors of LiMn2O4//NaV6O15 aqueous rechargeable lithium battery (ARLB) at the current densities of 50, 100, 200, 500, 800 and 1000mAg−1 indicate that this ARLB has larger discharge capacity and better cycle ability at higher current density than that at lower current density, which is much more different from those in the traditional lithium ion battery. Most notably, this abnormal electrochemical phenomenon is very crucial in the applications of the large-scale power source and the energy storage devices.

Study of the Reaction Mechanism of Aqueous Li-O2 Batteries

Li-O2 battery is one of the most expected electrochemical energy storage systems beyond lithium ion batteries, because of its high theoretical energy density. Most of the groups are working on the non-aqueous Li-O2 battery system whose discharge reaction is described in the equation (1).2Li+ + O2 + 2e ➔ Li2O2 (1)Even though recent studies proved that the reversibility of the reaction, there still remains a lot of fundamental problems before the development of a practical Li-O2 battery. Especially the overpotential of the air electrode during the charging process is an essential problem considering the energy efficiency of the battery system, hence a lot of research groups have been focusing on finding a new catalyst to reduce the overpotential. Besides these studies for the non-aqueous system, our group has been focusing on an aqueous Li-O2 battery system based on the reaction (2), because overpotential of the charge-discharge reaction is much lower than that of the non-aqueous one. 4Li ++ O2 + 2H2O + 4e ➔ 4LiOH (2)Since the reaction is well known as the cathode reaction of alkaline fuel cell, the detail of the reaction mechanism of aqueous Li-O2 battery has never been investigated recently. Previously we reported that the discharging product remaining at the surface of the air-electrode was NOT LiOH but Li2O2. We suspect that the saturated electrolyte solution hindered the hydrolysis of the Li2O2 formed during the discharging process resulting in the stabilization of the Li2O2 even in the aqueous electrolyte solution. In the present study we performed further investigation for the reaction mechanism of the aqueous Li-O2 battery, using various analytical tools such as XRD, SEM-EDX, FTIR and so forth. The electrochemical studies were carried out using a three-electrode cell consists of a gas-diffusion electrode as a working electrode, a Ag/AgCl reference electrode and a Pt/Pt-black counter electrode. The gas-diffusion electrode was prepared by mixing carbon black and PTFE powder and layered with a carbon paper. The electrolyte solution was 10 LiCl and saturated LiOH aqueous solution. The electrochemical tests were performed under pure O2. SEM images for an air-electrode after the discharging process showed flake-like deposits suggesting the formation of crystalline Li2O2. The deposits were mostly disappeared after the charging process. Furthermore, an XRD pattern for a charged electrode also showed that the Li2O2 completely disappeared after the charging process. However some side-reactions could have been taken place during the charging process, because small diffraction peaks corresponding to LiOH·H2O and Li2CO3 were observed. The possible side reactions for these products could be 1. a hydrolysis of Li2O2 for LiOH·H2O and 2. a decomposition of carbon electrode. In addition, the electrode potential observed in the charging-discharging test indicated that the actual electrochemical reaction is not based on oxygen-water couple but on oxygen-peroxide couple. Detailed discussions concerning the reaction mechanism will be held in the meeting.

Studies on polymer nanofibre membranes with optimized core–shell structure as outstanding performance skeleton materials in gel polymer electrolytes

The polyporous polymer nanofibre membranes with optimized core (polyacrylonitrile, PAN)-shell (polymethylmethacrylate, PMMA) structure are prepared by coaxial electrospinning, and then converted to gel polymer electrolytes (GPEs) after the activation process of stacked nanofibre membranes in liquid electrolyte. Based on the proper collocation of polymer materials, the desirable microstructure of polymer membranes as well as the affinity between fibre shell and the electrode/electrolyte result in a high saturated electrolyte uptake and conservation rate. The electrochemical testing results of the GPEs indicate high ionic conductivities, good electrochemical stability and appropriate lithium-ion transference numbers, which are realized through choosing optimal core–shell flow rate ratio. Furthermore, the interface impedance performance of the GPEs shows good stability and compatibility with lithium electrode, which is beneficial for long-term storage and use of the lithium-ion battery. The Li/GPE/LiCoO2 cells with GPEs based on the electrospun membranes with optimized core–shell structure present excellent cycle performance compared to the cell involved with GPEs based on PAN and commercial Celgard 2500. Thus, the polymer membranes consisting of nanofibres with well-designed core–shell structure can be used as a new type of skeleton material in GPEs used in lithium-ion batteries.

Determination of the Electrochemically Active Surface Area of Metal-Oxide Supported Platinum Catalyst

The electrochemically active surface area (ECSA) of metal-oxide supported platinum catalysts as obtained from hydrogen underpotential deposition (Hupd) and from carbon monoxide stripping experiments was investigated. It was demonstrated that both methods fail to give meaningful values of the ECSA if they are performed in the conventional way as known for pure Pt and carbon supported Pt catalysts, respectively. For both methods, the reason for this failure is the lack of a correct baseline for the integration of the associated charges. It was found that the cyclic voltammogram recorded in CO saturated electrolyte gives an improved baseline for the Hupd analysis. For CO stripping, a novel baseline method was developed by performing a “CO stripping simulation” (COSS) experiment in CO-free electrolyte. The first cycle of this COSS-experiment is an improved baseline for the integration of the CO stripping peak, since possible support reduction/oxidation currents can be accounted for. With these modifications, Hupd and CO stripping voltammetry can be used for metal-oxide supported platinum to yield true, reproducible and consistent values for the ECSA.

New Approach to High-Efficiency Non-PGM Catalysts Using Rationally Designed Porous Organic Polymers

To replace the current Pt/C catalyst with low- or non-PGM materials represents a critical technology challenge for commercialization of the proton exchange membrane fuel cell. To compete with the precious metal based catalyst, the non-PGM material must have higher active site density and improved turn-over-frequency. In this report, we discuss a new method of preparing “support-free” non-PGM catalysts produced by using the transition metal decorated porous organic polymers as precursors. The new approach has led to formation of catalysts with high efficiency towards the oxygen reduction reaction, tested in the oxygen saturated acidic electrolyte and under actual fuel cell operating condition.

Nitrogen-Doped Activated Graphene Supported Platinum Electrocatalyst for Oxygen Reduction Reaction in PEM Fuel Cells

Highly active and durable platinum catalyst was successfully synthesized employing nitrogen-doped activated graphene as a catalyst support material. The physical characterization using XRD and TEM indicates the presence of nitrogen-doping on graphene leads to uniform distribution of Pt nanoparticles and effective formation of active sites exposed for reaction. The electrocatalytic activity for oxygen reduction reaction of Pt/N-AG catalyst was confirmed by half-cell measurement, Accelerated durability test (ADT) was also conducted to investigate the durability of the catalyst by running the half-cell test for 1000 cycles in N2 saturated electrolyte. The catalyst demonstrates superior electrocatalyst activity and durability over Pt/XC72 catalyst for ORR under the studied conditions, rendering graphene as an ideal replacement to traditional nanostructured carbon support materials.