Anodic Half-cell Research Articles

Implementation of concurrent electrolytic generation of two homogeneous mediators under widened potential conditions to facilitate removal of air-pollutants

Electro-scrubbing is being developed as a futuristic technology for the removal of air-pollutants. To date, only one homogeneous mediator for the removal of air pollutants has been generated in each experiment using a divided electrolytic flow cell in an acidic medium. This paper reports the concurrent generation of two homogenous mediators, one at the anodic half-cell containing an acidic solution and the other at the cathodic half-cell containing a basic solution. The concept was inspired by the change in pH that occurs during water electrolysis in a divided cell. A 10 M KOH electrolyte medium assisted in the electrochemical generation of low valent 14% Co1+ ([CoI(CN)5]4−) mediator formed from reduction of [CoII(CN)5]3− which was accompanied by a change in the solution 'oxidation reduction potential' (ORP) of −1.05 V Simultaneously, 41% of Co3+ was generated from oxidation of CoIISO4 in the anodic half-cell. No change in the solution ORP was observed at the cathodic half-cell when both half-cells contain 5 M H2SO4, and Co3+ was formed in the anodic half-cell. An electro-scrubbing approach based on the above principles was developed and tested on gaseous-pollutants, CH3CHO and CCl4, by Co3+ and Co1+, respectively, with 90 and 96% removal achieved, respectively.

Pyrite oxidation in the presence of hematite and alumina: II. Effects on the cathodic and anodic half-cell reactions.

The oxidative dissolution of pyrite is an important process in the redox recycling of iron (Fe) and is well-known for its role in the formation of acid mine drainage (AMD), which is considered as the most serious and widespread problem after the closure of mines and mineral processing operations. Because this process requires the movement of electrons, common metal oxides in nature that have either semiconducting (e.g., hematite) or insulating (e.g., alumina) properties may have strong effects on it. In this study, changes in the electrochemical behavior of pyrite in the presence of hematite and alumina were investigated. Results showed that the formation of surface-bound species directly influenced the anodic and cathodic half-cell reactions as well as the transfer of electrons between these sites. Pyrite pretreated in the air became anodically more reactive than that pretreated in oxygenated water, but the type of oxidizing media had little effect on the cathodic half-cell reaction. The presence of hematite and alumina during pretreatment also had strong effects on the electrochemical properties of pyrite. Chronoamperometry measurements suggest that hematite and alumina enhanced the anodic half-cell reaction but suppressed the cathodic half-cell reaction of pyrite oxidation. Increased anodic half-cell reaction in the presence of hematite could be attributed to electron "bridging" and catalytic effects of this mineral. In contrast, the effects of alumina on the anodic half-cell reaction were indirect and could be explained by the formation of Fe3+-oxyhydroxide surface species during pretreatment. Suppression of the cathodic half-cell reaction by both minerals was attributed to their "protective" effect on cathodic sites. Our results also point to the cathodic half-cell reaction as the rate determining-step of the overall oxidative dissolution process.

Modified Metal Organic Frameworks (MOFs)/Ionic Liquid Matrices for Efficient Charge Storage

In this study, an ionic liquid incorporated modified MOF was synthesized to serve as an efficient electrolyte system for Li-ion batteries. Further, the MOF (IL) was doped with a lithium salt, lithium bis(triflouromethylsulfonyl) imide (LiTFSI) by a modified procedure. Samples with varying amount of MOF (IL) in ionic liquid were prepared, characterized and evaluated for their electrochemical behavior. A high conductivity in order of 10−2–10−3 Scm−1 at 51°C and a low activation energy of ion transport was observed in all samples. The systems showed high electrochemical stability to be employed as gel electrolyte in Li ion secondary batteries. These systems showed highly reversible capacity of over 3000 mAhg−1 in the charge-discharge studies carried out after fabricating anodic half-cell composed of Si/electrolyte/Li. These results illustrate the feasibility of the prepared modified MOF (IL) as potential solid state electrolytes for Li ion secondary batteries.

Yttria-stabilized zirconia thin film electrolyte deposited by EB-PVD on porous anode support for SOFC applications

Electron beam physical vapor deposition (EB-PVD) has been used to deposit thin film (YSZ) electrolytes on NiO-YSZ composite substrates pre-sintered at 1100°C, followed by further sintering at 1400°C in order to achieve dense films. Surface morphology of deposited layers has been investigated by AFM and FE-SEM. Increasing the deposition time and YSZ films thickness results in higher roughness and mean particle size of the thin film layer. FE-SEM observations of fresh fractured anodic half cells confirmed dense, crack-free, homogeneous and intensely adhered YSZ electrolyte layers. Sintering behavior of NiO and YSZ grains has been also investigated by the micrographs of cross sections of NiO-YSZ substrates.

Bian Based Copolymer As Binder Material for Graphite Anode in Lithium Ion Batteries

Lithium-ion batteries (LIBs) employing graphite carbon anodes are widely used in consumer electronics and hence over the past few years, intense research has been pursued to develop different components of LIBs. However relatively less focus have been dedicated towards development of efficient binder materials. Over the years, poly(vinylidene) fluoride (PVDF) has been the primary choice as binder in electrodes of LIBs, owing to its good electrochemical, chemical and thermal stability, acceptable adhesion to the electrode materials and current collector, and ability to absorb electrolytes. However the prime disadvantage of PVDF is that it fails to maintain a conducting linkage between the active material and the conductive additive, owing to its inherent non-conducting nature. This particular drawback is further magnified upon continuous Li insertion/de-insertion, ultimately leading to increased cell resistance[1]. The coating of conjugated polymers helps mitigating the low intrinsic electronic conductivity, builds up effective paths for electronic transport and Li ion diffusion [2][3]. Recently Liu et.al reported a conjugated polymeric binder material for silicon based anodes in LIBs. However, no such strategized effort has been put for performance enhancement of graphite anodes. Hence in this work, we put effort to develop a new class of polymeric binder material to enhance the performance of graphite anodes, addressing it from two perspectives. i. To use the polymeric binder as a part of the active material. ii. To obtain improved conductivity by exploiting the presence of inherent conjugation and redox active groups in the polymeric binder material. In this regard, compounds of the family bis(aryl)acenaphthenequinonediimine (Ar-BIAN), which have long been employed as ligands for transition metals, were considered. The rich redox chemistry of Ar-BIAN based compounds have been evaluated. Ar-BIAN based compounds are characterised by high chemical stability and have wide scope for functionalisation owing to the availability of suitable precursors. But no reports exist on application of Ar-BIAN based polymers, drawing upon their redox chemistry in energy storage devices. In an effort to capitalise on these unexplored but potential properties of these group of polymers, we utilise them as polymeric binder materials for LIBs both independently and in combination with PVDF to see their feasibility as part of active material in graphite anodes. Ar-BIAN-Dioctylfluorene (BIAN-Flu) copolymers were synthesised via Sonogashira coupling and characterised (IR, NMR, UV, GPC, MS, CV). A series of graphite/BIAN-Flu polymer composites were prepared and electrode fabrication was achieved by doctor blading the composite on copper foil. Charge discharge (C/D) behaviour of the prepared polymer as a binder as well as an active material was evaluated in an anodic half-cell at 0.05C with 0.1M LiTFSI/EC:DEC as electrolyte. The electrode reaction kinetics was also evaluated by dynamic electrochemical impedance spectroscopy (DEIS) confirming efficient Li intercalation and de-intercalation. Studies were performed with different weight percent of the polymeric additive to optimise the amount of the polymeric additive to be taken in electrode fabrication. Long term cycling studies were also undertaken with 0.025C charging and 0.05C discharging to evaluate the effect of cycling. The C/D studies indicate that the polymeric active material significantly enhanced the capacity of the anodic half cells compared to only PVDF as the binder. This can be attributed to the inherent redox activity in the polymeric active material which also contains binding sites for Li ion. The reversible capacity increased from 180 mAhg-1 (in case of only PVDF as binder) to 225 mAhg-1 (in case of the polymeric active material). Additionally, the high columbic efficiency of 99% demonstrates the supporting role of the polymeric additive material in maintaining the reversibility of the C/D process. The polymeric material thus serves two important roles, i. Enhances the capacity because of the ability to reversibly bind to Li ion. ii. Enhances the overall C/D process of the half-cell because of its inherent redox activity, reflected in relatively low over-potential in the C/D profiles and reduced cell impedance as exhibited in the DEIS studies.

Ionic Liquid/Borane Binary Electrolyte with Remarkably High Lithium Transference Number

Design of organoboron electrolytes has been a fruitful method to improve ion conductive properties of various electrolyte matrices [1-7]. Due to boron-anion interaction, either enhanced lithium transference number or improved dissociation degree of lithium salt was observed depending on the strength of boron-anion interaction. In order to enhance lithium transference number of ionic liquid based electrolytes, various organoboron molten salts in which organoboron unit and ionic liquid structure were covalently tethered were reported [6-7]. Such molecular designs were carried out because most ionic liquids were not miscible with typical tricoordinate boron compounds such as trimethoxyborane. Very recently, we have systematically studied miscibility of various ionic liquids (1) with boron compounds (2 and 3), and it was found that some types of ionic liquids are miscible with mesityldimethoxyborane [Mes(OMe)2] (3). Although immediate phase separation was observed under most combinations of IL/boron compounds, homogeneous solution was readily obtained by mixing ionic liquids (imidazolium TFSI based ILs and some other types) with mesityldimethoxyborane. After mixing, the resulting homogeneous solution showed significantly lower viscosity in comparison with those for ionic liquids themselves. Further, 1:1 volume mixtures of ionic liquids/boron compounds showed high lithium transference number of over 0.5 at ambient temperature. The properties of 1:2 volume mixtures (IL: B) were also studied, and these mixtures showed both higher ionic conductivity and lithium transference number at the same time. For instance, lithium transference number for AMImTFSI /Mes(OM2)2 = 1/2(v/v) reached 0.86, which was extraordinary high as liquid electrolyte (Figure 1). However, further increase in boron content did not result in higher lithium transference number possibly due to unselective motions of ions under very low viscosity of electrolyte. In spite of restricted carrrier ion number under very high lithium transference number, binary electrolytes retained high ionic conductivity of around 10-3 Scm-1 at 51oC. These binary electrolytes also showed relatively wide electrochemical window (from 4 to 5 V). Moreover, successful charge-discharge profiles were obtained after fabricating anordic half cells with moderate coulobmic efficiency. In conclusion, we developed facile methodology to obtain highly conductive IL/boron binary electrolyte with remarkably high lithium transference number. As far as we know, all the organoboron molten salts reported so far was solid at room temperature. The obtained liquid binary solutions exhibited far better ionic conductivity and lithium transference number at the same time than those for previously reported organoboron molten salts. Furthermore, their moderate potential window (from 4 to 5 V) allowed stable charge-discharge behavior of anodic half cell fabricated using these electrolytes.1) Joshi, P.; Vedarajan, R.; Matsumi, N. Chem. Commun. 2015, 51, 15035-15038. 2) Smaran, K. S.; Joshi, P.; Vedarajan, R.; Matsumi, N. ChemElectroChem, 2015, 2 (12), 1913-1916. 3) Smaran, K. S.; Vedarajan, R.; Matsumi, N. Int. J. Hydrogen Energy, 2014, 39, 2936-2942. 4) Matsumi, N.; Toyota, T.; Prerna, J.; Puhup, P.; Vedarajan, R.; Takekawa, T. Int. J. Mol. Sci. 2014, 15, 21080-21089. 5) Matsumi, N.; Kagata, A.; Aoi, K. J. Power Sources, 2010, 195, 6182-6186. 6) Matsumi, N.; Sugai, K.; Miyake, M.; Ohno, H. Macromolecules 2006, 39, 6924-6927. 7) Matsumi, N.; Miyake, M.; Ohno, H. Chem. Commun. 2004, 2852-2853. Figure 1

Metal Organic Frameworks/Ionic Liquid Composites As Electrolytes for Li-Ion Batteries

Metal Organic Frameworks (MOFs), as a novel class of crystalline porous material have gained great attention in the fields of gas storage, separation, drug delivery, catalysis, sensors and so forth. The supramolecular design of MOFs allow a number of organic ligands, with two or more functional groups, to be linked to metal ion coordination centers giving myriad variations and tunable properties in synthesized structures. Metal Organic Frameworks (MOFs) are of great interest due to several unique features and their applications have been extended to the field of Li-ion batteries. Simultaneously, ionic liquids (ILs) are becoming popular in a range of areas including biphasic reaction catalysis, electromechanical actuator membranes and diluents and separation membranes. Many studies have been conducted for the application of MOFs in energy storage devices [1]-[3], but scarcely any investigation was performed to understand the effect of ionic liquid incorporated MOFs in electrochemical storage devices especially batteries. Hence, an attempt has been made by our group with ionic liquid incorporated modified MOFs to serve as a better electrolyte system for Li-ion batteries with increased thermal and electrochemical stability, high ionic conductivity and other electrochemical aspects. Further, dimensionally and morphologically controlled MOFs will be carefully used to ease the ion transport in the electrolyte system by the regulation of ion conductive path. MOF-1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (AMImTFSI), synthesized by a facile in-situ electrochemical method [4] was doped with a lithium salt, lithium bis (triflouromethylsulfonyl) imide (LiTFSI) by a modified procedure for electrochemical measurements. Morphological features and crystal size of these matrices were evaluated by TEM (Transmission Electron Microscopy) and XRD measurements. Temperature dependence of ionic conductivity of the MOF/ionic liquid matrix was studied by AC-impedance method. Combination of AC-impedance and DC-polarization method was used to determine the lithium ion transference number of the samples. Electrochemical window of different electrolyte compositions was studied by linear sweep voltammetry. A coin cell was fabricated to study the charge discharge characteristics of the resulting cell. Synthesis of MOF-5/ionic liquid matrix by electrochemical method - MOF was successfully synthesized by a mild in-situ electrochemical method using 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (AMImTFSI) as a templating agent employing a modified procedure of reported method [4]. Synthesis of the MOF (AMImTFSI) was achieved by a constant dissolution of Zn2+ ion from Zn anode. The dissolution was carried out by applying a constant direct current (DC) of 0.15A. A titanium electrode was employed as cathode. The electrolyte used in this procedure was a solution containing 0.07 M terephthalic acid and 0.04 M zinc nitrate hexahydrate in DMF. The electrochemical galvanostatic procedure was carried out for 3hrs. A white powder formed during the above mentioned procedure, was filtered and washed with DMF first and then, with chloroform. The sample was then dried in oven at 80 oC to get pure MOF (IL). For further electrochemical analysis, MOF (IL) was doped with lithium salt, LiTFSI. A set of samples were synthesized with varying content of MOF (IL) in ionic liquid system and ionic conductivity was measured by AC-impedance method. Three samples with different weight % of MOF (IL) in AMImTFSI were prepared and temperature dependent ionic conductivity measurements were performed by AC impedance method. All the samples showed linear profiles in Arrhenius plots. As expected the ionic conductivity decreased with increase in wt% of MOF (IL) because of change in state from liquid to gel. Interestingly a decrease in activation energy of ion transport was observed. The ionic conductivities of the samples were calculated by the Vogel-Fulcher-Tammann (VFT) equation, resulting out to be highest for the sample with 10 wt% of MOF (IL) in AMImTFSI i.e. 1.0 x 10-2 Scm-1 at 51 oC . The highest tLi + of 0.31 was observed for 20 wt% MOF (IL) in AMImTFSI. The systems showed a potential window of 5.22-5.55 V. Charge discharge studies were also carried out after fabricating a coin anodic half-cell composed of Si/electrolyte/Li which showed 90% coulombic efficiency in the presence of 30 mL of EC: DC=1:1 in electrolyte. Conclusion Modified MOF with ionic liquid framework was prepared in ionic liquid system by electrochemical method. Measurements of temperature dependence of ionic conductivity using AC impedance showed relatively high ionic conductivity. These encouraging results affirm the prepared modified MOF (IL) to be a prospective electrolyte in energy storage devices.

(Invited) Bioinspired Water Oxidation and CO2 Reduction Electrocatalysts

Water splitting is regarded as a promising step towards environmentally sustainable energy schemes because electrolysis produces only hydrogen and oxygen, without any by-products. Within the overall water splitting process, the oxygen evolution reaction (OER), an anodic half-cell reaction that generates an oxygen molecule from two water molecules, requires extremely high overpotential due to its slow reaction kinetics. In this regard, development of cost-effective and robust catalyst has been demanding challenge to solve the modern energy crisis. In nature, there exists a water oxidation complex (WOC) in photosystem II (PSII) comprised of the earth-abundant elements Mn and Ca. The WOC in PSII, in the form of a cubical Mn4CaO5 cluster, efficiently catalyzes water oxidation under neutral conditions with extremely low overpotential value (~160 mV) and a high turnover frequency (TOF) number (~25,000 mmolO2 mol-1 Mn s-1). Inspired from the asymmetric geometry and flexible ligation of the biological CaMn4O5 cluster, we designed new manganese based water oxidation catalysts, Mn3(PO4)2-3H2O and Li2MnP2O7.We first identified a new crystal structure, Mn3(PO4)2-3H2O, and demonstrated its superior catalytic performance at neutral pH. From the combined ex-situ spectroscopic analysis and DFT calculations, we revealed that structural flexibility can stabilize Jahn-Teller distorted Mn(III), and thus facilitate Mn(II) oxidation during catalytic cycle. We also studied a new pyrophosphate based Mn compound, Li2MnP2O7 for water oxidation catalysis. We verified the influence of oxidation state of Mn and asymmetric Mn geometry on water oxidation catalysis using Li2MnP2O7 and its derivatives. We believe higher Mn(III) portion and asymmetric arrangement of Mn atoms which can be seen in the WOC, enhance catalytic water oxidation reaction. Specific questions that our group intensively focus for the further applications include 1) how we can translate the underlying principles in Manganese Calcium Clusters into the synthetic heterogeneous catalysts and 2) how we can mimic the redox molecule involved biological dark reaction for the CO2 reduction. Toward this vision, we have been developing a new catalytic platform based on sub-10 nm uniform nanoparticles to bridge the gap between atomically defined biological catalysts or their metalloenzyme counterparts and the scalable, electrode depositable heterogeneous catalysts. In this approach, the local atomic geometry is controlled by the nitrogen containing graphitic carbon and the heterogeneous atom doping, that enhance the catalytic activity and selectivity. Additional surface modification by the specific ligand allow for the atomic scale tunability to realize the unique electronic hybridization.

A completely spray-coated membrane electrode assembly

We present a proton exchange membrane fuel cell (PEMFC) manufacturing route, in which a thin layer of polymer electrolyte solution is spray-coated on top of gas diffusion electrodes (GDEs) to work as a proton exchange membrane. Without the need for a pre-made membrane foil, this allows inexpensive, fast, large-scale fabrication of membrane-electrode assemblies (MEAs), with a spray-coater comprising the sole manufacturing device. In this work, a catalyst layer and a membrane layer are consecutively sprayed onto a fibrous gas diffusion layer with applied microporous layer as substrate. A fuel cell is then assembled by stacking anode and cathode half-cells with the membrane layers facing each other. The resultant fuel cell with a low catalyst loading of 0.1mgPt/cm2 on each anode and cathode side is tested with pure H2 and O2 supply at 80°C cell temperature and 92% relative humidity at atmospheric pressure. The obtained peak power density is 1.29W/cm2 at a current density of 3.25A/cm2. By comparison, a lower peak power density of 0.93W/cm2 at 2.2A/cm2 is found for a Nafion NR211 catalyst coated membrane (CCM) reference, although equally thick membrane layers (approx. 25μm), and identical catalyst layers and gas diffusion media were used. The superior performance of the fuel cell with spray-coated membrane can be explained by a decreased low frequency (mass transport) resistance, especially at high current densities, as determined by electrochemical impedance spectroscopy.

Similarities Between the Cathode and Anode Solid Electrolyte Interphase As Determined By MALDI-MS and DESI-MS

The formation of the solid electrolyte interphase (SEI) on the surface of lithium-ion battery cathodes and anodes was studied with the help of two different mass spectroscopic techniques: matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and desorption electrospray ionization mass spectrometry (DESI-MS). MALDI-MS was used to study the formation of polymeric surface films on both model anode and cathode materials, namely thin films of Au and LiMn2O4, respectively. Thin films are useful model electrodes for MALDI-MS experiments to prevent the signal from polymers utilized as binders in commercial battery electrodes from obscuring signal from the SEI. Control experiments consisting of uncycled cells containing PF6 - electrolytes detected the presence of high mass oligomers associated1 with the formation of oligomeric structures, which means that LiPF6 electrolytes are unsuitable for MALDI-MS. Thus, the electrolyte systems chosen for MALDI-TOF experiments consist of propylene carbonate (PC) and ethylene carbonate (EC)/dimethyl carbonate (DMC) 1:1 mixtures with LiClO4 ­salts. The mass spectra obtained from both the Au anodes and the LiMn2O4 cathodes showed remarkable similarity, as seen in panel c. The composition of the electrolyte, however, has a large effect on the SEI composition. An average peak spacing of ~175 m/z was observed for the EC/DMC system (panel b), which corresponds with a polycarbonate structure formed by the co-polymerization of EC and DMC. In the case of the PC based electrolyte, a different polycarbonate with an average peak spacing of 167 m/z was observed in the mass spectra (panel a). Both polymers have been reported in the past and DFT calculations suggest a formation mechanism in which carbonate rings open at low voltages forming a reactive radical that induces polymerization of the other solvent molecules.1Lastly, different electrodes materials were studied at cathode potentials (Au, Pt, LMO and Au coated LMO), but no effect was observed on the final structure of the SEI. In order to further study the organic SEI formed on cathode/electrolyte systems which more closely resemble commercial lithium-ion battery systems, DESI-MS was introduced as a powerful alternative to MALDI-MS, since it does not present the limitations discussed in the previous part of this work. It was found that it is possible to obtain high quality, high resolution polymeric mass spectra directly from the surface of slurry electrodes cycled in EC\\DMC\\LiPF6. The presence of poly(ethylene glycol) dimethyl ether (PEG) as a product of the copolymerization of EC and DMC was observed using this method. The presence of PEG in the SEI was confirmed for both anodic and cathodic half-cells, similarly to the results obtained by MALDI-MS. The interesting similarity in the composition of the SEI at completely different environments and potential ranges (cathode and anode) suggests that the oligomerization of the organic electrolyte is not sensitive to the electric potential applied to the electrode surface. We also carried out investigations of polymerization mechanisms of the solvent molecules using density functional methods. All calculation of energies, forces and force constants were performed using the B3LYP hybrid-density functional method with the cc-pVDZ basis set as implemented in the Gaussian 09 code. Equilibrium and transition state structures were determined for formation of dimers and trimers resulting from reaction of the oxidized EC molecule and solvent molecules. The reaction energies are consistent with the observation of polymeric species. 1. Tavassol H., Butchker J.W., Ferguson G.A., Curtiss L.A., Gewirth A.A., Solvent oligomerization during SEI formation in Li-ion battery anodes, J. Electrochem. Soc. 159(6) (2012) A730-A738. Figure 1

High Performance Sulfur-Composite Cathode for Lithium-Ion Sulfur Batteries

Rapid development of portable electronics, electric transport and renewable energy demands for high performance rechargeable batteries. Conventional lithium-ion batteries with intercalation cathodes have limited energy density and expensive. Lithium sulfur (Li/S) battery is an attractive alternative due to a higher theoretical capacity and energy density of 1672 mAh g-1 and 2600 Wh kg-1, respectively [1]. Sulphur is a promising cathode because of its abundance, low-cost and environmentally friendliness as well compared with commercial transition-metal cathodes. However, practical application of Li/S batteries is hindered by several drawbacks: use of dangerous lithium-metal anode, electrical-insulating nature of sulfur causing its low utilization; solubility of lithium polysulfides formed in the electrode process leading to severe capacity fading and low coulombic efficiency. Numerous attempts have been made to overcome these disadvantages by mixing sulfur with conducting agents such as carbonaceous materials and/or conductive polymers, which allows for enhanced utilization of sulfur and capacity per unit mass of sulfur [2-3]. In this work a Sulfur/Polyacrylonitrile/Ketjen Black ternary composite electrode (S/PAN/KB) was prepared and examined as a cathode for Li-ion/S battery coupled with prelithiated graphite anode (Li-Gr) in Li-Gr | Electrolyte| S/PAN/KB cell. The partially pyrolyzed and cyclized PAN stabilizes sulfur and suppresses its dissolution into electrolyte [4]. Formation of a homogeneous hierarchical mesoporous structure in S/PAN/KB was observed by SEM, EDS mapping and XRD techniques. The cell with this composite cathode delivered a reversible discharge capacity of 600 mAh g-1 of composite (1450 mAh g−1 of S) at 0.2 C, and retained about 85% of this value over 200 cycles. Even at high cycling rates up to 1 C, the cell demonstrated a good rate capability, delivering a highly reversible discharge capacity of 750 mAh g−1, which was superior to the performance of a Li-metal anode half-cell counterpart. Using this cell, the batteries of different size were assembled (Fig. a) and tested; the battery stack exhibited stable cycling performance (Fig. b). Further details of this work will be presented at the Meeting.

Driving the Oxygen Evolution Reaction by Nonlinear Cooperativity in Bimetallic Coordination Catalysts.

Developing efficient catalysts for electrolysis, in particular for the oxygen evolution in the anodic half cell reaction, is an important challenge in energy conversion technologies. By taking inspiration from the catalytic properties of single-atom catalysts and metallo-proteins, we exploit the potential of metal-organic networks as electrocatalysts in the oxygen evolution reaction (OER). A dramatic enhancement of the catalytic activity toward the production of oxygen by nearly 2 orders of magnitude is demonstrated for novel heterobimetallic organic catalysts compared to metallo-porphyrins. Using a supramolecular approach we deliberately place single iron and cobalt atoms in either of two different coordination environments and observe a highly nonlinear increase in the catalytic activity depending on the coordination spheres of Fe and Co. Catalysis sets in at about 300 mV overpotential with high turnover frequencies that outperform other metal-organic catalysts like the prototypical hangman porphyrins.

Catalytic performance of structured packages coated with perovskite-based nanocomposite in the methane steam reforming reaction

A conventional Ni + YSZ/YSZ anode half-cell (the Research Center Jülich) and the Ni + YSZ/YSZ planar half cell washcoated by a layer of the Ru + Ni-doped perovskite-based nanocomposite (Ru + Ni/LaPrMnCr/YSZ) were compared in terms of their activities and selectivities in the steam reforming of methane. The kinetic measurements were carried out in a laboratory scale plate-type reactor, and results were interpreted using computational models. A power-law kinetic model was verified against the experimental data, and parameters were estimated. Both numerical prediction and experimental testing indicate that the nanocomposite coated Ni + YSZ/YSZ plate shows much better catalytic performance under the middle-temperature operating conditions. CFD simulations show that for the high activity of thermally conductive catalytic plates, superior heat transfer performance is observed in the lab-scale reactor. The lab-scale data were successfully up-scaled for the case of steam reforming of natural gas on a structured catalyst at realistic operation conditions. Up to 700 °C, the pilot test data obtained with the structured catalyst comprised of three stacked parallel Ni–Al plates (50 × 50 × 1 mm) coated with perovskite-based nanocomposite correlate quite good with the 1-D plug-flow reactor model predictions assuming the proposed kinetics.

Synergistic Effect of Mediated Electrochemical Reduction and Mediated Electrochemical Oxidation on NO Removal by Electro-Scrubbing

A combined MER (mediated electrochemical reduction) and MEO (mediated electrochemical oxidation) approach was examined for the first time for the efficient removal of NO by electro-scrubbing. The generation of a mediator (Ni(I) from Ni(II)(CN)42− in 9 M KOH) by electrochemical reduction was identified by the changes in the ORP value and potentiometric titration. The Ni(I) formation found to be 9% (4.3 mM) in 2 h electrolysis, which is decreased to 1.83 mM (4%) during addition of NO demonstrates NO removal occurred. The MER of NO at the cathodic half-cell by electro-scrubbing revealed the formation of NH3 and N2. The reductive removal efficiency of NO was almost 100% up to a gas flow rate of 0.25 g min−1. At the anodic half-cell, the Co(III) mediator from Co(II)SO4 in 5 M H2SO4 was generated electrochemically with concomitant conversion of NO to NO3− in the solution phase with a removal efficiency of 28%. The combination of MEO and MER with electro-scrubbing demonstrates 97% removal efficiency of NO up to 0.5 g min−1. The combined removal approach is more suitable for high concentrated NO with energy efficiency of 0.99 g/kWh compared to the individual MEO (0.221 g/kWh) and MER (0.769 g/kWh) approaches.

Degradation Behavior in Lithium Iron Phosphate Secondary Cells Under High Rate Pulsed Discharge

Three 26650 LiFePO4 (LFP) cells cycled at 15C (40 A) under a pulsed discharge (PD) profile showed an abrupt drop in their 15C recharge capacity to 0 Ahr within a 60 cycle span. EIS at 100% state of charge (SOC) shows separation in the mid-frequency semi-circle indicating rapid increase of one electrochemical component’s impedance. XAS analyses on cycled cathodes show 85% retention of active material at the bulk level and almost 100% in the surface region. XPS on PD anodes show surface films that are rich in LiF which have high impedance compared to Li2CO3 rich films. LiF rich films on the anode cause the real impedance of the anodic half-cell to increase faster than the other, slowing the charge transfer kinetics of the battery dramatically. Results indicate the bipolar PD profile increases the rate of LiF deposition on the surface of the anode compared to high rate continuous cycling.

Strength of an electrolyte supported solid oxide fuel cell

For the proper function of solid oxide fuel cells (SOFC) their structural integrity must be maintained during their whole lifetime. Any cell fracture would cause leakage and partial oxidization of the anode, leading to a reduced performance, if not catastrophic failure of the whole stack.In this study, the mechanical strength of a state of the art SOFC, developed and produced by Hexis AG/Switzerland, was investigated with respect to the influence of temperature and ageing, whilst for the anode side of the cell the strength was measured under reducing and oxidizing atmospheres.Ball-on-3-Ball bending strength tests and fractography conducted on anode and cathode half-cells revealed the underlying mechanisms, which lead to cell fracture. They were found to be different for the cathode and the anode side and that they change with temperature and ageing. Both anode and cathode sides exhibit the lowest strength at T = 850 °C, which is greatly reduced to the initial strength of the bare electrolyte. This reduction is the consequence of the formation of cracks in the electrode layer which either directly penetrate into the electrolyte (anode side) or locally increase the stress intensity level of pre-existing flaws of the electrolytes at the interface (cathode side).

All-Solid-State Lithium Secondary Battery Using Plastic Crystal As Solid Electrolyte

Introduction All-solid-state lithium ion batteries (ASS-LIBs), which consist of nonflammable solid electrolyte, are expected as high capacity and safety secondary batteries for vehicle and industrial use. Bulk-type ASS-LIBs, whose positive and negative electrodes are composed of an active material, a conductive agent, a binder and a solid electrolyte, are more desirable than film type electrode, in terms of capacity and energy density. A main issue of the bulk-type ASS-LIBs is reduction of internal resistance of the electrodes, which originated from a poor contact between the electrolyte and the active materials to form the micro void. Plastic crystalline fast ion conductors have been studied as the solid-state electrolyte for ASS-LIBs [1, 2]. As these materials readily deform above relatively low melting point, for example 1-ethyl-1-methyl pyrolidinium bis(trifluoromethylsulfonyl imide (12PyrTFSI) melt at 90 °C, it will form a favorable active material-electrolyte solid-solid interface. In this study, to reduce the internal resistance of the electrode, lithium ion conductive plastic crystals which show thermoplasticity was used as solid electrolyte. Experimental In this research, a mixture of 12PyrTFSI and lihium sulfonyl imide (LiTFSI) was used as lithium conductive plastic crystal. We developed a negative electrodes consisting of lithium titanium oxide (LTO), acetylene black, polyvinylidene fluoride, the mixture of 12PyrTFSI, LiTFSI. The negative electrode was obtained by coating the dispersion slurry containing the above mentioned materials and N-methylpyrrolidone (NMP), and thereby drying NMP solvent. Drying temperature was selected more than 71 °C that is a melting point of the mixture of 12PyrTFSI and LiTFSI [3]. The negative electrodes were structurally characterized by SEM-EDX. The anode half cell was prepared by assembling the anode on a polyethylene oxide (PEO) polymer sheet and Li foil as reference counter electrode to measure the charge and discharge property of the negative electrodes. At 50 °C, the charge and discharge were operated in the galvanostatic mode at 5.57 μA¥cm-2 (0.02C). The internal resistance of the negative electrode after charge was obtained using an impedance analyzer over a frequency range of 0.1 to 106 Hz and amplitude of 10 mV at 50 °C. The cells were cycled between 1 to 1.35 V vs. Li/Li+. Fig.1 illustrates the charge and discharge curves of the LTO negative electrode with a plastic crystal. The discharge capacity at the first cycle was 82 mA¥g-1 at 0.02 C, which is only 47 % of theoretical capacity. The cross sectional SEM images showed that the plastic crystal was not uniformly distributed in the electrode. Conceivably, the non-uniform distribution resulted in the formation of heterogeneous lithium ion conduction path over the negative electrode, deteriorating the discharge capacity. Fig. 2 shows Nyquist plots of the negative cell after first charging. The interfacial resistance between lithium metal and PEO polymer sheet and internal resistance of the negative electrode forms an arc. It shows the small resistance of the negative cell 55 Ωcm2. Evidently, partial ion conduction path comprising of 12PyrTFSI and LiTFSI contributed to the low internal resistance of the negative cell. It was concluded that the formation of the homogeneous ion conduction path was needed to increase the capacity of the negative electrode.

Self-sustainable electricity production from algae grown in a microbial fuel cell system

This paper describes the potential for algal biomass production in conjunction with wastewater treatment and power generation within a fully biotic Microbial Fuel Cell (MFC). The anaerobic biofilm in the anodic half-cell is generating current, whereas the phototrophic biofilm on the cathode is providing the oxygen for the Oxygen Reduction Reaction (ORR) and forming biomass. The MFC is producing electricity with simultaneous biomass regeneration in the cathodic half-cell, which is dependent on the nutrient value of the anodic feedstock. Growth of algal biomass in the cathode was monitored, assessed and compared against the MFC power production (charge transfer), during this process. MFC generation of electricity activated the cation crossover for the formation of biomass, which has been harvested and reused as energy source in a closed loop system. It can be concluded that the nutrient reclamation and assimilation into new biomass increases the energy efficiency. This work is presenting a simple and self-sustainable MFC operation with minimal dependency on chemicals and an energy generation system utilising waste products and maximising energy turnover through an additional biomass recovery.

Investigating the effect of thermal gradients on stress in solid oxide fuel cell anodes using combined synchrotron radiation and thermal imaging

Thermal gradients can arise within solid oxide fuel cells (SOFCs) due to start-up and shut-down, non-uniform gas distribution, fast cycling and operation under internal reforming conditions. Here, the effects of operationally relevant thermal gradients on Ni/YSZ SOFC anode half cells are investigated using combined synchrotron X-ray diffraction and thermal imaging. The combination of these techniques has identified significant deviation from linear thermal expansion behaviour in a sample exposed to a one dimensional thermal gradient. Stress gradients are identified along isothermal regions due to the presence of a proximate thermal gradient, with tensile stress deviations of up to 75 MPa being observed across the sample at a constant temperature. Significant strain is also observed due to the presence of thermal gradients when compared to work carried out at isothermal conditions.

Amorphous Soft Carbon Coated Graphite As Anode Material for Lithium Ion Battery

The natural graphite was used without a purification process and processing step that results in the folding of the graphite fragments into small spheres. It is well known that spherically shaped anode material is preferable as a means of improving the anode characteristics due to its high tapping density [1]. To reduce movement of impurities and side reaction with electrolyte impurities [2], the amorphous soft carbon was coated on the spherical graphite surface.In this study, we report the characteristics of anode which is made from the amorphous soft carbon coated natural graphite and charge-discharge behavior of half cells. The electrodes were prepared by pasting an aqueous slurry with styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC).The charge–discharge tests were performed in CR2032 coin cell. Half cells consisted of the working electrode to be studied, Li metal as the counter electrode, and Celgard 2400 separator. 1 M LiPF6in ethylene carbonate and dimethyl carbonate (1:1 by volume) was used to electrolyte. Anode half-cells were tested between 1.5 V and 5 mV at a C-rate of 0.1 C. Microstructure of the amorphous soft carbon coating layer on graphite particle was observed using TEM to examine the cycle stability. Fig. 1 shows structural stability of carbon layer after charge-discharge cycles and thickness of carbon layer was about 50nm. Fig. 2 shows the charge(Li insertion)-discharge(Li extraction) curves of the amorphous soft carbon coating sample versus non-coating sample for the first cycle, charged in CC-CV mode and discharged in CC mode. The discharge capacity obtained at carbon coated sample is about 330 mAh/g and the columbic efficiency is about 90 %.This research was financially supported by the Ministry of Trade, Industry and Energy(MOTIE) and Korea Institute for Advancement of Technology(KIAT) through the Promoting Regional specialized Industry References [1] Y. Chen, G.X. Wang, J.P. Tian, K. Konstantinov, H.K. Liu, Electrochim. Acta 50 (2004) 435–441.[2] C. Wang, X. Zhang, A.J. Appleby, X. Chen, F.E. Little, J. Power Sources 112 (2002) 98-104.