Fabrication of flexible polypyrrole/graphene oxide/manganese oxide supercapacitor

A flexible polypyrrole/graphene oxide/manganese oxide‐based supercapacitor was prepared via an electrodeposition process. The polypyrrole, graphene oxide, and manganese oxide were deposited onto a flexible and highly porous nickel foam, which acted as a current collector to enhance the electrochemical performances. The good coverage of the polypyrrole, graphene oxide, and manganese oxide onto the scaffold of the nickel foam was evidenced using field emission scanning electron microscopy and X‐ray diffraction. The manganese species, which were present in the oxidation states of Mn³⁺ and Mn⁴⁺, were shown using X‐ray photoelectron spectroscopy. The presence of Mn₂O₃ and MnO₂ polymorphs was detected using Fourier transform infrared and Raman spectroscopies. The cyclic stability of the ternary supercapacitor was consistent regardless of its geometry and curvature. In contrast, an activated carbon supercapacitor possesses limited energy storage capability compared to a ternary supercapacitor, which suppresses the electrochemical performances of activated carbon. The ternary as‐fabricated supercapacitor could retain a specific capacitance of 96.58% after 1000 cycles, and the as‐synthesized energy storage device was able to light up a light emitting diode. Copyright © 2014 John Wiley & Sons, Ltd.     

Carbon-supported manganese oxide nanocatalysts for rechargeable lithium-air batteries

Manganese oxide based catalysts were synthesised in the form of nano-particles using a redox reaction of MnSO₄ and KMnO₄, housed into the pores of a carbon matrix and followed by a thermal treatment. Particle sizes of the manganese oxide nanocatalysts were around 50 nm, based on the tunnelling electron microscope measurement. They were uniformly distributed in the carbon matrix, which contributed to an improved electrical connection among the catalyst and current collectors. The charge/discharge tests using this material as the cathode material in a rechargeable lithium-air battery showed high discharge capacities up to 4750 mAh (g carbon)⁻¹. The cycle ability of the composite electrode was superior to those of the commercial electrolytic manganese dioxide electrodes.     

Optimisation of processing and microstructural parameters of LSM cathodes to improve the electrochemical performance of anode-supported SOFCs

To improve the electrochemical performance of LSM-based anode-supported single cells, a systematic approach was taken for optimising processing and materials parameters. Four parameters were investigated in more detail: (1) the LSM/YSZ mass ratio of the cathode functional layer, (2) the grain size of LSM powder for the cathode current collector layer, (3) the thickness of the cathode functional layer and the cathode current collector layer, and (4) the influence of calcination of YSZ powder used for the cathode functional layer.Results from electrochemical measurements performed between 700 and 900 °C with H₂ (3 vol.% H₂O) as fuel gas and air as the oxidant showed that the performance was the highest using an LSM/YSZ mass ratio of 50/50. A further increase of the electrochemical performance was obtained by increasing the grain size of the outer cathode current collector layer: the highest performance was achieved with non-ground LSM powder. In addition, it was found that the thickness of the cathode functional layer and cathode current collector layer also affects the electrochemical performance, whereas no obvious detrimental effects occurred with the different qualities of YSZ powder for the cathode functional layer. The highest performance, i.e. 1.50 ± 0.05 A cm⁻² at 800 °C and 700 mV, was obtained with a cathode functional layer, characterised by an LSM/YSZ mass ratio of 50/50, a d₉₀ of the LSM powder of 1.0 μm, non-calcined YSZ powder, and a thickness of about 30 μm, and a cathode current collector layer, characterised by d₉₀ of the LSM powder of 26.0 μm (non-ground), and a thickness of 50–60 μm. Also interesting to note is that the use of non-ground LSM for the cathode current collector layer and non-calcined YSZ powder for the cathode functional layer obviously simplifies the production route of this type of fuel cell.     

Recycling manganese from spent Zn-MnO2 primary batteries

The cathode of spent Zn-MnO₂ primary batteries is made up of mainly Mn₃O₄ and α-MnO_2. Energy dispersive X-ray analysis of the cathode surface also shows the presence of zinc from the anode and chloride from the electrolyte. Manganese was recovered by precipitation, electrodeposition and anodization. X-ray diffraction measurements confirmed that the Mn₃O₄ material was recycled by chemical precipitation. The charge efficiency by electrodeposition was 85% at 25.0 mA cm⁻². In the current density range studied, the potential/current density plots follow a Tafel-like relation. In the anodic process, the material oxidizes at the electrode/solution interface and precipitates to the bottom of the cell. Only a fraction corresponding to 20% of the charge density is deposited onto the electrode. This happens because Mn²⁺ oxidizes to Mn³⁺, which then suffers disproportionation.     

Effect of structure on the storage characteristics of manganese oxide electrode materials

Eleven types of manganese-containing electrode materials were subjected to long-term storage at 55 °C in 1 M LiPF₆ ethylene carbonate/dimethyl carbonate (EC/DMC) solutions. The amount of manganese dissolution observed depended upon the sample surface area, the average Mn oxidation state, the structure, and substitution levels of the manganese oxide. In some cases, structural changes such as solvate formation were exacerbated by the high temperature storage, and contributed to capacity fading upon cycling even in the absence of significant Mn dissolution. The most stable materials appear to be Ti-substituted tunnel structures and mixed metal layered oxides with Mn in the +4 oxidation state.     

Polarization measurements on single-step co-fired solid oxide fuel cells (SOFCs)

Anode-supported planar solid oxide fuel cells (SOFC) were successfully fabricated by a single step co-firing process. The cells comprised of a Ni + yttria-stabilized zirconia (YSZ) anode, a YSZ or scandia-stabilized zirconia (ScSZ) electrolyte, a (La_0.85Ca_0.15)_0.97MnO₃ (LCM) + YSZ cathode active layer, and an LCM cathode current collector layer. The fabrication process involved tape casting of the anode, screen printing of the electrolyte and the cathode, and single step co-firing of the green-state cells in the temperature range of 1300–1330 °C for 2 h. Cells were tested in the temperature range of 700–800 °C with humidified hydrogen as fuel and air as oxidant. Cell test results and polarization modeling showed that the polarization losses were dominated by the ohmic loss associated with the electrodes and the activation polarization of the cathode, and that the ohmic loss due to the ionic resistance of the electrolyte and the activation polarization of the anode were relatively insignificant. Ohmic resistance associated with the electrode was lowered by improving the electrical contact between the electrode and the current collector. Activation polarization of the cathode was reduced by the improvement of the microstructure of the cathode active layer and lowering the cell sintering temperature. The cell performance was further improved by increasing the porosity in the anode. As a result, the maximum power density of 1.5 W cm⁻² was achieved at 800 °C with humidified hydrogen and air.     

Engineering of hybrid interfaces in organic photovoltaic devices

In this study, we engineer and investigate the interface structure and chemistry at the indium tin oxide (ITO) anode (front-side electrode) as well as at the Mg−Ag cathode (back-side electrode) in metal phthalocyanine (MePc)/C₆₀ organic solar cells (OSCs).For the front-side electrode, Zn-phthalocyaninetetraphosphonic acid (Zn-PTPA) and Sn-phthalocyanine axially substituted with tartaric acid (Sn-PTA) have been used for the surface termination of ITO coated glass substrates. Both terminations yielded OSCs with higher fill factors and open circuit voltages, thus increasing the power conversion efficiency by 33% and 67%, respectively. A possible influence of a chemisorbed Zn-PTPA on the film growth of the adjacent ZnPc absorber in the vicinity of the hybrid interface is discussed using X-ray reflectivity and near edge X-ray absorption fine structure data. Distinct effects of the Zn-PTPA and Sn-PTA terminations on the electronic properties of the ITO surface were found by X-ray photoelectron spectroscopy (XPS) measurements at the valence band edge. We demonstrate the possibility to engineer the hybrid interface without additional buffer.For the back-side electrode we report the formation of buffer-free charge carrier selective Mg−Ag cathodes, which are applied for bulk heterojunction organic absorbers consisting of copper phthalocyanine (CuPc) donor and fullerene C₆₀ acceptor materials. The chemical and structural properties of the CuPc:C₆₀/Mg−Ag interface are investigated by element depth profiling using secondary ion mass spectrometry (SIMS), grazing incidence X-ray diffraction analysis (GI-XRD) and XPS.We demonstrate that an optimum charge carrier selectivity is achieved with Mg:Ag/Ag cathode structures, where the Mg:Ag alloy layer has a composition close to that of Ag₃Mg. In addition, Mg diffusion into CuPc:C₆₀ layer is observed. As a result, an interaction between Mg and Cu²⁺ with a concurrent change in oxidation state of both metals takes place. However, no formation of MgPc is observed.The findings of this work are discussed against the background of the performance and electrical properties of the corresponding MePc/C₆₀-based organic solar cells.     

High performance of ceramic current collector fabricated at 550 °C through in-situ joining of reduced Mn1.5Co1.5O4 for metal-supported solid oxide fuel cells

A well-connected and high-porosity current collector layer fabricated at a low temperature of 550 °C is designed for metal-supported solid oxide fuel cells (SOFCs). Reduced Mn_1.5Co_1.5O₄ (MCO) powders are used as the binder through the reforming of MCO in the air atmosphere. A high conductivity phase La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) is added to keep the porous frame microstructure and decease the ohmic polarization of the current collector layer. Three current collector layers are prepared: MCO, MCO/LSCF, and LSCF. The working state of each current collector layer in planar SOFC stack is reproduced by special experimental design; the performance is tested in the range of 550–750 °C. The results show that the current collector layer for SOFC is achieved at low temperatures using the reduction-oxidation properties of MCO, and the performance is improved by adding high conductivity phase LSCF. The gas distribution at the cathode side is also simulated for designing a high performance SOFC.     

Preparation of manganese oxide with high density by decomposition of MnCO3 and its application to synthesis of LiMn2O4

Manganese oxide with high tap density was prepared by decomposition of spherical manganese carbonate, and then LiMn₂O₄ cathode materials were synthesized by solid-state reaction between the manganese oxide and lithium carbonate. Structure and properties of the samples were determined by X-ray diffraction, Brunauer–Emmer–Teller surface area analysis, scanning electron microscope and electrochemical measurements. With increase of the decomposition temperature from 350 °C to 900 °C, the tap density of the manganese oxide rises from 0.91 g cm⁻³ to 2.06 g cm⁻³. Compared with the LiMn₂O₄ cathode made from chemical manganese dioxide or electrolytic manganese dioxide, the LiMn₂O₄ made from manganese oxide of this work has a larger tap density (2.53 g cm⁻³), and better electrochemical performances with an initial discharge capacity of 117 mAh g⁻¹, a capacity retention of 93.5% at the 15th cycle and an irreversible capacity loss of 2.24% after storage at room temperature for 28 days.     

Plastic bonded electrodes for nickel-cadmium accumulators II. Basic electrochemical parameters of the nickel oxide electrode

Plastic bonded nickel oxide electrodes, prepared at normal temperature by one-stage rolling onto a current collector of steel net or perforated sheet of a mixture of active mass used in pocket-type electrodes, a conducting component and a PTFE binder, were tested in alkaline electrolyte. At current loads of 3–100 mA/cm₂ the type of conducting admixture, the current collector and its surface treatment were found to have a pronounced influence on the current carrying capability of the electrode. The electrode performance, especially at 100 mA/cm² is dependent not only on the composition of the active layer but also on the quality (or nature) - but not degree of contact between it and the current collector.     

Significant impact of the current collection material and method on the performance of Ba0.5Sr0.5Co0.8Fe0.2O3−δ electrodes in solid oxide fuel cells

The effects of the current collection material and method on the performance of SOFCs with Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) cathodes are investigated. Ag paste and LaCoO₃ (LC) oxide are studied as current collection materials, and five different current collecting techniques are attempted. Cell performances are evaluated using a current-voltage test and electrochemical impedance spectra (EIS) based on two types of anode-supported fuel cells, i.e., NiO + SDC|SDC|BSCF and NiO + YSZ|YSZ|SDC|BSCF. The cell with diluted Ag paste as the current collector exhibits the highest peak power density, nearly 16 times that of a similar cell without current collector. The electrochemical characteristics of the BSCF cathode with different current collectors are further determined by EIS at 600 °C using symmetrical cells. The cell with diluted Ag paste as the current collector displays the lowest ohmic resistance (1.4 Ω cm²) and polarization resistance (0.1 Ω cm²). Meanwhile, the surface conductivities of various current collectors are measured by a four-probe DC conductivity technique. The surface conductivity of diluted Ag paste is 2-3 orders of magnitude higher than that of LC or BSCF. The outstanding surface conductivity of silver may reduce the contact resistance at the current collector/electrode interface and, thus, contributes to better electrode performance.     

Adhesive copper films for an air-breathing polymer electrolyte fuel cell

A design for an air-breathing and passive polymer electrolyte fuel cell is presented. Such a type of fuel cell is in general promising for portable electronics. In the present design, the anode current collector is made of a thin copper foil. The foil is provided with an adhesive and conductive coating, which firstly tightens the hydrogen compartment without mask or clamping pressure, and secondly secures a good electronic contact between the anode backing and the current collector. The cathode comprises a backing, a gold-plated stainless steel mesh and a current collector cut out from a printed circuit board. Three geometries for the cathode current collector were evaluated. Single cells with an active area of 2 cm² yielded a peak power of 250–300 mW cm⁻² with air and pure H₂ in a complete passive mode except for the controlled flow of H₂. The cells’ response was investigated in steady state and transient modes.     

Composite of manganese dioxide impregnated in porous hollow carbon spheres for flexible asymmetric solid‐state supercapacitors

Compared with symmetric supercapacitors, asymmetric supercapacitors are been widely applied in energy storage devices because of delivering an impressible energy density. Herein, a simple temple strategy was used to fabricate the porous hollow carbon spheres (PHCS) with high specific surface area of 793 m² g^?1, large pore volume of 1.0 cm³ g^?1 and pore size distribution from micropores to mesopores, serving as the capacitive electrodes of asymmetric supercapacitors. Subsequently, manganese dioxide (MnO₂) was impregnated into the PHCS to form a faradic electrode with a promising performance, owing to a synergistic effect between high capacity MnO₂ and conductive PHCS. Furthermore, the flexible asymmetric solid‐state devices were constructed with PHCS anode, PHCS@MnO₂ cathode, and PVA/LiCl electrolyte, extending a voltage window up to 1.8 V. The extensive voltage window would lead to an increased energy density. In our case, the flexible asymmetric sandwich exhibit excellent electrochemical performance in terms of a high energy density capacity of 26.5 W·h kg^?1 (900 W kg^?1) and superior cycling performance (10 000 cycles). Therefore, the developed strategy provides a strategy to achieve the PHCS‐based composites for the application in the asymmetric solid‐state supercapacitors, which will enable a widely field of flexible energy storage devices.     

Improved lithium manganese oxide spinel/graphite Li-ion cells for high-power applications

The degradation mechanism of lithium manganese oxide spinel/graphite Li-ion cells using LiPF₆-based electrolyte was investigated by a Mn-dissolution approach during high-temperature storage, and by ac impedance measurement using a reference electrode-equipped cell. Through these studies, we confirmed that Mn ions were dissolved from the spinel cathode in the electrolyte and were subsequently reduced on the lithiated graphite electrode surface, due to the chemical activity of the lithiated graphite, and caused a huge increase in the charge-transfer impedance at the graphite/electrolyte interface, which consequently deteriorated cell performance. To overcome the significant degradation of the spinel/graphite Li-ion cells, we investigated a new electrolyte system using lithium bisoxalatoborate (LiBoB, LiB(C₂O₄)₂) salt not having fluorine species in its chemical structure. Superior cycling performance at elevated temperature was observed with the spinel/graphite cells using LiBoB-based electrolyte, which is attributed to the inert chemical structure of LiBoB that does not generate HF. Mn-ion leaching experiments showed that almost no Mn ions were dissolved from the spinel powder after 55 °C storage for 4 weeks. Through optimization of organic solvents for the LiBoB salt, we developed an advanced Li-ion cell chemistry that used lithium manganese oxide spinel, 0.7 M LiBoB/EC:PC:DMC (1:1:3), and graphite as the cathode, electrolyte, and anode, respectively. This cell provides excellent power characteristics, good calendar life, and improved thermal safety for hybrid electric vehicle applications.     

Problems of corrosion and other electrochemical side processes in lithium chemical power sources with non-aqueous electrolytes

The following electrochemical side processes were studied: (i) electrochemical corrosion processes in a short-circuited couple of active cathode material (FeS₂)-current-collector material (ii) electrochemical and chemical decomposition of non-aqueous electrolytes proceeding in parallel with the base electrochemical reaction in power sources with a working discharge voltage of 1.5 V. The dynamics and direction of corrosion processes in the couple of FeS₂-current collector depend on the potential difference between the active cathode substance and the current-collector material and on the overvoltage value of conjugated electrochemical processes. In the case of a starting unreduced cathode, the reduction process takes place on pyrite and the oxidation process occurs on the current collector. After a partial cathode reduction the process direction changes. The rate of decomposition of the electrolyte in the potential range of 1.5 V is determined by its composition, the conditions of its, preparation and purification, and the cathode material used as catalyst in the process of the decomposition of the electrolyte.     

Effect of LiNiO2-coated cathode on cell performance in molten carbonate fuel cells

A double-layered electrode by coating a layer of nano-sized LiNiO₂ particles on a conventional electrode was fabricated to improve the performance of the cathode of the molten carbonate fuel cell. The layer consisting of nano-sized LiNiO₂ particles has a larger surface area than that of the conventional electrode, which is a lithiated NiO cathode. Therefore, it can provide numerous reaction sites and has higher electrical conductivity than the lithiated NiO electrode. Consequently, the cell performance can be improved at lower operating temperatures (600 °C or below). The performance of the nano LiNiO₂-coated cathode was examined in various ways such as by single-cell operation and electrochemical impedance spectroscopy (EIS). The improvement in performance was demonstrated by high cell voltage of over 0.87 V at 600 °C and current density of 150 mA cm⁻². This result was better than 0.81 V generated by the uncoated cathode cell. In the EIS analysis, the nano LiNiO₂ layer coating tended to significantly decrease the charge transfer resistance and increase the mass transfer resistance but caused an overall decrease in the cathode polarization. Thus, high performance was observed at low temperatures.     

A direct carbon fuel cell with (molten carbonate)/(doped ceria) composite electrolyte

A composite electrolyte containing a Li/Na carbonate eutectic and a doped ceria phase is employed in a direct carbon fuel cell (DCFC). A four-layer pellet cell, viz. cathode current collector (silver powder), cathode (lithiated NiO/electrolyte), electrolyte and anode current collector layers (silver powder), is fabricated by a co-pressing and sintering technique. Activated carbon powder is mixed with the composite electrolyte and is retained in the anode cavity above the anode current collector. The performance of the single cell with variation of cathode gas and temperature is examined. With a suitable CO₂/O₂ ratio of the cathode gas, an operating temperature of 700 °C, a power output of 100 mW cm⁻² at a current density of 200 mA cm⁻² is obtained. A mechanism of O²⁻ and CO₃²⁻ binary ionic conduction and the anode electrochemical process is discussed.     

Electrochemical contribution of silver current collector to oxygen reduction reaction over Ba0.5Sr0.5Co0.8Fe0.2O3−δ electrode on oxygen-ionic conducting electrolyte

Nowadays, there is a doubt about the electrochemical contribution of silver current collector on the oxygen reduction reaction (ORR) over oxide electrodes in SOFCs since many reports have demonstrated that the modification of porous oxide electrodes with nano-size silver can obviously improve the electrocatalytic activity for ORR. In this study, the electrochemical contribution of silver current collector to the performance of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) electrode on Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte for ORR was specifically investigated. The active layer of BSCF electrode was found to be around 25 μm by using both silver and gold current collectors. Much better performance was demonstrated by using silver current collector, both from symmetric cell and single cell tests. However, EIS of silver on SDC electrolyte demonstrated the silver alone as electrode actually had poor performance for ORR. In addition, SEM-EDX confirmed that there was no silver diffused from the current collector layer to modify the porous BSCF electrode. Interestingly, the activation energy for oxygen reduction over BSCF electrode was reduced by applying silver current collector. We then proposed a mechanism to explain the improved electrochemical performance of BSCF electrode by considering the high activity of silver for oxygen surface diffusion.     

Towards a rechargeable alcohol biobattery

This research focused on the transition of biofuel cell technology to rechargeable biobatteries. The bioanode compartment of the biobattery consisted of NAD-dependent alcohol dehydrogenase (ADH) immobilized into a carbon composite paste with butyl-3-methylimidazolium chloride (BMIMCl) ionic liquid serving as the electrolyte. Ferrocene was added to shuttle electrons to/from the electrode surface/current collector. The bioanode catalyzed the oxidation of ethanol to acetaldehyde in discharge mode. This bioanode was coupled to a cathode that consisted of Prussian Blue in a carbon composite paste with Nafion 212 acting as the separator between the two compartments. The biobattery can be fabricated in a charged mode with ethanol and have an open circuit potential of 0.8 V in the original state prior to charging or in the discharged mode with acetaldehyde and have an open circuit potential of 0.05 V. After charging it has an open circuit potential of 1.2 V and a maximum power density of 13.0 μW cm⁻³ and a maximum current density of 35.0 μA cm⁻³, respectively. The stability and efficiency of the biobattery were studied by cycling continuously at a discharging current of 0.4 mA and the results obtained showed reasonable stability over 50 cycles. This is a new type of secondary battery inspired by the metabolic processes of the living cell, which is an effective energy conversion system.     

Enhanced hydrogen generation using a saline catholyte in a two chamber microbial electrolysis cell

High rates of hydrogen gas production were achieved in a two chamber microbial electrolysis cell (MEC) without a catholyte phosphate buffer by using a saline catholyte solution and a cathode constructed around a stainless steel mesh current collector. Using the non-buffered salt solution (68 mM NaCl) produced the highest current density of 131 ± 12 A/m³, hydrogen yield of 3.2 ± 0.3 mol H₂/mol acetate, and gas production rate of 1.6 ± 0.2 m³ H₂/m³·d, compared to MECs with catholytes externally sparged with CO₂ or containing a phosphate buffer. The salinity of the catholyte achieved a high solution conductivity, and therefore the electrode spacing did not appreciably affect performance. The coulombic efficiency with the cathode placed near the membrane separating the chambers was 83 ± 4%, similar to that obtained with the cathode placed more distant from the membrane (84 ± 4%). Using a carbon cloth cathode instead of the stainless steel mesh cathode did not significantly affect performance, with all reactor configurations producing similar performance in terms of total gas volume, COD removal, r_cat and overall energy recovery. These results show MEC performance can be improved by using a saline catholyte without pH control.