Redox Electrolyte

Solid polymer electrolytes based on chitosan NaCF3SO3 have been prepared by the solution cast technique. X-ray diffraction shows that the crystalline phase of the pure chitosan membrane has been partially disrupted. The fourier transform infrared (FTIR) results reveal the complexation between the chitosan polymer and the sodium triflate (NaTf) salt. The dielectric constant and DC conductivity follow the same trend with NaTf salt concentration. The increase in dielectric constant at different temperatures indicates an increase in DC conductivity. The ion conduction mechanism follows the Arrhenius behavior. The dependence of DC conductivity on both temperature and dielectric constant (σdc(T,ε′)=σ0e−Ea/KBT) is also demonstrated.

Electric double layer capacitors (EDLCs), also known as supercapacitors, are electrical storage components that have a higher power density and lower storage capability in comparison to batteries. In terms of energy density, EDLC performance is currently between that of batteries and conventional dielectric capacitors. One of the main advantages of capacitors is their wide temperature operating range, whereas their main drawback is their low energy density. This paper presents design considerations for the selection of EDLCs as energy storage components for nanosatellites. As nanosatellite development is driven by a short development time and low cost, a simple EDLC was designed using commercial off-the-shelf (COTS) components. Ground tests simulating real low Earth orbit (LEO) environment conditions were performed. Sunlight and eclipse periods were 65% and 35% for one orbit, respectively, and EDLC performance was analyzed under the simulated conditions. Testing demonstrated EDLC ca...

The relation between electrolyte pH and electrochemical hydrogen uptake was discussed. The moderate pH solution has the higher hydrogen uptake than in strong acid and base. Hydrogen evolution overvoltage was increased in the moderate pH solutions. The moderate pH extends the operational potential in asymmetric capacitor.

Alternate floating remarkably prolongs the capacitor lifetime. •Electrolyte concentration is a key factor of aging rate. •Alternate floating ages both electrodes to the same extend. •Almost 2-fold lifespan improvement achieved for 0.2 mol L − 1 LiNO 3 .

Chitosan and poly(ethylene oxide) powders have been mixed in different weight ratios. To each mixture, a fixed amount of ammonium iodide has been added. All mixtures have been dissolved in 1% acetic acid solution to form polymer blend electrolyte films by the solution cast technique. X-ray diffraction indicates that the polymer blend electrolytes are amorphous. Fourier transform infrared spectroscopy shows shifting of the amine, carboxamide and CeOeC bands to lower wavenumbers indicating the occurrence of complexation. Electrochemical impedance spectroscopy has been used to study the electrical properties of the samples. The ionic conductivity for 55 wt.% chitosane45 wt.% NH 4 I electrolyte system is 3.73 Â 10 À7 S cm À1 at room temperature and is increased to 3.66 Â 10 À6 S cm À1 for the blended film (16.5 wt.% chitosan-38.5 wt.% PEO)e45 wt.% NH 4 I film. Dye-sensitized solar cells (DSSCs) have been fabricated by sandwiching the polymer electrolyte between the TiO 2 /dye photoelectrode and Pt counter electrode. DSSCs fabricated exhibits short-circuit current density (J sc) of 2.71 mA cm À2 , open circuit voltage (V oc) of 0.58 V and efficiency of 0.78% with configuration ITO/TiO 2 /N3 dye/(16.5 wt.% chitosan-38.5 wt.% PEO)e45 wt.% NH 4 I(þI 2)/Pt/ITO and J sc of 2.84 mA cm À2 , V oc of 0.58 V and efficiency of 1.13% with configuration ITO/TiO 2 þ Ag nanoparticles/N3 dye/(16.5 wt.% chitosane38.5 wt.% PEO)e45 wt.% NH 4 I(þI 2)/Pt/ITO.

This research article reports on a systematic approach to the development of polymer gel electrolytes (PGEs) for the applications of dye-sensitized solar cells (DSSCs). The authors prepared PGE blend using poly(acrylonitrile) (PAN) and poly(ethylene glycol) (PEG) polymers along with three different ionic salts. They demonstrated a good ionic conductivity of 1.52 Â 10 À2 S cm À1 , which improved PV performance. The conduction mechanism of the (PAN/PEG) PGE is based on the interaction of three cations of distinct sizes, Hex 4 N + , K + , and Li + ions, with the polymer host. The rapid diffusion of I À /I 3 À iodide ions through the pores formed by PEG in the PGE is the primary cause of improved ionic conductivity. Various compositions of (PAN/PEG) have been optimized to obtain a sufficient porous structure and improved photon conversion efficiency (PCE) of the cell, achieving 8.6% in this research. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), impedance spectroscopy, incident photon conversion efficiency (IPCE) and finally current density voltage (J-V) characterization techniques are used to analyze and compare the results with those of liquid electrolyte-based cells.

Highlights Products derived from algae are chemically modified for applied energy purposes. A new smart activation process by sublimation is proposed. The prepared materials are used as green solid electrolytes in photovoltaic cells. The ionic conductivity highest ever obtained for a biopolymeric electrolyte was measured.

In the present work, phthaloyl chitosan (PhCh)-based gel polymer electrolytes (GPEs) were prepared using dimethylformamide (DMF) as a solvent, ethyl carbonate (EC) as a co-solvent, and a set of five quaternaries of potassium iodide (KI) as a doping salt, which is a mixed composition of iodine (I2). The prepared GPEs were applied to dye-sensitized solar cells (DSSC) to observe the effectiveness of the electrolyte, using mesoporous TiO2, which was sensitized with N3 dye as the sensitizer. The incorporation of the potassium iodide-based redox couple in a polymer electrolyte is fabricated for dye-sensitized solar cells (DSSCs). The number of compositions was based on the chemical equation, which is 1:1 for KI:I2. The electrical performance of prepared GPE systems have been assessed using electrical impedance spectroscopy (EIS), and dielectric permittivity. The improvement in the ionic conductivity of PhCh-based GPE was observed with the rise of salt concentration, and the maximum ionic ...

A nanocomposite polymer electrolyte (NCPE) comprising of 49% poly(methyl methacrylate) grafted natural rubber (MG49) as polymer host, titanium dioxide (TiO2) as a ceramic filler, lithium tetrafluoroborate (LiBF4) as dopant salt, and ethylene carbonate (EC) as plasticizer was prepared by solution casting technique. The ceramic filler, TiO2, was synthesized in situ by a sol-gel process. The ionic conductivity, chemical interaction, structure, and surface morphology of nanocomposite polymer electrolyte have been investigated as a function of wt% LiBF4. The interaction between lithium ions and oxygen atoms occurred at carbonyl and ether groups. The crystalline phase of polymer host slightly decreases with the addition of salt. TGA and DTG analysis suggested that the thermal stability of the electrolyte decreases with the salt content. The ionic conductivity of the electrolyte was found to increase with the increase of salt concentration and then decreased after an optimum value. The hig...

We investigated the structural and thermal properties of a gel polymer electrolyte prepared with poly(ethylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether) (P(EO/ EM) matrix, γ-butyrolactone (GBL), and LiI/I 2. Nuclear magnetic resonance spectroscopy measurements were carried out in different temperatures for the aforementioned electrolyte composition in order to understand the interaction between the components of the gel. Within the studied temperature range, the overall Li ion mobility depends on the contribution of the Li ion mobility in GBL molecules and in the polymer matrix. Small angle X-ray scattering (SAXS) measurements of the gel electrolyte indicated an order periodicity of 7-8 nm, which provides evidence for an effective miscibility of GBL and P(EO/EM), since no structural changes were observed by SAXS data (the systems are stable within the studied temperature range). Indeed, this result corroborates Nuclear Magnetic Resonance Spectroscopy (NMR) data, since at room temperature, it is not possible to distinguish magnetic interactions between P(EO-EM) and GBL molecules, indicating the existence of a single phase. Thermogravimetric analysis shows that the gel electrolyte meets thermal stability requirements for application in photoelectrochemical devices. The performance of dye-sensitized solar cells (DSSC) based on this polymer electrolyte with different GBL concentrations was monitored for 30 days. Device with electrolyte containing 30 wt.% of GBL gave the most promising durability results in this study; the performance of this device decreased by less than 10 % in the course of 30 days.

In situ Raman spectroscopy was exploited to analyze the interaction between carbon and hydrogen during electrochemical hydrogen storage at cathodic conditions. Two different activated carbons were used and characterized by different electrochemical techniques in two electrolytes (6 M KOH and 0.5 M Na 2 SO 4). The in situ Raman spectra collected showed that, in addition to the D and G bands associated to the graphitic carbons, two bands appear simultaneously at about 1110 and 1500 cm À1 under cathodic conditions, and then they disappear when the potential increases to more positive values. This indicates that carbon-hydrogen bonds are formed reversibly in both electrolytes during cathodic conditions. Comparing the two activated carbons, it was confirmed that, in both electrolytes, the hydrogenation of carbon atoms is produced more easily for the sample with lower amount of surface oxygen groups. In KOH medium, for the two samples, the formation of carbon-hydrogen bonds proceeds at more positive potential with respect to the thermodynamic potential value for hydrogen evolution. Furthermore, changes in the shape of the D band (due to an intensity increase of the D1 band) during the formation of carbon-hydrogen bonds suggest that hydrogenation of the carbon atoms increases the number of edge planes.

The ever-increasing characteristics of microcomputers, sensors, actuators, and communication systems require more powerful and more compact autonomous power sources. Al/bromate and Al/iodate flow batteries are proposed as new power supply units for use in oxygen-deficient environments. The batteries employ a mechanically rechargeable aluminum anode flooded with aqueous salt electrolytes or seawater, a cation-exchange membrane, and a carbonaceous porous cathode, where acidified alkali metal bromate, or iodate, is reduced in a six-electron process. The theoretical energy density of an Al/bromate flow cell per reactants is 0.65 kWh kg−1. Seawater is assumed as an electrolyte for the anode compartment. Using a H2/iodate flow cell, it is shown that iodate–iodine–iodide electrochemical transformations can be realized in both directions in acidic media at carbonaceous electrodes. At 30 °C, the area-specific power of the single cells of the Al/bromate and Al/iodate flow batteries reaches 0....

Pumping of fluids is universally performed by using mechanical or thermal compressors. We introduce a new solid-state molecular pumping approach induced by switching the adsorption affinity for a gas through polarization of a chromophore under an applied electric field. Mass spectrometry was used to trace refrigerant gas (difluoromethane) uptake on a chromophore-coated capacitor under applied voltage and subsequent desorption when the voltage and electrode polarization was removed, showing an exchange capacity of 0.11 mol of refrigerant/(L of chromophore). Calorimetry confirmed a reversible enthalpy change of 9 kcal/mol in the polarization-induced sorption−desorption process. The present work establishes the principle and feasibility of nonmechanical molecular pumping, which could be exploited to transport any fluid, opening numerous potential applications.

Converting CO 2 to valuable materials is attractive. Herein, we report using simple metallothermic reactions to reduce atmospheric CO 2 to dense nanoporous graphene. By using a Zn/Mg mixture as a reductant, the resulted nanoporous graphene exhibits highly desirable properties: high specific surface area of 1900 m 2 /g, a great conductivity of 1050 S/m and a tap density of 0.63 g/cm 3 , comparable to activated carbon. The nanoporous graphene contains a fine mesoporous structure constructed by curved few-layer graphene nanosheets. The unique property ensemble enables one of the best high-rate performances reported for electrochemical capacitors: a specific capacitance of $ 170 F/g obtained at 2000 mV/s and 40 F/g at a frequency of 120 Hz. This simple fabricating strategy conceptually provides opportunities for materials scientists to design and prepare novel carbon materials with metallothermic reactions.

The relation between electrolyte pH and electrochemical hydrogen uptake was discussed. The moderate pH solution has the higher hydrogen uptake than in strong acid and base. Hydrogen evolution overvoltage was increased in the moderate pH solutions. The moderate pH extends the operational potential in asymmetric capacitor.

The energy density of carbon based supercapacitors (CBSCs) was significantly increased by the addition of an inorganic redox species [Ce 2 (SO 4) 3 ] to an aqueous electrolyte (H 2 SO 4). The development of the faradaic processes on the positive electrode not only significantly increased the capacitance but also the operational cell voltage of these devices (up to 1.5 V) due to the high redox potentials at which the Ce 3+ /Ce 4+ reactions occur. Therefore, in asymmetric CBSCs assembled using an activated carbon as negative electrode and MWCNTs as the positive one, the addition of Ce 2 (SO 4) 3 moderately increases the energy density of the device (from 1.24 W h kg-1 to 5.08 W h kg-1). When a modified graphite felt is used as positive electrode the energy density of the cell reaches values as high as 13.84 W h kg-1. The resultant systems become asymmetric hybrid devices where energy is stored due to double layer formation in the negative electrode and the development of the faradaic process in the positive electrode, which acts as a battery-type electrode.

The energy density of carbon based supercapacitors (CBSCs) was significantly increased by the addition of an inorganic redox species [Ce 2 (SO 4) 3 ] to an aqueous electrolyte (H 2 SO 4). The development of the faradaic processes on the positive electrode not only significantly increased the capacitance but also the operational cell voltage of these devices (up to 1.5 V) due to the high redox potentials at which the Ce 3+ /Ce 4+ reactions occur. Therefore, in asymmetric CBSCs assembled using an activated carbon as negative electrode and MWCNTs as the positive one, the addition of Ce 2 (SO 4) 3 moderately increases the energy density of the device (from 1.24 W h kg-1 to 5.08 W h kg-1). When a modified graphite felt is used as positive electrode the energy density of the cell reaches values as high as 13.84 W h kg-1. The resultant systems become asymmetric hybrid devices where energy is stored due to double layer formation in the negative electrode and the development of the faradaic process in the positive electrode, which acts as a battery-type electrode.

Inclusion of an appropriate form of carbon as an additive in the negative active material (NAM) improves the performance of lead-acid batteries in high rate partial state of charge (HRPSoC) cycling. We have used cyclic voltammetry to evaluate the performance of different carbonscarbon black, acetylene black and graphitein this study and found the technique to be useful in separating the capacitive and the Faradaic contributions to the total charge. It is noted that the presence of carbon at the Pb-interface substantially enhances the electrochemical activity and increases the Faradaic charge, while high surface area carbons add to the capacitive charge. The technique is further used to study combinations of carbons as physical mixtures and bilayers. 2015 Published by Elsevier Ltd.

The energy density of carbon based supercapacitors (CBSCs) was significantly increased by the addition of an inorganic redox species [Ce 2 (SO 4) 3 ] to an aqueous electrolyte (H 2 SO 4). The development of the faradaic processes on the positive electrode not only significantly increased the capacitance but also the operational cell voltage of these devices (up to 1.5 V) due to the high redox potentials at which the Ce 3+ /Ce 4+ reactions occur. Therefore, in asymmetric CBSCs assembled using an activated carbon as negative electrode and MWCNTs as the positive one, the addition of Ce 2 (SO 4) 3 moderately increases the energy density of the device (from 1.24 W h kg-1 to 5.08 W h kg-1). When a modified graphite felt is used as positive electrode the energy density of the cell reaches values as high as 13.84 W h kg-1. The resultant systems become asymmetric hybrid devices where energy is stored due to double layer formation in the negative electrode and the development of the faradaic process in the positive electrode, which acts as a battery-type electrode.

The mechanism of operation of a supercapacitor based on methylene blue (MB) as redox shuttle in cells containing activated carbon as electrodes and aqueous electrolyte has been studied. Attention is focused on the instability of these molecules which can undergo secondary reactions that impact negatively on the cell, generating fluctuations in its performance and reducing its cycling life. It is demonstrated that MB interacts strongly with activated carbons and modifies their structure, decreasing the resistance of the electrodes and increasing the energy density of the cell by more than 40%. It is also shown that MB is not stable in acidic electrolyte at the high potentials attained by the electrodes of the supercapacitor. Demethylation byproducts and oxidized derivates of the MB were detected after cycling by means of electrospray ionization mass spectrometry. These products were observed to cause a constant change in the equilibrium potential of the cell, substantially modifying the storage mechanism and the ranges of operation potential of the electrodes.

Thin films composites of poly(ethylene oxide)-graphene oxide were fabricated with and without lithium salts by solvent cast method. The ionic conductivity of these composites was studied at various concentrations of salt polymer-GO complexes and at different temperatures. The effects of temperature and graphene oxide concentration were measured from Arrhenius conductance plots. It is shown that the addition of salts in pure PEO increases conductance many times. The graphene oxide addition has enhanced the conductance approximately 1000 times as compared to that of pure PEO. The activation energies were determined for all the systems which gave higher values for pure PEO and the value decreased with the addition of LiClO4and LiCl salts and further decreases with the addition of graphene oxide. The composite has also lowered the activation energy values which mean that incorporation of GO in PEO has decreased crystallinity and the amorphous region has increased the local mobility of p...

In the existing study, the performance of (I2/I3-) as the efficient redox catholyte for escherchia coli based microbial fuel cell (MFC) was investigated and compared with conventional ferricyanide based system. This studies also examined the effect of applied current density, linear sweep voltammetry, open circuit voltage, discharge capacitance, Impedance, Energy and power density of the microbial fuel cell. Linear sweep voltammetry studies revealed the higher current density (3.3768 mAcm-2) for(I2/I3-)additive owing to its electro-reduction and this value is about 1.5 times higher in comparison to ferricyanide based system.The characteristics of (I2/I3-)based MFC is attributed to its higher capacitive contribution, high conductivity, and high power, when compared to ferricyanide based MFC. The extreme power density of the MFC fabricated using (I2/I3-)and ferricyanide additive at the measured current density of 50 µAcm-2 were observed to be 1,140 and 1,670.8303mWm-2. Among the results, (I2/I3-) basedMFCperformance displays excessive potential for enlightening the power generation of MFC.

Electric double layer capacitors (EDLCs), also known as supercapacitors, are electrical storage components that have a higher power density and lower storage capability in comparison to batteries. In terms of energy density, EDLC performance is currently between that of batteries and conventional dielectric capacitors. One of the main advantages of capacitors is their wide temperature operating range, whereas their main drawback is their low energy density. This paper presents design considerations for the selection of EDLCs as energy storage components for nanosatellites. As nanosatellite development is driven by a short development time and low cost, a simple EDLC was designed using commercial off-the-shelf (COTS) components. Ground tests simulating real low Earth orbit (LEO) environment conditions were performed. Sunlight and eclipse periods were 65% and 35% for one orbit, respectively, and EDLC performance was analyzed under the simulated conditions. Testing demonstrated EDLC ca...

Solid polymer electrolyte films based on Poly(ethylene oxide) (PEO) complexed with lithium hexafluorophosphate (LiPF 6 ), ethylene carbonate (EC) and amorphous carbon nanotube (aCNTs) were prepared by the solution cast technique. The conductivity increases from 10 À 10 to 10 À 5 Scm À 1 upon the addition of salt. The incorporation of EC and aCNTs to the salted polymer enhances the conductivity significantly to 10 À 4 and 10 À 3 Scm À 1 . The complexation of doping materials with polymer were confirmed by X-ray diffraction and infrared studies. Optical properties like direct band gap and indirect band gap were investigated for pure and doped polymer films in the wavelength range 200-400 nm. It was found that the energy gaps and band edge values shifted to lower energies on doping.

Hybrid electrochemical capacitors have emerged as attractive energy storage option, which perfectly fill the gap between electric double-layer capacitors (EDLCs) and batteries, combining in one device the high power of the former and the high energy of the latter. We show that the charging characteristics of the positive carbon electrode are transformed to behave like a battery operating at nearly constant potential after it is polarized in aqueous iodide electrolyte (1 mol L−1 NaI). Thermogravimetric analysis of the positive carbon electrode confirms the decomposition of iodides trapped inside the carbon pores in a wide temperature range from 190 °C to 425 °C, while Raman spectra of the positive electrode show characteristic peaks of I3− and I5− at 110 and 160 cm−1, respectively. After entrapment of polyiodides in the carbon pores by polarization in 1 mol L−1 NaI, the positive electrode retains the battery-like behavior in another cell, where it is coupled with a carbon-based negat...

The use of hybrid electrodes prepared from phosphotungstic acid (H 3 PW 12 O 40 , PW 12) and activated carbon (AC) allows the fabrication of highly durable aqueous supercapacitors operating at a superior voltage (1.6 V) thanks to the high overpotential of PW 12 towards H 2 generation. The combination of the double-layer capacitance plus the redox activity of the polyoxometalate clusters leads to an intrinsic increase in specific capacitance (from 185 F g À1 for AC to 254 F g À1 for AC-PW 12) and a 60% increase in the operating voltage (compared to conventional AC supercapacitors with aqueous electrolytes, e.g. 1 M sulphuric acid). The hybrid energy storage mechanism and the increased operating voltage converge to yield improved specific energy and power. Moreover, the hybrid AC-PW 12 electrode material showed an outstanding stability even after 30 000 cycles (0 to 1.6 V) with 98% retention of the initial capacitance, much superior to the stability of the parent supercapacitor based on plain AC under the same conditions.

Recent advances in photoelectrochemical redox flow cells, such as solar redox flow batteries, have received much attention as an alternative integrated technology for simultaneous conversion and storage of solar energy. Theoretically, it has been reported that even single-photon devices can demonstrate unbiased photo-charging with high solar-to-chemical conversion efficiency; however, the poor redox kinetics of photoelectrodes reported thus far severely limit the photo-charging performance. Here, we report a band alignment design and propose surface coverage control to reduce the charge extraction barrier and create a facile carrier pathway from both n- and p-type photoelectrodes to the electrolyte with the respective redox reaction. Based on these observations, we develop a single-photon photo-charging device with a solar-to-chemical conversion efficiency over 9.4% for a redox flow cell system. Along with these findings, we provide design principles for simultaneous optimisation, w...

Redox-active polyfluorododecaborate cluster ions, [B 12 F x H 12 − x ] 2− , were investigated as electrolytes for electrochemical double layer capacitors. In particular, the performance of tetraethylammonium undecafluorododecaborate, (Et 4 N) 2 B 12 F 11 H, was compared against a standard electrolyte made with tetraethylammonium tetrafluoroborate (Et 4 NBF 4). Overcharge tests in single cells and in cells assembled in series demonstrated that the redox-active anion can be effectively used as a shuttle to reduce solvent degradation under harsh conditions, thus extending cell life.

Redox-active polyfluorododecaborate cluster ions, [B 12 F x H 12 − x ] 2− , were investigated as electrolytes for electrochemical double layer capacitors. In particular, the performance of tetraethylammonium undecafluorododecaborate, (Et 4 N) 2 B 12 F 11 H, was compared against a standard electrolyte made with tetraethylammonium tetrafluoroborate (Et 4 NBF 4). Overcharge tests in single cells and in cells assembled in series demonstrated that the redox-active anion can be effectively used as a shuttle to reduce solvent degradation under harsh conditions, thus extending cell life.

For the oxidation of water to dioxygen, oxide-covered ruthenium metal is known as the most efficient catalyst, however, with limited stability. Herein, we present a strategy for incorporating a Ru/C composite onto a novel nanoporous electrode surface with low noble metal loading and improved stability. The Ru/C is coated on the pore walls of anodic alumina templates in a one-step laser-induced deposition method from Ru3(CO)12 solutions. Scanning electron microscopy proves the presence of a continuous Ru/C layer along the inner pore walls. The amorphous material consists of metallic Ru incorporated in a carbonaceous C matrix as shown by X-ray diffraction combined with Raman and X-ray photoelectron spectroscopies. These porous electrodes reveal enhanced stability during water oxidation as compared to planar samples at pH 4. Finally, their electrocatalytic performance depends on the geometric parameters and is optimized with 13 μm pore length, which yields 2.6 mA cm−2, or 49 A g−1, at ...

The membranes 55 wt.% chitosan-45 wt.% NH 4 I, 33 wt.% chitosan-27 wt.% NH 4 I -40 wt.% EC, and 27.5 wt.% chitosan-22.5 wt.% NH 4 I -50 wt.% buthyl-methyl-imidazolium-iodide (BMII) exhibit conductivity of 3.73× 10 -7, 7.34× 10 -6, and 3.43× 10 -5 S cm -1, respectively, at room temperature. These membranes have been used in the fabrication of solid-state solar cells with configuration ITO/ TiO 2 /polymer electrolyte membrane/ITO. It is observed that the short-circuit current density increases with conductivity of the electrolyte. The use of anthocyanin pigment obtained by solvent extraction from black rice and betalain from the callus of Celosia plumosa also helps to increase the short-circuit current.

We present an electrochemical advanced oxidation process (eAOP) reactor employing expanded graphite, potassium iodide (KI), and electrical current, which demonstrates an exceptionally high rate of inactivation of E. coli (6log reduction in viable cells) at low current density 0.6 mA/cm^2), with low contact time (5 minutes) and low concentration of KI (10 ppm). Operando X-ray fluorescence mapping is used to show the distribution of iodine species in the reactor, and operando X-ray absorption spectroscopy in the anodic chamber reveals iodine species with higher effective oxidation state than periodate. Operando electrochemical measurements confirm the conditions in the anodic chambers are favourable for the creation of highly oxidized iodine products. The killing efficiency of this new eAOP reactor far exceeds that expected from either traditional iodine-based electrochemical water treatment or advanced oxidation systems alone, a phenomenon that may be associated with the production o...

h i g h l i g h t s g r a p h i c a l a b s t r a c t < An ultracapacitor based on carbon electrodes and sodium sulfate electrolyte was tested in the voltage range 0e1.8 V. < The UCap exhibited good capacitance, high specific energy and excellent cycling stability. < The UCap had specific energy (17.5 Wh kg À1) remarkably higher than similar UCaps reported in literature.

Steel was anodized in 10 M NaOH to enhance its surface texture and internal surface area for application as an electrode in supercapacitors. A mechanism was proposed for the anodization process. Field-emission gun scanning electron microscopy (FEGSEM) studies of anodized steel revealed that it contains a highly porous sponge like structure ideal for supercapacitor electrodes. X-ray photoelectron spectroscopy (XPS) measurements showed that the surface of the anodized steel was Fe 2 O 3 , whereas X-ray diffraction (XRD) measurements indicated that the bulk remained as metallic Fe. The supercapacitor performance of the anodized steel was tested in 1 M NaOH and a capacitance of 18 mF cm −2 was obtained. Cyclic voltammetry measurements showed that there was a large psueudocapacitive contribution which was due to oxidation of Fe to Fe(OH) 2 and then further oxidation to FeOOH, and the respective reduction of these species back to metallic Fe. These redox processes were found to be remarkably reversible as the electrode showed no loss in capacitance after 10000 cycles. The results demonstrate that anodization of steel is a suitable method to produce high-surface-area electrodes for supercapacitors with excellent cycling lifetime.

We present an electrochemical advanced oxidation process (eAOP) reactor employing expanded graphite, potassium iodide (KI), and electrical current, which demonstrates an exceptionally high rate of inactivation of E. coli (6log reduction in viable cells) at low current density 0.6 mA/cm^2), with low contact time (5 minutes) and low concentration of KI (10 ppm). Operando X-ray fluorescence mapping is used to show the distribution of iodine species in the reactor, and operando X-ray absorption spectroscopy in the anodic chamber reveals iodine species with higher effective oxidation state than periodate. Operando electrochemical measurements confirm the conditions in the anodic chambers are favourable for the creation of highly oxidized iodine products. The killing efficiency of this new eAOP reactor far exceeds that expected from either traditional iodine-based electrochemical water treatment or advanced oxidation systems alone, a phenomenon that may be associated with the production o...

Stabilization of tetragonal copper ferrite super-architectures has been proposed for the fabrication of highperformance supercapacitor and water splitting electrodes. The reaction parameters are optimized to keep the tetragonal phase intact (with high yield per batch ~ 7.5 g) in order to have better ions intercalation/deintercalation processes and longer cycling stability, according to Jahn-Teller distortion theory. The developed porous layered architectures are mesoporous with large specific surface area available for ionic interactions. The redox additive insertion in the electrolyte raises the specific capacity to ~ 450 mAh g − 1 (~2490F g − 1) from the fabricated electrode. The physical mechanism involved behind the electrochemical performance in presence of redox additives is elaborately discussed to gain insight into the charge storage characteristics. The fabricated asymmetric solid-state supercapacitor exhibits broad potential window (~1.8 V) with excellent energy (128 Wh kg − 1) cum power traits, and a long-lasting stable performance for > 10000 cycles. For water splitting, the superarchitectures based electrode displays promisingly lower OER/HER (~298/103 mV) overpotentials with excellent stability over longer durations (>30 h). The fabricated symmetric device with the alkaline electrolyte is highly stable with cell voltage of 1.62 V, which being an oxide material is excellent and superior to various oxides/chalcogenides based high-grade materials.

Porous carbon materials, with different porosities and surface chemistry have been prepared and characterized to obtain a better understanding of the mechanism of the electrochemical storage of hydrogen. The hydrogen storage capacity depends, not only on the porosity of the material, but also on the surface chemistry, which is a critical factor. The results show that the higher the amount of surface oxygen groups, the lower is the hydrogen uptake. Measurement of the number of active carbon sites shows the important role of the unsaturated carbon atoms in the process. In situ Raman spectroscopy has been used in order to further explore the structural changes in the carbon material during the chargedischarge processes. This technique has allowed us to observe the formation of the C(sp 2)AH bonds during the cathodic process and its reversibility during the oxidation step.

This paper reports on the electrochemical performance of symmetric carbon/carbon electrochemical capacitors operating in aqueous electrolyte (0.5 mol L À1 K 2 SO 4 solution) and modified with various amounts of agar (up to 5 wt%). It has been found that a change in electrolyte form (from liquid to gel-like) increases the hydrogen storage efficiency on the negative electrode (confirmed by operando Raman spectroscopy), improves the cycle life at elevated voltages and reduces the self-discharge. Furthermore, it has been found that the gas generation rate during capacitor operation is remarkably diminished (by ca. 4 times), and thus, the detrimental impact of increased internal pressure is noticeably reduced.

Symmetrical electrochemical capacitors are attracting immense attention because of their fast charging−discharging ability, high energy density, and low cost of production. The current research in this area is mainly focused on exploring novel low-cost electrode materials with higher energy and power densities. In the present work, we fabricated an electrochemical double-layer capacitor using methylammonium bismuth iodide (CH 3 NH 3) 3 Bi 2 I 9 , a lead-free, zero-dimensional hybrid perovskite material. A maximum areal capacitance of 5.5 mF/cm 2 was obtained, and the device retained 84.8% of its initial maximum capacitance even after 10 000 charge−discharge cycles. Impedance spectroscopy measurements revealed that the active layer provides a high surface area for the electrolyte to access. As a result, the charge transport resistance is reasonably low, which is advantageous for delivering excellent performance. ■ INTRODUCTION Organic−inorganic halide perovskite materials captured the attention of scientific community during the past few years because of their unique optical and electronic properties. 1−5 Three-dimensional hybrid perovskites with a general formula of AMX 3 (A = methylammonium or formamidinium cation; M = Pb 2+ , Sn 2+ , etc., and X = I, Br, and Cl) are highlighted as efficient light-absorbing layers in solar cells with an efficiency surpassing 22%. 6−8 Apart from photovoltaic applications, these materials are promising for light-emitting diodes, photo-detectors, sensors, memories, and so forth. 9−20 The widespread applications of this class of materials could be attributed to their properties such as tunable band gap, large absorption coefficient, high electron and hole diffusion lengths, good charge carrier mobility, ease of defect state formation, and excellent ion migration. 21−23 Even though hybrid perovskites exhibit very interesting properties and are useful for a large number of applications, the toxicity of lead and instability in the presence of moisture and oxygen are prime concerns preventing their commercialization. 24−26 Storage of energy is as important as its production. Development of novel, environmentally friendly, and sustainable energy storage devices has attracted considerable research attention in modern times because of the rapid depletion of unsustainable fossil fuels and environmental deterioration, which are also necessary to satisfy the demands of the fast-growing electronic industry. Electrochemical capacitors with long life span, high power density, and fast charge−discharge characteristics are regarded as excellent energy storage devices, as they have the potential to complement or even replace batteries in numerous applications. 27 However, their low energy density is a limiting factor in their widespread practical applications. Hence, the current research in electrochemical capacitors is mainly focused on exploring novel low-cost electrode materials with higher energy and power densities. 28 In this context, hybrid perovskite materials are promising because of their high ionic conductivity; a recent study suggests that the ionic conductivity of methylammonium lead iodide (MAPbI 3) is higher than its electronic conductivity. 29 By exploring this property, Zhao et al. have reported a MAPbI 3-based thin-film electrochemical double-layer capacitor (EDLC). 30 The capaci-tance obtained was 5.89 μF/cm 2 , which proved that hybrid perovskite materials are good candidates for capacitor applications. However, the toxicity of lead is a major factor of concern here also. ■ RESULTS AND DISCUSSION In this work, we have explored the potential of methylammo-nium bismuth iodide (MBI), which is a lead-free, zero-dimensional perovskite having a unit cell formula of (CH 3 NH 3) 3 Bi 2 I 9 , for energy storage applications. This bismuth-based perovskite is an environment-friendly alternative with better atmospheric stability than that of the corresponding lead-based perovskites. The unit cell of MBI consists of isolated

Graphite oxide is introduced as an excellent material for the preparation of supercapacitors. It was prepared through chemical oxidation of natural graphite, and the resulting graphite oxide was employed to fabricate a paste-based electrode. This electrode exhibits pseudocapacitive behavior across a potential region with wideness of 3 V (i.e. a quaint potential window for aqueous media). In addition to the wideness of the potential window, this electrochemical capacitor has a high specific capacitance of ca. 118 F g -1 , which is comparable with that of highly porous carboneous materials. Both essential requirements of electrochemical capacitors, i.e. wide range of potential and high specific capacitance, are indeed superior for the case of graphite oxide. Combined enhancement of these two parameters results in an extremely high energy density in order of 20 Wh kg -1 . Contrary to other carboneous materials, this supercapacitor is not merely based on double layer capacitance, and a redox process is mainly responsible for this superiority, as the counter ions can penetrate into the specious interlayers of graphite oxide. Moreover, due to its low cost, it provides a new opportunity for the preparation of supercapacitors. depicts a cyclic voltammetric behavior of the graphite oxide electrode in an aqueous solution of saturated Na 2 SO 4 . This indicates a good pseudocapacitive behavior in a wide potential window. This is indeed an extraordinary wideness for pseudo-capacitive behavior in aqueous media. In addition to the wideness of the potential window, the graphite oxide electrode displays a high specific capacitance (SC) of ca. 109.1 F g -1 . This value is comparable with those of highly porous carboneous materials having large specific surface area in order of 2,000 m 2 g -1 . Therefore, one can conclude that this high SC cannot be attributed to the usual double layer capacitance of carboneous materials, and it should be related to the chemical structure of graphite oxide, as this issue will be discussed later.

A one-dimensional morphology comprising nanograins of two metal oxides, one with higher electrical conductivity (CuO) and the other with higher charge storability (Co3O4), is developed by electrospinning technique. The CuO-Co3O4 nanocomposite nanowires thus formed show high specific capacitance, high rate capability, and high cycling stability compared to their single-component nanowire counterparts when used as a supercapacitor electrode. Practical symmetric (SSCs) and asymmetric (ASCs) supercapacitors are fabricated using commercial activated carbon, CuO, Co3O4, and CuO-Co3O4 composite nanowires, and their properties are compared. A high energy density of ∼44 Wh kg(-1) at a power density of 14 kW kg(-1) is achieved in CuO-Co3O4 ASCs employing aqueous alkaline electrolytes, enabling them to store high energy at a faster rate. The current methodology of hybrid nanowires of various functional materials could be applied to extend the performance limit of diverse electrical and electro...

We introduce a novel bipolar assembly of ion-exchange membranes as the separator for aqueous supercapacitors. The new bipolar separator enables the positive electrode and the negative electrode to operate in acidic electrolyte and alkaline electrolyte, separately. The bipolar separator increases the theoretically stable voltage window from 1.23 to 1.76 V for the device when pH 1 and pH 10 are selected for the positive and negative electrode, respectively, based on the pH tolerance of commercial ion exchange membranes. By considering the results from comprehensive electrolyte stability investigation, we charge the cells to 1.8 V, which increases the maximum cell discharge voltage to 1.77 V. A specific energy of 12.7 Wh/kg is achieved based on the electrodes' mass, which is twice the value of the comparative best performing single electrolyte. The new cell configuration with the three-compartment bipolar separator effectively prevents the acid/base electrolyte cross diffusion, where after 10,000 cycles, the capacitance retention is 97% with coulombic efficiency maintained above 99.6% all through cycling. The design here may open up a new avenue toward high-energy aqueous energy storage devices.

We report a new biopolymer electrolyte for dye sensitized solar cell application. To develop polymer electrolyte, potassium iodide have been added in agarose biopolymer matrix and characterized using various techniques like complex impedance spectroscopy, Infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM). Complex impedance spectroscopy shows many folds enhancement in ionic conductivity ( ) by salt doping and conductivity maxima was obtained near 60:40 composition. Infrared spectroscopy confirms the formation of composite nature. XRD revels the reduction of crystallinity by salt doping as well affirms the composite nature. Scanning electron microscopy (SEM) shows reduction in crystallinity of gel matrix by salt doping which is a known favorable condition for ionic conductivity enhancement. To further affirm the conductivity enhancement in the gel electrolyte system a theoretical hopping model is also described in details. A DSSC has been developed using maximum electrical conductivity film which shows 0.54% efficiency at 1 sun condition.

Nickel hexacyanoferrate (NiHCFe) is an attractive cathode material in both aqueous and organic electrolytes due to a low-cost synthesis using earth-abundant precursors and also due to its open framework, Prussian blue-like crystal structure that enables ultra-long cycle life, high energy efficiency, and high power capability. Herein, we explored the effect of different alkali ions on the insertion electrochemistry of NiHCFe in aqueous and propylene carbonate-based electrolytes. The large channel diameter of the structure offers fast solid-state diffusion of Li(+), Na(+), and K(+) ions in aqueous electrolytes. However, all alkali ions in organic electrolytes and Rb(+) and Cs(+) in aqueous electrolytes show a quasi-reversible electrochemical behavior that results in poor galvanostatic cycling performance. Kinetic regimes in aqueous electrolyte were also determined, highlighting the effect of the size of the alkali ion on the electrochemical properties.

The steady-state current-voltage curve and dynamic response of a dye-sensitized solar cell (DSSC) is mathematically modeled based on electrical equivalent circuit. The effect of temperature and illumination on the steady-state and dynamic parameters of dye-sensitized solar cells is studied. It is found that the dynamic resistance of DSSC decreases from 619.21 Ω to 90.34 Ω with the increase in illumination level from 200 W/m 2 to 800 W/m 2 . A positive temperature coefficient of dynamic resistance is observed. The interfacial charge transfer and recombination losses at the oxide/dye/electrolyte interface are found to be the most influential factor on the overall conversion efficiency and included in the mathematical model. The saturation current of rectifying diode and saturation current of recombination diode are responsible for the transfer recombination losses and have major influence on the overall conversion efficiency.

A polymeric ionic liquid issued from an ionic liquid monomer composed of a methacrylate polymerizable group, a polar tri(ethylene oxide) spacer, a trifluoromethane sulfonic anion and a free imidazolium cation was employed as a solid electrolyte for dye-sensitized solar cells. The simple device configuration based on dip-coated nanoporous TiO2 electrode sensitized by N3 ruthenium-based dye gave the conversion efficiency of up to 1.74% under AM 1.5 simulated solar light illumination. Effect of TiO2 porous film thickness on overall energy conversion efficiency was discussed. It has been found that the most appropriate thickness for the polymeric ionic liquid based electrolyte dye sensitized solar cell is around 7 µm.