Cathodic Reduction Potentials Research Articles

In situ synthetic H2 on composite cathode surface for CH4 production from CO2 in microbial electrosyntshesis

Microbial electrosynthesis (MES) is an innovative technology that employs microbes to synthesize chemicals by reducing CO2.This study explores the CH4 production performance at different cathodic reduction potentials in MES. In this study, in situ H2 production on the surface of composite electrode was realized by regulating cathode potential. Pathway for H2-mediated CH4 synthesis was the main synthesis pathway, but it was susceptible to interfere from the external environment (such as cathode potential, pH). The optimal CH4 production potential was −1.0 V vs Ag/AgCl, meanwhile the CH4 synthesis rate was 58 ± 0.4 mLm−2d−1 and the CE was 67 ± 0.5%. Excessively high reduction potentials (−1.4 V vs Ag/AgCl) reduce the activity of microbial populations at the cathode. Synergistic interactions between H2-producing bacteria (Hydrogenophaga, Clostridium, Enterobacter, and Escherichia coli) and Hydrogenotrophic methanogens (Methanobacterium and Methanomassiliicocus) promoted efficient synthesis of CH4. These insights provide new perspectives on reactor operation, thus contributing to the efficiency of MES.

Electrocatalytic Performance of Interconnected Self‐Standing Tin Nanowire Network Produced by AAO Template Method for Electrochemical CO2 Reduction**

AbstractIn this study, we used a specially designed aluminum anodic oxide (AAO) template technique to produce interconnected self‐standing tin nanowire electrocatalysts having a high surface‐to‐volume ratio for CO2 reduction toward formate. These electrodes consisted of interconnected tin nanowires with 150 nm diameter and 7 μm length supported on 70–100 μm thick tin film. As prepared electrodes produced 6 times higher formate than the flat tin sheets, yet Faradaic efficiencies (FE%) were unsatisfactory. The main reason for low FE% is determined as the etching of native oxide on tin nanowires during hot alkali treatment to remove AAO and remnant aluminum. Porous anodic oxidation in 1 M NaOH solution was realized to recover tin oxides on the surface. Anodized tin nanowire electrocatalysts produced higher formate than anodized tin sheets, reaching FEformate% of ~87 at −1 V vs. RHE cathodic reduction potential. Moreover, while anodic oxide on flat tin flaked off the surface in 1 h, these electrodes preserved their integrity and formate production ability even after 12 h.

The Role of Carbon to Nitrogen Ratio on the Performance of Denitrifying Biocathodes for Decentralized Wastewater Treatment

Bioelectrochemical systems with denitrifying biocathodes have been of interest for the removal of nitrate in decentralized wastewater treatment applications. Only a few studies have directly focused on this application, but the removal rates have been very low. This study evaluated the operational parameters that affect the nitrate removal of two-chambered microbial fuel cells (MFCs) with a biocathode, particularly, the carbon to nitrogen ratio (C:N) and proton diffusivity across electrode chambers. The results show that proton diffusion across a proton exchange membrane is not a limiting step in nitrogen removal performance. At C:N ratios of 4 and 8, biocathodes with a continuously supplied carbon source at the anode were able to achieve complete nitrogen removal at a rate of 0.97 ± 0.21 and 1.15 ± 0.13 mg N L−1 d−1, respectively. However, as the C:N ratio increased from 4, 8, 16, and 32, the electrode potentials decreased accordingly. Ratio 4 C:N had a cathodic reduction potential of +66.1 ± 5.3 mV vs. SHE and dropped to −78.6 ± 9.8 mV vs. SHE at 32 C:N. The cathode electrode potential can be controlled by way of the carbon concentrations at the anode, which can have major indirect implications on the evolution of cathodic microbial communities that have preference to particular ranges of reduction potentials. The cathodic biofilms in this study were dominated by the phyla Proteobacteria, Acidobacteria, Bacteroidetes and Nitrospirae, which are known to have key denitrifying microorganisms. The genus Stenotrophomonas was found in abundance within the attached cathode biofilm and to a lesser extent in the suspended biomass. Vibrio, Acidobacteria_Gp4, Nitrosomonas, and Candidatus Competibacter were also cultivated in both the suspended and attached biomass. Nitrospira was only found in the attached biofilm. Regardless of operational scheme, nitrogen removal was improved at low C:N ratios, with 8 C:N having the best performance overall. This indicates that higher C:N ratios than were previously explored (>4 C:N) provide sufficient coulombs to facilitate denitrification at the cathode even while the anodic CEs remain low. Reactor design modifications should be considered to fully support robust denitrifying communities, enhancing the overall nitrogen removal for decentralized wastewater treatment applications.

Highly selective electrocatalytic hydrogenation of cinnamaldehyde over tin dioxide-supported palladium nanocatalysts

Selective hydrogenation of α, β-unsaturated aldehydes has always been a hot research topic owing to favorable thermodynamics in CC hydrogenation. In this work, a series of Pd/SnO2 nanocatalysts were facilely synthesized under mild conditions, via the reduction of Na2PdCl4 by dimethylaminoborane. Under galvanostatic electrolysis at 3.33 mA cm−2 for 8 h, the selective conversion of cinnamaldehyde (CAL) was achieved over Pd/SnO2-coated carbon fiber in neutral phosphate buffer, giving the cinnamyl alcohol (COL) selectivity of 78.85% at the conversion of 84.88%. The Pd/SnO2 nanocatalysts outperform commercial Pd/C catalysts, showing high COL selectivity and faradaic efficiency. The cathodic reduction potential of CAL over Pd4·3/SnO2 occurs at −0.92 V. The SnO2 support is beneficial to promote the CO adsorption of CAL and lower the HER activity of Pd nanocatalysts, thereby contributing to superior activity of Pd4·3/SnO2 for selective hydrogenation of CAL.

Modulating the Conduction Band Energies of Si Electrode Interfaces Functionalized with Monolayers of a Bay-Substituted Perylene Bisimide.

The confinement of π-conjugated chromophores on silicon (Si) electrode surfaces is a powerful approach to engineer electroresponsive monolayers relevant to microelectronics, electrocatalysis, and information storage and processing. While common strategies to functionalize Si interfaces exploit molecularly dissolved building blocks, only a handful number of studies have leveraged the structure-function relationships of π-aggregates to tune the electronic structures of hybrid monolayers at Si interfaces. Herein, we show that the semiconducting properties of n-type monolayers constructed on Si electrodes are intimately correlated to the initial aggregation state of π-conjugated chromophore precursors derived from bay-substituted perylene bisimide (PBI) units. Specifically, our study unravels that for n-type monolayers engineered using PBI π-aggregates, the cathodic reduction potentials required to inject negative charge carriers into the conduction bands can be stabilized by 295 mV through reversible switching of the maximum anodic potential (MAP) that is applied during the oxidative cycles (+0.5 or +1.5 V vs Ag/AgCl). This redox-assisted stabilization effect is not observed with n-type monolayers derived from molecularly dissolved PBI cores and monolayers featuring a low surface density of the redox-active probes. These findings unequivocally point to the crucial role played by PBI π-aggregates in modulating the conduction band energies of n-type monolayers where a high MAP of +1.5 V enables the formation of electronic trap states that facilitate electron injection when sweeping back to cathodic potentials. Because the structure-function relationships of PBI π-aggregates are shown to modulate the semiconducting properties of hybrid n-type monolayers constructed at Si interfaces, our results hold promising opportunities to develop redox-switchable monolayers for engineering nonvolatile electronic memory devices.

Performance of recirculatory Microbial Desalination Cell-Microbial Electrolysis Cell coupled system with different catholytes

Microbial Desalination Cell-Microbial Electrolysis Cell (MDC-MEC) coupled system, are very important and efficient in several processes including wastewater treatment; heavy metal removal; desalination; and chemical production. The performances of ferricyanide (MDCF) and 100 mM potassium phosphate buffer (MDCP100) as catholytes in the MDC were tested over a fed-batch cycle. The MDC systems (MDCF and MDCP100) were coupled with MEC to determine their effect on Pb and Fe removal. The COD removal efficiencies in MDCF, MDCP100, and control 1 were 92.96%, 90.54%, and 89.03% respectively. All the MDC systems were able to achieve a very high Pb2+ and Fe2+ removal efficiency, >90%. A high cathodic reduction potential was reached and maintained by the MDC-MEC systems, enable the reduction of Pb2+ and Fe2+ to Pb and Fe metals, through precipitation at the cathode of the MEC. MDCF had higher current and power densities of 550 mAm−2 and 166.08 mWm−2 respectively than that of MDCP100. More wastewater can be treated in the MDCP100 for ammonium removal in the middle chamber than that of MDCF. Therefore, the volume ratio of COD and NH4Cl removal in the MDC for balanced COD/Ammonium ions removal is a key driving force to the Industrial scale-up of the coupled system.

Comparative Studies of Recirculatory Microbial Desalination Cell-Microbial Electrolysis Cell Coupled Systems.

The recirculatory microbial desalination cell–microbial electrolysis cell (MDC–MEC) coupled system is a novel technology that generates power, treats wastewater, and supports desalination through eco-friendly processes. This study focuses on the simultaneous efficient removal of Fe2+ and Pb2+ in the MEC and ammonium ions in the MDC. It also evaluates the performances of dual-chambered MEC (DCMEC) and single-chambered MEC (SCMEC), coupled with MDC with Ferricyanide as catholyte (MDCF) in heavy metals (Pb2+ and Fe2+) removal, in addition to the production of voltage, current, and power within a 48-h cycle. The SCMEC has a higher Pb2+ (74.61%) and Fe2+ (85.05%) removal efficiency during the 48-h cycle than the DCMEC due to the simultaneous use of microbial biosorption and the cathodic reduction potential. The DCMEC had a higher current density of 753.62 mAm−2 than that of SCMEC, i.e., 463.77 mAm−2, which influences higher desalination in the MDCF than in the SCMEC within the 48-h cycle. The MDCF produces a higher voltage (627 mV) than Control 1, MDC (505 mV), as a power source to the two MECs. Stable electrolytes’ pH and conductivities provide a conducive operation of the coupled system. This study lays a solid background for the type of MDC–MEC coupled systems needed for industrial scale-up.

Performance of Recirculatory Microbial Desalination Cell-Microbial Electrolysis Cell Coupled System with Different Catholytes

Microbial Desalination Cell-Microbial Electrolysis Cell (MDC-MEC) coupled system, are very important and efficient in several processes including wastewater treatment; heavy metal removal; desalination; and chemical production. The performances of ferricyanide (MDCF) and 100mM potassium phosphate buffer (MDCP100) as catholytes in the MDC were tested over a fed-batch cycle. The MDC systems (MDCF and MDCP100) were coupled with MEC to determine their effect on Pb and Fe removal. The COD removal efficiencies in MDCF, MDCP100, and control 1 were 92.96%, 90.54%, and 89.03% respectively. All the MDC systems were able to achieve a very high Pb2+ and Fe2+ removal efficiency, >90%. A high cathodic reduction potential was reached and maintained by the MDC-MEC systems, enable the reduction of Pb2+ and Fe2+ to Pb and Fe metals, through precipitation at the cathode of the MEC. MDCF had higher current and power densities of 550 mAm-2 and 166.08 mWm-2 respectively than that of MDCP100. More wastewater can be treated in the MDCP100 for ammonium removal in the middle chamber than that of MDCF. Therefore, the volume ratio of COD and NH4Cl removal in the MDC for balanced COD/Ammonium ions removal is a key driving force to the Industrial scale-up of the coupled system.

Electrolytic Reduction of Titanium Dioxide in Molten LiCl–Li2O

The electrolytic reduction of TiO2 in LiCl–Li2O (1 wt.%) at 650 °C was investigated under a series of cathodic reduction potentials and applied charges to provide a mechanistic understanding of the electrochemical characteristics of the system. The optimal cathodic reduction potential was determined as being −0.3 V vs. Li/Li+. Li2TiO3 and LiTiO2 were structurally identified as intermediate and partial reduction products of the TiO2 electrolytic reduction. The reduction of LiTiO2 was extremely slow and reversible due to its high stability and the detrimental effect of Li2O accumulation within the solid particles. The most reduced product obtained in this study was LiTiO2, which was achieved when using 150% of the theoretical charge under the optimal reduction potential. The highest reduction extent obtained in this study was 25%. Based on theoretical DFT modeling, a detailed multistep reduction mechanism and scheme were proposed for TiO2 electrolytic reduction in LiCl–Li2O (1 wt.%) at 650 °C.

Unidirectional Magnetic Anisotropy in Dense Vertically-Standing Arrays of Passivated Nickel Nanotubes.

We report the facile and low-cost preparation as well as detailed characterization of dense arrays of passivated ferromagnetic nickel (Ni) nanotubes (NTs) vertically-supported onto solid Au-coated Si substrates. The proposed fabrication method relies on electrochemical synthesis within the nanopores of a supported anodic aluminum oxide (AAO) template and allows for fine tuning of the NTs ferromagnetic walls just by changing the cathodic reduction potential during the nanostructures’ electrochemical growth. Subsequently, the experimental platform allowed further passivation of the Ni NTs with the formation of ultra-thin antiferromagnetic layers of nickel oxide (NiO). Using adequately adapted magnetic measurements, we afterwards demonstrated that the thickness of the NT walls and of the thin antiferromagneticNiO layer, strongly influences the magnetic behavior of the dense array of exchange-coupled Ni/NiO NTs. The specific magnetic properties of these hybrid ferromagnetic/antiferromagnetic nanosystems were then correlated with the morpho-structural and geometrical parameters of the NTs, as well as ultimately strengthened by additionally-implemented micromagnetic simulations. The effect of the unidirectional anisotropy strongly amplified by the cylindrical geometry of the ferromagnetic/antiferromagnetic interfaces has been investigated with the magnetic field applied both parallel and perpendicular to the NTs axis.

Electrodeposition of Gadolinium Metal from Organic Solvents

Neutron phase contrast imaging (NPCI) is a non-destructive analysis tool currently in use with thermal neutrons. It relies on neutron transmission gratings to detect the phase signal. These gratings are typically fabricated from gadolinium (Gd), as this element has the highest neutron absorption cross section at 250,000 barns. There is a wealth of literature documenting the fabrication process of these gratings, including depositing Gd via sputter coating, evaporation and particle settling techniques at dimensions appropriate to absorb thermal neutrons. However tighter packing density, less contamination and thicker Gd films are necessary for neutrons at higher energy levels ( >0.025 eV). With these requirements in mind, we investigated the electrodeposition of Gd on Si substrate gratings for use with higher energy neutrons.Electrodeposition of Gd alloys is well documented in literature. With a very cathodic reduction potential of -2.28 V (acidic solution), depositing pure Gd metal is a tricky endeavor. In addition to excessive hydrogen evolution during plating, Gd undergoes rapid oxidation when exposed to air. This phenomenon is exacerbated with thin films due to their high surface area and can lead to pyrophoric events and brittle films that sluff off the substrate over time. We investigated aqueous solutions and with the use of many oxygen scavengers, we successfully plated gadolinium oxide (Gd2O3) thin films. However, this technique was not viable due to poor adhesion and rapid oxidation. Hoping for less oxygen contamination, we moved to two polar, aprotic organic solvents with promising potential windows: dimethylformamide (DMF) and dimethylsulfoxide (DMSO). The solubility of gadolinium(III) salts was investigated in the two solvents. At elevated temperatures, gadolinium(III) fluoride and gadolinium(III) chloride were soluble compounds, as well as gadolinium toluenesulfonic acid (GdTsOH). To increase conductivity, potassium chloride (KCl) and tetrabutylammonium tetrafluoroborate (TBATFB) were used as conducting salts. Pulsed plating techniques led to repeatable thin film deposition and EDS confirmed the presence of gadolinium uniformly spread over the surface. However, these films also suffered from poor adhesion, likely due to water contamination in the bath.The limitations outlined above led to electroplating Gd in dimethyl sulfone (DMSO2). DMSO2 is used in industry as a high-temperature solvent; its large dielectric constant reflects its high polarity, indicating strong intermolecular interactions in liquid phase. A melting temperature of 109 °C eliminates the concern of water contamination in the bath. Solubility tests are being repeated in this new polar solvent and linear sweeps and EIS continue to indicate favorable plating conditions. Parameters, such as Gd metal loading and substrate pretreatments are being optimized for thick films with good adhesion. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2020-5179 A

Redox Behavior of Moisture in LiCl-KCl Eutectic Melts: A Cyclic Voltammetry Study

In order to develop a flow sheet for the purification procedure of a LiCl-KCl eutectic mixture with the underlying aim of avoiding Cl2 handling in an engineering-scale laboratory, the present work focuses on electrochemical investigations on vacuum dried eutectic mixtures LiCl-KCl + H2O and vacuum dried LiCl-KCl + H2O mixtures using cyclic voltammetry at 500°C. Complicated voltammetric features were observed that were attributed to the cathodic reduction of H2O to form OH−, adsorption of OH− on tungsten electrode, and cathodic reduction of OH− to form O2−. The onset of cathodic current around −0.45 V (versus AgAg as reference) was due to both cathodic reductions of H2O and HCl, the latter being formed in melt due to high-temperature hydrolysis of LiCl, although it had limited solubility as compared to that of H2O. Cyclic voltammograms also showed an anodic peak at around −0.30 V attributable to the adsorption of O2− on the tungsten electrode. A total of 19 different LiCl-KCl eutectic melts subjected to various vacuum drying conditions and moisture content were investigated in this work using cyclic voltammetry. The LiCl-KCl + H2O mixtures were prepared to simulate conditions when there is an ingress of moisture in LiCl-KCl mixtures during long storage to determine whether the mixture can be purified. A larger composition range of moisture in the LiCl-KCl eutectic mixtures was used that not only helped in the attribution of cathodic reduction peaks to reactions mentioned above but also served as references to investigate the influence of vacuum drying of moisture-containing eutectic mixtures. A two-point criterion consisting of cathodic onset LiLi potential and residual cathodic current density estimated from cyclic voltammograms in the potential region −1.5 to −2.0 V at 500°C was used to quantify the purity of the eutectic melts. Former data were compared with the theoretical equilibrium potential of −3.637 V for the LiLi couple in LiCl-KCl eutectic melt at 500°C and those obtained from cyclic voltammograms of chlorinated melt. Cathodic reduction potentials for the above reactions were then compared with literature data where they were measured against Li-Al or NiNi reference electrodes in LiCl-KCl melts. Although reduction of HCl at Pt electrode in LiCl-KCl eutectic melts was known to be reversible from literature, it was not found to be so in the present work where a tungsten working electrode was used. The LiCl-KCl eutectic mixtures vacuum dried at 300°C were found to be closer in purity to those of chlorinated melt in that the onset LiLi potential and residual cathodic current density were similar. A lower residual cathodic current density for LiCl-KCl + 2 wt% H2O vacuum dried at 300°C was also achieved with the onset LiLi potential quite close to the theoretical equilibrium potential of LiCl (−3.637 V) in the eutectic melt.

Enhancement of Al-Ti Alloy Electrodeposition from AlCl3-EMIC Ionic Liquid Based Bath by Mg Additive

Al-Ti was electrodeposited from 1-ethyl-3-methyl-imidazolium chloride (EMIC)-AlCl3 ionic liquid containing TiCl4 on a copper working electrode using a potentiostatic or potential-pulse polarization. Deposits of Al-Ti alloy was obtained beneath the loose precipitate composed of mainly insoluble titanium chloride. Potential-pulse polarization that switched the potential between the two cathodic reduction potential of the multistep reduction of Ti ions improved the efficiency of electrodeposition of Al-Ti alloy. The ratio of Al-Ti alloy against the loose precipitate was increased by adding the Mg powder to the ionic liquid bath. It was supposed that Ti[IV] was reduced to Ti[II] by the substitutional dissolution of Mg and the resultant Ti[II] species such as TiCl42– contributed the electrodeposition of Ti. Simultaneous deposition of Al protected as-deposited Ti from re-oxidation (chlorination) by encapsulation them in the Al-Ti alloy. Although the deposition efficiency increased using Mg additive, the atomic content of Ti in Al-Ti deposits was reduced from ca. 21% for the bath absent of Mg powder to ca. 10% for the bath containing Mg. The decrease in the Ti content in the deposits was probably due to the insufficient supply rate of Ti[II] ions compared to the deposition rate of Al.

A Computational Mechanistic Investigation into Reduction of Gold(III) Complexes by Amino Acid Glycine: A New Variant for Amine Oxidation.

Density functional theory (DFT) was utilized to explore the reduction of gold(III) complexes by the amino acid glycine (Gly). Interestingly, when the nitrogen atom of Gly coordinates to the gold(III) center, its Cα -hydrogen atom becomes so acidic that it can be easily deprotonated by a mild base like water. The deprotonation converts the amino acid into a potent reductant by which gold(III) is reduced to gold(I) with a moderate activation energy. To our knowledge, this is the first contribution suggesting that primary amines are oxidized to imines via direct α-carbon deprotonation. This finding may provide new insights into the mechanistic interpretation of amine oxidations catalyzed/mediated by a center with high cathodic reduction potential. This work also provides a rationalization behind why gold(III) complexes with amine-based polydentate ligands are reluctant to undergo a redox process. Gold(III) reduction occurs most efficiently if the Cα proton leaves in the plane of the Cα , N and Au atoms. Chelation prevents this alignment, resulting in the gold(III) complex being unreactive toward reduction. It has been experimentally found that gold(III) is capable of oxidizing Gly to glyoxylic acid (GA) as the initial product. The latter, in the presence of another gold(III) complex, has been reported to undergo oxidative decarboxylation to afford CO2 and HCOOH. This process is found to be mediated by formation of a geminal diol intermediate produced by reaction of water with the aldehyde functional group of the coordinated GA.

On the stability and biological behavior of cyclometallated Pt(IV) complexes with halido and aryl ligands in the axial positions

A series of cyclometallated platinum(IV) compounds (3a, 3a′ and 3b′) with a meridional [C,N,N′] terdentate ligand, featuring an halido and an aryl group in the axial positions has been evaluated for electrochemical reduction and preliminary biological behavior against a panel of human adenocarcinoma (A-549 lung, HCT-116 colon, and MCF-7 breast) cell lines and the normal bronquial epithelial BEAS-2B cells. Cathodic reduction potentials (shifting from −1.463 to −1.570V) reveal that the platinum(IV) compounds under study would be highly reluctant to be reduced in a biological environment. Actually ascorbic acid was not able to reduce complex 3a′, the most prone to be reduced according its reduction potential, over a period of one week. These results suggest an intrinsic activity for the investigated platinum(IV) complexes (3a, 3a′ and 3b′), which exhibit a remarkable cytotoxicity effectiveness (with IC50 values in the low micromolar range), even greater than that of cisplatin. The IC50 for A-549 lung cells and clog P values were found to follow the same trend: 3b′>3a′>3a. However, no correlation was observed between reduction potential and in vitro activity. As a representative example, cyclometallated platinum(IV) compound 3a′, exercise its antiproliferative activity directly over non-microcytic A-549 lung cancer cells through a mixture of cell cycle arrest (13% arrest at G1 phase and 46% arrest at G2 phase) and apoptosis induction (increase of early apoptosis by 30 times with regard to control). To gain further insights into the mode of action of the investigated platinum(IV) complexes, drug uptake, cathepsin B inhibition and ROS generation were also evaluated. Interestingly an increased ROS generation could be related with the antiproliferative activity of the cyclometallated platinum(IV) series under study in the cisplatin-resistant A-549 lung and HCT-116 cancer cell lines.

The effect of the electrode material on the electrodeposition of zinc from deep eutectic solvents

The voltammetric behaviour of the ZnCl2 containing deep eutectic solvent choline chloride/ethylene glycol 1:2 was investigated on glassy carbon, stainless steel, Au, Pt, Cu, and Zn electrodes. While cyclic voltammetry on glassy carbon and stainless steel showed a cathodic peak for zinc electrodeposition only in the anodic reverse sweep, a cathodic peak was found also in the cathodic forward sweep on Au, Pt, Cu, and Zn. This behaviour is in agreement with the proposed mechanism of zinc deposition from an intermediate species Z, whose formation depends on the cathodic reduction potential of the solvent. The voltammetric reduction of the electrolyte involves hydrogen evolution and as a result the formation of Z and its reduction to zinc depend on the hydrogen overpotential for each electrode material. On Au, Pt, and Cu also the anodic stripping was different from that on glassy carbon and steel due to the formation of surface zinc alloys with the three former metals. The morphology of the zinc layers on Cu has been characterised by scanning electron microscopy and focussed ion beam. X-ray diffraction confirmed the presence of crystalline zinc and a Cu4Zn phase. Spectroelectrochemistry by means of polarization modulation reflection-absorption spectroscopy (PM-IRRAS) on a glassy carbon electrode in the ZnCl2 containing deep eutectic solvent showed characteristic potential dependent changes. The variation of band intensities at different applied potentials correlate with the voltammetry and suggest the formation of a compact blocking layer on the electrode surface, which inhibits the electrodeposition of zinc at sufficiently negative potentials.

Electrochemical Performance of Ionic Liquids with Bis(trifluorosulfonyl)Imide Anion for Lithium-Ion Battery Application

Room temperature ionic liquids (RTILs) formed from bulky cations and anions have attracted significant attention as potential electrolyte components for the next generation of lithium-ion batteries. Unfortunately, the lithium–ion batteries fabricated with neat ILs as electrolytes possess low ionic conductivity and lithium corrosion problems. Both surface-active and ionic IL additives have been used overtime to improve the electrochemical performance.a Bis(trifluoromethylsulfonyl)imide (TFSI-) - based ionic liquids (Fig.1) are known to have low cathodic reduction potentials at graphite electrodes that affect formation of protective layer on solid electrolyte interface (SEI)b. On the contrary, at metal electrodes including lithium, TFSI- anions favor electrolyte reduction which is due to stabilization of LiTFSI ion pair formed under reducing conditions in presence of lithium cations and TFSI anions.Compared to other lithium salts as IL ionic additives, such as LiBF4 and LiTFSI, lithium hexafluorophosphate (LiPF6) demonstrated an improved electrochemical cathodic behavior. Furthermore, the presence and concentration of a lithium salt have an influence on the cathodic potential electrochemical window. For example, addition of LiPF6 to a neat solution of 1-butyl-2,3-dimethyl-imidazolium bis(fluoromethyl-sulfonyl)imide (FSI) has been shown to change the cathodic electrochemical window from -2.8 to -4.10V.c Present study is focused on electrochemical performance evaluation of ionic liquids, specifically 1-ethyl-3 methylimidazolium (EMIM TFSI) and 1-butyl-1-methylpyrrolidonium (PYR14 TFSI) (Fig.1) in symmetrical cells with two lithium metal electrodes and CelgardTM separator.The results for symmetrical coin cells (CR2025) constructed with lithium disks deposited onto 0.5mm spacers and separated by CelgardTM 20mm polyethylene membrane with 12 mL of ionic liquid on each side of the separation membrane will be presented. The electrochemical performance of the symmetrical cells will be compared with the results obtained for the half-cells with the earlier developed silicon-based working electrode. EMIM TFSI and PYR14 TFSI ionic liquids in presence and absence of LiPF6 for symmetrical cells and half-cells will be discussed in terms of coin cell performance, impedance, chemical transformations, and changes to the morphology that take place during cell storage, solid electrolyte interface (SEI) formation, and charge-discharge cycling. NMR study of the ionic liquids will be addressed to study the dynamics of the cations, anions, and ion pairs in presence and absence of ionic additive LiPF6. Pulsed field gradient NMR is used to determine self-diffusion coefficients of 1H and 19F.REFERENCES: a J. Xiang, F. Wu, R. Chen, L.Li, H. Yu, J. of Power Sources, 233, 115 (2013) b Y. Katayama, T. Morita, M. Yamagata, and T. Miura, Electrochemistry (Tokyo, Jpn.), 71, 1033 (2003) c A. S. Best, A. I. Bhatt, and A.F. Hollendamp, J. of the electrochemical Society, 157 (8) A903-A911 (2010)

The solvation and electrochemical behavior of copper acetylacetonate complexes in ionic liquids

The behavior of copper(II) complexes of pentane-2,4-dione and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, [Cu(acac)2] (1) and [Cu(HFacac)2(H2O)] (2), in ionic liquids and molecular organic solvents, was studied by spectroscopic and electrochemical techniques.The electron paramagnetic resonance characterization (EPR) showed well-resolved spectra in most solvents. In general the EPR spectra of [Cu(acac)2] show higher gz values and lower hyperfine coupling constants, Az, in ionic liquids than in organic solvents, in agreement with longer CuO bond lengths and higher electron charge in the copper ion in the ionic liquids, suggesting coordination of the ionic liquid anions. For [Cu(HFacac)2(H2O)] the opposite was observed suggesting that in ionic liquids there is no coordination of the anions and that the complex is tetrahedrically distorted.The redox properties of the Cu(II) complexes were investigated by cyclic voltammetry (CV) at a Pt electrode (d=1mm), in bmimBF4 and bmimNTf2 ionic liquids and, for comparative purposes, in neat organic solvents. The neutral copper(II) complexes undergo irreversible reductions to Cu(I) and Cu(0) species in both ILs and common organic solvents (CH2Cl2 or acetonitrile), but, in ILs, they are usually more easier to reduce (less cathodic reduction potential) than in the organic solvents. Moreover, 1 and 2 are easier to reduce in bmimNTf2 than in bmimBF4 ionic liquid.

Physical Characterization and Reactivity of the Uranyl Peroxide [UO2(η2-O2)(H2O)2]·2H2O: Implications for Storage of Spent Nuclear Fuels

The unusual uranyl peroxide studtite, [UO(2)(η(2)-O(2))(H(2)O)(2)]·2H(2)O, is a phase alteration product of spent nuclear fuel and has been characterized by solid-state cyclic voltammetry. The voltammogram exhibits two reduction waves that have been assigned to the U(VI/V) redox couple at -0.74 V and to the U(V/IV) redox couple at -1.10 V. This potential shows some dependence upon the identity of the cation of the supporting electrolyte, where cations with larger ionic radii exhibit more cathodic reduction potentials. Raman spectroelectrochemistry indicated that exhaustive reduction at either potential result in a product that does not contain peroxide linkers and is likely to be UO(2). On the basis of the reduction potentials, the unusual behavior of neptunium in the presence of studtite can be rationalized. Furthermore, the oxidation of other species relevant to the long-term storage of nuclear fuel, namely, iodine and iodide, has been explored. The phase altered product should therefore be considered as electrochemically noninnocent. Radiotracer studies with (241)Am show that it does not interact with studtite so mobility will not be retarded in repositories. Finally, a large difference in band gap energies between studtite and its dehydrated congener metastudtite has been determined from the electronic absorption spectra.

Role of the Triiodide/Iodide Redox Couple in Dye Regeneration in p-Type Dye-Sensitized Solar Cells

A series of perylene dyes with different optical and electronic properties have been used as photosensitizers in NiO-based p-type dye-sensitized solar cells. A key target is to develop dyes that absorb light in the red to near-infrared region of the solar spectrum in order to match photoanodes optically in tandem devices; however, the photocurrent produced was found to decrease dramatically as the absorption maxima of the dye used was varied from 517 to 565 nm and varied strongly with the electrolyte solvent (acetonitrile, propionitrile, or propylene carbonate). To determine the limitations of the energy properties of the dye molecules and to provide guidelines for future sensitizer design, we have determined the redox potentials of the diiodide radical intermediate involved in the charge-transfer reactions in different solvents using photomodulated voltammetry. E°(I(3)(-)/I(2)(•-)) (V vs Fe(Cp)(2)(+/0)) = -0.64 for propylene carbonate, -0.82 for acetonitrile, and -0.87 for propionitrile. Inefficient regeneration of the sensitizer appears to be the efficiency-limiting step in the device, and the values presented here will be used to design more efficient dyes, with more cathodic reduction potentials, for photocathodes in tandem dye-sensitized solar cells.