Unusual Electrochemical Properties Research Articles

Unusual electrochemical properties of boron and silicon Co-doped diamond electrodes

Boron-doped diamond (BDD) films exhibit exceptional physicochemical properties and have been utilized in numerous fields. As a common impurity in diamond, silicon is inevitably introduced into the diamond lattice during certain growth process. However, there are limited reports on the impact of silicon co-doping on the electrochemical properties of BDD electrodes. In this paper, we prepared a series of BDD electrodes with various silicon contents and made a systematic evaluation of these electrodes in terms of physicochemical properties. The results indicated that silicon and boron co-doped diamond (SiBDD) electrodes displayed a broader potential window and lower background current compared to the pure BDD electrode. Additionally, we observed that the electron transfer rate of the electrodes in the inner ([Fe(CN)6]3−/4−) redox systems exhibited a rising trend with increasing silicon content, whereas the electron transfer rate of the outer ([Ru(NH3)6]3+/2+) redox systems displayed contrasting trend. Surface analyses and electrochemical measurements results suggested that the unusual phenomena might stem from the alterations in surface functional groups and carrier density of the electrode inducing by silicon co-doping. In general, our results demonstrate, for the first time, that Si co-doping can influence the surface functional groups and carrier behavior of BDD electrodes, thereby altering the electrode's electrochemical performance. This provides new insights for the design of high-performance diamond electrodes.

Facile hydrothermal synthesized MoV2O8/MoO3 microclusters-based electrode materials for high-capacity asymmetric supercapacitors

Engineering novel transition metal oxide materials with micro/nanostructures has endowed unusual electrochemical properties. Herein, we reported the MoV2O8/MoO3 microclusters (MVO/MO MCs) synthesized by a simple and facile hydrothermal process. Furthermore, the MVO/MO MC-based electroactive materials were studied at various annealing temperatures of 300, 400, and 500 °C. The prepared materials wrere characterized via different analysis methods for the investigation of phase, morphology, surface area, and oxidation states. The optimized MVO/MO MC electrode revealed a superior specific capacity of 392.58 mAh g−1 at 1 A g−1 (2844 F g−1) in a 1 M KOH electrolyte solution. The MVO/MO MC electrode also exhibited excellent capacity retention of 101% with a corresponding coulombic efficiency of 99%. Accordingly, the fabricated pouch-like asymmetric supercapacitor (ASC) with the MVO/MO MCs and activated carbon materials delivered maximum power and energy densities of 2306.95 W Kg−1 and 37.06 Wh kg−1, respectively. Additionally, the ASC showed superior capacity retention of 128% with 97% of coulombic efficiency. Also, the ASC devices were employed to test the practical application by powering electronic gadgets.

Transparent wafer-scale self-standing fluorinated graphene films

The fluorination of self-standing graphene oxide (GO) films under mild conditions at 70 °C for 1h using a mixture of elemental fluorine and nitrogen gases (0.35 F2/0.65 N2 v/v) results in transparent, highly fluorinated (F/C = 1 as seen by XPS) graphene oxide (FGO) films which maintain initial densely packed structure and mechanical strength. Most of the oxygen atoms in the GO film were replaced by fluorine after fluorination, and two types of carbon-fluorine bonds coexist, i.e. primarily weakened C⋯F bonds and also pure covalent C–F bonds as evidenced by FTIR, XPS, NMR, and cyclic voltammetry when FGO is used as electrode in Li/electrolyte (PC:EC:3DMC/LiTFSI 1 M)/FGO cell similar to a lithium battery. To further understand the fluorination mechanism and to distinguish the reaction steps, xenon difluoride XeF2 was used as fluorinating agent for GO and in situ EPR and FTIR analyses suggest hydroxyl groups as preferential reactive sites. These self-standing transparent FGO films exhibit unusual electrochemical properties in lithium battery and can be used as hydrophobic lubricant membranes because of the low and stable coefficient of friction evidenced in the present work.

(Charles W. Tobias Award) Advancing Porous Electrodes for Electrochemical Systems

Electrochemical processes are poised to play a pivotal role in the evolving global power system as the efficient interconversion of electrical and chemical energy can enable the deployment of sustainable technologies that support the decarbonization of the electric grid, power the automotive fleet, and offer new opportunities in chemical manufacturing. However, advances in electrochemical science and engineering are needed to address the stringent performance, cost, and scale requirements of these emerging application spaces. Many prominent electrochemical technologies (e.g., flow batteries, fuel cells, electrolyzers) leverage forced convection to increase volumetric productivity. Of particular importance to these systems are porous electrodes which provide surfaces for electrochemical reactions, manage reactant distribution, facilitate mechanical compression, and conduct electrons and heat. Accordingly, the systematic design and engineering of porous electrodes can greatly improve cell performance and durability.In this presentation, I will describe methods for disaggregating and quantifying resistive losses in porous electrodes using redox probes, diagnostic flow cells, and electrochemical modeling. I will then discuss how these tools can be used to guide the design of new electrode architectures with tailored property sets. Specifically, using redox flow batteries as an example, I will offer three vignettes. First, I will discuss the role of electrode microstructure and surface chemistry in balancing electrochemical and fluid dynamic performance within flow cells. Second, building on these results, I will describe efforts to develop electrodes using non-solvent induced phase separation, a synthetic approach which enables property combinations difficult to achieve via current manufacturing processes. Third and finally, I will highlight the potential of conductive particle suspensions as flowable, reconfigurable electrodes whose unusual electrochemical, rheological, and transport properties may unlock more versatile reactor designs.

Recent advances of boron-doped diamond electrochemical sensors toward environmental applications

The electrocatalytic properties of boron-doped diamond (BDD) electrodes have been considered for a variety of sensing applications. The unusual electrochemical properties of BDD include a large potential window, a small background current, and better resistance to fouling than other carbon-based electrodes. The use of BDD for remediation and environmental sensing applications has recently attracted the interest of the sensor research community. This review focuses on recent developments that involve the use of BDD as an environmentally friendly sensing material for environmental analysis. The electrochemical properties of boron-doped diamond that has undergone surface modification (e.g., with metals or enzymes) will be considered. Recent achievements involving the use of BDD electrodes for detecting pesticides, mycotoxins, peroxides, and phenolic compounds are considered.

Intrinsic electrochemical activity of Ni in Ni3Sn4 anode accommodating high capacity and mechanical stability for fast-charging lithium-ion batteries

Fast interfacial kinetics derived from bicontinuous three-dimensional (3D) architecture is a strategic feature for achieving fast-charging lithium-ion batteries (LIBs). One of the main reasons is its large active surface and short diffusion path. Yet, understanding of unusual electrochemical properties still remain great challenge due to its complexity. In this study, we proposed a nickel–tin compound (Ni3Sn4) supported by 3D Nickel scaffolds as main frame because the Ni3Sn4 clearly offers a higher reversible capacity and stable cycling performance than bare tin (Sn). In order to verify the role of Ni, atomic-scale simulation based on density functional theory systematically addressed to the reaction mechanism and structural evolution of Ni3Sn4 during the lithiation process. Our findings are that Ni enables Ni3Sn4 to possess higher mechanical stability in terms of reactive flow stress, subsequently lead to improve Li storage capability. This study elucidates an understanding of the lithiation mechanism of Ni3Sn4 and provides a new perspective for the design of high-capacity and high-power 3D anodes for fast-charging LIBs.

Indeno[1,2‐b]fluorene‐Based [2,2]Cyclophanes with 4n/4n and 4n/[4n+2] π Electrons: Syntheses, Structural Analyses, and Excitonic Coupling Properties

AbstractIndeno[1,2‐b]fluorene‐based [2,2]cyclophanes with 4n/4n and 4n/[4n+2] π‐electron systems were prepared, and their structures were identified by X‐ray crystallography. With short π–π distances around 3.0 Å, [2.2](5,11)indeno[1,2‐b]fluorenophane and its precursor [2.2](5,11)indeno[1,2‐b]fluorene‐6,12‐dionophane exhibit remarkable transannular interactions, leading to their unusual electrochemical and photophysical properties. With the aid of femtosecond transient absorption spectroscopy, the transition from the monomeric excited state to the redshifted H‐type dimeric state was first observed, correlating to the calculated excitonic energy splitting and the steady‐state absorption spectra induced by charge‐transfer‐mediated superexchange interaction.

Indeno[1,2-b]fluorene-Based [2,2]Cyclophanes with 4n/4n and 4n/[4n+2] π Electrons: Syntheses, Structural Analyses, and Excitonic Coupling Properties.

Indeno[1,2-b]fluorene-based [2,2]cyclophanes with 4n/4n and 4n/[4n+2] π-electron systems were prepared, and their structures were identified by X-ray crystallography. With short π-π distances around 3.0 Å, [2.2](5,11)indeno[1,2-b]fluorenophane and its precursor [2.2](5,11)indeno[1,2-b]fluorene-6,12-dionophane exhibit remarkable transannular interactions, leading to their unusual electrochemical and photophysical properties. With the aid of femtosecond transient absorption spectroscopy, the transition from the monomeric excited state to the redshifted H-type dimeric state was first observed, correlating to the calculated excitonic energy splitting and the steady-state absorption spectra induced by charge-transfer-mediated superexchange interaction.

Synthesis and Characterization of a Novel KFeSO4 F Polymorph: Structural, Electrochemical and Magnetic Properties

Since the discovery of the promising electrode material LiFePO4, recent research has been focusing on the development of new iron-based polyanionic materials for next generations Li- and Na-ion batteries displaying better performances while still preserving cost and sustainability benefits.1,2 Towards this quest, our group explored the wide family of sulfate-based compounds, with the most prominent members being monoclinic Li2Fe(SO4)2 and triplite LiFeSO4F having redox potentials of 3.83 V and 3.9 V vs. Li+/Li0, respectively.3,4 In order to further investigate the rich crystal chemistry offered by 3d-metal-based fluorosulfates, we explored the feasibility of using other alkali metals such as Na and K instead of Li. Through this approach we discovered a KFeSO4F phase, which adopts a KTiOPO4 structure and releases K+ ions via a complex electrochemical process.5 Knowing that sulfate-based compounds are prone to polymorphism, we recently unveiled a new low-temperature KFeSO4F polymorph.6 Using combined synchrotron and neutron powder diffraction as well as electron diffraction, it was shown that the compound adopts a complex layered-like structure that crystallizes in a large monoclinic unit cell. Impedance measurements together with the Bond Valence Energy Landscape approach show that the K+ ions, which are located between the layers, are mobile within the structure and can be electrochemically removed at an average potential of 3.7 V vs. Li+/Li0. Lastly, neutron diffraction experiments coupled with SQUID measurements reveal a long range antiferromagnetic ordering of the Fe2+ magnetic moments. These results confirm once again the richness of polymorphisms in sulfate-based materials, which, besides unusual electrochemical properties, show interesting physical properties. (1) Padhi, A. K.; Nanjundaswamy, K. S.; Masquelier, C.; Goodenough, J. B. Mapping of Transition Metal Redox Energies in Phosphates with NASICON Structure by Lithium Intercalation. J. Electrochem. Soc. 1997, 144 (8), 2581–2586. (2) Masquelier, C.; Croguennec, L. Polyanionic (Phosphates, Silicates, Sulfates) Frameworks as Electrode Materials for Rechargeable Li (or Na) Batteries. Chem. Rev. 2013, 113 (8), 6552–6591. (3) Reynaud, M.; Ati, M.; Melot, B. C.; Sougrati, M. T.; Rousse, G.; Chotard, J.-N.; Tarascon, J.-M. Li2Fe(SO4)2 as a 3.83 V Positive Electrode Material. Electrochem. Commun. 2012, 21, 77–80. (4) Ati, M.; Melot, B. C.; Chotard, J.-N.; Rousse, G.; Reynaud, M.; Tarascon, J.-M. Synthesis and Electrochemical Properties of Pure LiFeSO4F in the Triplite Structure. Electrochem. Commun. 2011, 13 (11), 1280–1283. (5) Recham, N.; Rousse, G.; Sougrati, M. T.; Chotard, J.-N.; Frayret, C.; Mariyappan, S.; Melot, B. C.; Jumas, J.-C.; Tarascon, J.-M. Preparation and Characterization of a Stable FeSO 4 F-Based Framework for Alkali Ion Insertion Electrodes. Chem. Mater. 2012, 24 (22), 4363–4370. (6) Lander, L.; Rousse, G.; Abakumov, A. M.; Sougrati, M.; Tendeloo, G. van; Tarascon, J.-M. Structural, Electrochemical and Magnetic Properties of a Novel KFeSO4F Polymorph. J. Mater. Chem. A 2015, 3 (39), 19754–19764.

Anomalous Interface and Surface Strontium Segregation in (La1-ySry)2CoO4±δ/La1-xSrxCoO3-δ Heterostructured Thin Films.

Heterostructured oxides have shown unusual electrochemical properties including enhanced catalytic activity, ion transport, and stability. In particular, it has been shown recently that the activity of oxygen electrocatalysis on the Ruddlesden-Popper/perovskite (La1-ySry)2CoO4±δ/La1-xSrxCoO3-δ heterostructure is remarkably enhanced relative to the Ruddlesden-Popper and perovskite constituents. Here we report the first atomic-scale structure and composition of (La1-ySry)2CoO4±δ/La1-xSrxCoO3-δ grown on SrTiO3. We observe anomalous strontium segregation from the perovskite to the interface and the Ruddlesden-Popper phase using direct X-ray methods as well as with ab initio calculations. Such Sr segregation occurred during the film growth, and no significant changes were found upon subsequent annealing in O2. Our findings provide insights into the design of highly active catalysts for oxygen electrocatalysis.

Lanthanide(III) Double‐Decker Complexes with Octaphenoxy‐ or Octathiophenoxyphthalocyaninato Ligands – Revealing the Electron‐Withdrawing Nature of the Phenoxy and Thiophenoxy Groups in the Double‐Decker Complexes

AbstractA series of heteroleptic and homoleptic bis(phthalocyaninato) lanthanide(III) complexes, namely M(Pc)[Pc(OPh)8], M[Pc(OPh)8]2, Eu(Pc)[Pc(SPh)8], and Eu[Pc(SPh)8]2 [M = Eu, Ho, Lu; Pc = unsubstituted phthalocyaninate; Pc(OPh)8 = 2,3,9,10,16,17,23,24‐octaphenoxyphthalocyaninate; Pc(SPh)8 = 2,3,9,10,16,17,23,24‐octathiophenoxyphthalocyaninate](1–8) have been prepared. The molecular structure of Eu[Pc(OPh)8]2 (4) has been determined by single‐crystal X‐ray diffraction analysis. All of the new sandwich compounds have been characterized with various spectroscopic methods. Their electrochemical characteristics show that the introduction of phenoxy or thiophenoxy groups onto the peripheral positions of the phthalocyaninato ligand makes the double‐decker harder to oxidize and easier to reduce than the analogous compounds without the (thio)phenoxy group. Theoretical calculations, with the semi‐empirical PM3 method, indicate that the change in the energy level of the frontier orbitals of these ligands induced by the electron‐withdrawing substituents is responsible for these unusual electrochemical properties. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The structure of the 2[4Fe–4S] ferredoxin from Pseudomonas aeruginosa at 1.32-Å resolution: comparison with other high-resolution structures of ferredoxins and contributing structural features to reduction potential values

The structure of the 2[4Fe-4S] ferredoxin (PaFd) from Pseudomonas aeruginosa, which belongs to the Allochromatium vinosum (Alvin) subfamily, has been determined by X-ray crystallography at 1.32-A resolution, which is the highest up to now for a member of this subfamily of Fds. The main structural features of PaFd are similar to those of AlvinFd. However, the significantly higher resolution of the PaFd structure makes possible a reliable comparison with available high-resolution structures of [4Fe-4S]-containing Fds, in an effort to rationalize the unusual electrochemical properties of Alvin-like Fds. Three major factors contributing to the reduction potential values of [4Fe-4S]2+/+ clusters of Fds, namely, the surface accessibility of the clusters, the N-H...S hydrogen-bonding network, and the volume of the cavities hosting the clusters, are extensively discussed. The volume of the cavities is introduced in the present work for the first time, and can in part explain the very negative potential of cluster I of Alvin-like Fds.

Peculiar electrochemical behaviors of (1 − x)LiNiO 2· xLi 2TiO 3 cathode materials prepared by spray drying

The cathode materials, (1− x)LiNiO 2· xLi 2TiO 3 with 0.05≤ x≤0.5, were first prepared by a spray drying route. The XRD results indicated that co-substituting Li and Ti for Ni in LiNiO 2 contributes to increasing cations disorder in the materials. Charge–discharge tests in the voltage range of 3.0–4.4 V exhibited expected results: the more simple charge–discharge curves, the deceased capacity and the increased Columbic irreversibility with increasing x. However, when charged up to 4.8 V, the materials with x≥0.075 surprisingly presented unusual electrochemical properties, an excess charge capacity beyond the oxidization of Ni 3+ to Ni 4+ in materials with the presence of a charge plateau at about 4.5–4.7 V during the initial cycle. These phenomena are very similar to those reported in (1− y)LiNi 0.5Mn 0.5O 2· yLi 2MnO 3 [J. Electrochem. Soc. 149 (2002) A815]. The sample with x=0.05 indicated promising electrochemical properties in term of capacity and cyclability even charged to 4.8 V.

Metal binding studies with macrocyclic hexathioethers: Transition metal complexes of 22S6 and 20S6

AbstractThe two macrocyclic hexathioethers, 1,4,7,12,15,18‐hexathiacyclodocosane (22S6) and 1,4,7,11,14,17‐hexathiacycloeicosane (20S6) have been examined with respect to their complexation behavior towards a variety of transition metals ions. In all of these complexes, the two ligands generate relatively strong ligand field, but their field strengths fall between the smaller ring and stronger field hexathioether ligands (such as 18S6) and larger ring and weaker field ligands, such as 24S6. The stability of the complexes towards hydrolysis parallels their reduced field strengths with first row transition metal complexes of both ligands showing enhanced sensitivity to solvolysis reactions compared to the analogous 18S6 complexes. In general, the electrochemical behavior of the hexathioether complexes shows metal centered oxidations which occur at higher potentials than those complexes involving trithioethers. We suggest that the hexathioether ligand is less able to expand and contract during the reduction and oxidation of the metal center. The complex [Pd(22S6)]2+ does not display the unusual spectroscopic and electrochemical properties observed in the analogous 18S6 complex.

A New Class of Cyclic Hexamer: [Co6 L6 ]24- (H6 L=hexaazatriphenylene hexacarboxylic acid).

The construction of nanostructured polynuclear metal complexes with cyclic topologies, particularly those containing multifunctional ligands containing π-electronic structures, is of great interest since they can potentially lead to compounds with unusual electrochemical properties. A novel cyclic module with a hexacarboxylate derivative is described. The results show that the peripheral substituents not only control the electronic structure, but also influence its mode of coordination.

Low temperature synthesis and electrochemical performance of crystallized FeVO 4·1.1H 2O

A wet synthesis method, which consists in a precipitation reaction occurring without pH control, is described to obtain a hydrated crystallized iron orthovanadate. Both reaction time and temperature parameters were used to reach the thermodynamic equilibrium formation conditions of FeVO 4·1.1H 2O. By means of several characterization techniques this compound was identified as similar to the fervanite mineral Fe 4V 4O 16·5H 2O. Like the other iron-based orthovanadates, this fervanite-type phase displays unusual electrochemical properties with respect to Li acceptance/removal at low average voltages. From the electrochemical data collected on the artificial fervanite and its dehydrated products, a linear correlation between the material water content and its electrochemical performances, namely in terms of irreversible and reversible capacities, has been found.

π Conjugation Across the Tetrathiafulvalene Core: Synthesis of Extended Tetrathiafulvalene Derivatives and Theoretical Analysis of their Unusual Electrochemical Properties

π Conjugation Across the Tetrathiafulvalene Core: Synthesis of Extended Tetrathiafulvalene Derivatives and Theoretical Analysis of their Unusual Electrochemical Properties

Pi conjugation across the tetrathiafulvalene core: synthesis of extended tetrathiafulvalene derivatives and theoretical analysis of their unusual electrochemical properties

A series of extended tetrathiafulvalene (TTF) derivatives bearing one or two 1,4-dithiafulven-6-yl substitutents has been prepared. The new compounds present remarkable electrochemical singularities compared with other TTF derivatives, which are strongly affected by the nature of the substitution on the lateral heterocycle(s). This unusual electrochemical behaviour follows a square-scheme sequence and is attributed to structural changes upon oxidation of the pi-donating molecules. Digital simulations of the electrochemical data have been used to reach the values of the kinetic and thermodynamic constants involved in the square scheme. Theoretical calculations establish an important contribution of a highly delocalised resonant form involving a tetravalent sulphur in oxidised species, which could justify the occurrence of an electrochemical behaviour distinct from that of TTF. Finally, third-order susceptibilities chi 3 of two of these systems, for which electron-donating and electron-withdrawing substituents coexist and are conjugated through the TTF pi system, are given.

Unusual spectroscopic and electrochemical properties of the 2[4Fe-4S] ferredoxin of Thauera aromatica.

A reduced ferredoxin serves as the natural electron donor for key enzymes of the anaerobic aromatic metabolism in the denitrifying bacterium Thauera aromatica. It contains two [4Fe-4S] clusters and belongs to the Chromatium vinosum type of ferredoxins (CvFd) which differ from the "clostridial" type by a six-amino acid insertion between two successive cysteines and a C-terminal alpha-helical amino acid extension. The electrochemical and electron paramagnetic resonance (EPR) spectroscopic properties of both [4Fe-4S] clusters from T. aromatica ferredoxin have been investigated using cyclic voltammetry and multifrequency EPR. Results obtained from cyclic voltammetry revealed the presence of two redox transitions at -431 and -587 mV versus SHE. X-band EPR spectra recorded at potentials where only one cluster was reduced (greater than -500 mV) indicated the presence of a spin mixture of S = (3)/(2) and (5)/(2) spin states of one reduced [4Fe-4S] cluster. No typical S = (1)/(2) EPR signals were observed. At lower potentials (less than -500 mV), the more negative [4Fe-4S] cluster displayed Q-, X-, and S-band EPR spectra at 20 K which were typical of a single S = (1)/(2) low-spin [4Fe-4S] cluster with a g(av) of 1.94. However, when the temperature was decreased stepwise to 4 K, a magnetic interaction between the two clusters gradually became observable as a temperature-dependent splitting of both the S = (1)/(2) and S = (5)/(2) EPR signals. At potentials where both clusters were reduced, additional low-field EPR signals were observed which can only be assigned to spin states with spins of >(5)/(2). The results that were obtained establish that the common typical amino acid sequence features of CvFd-type ferredoxins determine the unusual electrochemical properties of the [4Fe-4S] clusters. The observation of different spin states in T. aromatica ferredoxin is novel among CvFd-type ferredoxins.

Functional acetylenic molecular architecture

Abstract