Temperature-dependent Cyclic Voltammetry Research Articles

Thermal stability on solid state symmetric supercapacitors with hydrothermally synthesized Cu2CoSnS4 electrodes

The effects of thiourea concentration on crystal phase, morphology, and the elemental composition and electrochemical characteristics (ECs) of hydrothermally synthesized Cu2CoSnS4 (CCTS) electrodes are systematically studied. In a three-terminal (3T) configuration, layered structure morphology with Cu-rich chemical composition-based electrodes exhibits higher ECs than other electrodes. The thermal reliability of devices up to 60℃ is practically validated via temperature-dependent cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) measurements for single symmetric solid-state supercapacitor (SSC) devices. The maximum of Cp=(251.87 ± 30.56)Fg−1, E=(89.55 ± 10.35)Whkg−1, P=(800 ± 40.32)Wkg−1 and voltage window expanded up to 1.6 V including red LED operation for 6 min are achieved for the serially connected two SSCs at 1Ag−1, indicating that CCTS can be one promising electrode material for SSCs.

Electrochemical characterization of an engineered red copper protein featuring an unprecedented entropic control of the reduction potential

Copper is a ubiquitous metal in biology that, among other functions, is implicated in enzymatic redox catalysis and in protein electron transfer (ET). When it comes to ET, copper sites are found in two main forms, mononuclear type 1 (T1) and binuclear CuA sites, which share a common cupredoxin fold. Other relevant copper sites are the so-called type 2 (T2), which are more resilient to undergo direct electrochemistry and are usually involved in catalysis. Here we report the electrochemical and spectroscopic characterization of a novel T2-like copper site engineered following the loop swapping strategy. The ligand loop sequence of the newly discovered T1 copper site from Nitrosopumilus maritimus was introduced into the CuA scaffold from Thermus thermophilus yielding a chimeric protein that shows spectroscopic features different from both parental proteins, and resemble those of red T2 copper sites, albeit with a shorter Cu-S(Cys) bond length. The novel T2 site undergoes efficient direct electrochemistry, which allows performing temperature-dependent cyclic voltammetry studies. The obtained results reveal that this chimera constitutes the first example of a copper protein with entropically controlled reduction potential, thereby contrasting the enthalpic supremacy observed for all other copper sites reported so far. The underlying bases for this entropic control are critically discussed.

Comparison of molybdenum and rhenium oxo bis-pyrazine-dithiolene complexes - in search of an alternative metal centre for molybdenum cofactor models.

A pair of structurally precise analogues of molybdenum and rhenium complexes, [Et4N]/K2[MoO(prdt)2] and K[ReO(prdt)2] (prdt = pyrazine-2,3-dithiolene), were synthesized. These complexes serve as structural models for the active sites of bacterial molybdenum cofactor containing enzymes. They were comprehensively characterized and investigated by NMR, computationally supported IR and resonance Raman spectroscopy, cyclic voltammetry, mass spectrometry, elemental analysis and single-crystal X-ray diffraction. All compiled data are discussed in the context of comparing chemical and electronic structures and consequences thereof. This study constitutes the first investigation of a potential alternative Moco model system bearing rhenium as the central metal in an identical coordination environment to its molybdenum analogue. Structural evaluation revealed a slightly stronger M[double bond, length as m-dash]O bond in the rhenium complex in accordance with spectroscopic results, i.e. observed bond strengths. Thermodynamic parameters for the redox processes MoIV ↔ MoV and ReIV ↔ ReV were obtained by temperature dependent cyclic voltammetry. In contrast to molybdenum, rhenium loses entropy upon reduction and its redox potential is more temperature sensitive, indicating more significant differences than the respective diagonal relationship between the two metals in the periodic table might suggest and questioning rhenium's suitability as a functional artificial active site metal.

Electrochemical investigation of uranyl species reduction in alkaline oxalate electrolyte and microstructural characterization of deposited nanocrystalline UO2 thin films

In this study, electrochemical reduction behaviour of uranyl ions was investigated from an alkaline oxalate complex electrolyte. Detailed results of scan rates, pH and temperature dependent cyclic voltammetry were analysed to extract diffusion coefficients and to elucidate reduction mechanism. A two-step mechanism was established where the first step involving reduction of UO22+ to UO2+ was a slower and reversible in nature and the second step was proton assisted reduction of UO2+ to UO2. Detailed speciation study of the electrolyte confirmed [UO2(C2O4)3]4− as the predominant species in the pH range 5.0 to 8.5. XPS analyses of as-deposited oxide film confirmed about the formation of UO2 with a small percentage of UO3. For annealed films (at 973 K for 1 h), majority of oxide film was present in mixed valence state containing U6+ and U5+ with a small amount of U4+. High resolution transmission electron microscope (HR-TEM) examination of as-deposited film revealed the deposition of an ultra-nanocrystalline UO2 film with average gain size of 3.0 nm. However, annealed sample showed substantial grain growth associated with reduced inter-grain amorphous region. The average grain size obtained was 9.8 nm with lattice fringe spacing was 0.32 nm corresponding to the fcc UO2.

Cover Picture: Hydrogen-Bonding Effect on Spin-Center Transfer of Tetrathiafulvalene-Linked 6-Oxophenalenoxyl Evaluated Using Temperature-Dependent Cyclic Voltammetry and Theoretical Calculations (Chem. Asian J. 2/2014)

Cover Picture: Hydrogen-Bonding Effect on Spin-Center Transfer of Tetrathiafulvalene-Linked 6-Oxophenalenoxyl Evaluated Using Temperature-Dependent Cyclic Voltammetry and Theoretical Calculations (Chem. Asian J. 2/2014)

Hydrogen-Bonding Effect on Spin-Center Transfer of Tetrathiafulvalene-Linked 6-Oxophenalenoxyl Evaluated Using Temperature-Dependent Cyclic Voltammetry and Theoretical Calculations

The stable tetrathiafulvalene (TTF)-linked 6-oxophenalenoxyl neutral radical exhibits a spin-center transfer with a continuous color change in solution caused by an intramolecular electron transfer, which is dependent on solvent and temperature. Cyclic voltammetry measurements showed that addition of 2,2,2-trifluoroethanol (TFE) to a benzonitrile solution of the neutral radical induces a redox potential shift that is favorable for the spin-center transfer. Temperature-dependent cyclic voltammetry of the neutral radical using a novel low-temperature electrochemical cell demonstrated that the redox potentials change with decreasing temperature in a 199:1 CH2Cl2/TFE mixed solvent. Furthermore, theoretical calculation revealed that the energy levels of the frontier molecular orbitals involved in the spin-center transfer are lowered by the hydrogen-bonding interaction of TFE with the neutral radical. These results indicate that the hydrogen-bonding effect is a key factor for the occurrence of the spin-center transfer of TTF-linked 6-oxophenalenoxyl.

The influence of counter anions on the underpotential deposition of mercury(II) on Au(1 1 1): temperature-dependent studies

We have studied the temperature dependence of the underpotential deposition (upd) of mercury(II) onto Au(1 1 1) electrodes from a series of electrolytes in which anion interactions could be varied from essentially zero (i.e., HClO 4) to strongly interacting with either the Au(1 1 1) substrate (i.e., H 2SO 4) or with solution phase Hg 2+ ions (i.e., HC 2H 3O 2). Both isothermal and non-isothermal cells were used to make temperature-dependent cyclic voltammetry measurements. Analysis of the temperature-dependent cyclic voltammetric curves at a constant Γ Hg yielded values for the half-reaction entropy and enthalpy, Δ S 0 rc(upd) and Δ H 0 rc(upd), for the Hg upd reaction. Δ S 0 rc(upd) values of −30.9 and −18.3 J/mol K were measured for perchloric acid and sulfuric acid electrolytes, respectively. The respective Δ H 0 rc(upd) values for these electrolytes were −182 and −184 kJ/mol. In acetic acid media, thermodynamic functions were found to depend on the electrolyte pH. Δ S 0 rc(upd) values increased monotonically from +16.4 to +83.5 J/mol K as the pH was increased from 2.7 to 5.3 at a constant formal acetate concentration of 0.10 M. Under the same experimental conditions, Δ H 0 rc(upd) increased from −150 to −102 kJ/mol.

Structural Control of the Reversible Dimerization of π-Conjugated Oligomeric Cation Radicals

The reversible dimerization of the electrochemically or chemically generated cation radicals of diversely substituted tetrathienylenevinylenes (1−6) has been analyzed by concentration and temperature-dependent cyclic voltammetry, UV−vis, near-IR, and ESR spectroscopies, and time-resolved spectroelectrochemistry. For unsubstituted and end-substituted oligomers 1 and 2 the apparent redox potential corresponding to the formation of the cation radical (Eapp1) shifts negatively when increasing substrate concentration or when decreasing temperature, as expected for an ECDimE scheme. Such effects are not observed for compounds 3−6 containing β-substituted thiophene rings suggesting that the corresponding cation radicals do not dimerize. UV−vis and near-IR absorption spectra of the chemically generated cation radical 2•+ show, in addition to the two absorption bands of the monomeric cation radical, two hypsochromically shifted transitions confirming that 2•+ dimerizes already at room temperature. These additional...

Temperature-dependent cyclic voltammetry of oxo-bridged dimers of relevance to photosynthetic water oxidation

Temperature-dependent cyclic voltammetry of oxo-bridged dimers of relevance to photosynthetic water oxidation