Reversible Electron Transfer Reactions Research Articles

An acetate electrolyte for enhanced pseudocapacitve capacity in aqueous ammonium ion batteries

Ammonium ion batteries are promising for energy storage with the merits of low cost, inherent security, environmental friendliness, and excellent electrochemical properties. Unfortunately, the lack of anode materials restricts their development. Herein, we utilized density functional theory calculations to explore the V2CTx MXene as a promising anode with a low working potential. V2CTx MXene demonstrates pseudocapacitive behavior for ammonium ion storage, delivering a high specific capacity of 115.9 mAh g−1 at 1 A g−1 and excellent capacity retention of 100% after 5000 cycles at 5 A g−1. In-situ electrochemical quartz crystal microbalance measurement verifies a two-step electrochemical process of this unique pseudocapacitive storage behavior in the ammonium acetate electrolyte. Theoretical simulation reveals reversible electron transfer reactions with [NH4+(HAc)3]···O coordination bonds, resulting in a superior ammonium ion storage capacity. The generality of this acetate ion enhancement effect is also confirmed in the MoS2-based ammonium-ion battery system. These findings open a new door to realizing high capacity on ammonium ion storage through acetate ion enhancement, breaking the capacity limitations of both Faradaic and non-Faradaic energy storage.

Electrochemical and spectroelectrochemical characterizations of phthalocyanines bearing peripherally tetra-4-carboxyethylenephenoxy anchoring groups and usage as photosensitizers of dye-sensitized solar cell

A series of metal-free and metallo phthalocyanines (MPc) peripherally substituted with tetra-4-carboxyethylenephenoxy (M = 2H+ (H2Pc), Co2+ (CoPc), Zn2+ (ZnPc), and TiO2+ (TiOPc)) are used as dyes in the dye-sensitized solar cells (DSSCs). To predict the feasibility of MPcs as photosensitizers, electrochemical and in-situ spectroelectrochemical characterizations are first carried out since their redox mechanisms and optical responses under electrochemical excitations are the key factor for the requirement of the photosensitizers in DSSCs. The redox activities and opto-electrochemical responses of the compounds make them promising dye candidates with electrochemically reversible and multi-electron electron transfer reactions and suitable HOMO-LUMO band positions. The DSSCs using TiO2 film modified with these MPcs are developed and characterized. DSSC analyses indicate that especially H2Pc and TiOPc among the MPcs illustrate better photovoltaic performances than the others. The increase in efficiency of DSSC consisting of H2Pc and TiOPc is mainly associated with their suitable band positions and high electron lifetimes. When compared with the Pc bearing various substituents, ethylenephenoxy linkers between the Pc ring and the carboxyl anchoring groups significantly enhance the push-pull features between the dyes and TiO2 semiconductor, which results in 1.15, 2.98, 3.17 and 3.97 % power conversion efficiencies with CoPc, ZnPc, H2Pc, and TiOPc based DSSCs respectively.

Stereoselectivity of Interaction of Nonsteroidal Anti-Inflammatory Drug S-Ketoprofen with L/D-Tryptophan in Phospholipid Membranes.

The mechanisms of stereoselectivity of the interaction of chiral drugs with active sites of enzymes and cell receptors attract significant attention. The first reason is the difference in therapeutic activity of the enantiomers of the common drugs. Another reason is the interest in the role of chiral inversion of amino acids involved in various peptides in the development of many diseases including Alzheimer’s, Parkinson’s, type II diabetes, and a number of other pathological conditions. In our study we use elementary chemical process—electron transfer (ET) to simulate individual stages of ligand–receptor and enzyme–substrate interactions. In particular, previous studies of photoinduced ET in chiral donor-acceptor dyads consisting of the nonsteroidal anti-inflammatory drug (R/S)-ketoprofen and (L)-tryptophan show the stereo and spin selectivity of ET in diastereomers. The present study is devoted to the interaction of (S)-ketoprofen with L- and D-enantiomers of tryptophan in homogeneous aqueous solution and in phospholipid membranes. The study was done using the NMR technique and molecular modeling. These approaches confirm efficient penetration of ketoprofen into the lipid bilayer and binding with tryptophan molecule. The short-lived paramagnetic intermediates formed during the photoinduced ET from electron donor tryptophan to ketoprofen have been detected using the chemically induced dynamic nuclear polarization (CIDNP) technique. It was found that S-ketoprofen interacts stereoselectively with tryptophan enantiomers in the lipid membrane. The formation of the ketyl radical of ketoprofen under irradiation leads to the oxidation of membrane lipids and may be the cause of ketoprofen phototoxicity. However, in contrast to a homogeneous solution in phosphate buffer saline, where the amino acid tryptophan accelerates the photodecomposition of KP due to intramolecular hydrogen transfer, tryptophan in a lipid membrane significantly reduces the rate of photodegradation due to a reversible electron (or hydrogen) transfer reaction. The stereoselectivity in the rate of KP and lipids decomposition under UV irradiation of S-ketoprofen in the presence of tryptophan enantiomers in lipid bilayer has been detected.

Abiotic reduction of 3-nitro-1,2,4-triazol-5-one (NTO) and other munitions constituents by wood-derived biochar through its rechargeable electron storage capacity.

The environmental fate of 3-nitro-1,2,4-triazol-5-one (NTO) and other insensitive munitions constituents (MCs) is of significant concern due to their high water solubility and mobility relative to legacy MCs. Plant-based biochars have been shown to possess a considerable electron storage capacity (ESC), which enables them to undergo reversible electron transfer reactions. We hypothesized biochar can act as a rechargeable electron donor to effect abiotic reduction of MCs repeatedly through its ESC. To test this hypothesis, MC reduction experiments were performed using wood-derived biochars that were oxidized with dissolved oxygen or reduced with dithionite. Removal of aqueous NTO, an anion at circumneutral pH, by oxidized biochar was minimal and occurred through reversible adsorption. In contrast, NTO removal by reduced biochar was much more pronounced and occurred predominantly through reduction, with concomitant formation of 3-amino-1,2,4-triazol-5-one (ATO). Mass balance and electron recovery with ferricyanide further showed that (1) the amount of NTO reduced to ATO was relatively constant (85-100 μmol per gram of biochar) at pH 6-10; (2) the fraction of biochar ESC reactive toward NTO was ca. 30% of that toward ferricyanide; (3) the NTO-reactive fraction of the ESC was regenerable over multiple redox cycles. We also evaluated biochar transformation of other MCs, including nitroguanidine (NQ), 2,4-dinitroanisole (DNAN), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). While mass and electron balances could not be established due to sorption, DNAN and RDX reduction by reduced biochar was confirmed via detection of multiple reduction products. In contrast, NQ was not reduced under any of the conditions tested. This study is the first demonstration of organic contaminant degradation through biochar's rechargeable ESC. Our results indicate biochar is a regenerable electron storage medium and sorbent that can remove MCs from water through concurrent reduction and sorption, and is thus potentially useful for pollution control and remediation at military facilities.

Kinetics and Energetics of Intramolecular Electron Transfer in Single-Point Labeled TUPS-Cytochrome c Derivatives.

Electron transfer within and between proteins is a fundamental biological phenomenon, in which efficiency depends on several physical parameters. We have engineered a number of horse heart cytochrome c single-point mutants with cysteine substitutions at various positions of the protein surface. To these cysteines, as well as to several native lysine side chains, the photoinduced redox label 8-thiouredopyrene-1,3,6-trisulfonate (TUPS) was covalently attached. The long-lived, low potential triplet excited state of TUPS, generated with high quantum efficiency, serves as an electron donor to the oxidized heme c. The rates of the forward (from the label to the heme) and the reverse (from the reduced heme back to the oxidized label) electron transfer reactions were obtained from multichannel and single wavelength flash photolysis absorption kinetic experiments. The electronic coupling term and the reorganization energy for electron transfer in this system were estimated from temperature-dependent experiments and compared with calculated parameters using the crystal and the solution NMR structure of the protein. These results together with the observation of multiexponential kinetics strongly support earlier conclusions that the flexible arm connecting TUPS to the protein allows several shortcut routes for the electron involving through space jumps between the label and the protein surface.

Semimicroscopic Theory for Underscreening-Induced Anomalous Migration–Diffusion Coupling

We develop a novel theory for the impedance response of reversible electron transfer reactions under the influence of migration–diffusion coupling. Theory accounts for the influence of the supporting electrolyte, electroactive species, solvent, metal, and the interfacial electric field accounting underscreening. This semimicroscopic formalism is based on a modified electrode surface boundary constraint, which circumvents the essential nonlinearity in the Nernst–Planck equation. The interfacial electric field determines the kinetics of formation of compact electric double layer (C-EDL) embedded with electroactive species and influence the mass transport. This kinetics is governed by an intrinsic C-EDL formation resistance (RH), solution resistance (RΩ), and the extent of ion packing dependent on electrolyte composition. Theory unravels a characteristic ohmic-migration frequency, ω* = D/LMΩ2, a prerequisite for the outer sphere electron transfer step. A dimensionless migration–diffusion coupling number δM is unriddled, which quantifies the extent of migration contribution dependent on the potentials at IHP (ϕ1), OHP (ϕ2), diffuse layer (ϕDL), ion size-corrected screening length, charge on electroactive species, interfacial diffusivity, and RH. The magnitude of impedance (in low-frequency regime) evinces an anomalous nonmonotonic variation with ionic strength. Finally, theory accredits us to understand the underscreening-induced anomalies in migration–diffusion-controlled impedance response.

The Ultra-sensitive Electrochemical Detection of As(III) in Ground Water Using Disposable L-cysteine/Lipoic Acid Functionalised Gold Nanoparticle Modified Screen-Printed Electrodes

An ultrasensitive electrochemical sensor to detect arsenic (III), a highly toxic heavy metal ion, has been successfully developed. The sensing platform composed of L-cysteine (Lcyst) molecules conjugated to reduced lipoic acid (rLA) capped gold nanoparticles and exhibited an indirect band gap energy (Eg) of 1.96 eV. This is a characteristic of a semiconducting material; metals and semiconducting nanomaterials possess good electrochemical properties due to their trivial band gap energies. Surface ligation of the gold nanoparticles with rLA and Lcyst did not only prevent the nanoparticle agglomeration but also improved the susceptibility of the sensor to bind efficiently to heavy metal ions of interest. The electrochemical properties of the sensing platform were demonstrated by a reversible redox electron transfer reaction of the gold oxides due to the presence of gold nanoparticle clusters on the screen-printed carbon electrode surface. The sensor parameters such as the scan rate, pH and the deposition potential were optimised. The sensor was capable of detecting the arsenic (III) ions at the formal peak potential (Epa°′) of −0.307 ± 0.02 V. Subsequently, the sensor demonstrated a low limit of detection with the magnitude of 3 ppb (i.e. 3SD/SLOPE). The dynamic linear range of the developed sensing platform was between 3 and 25 ppb. The sensor was used to detect As(III) in ground water and demonstrated excellent recoveries in spiked samples. The AuNP-rLA-Lcyst sensing platform fabricated for the detection of As(III) heavy metal ion using the square-wave anodic stripping voltammetry.

Modulation of mitochondrial site-specific hydrogen peroxide efflux by exogenous stressors

Oxygen (O2) deprivation and metals are common environmental stressors and their exposure to aquatic organisms can induce oxidative stress by disrupting cellular reactive oxygen species (ROS) homeostasis. Mitochondria are a major source of ROS in the cell wherein a dozen sites located on enzymes of the electron transport system (ETS) and substrate oxidation produce superoxide anion radicals (O2˙‾) or hydrogen peroxide (H2O2). Sites located on ETS enzymes can generate ROS by forward electron transfer (FET) and reverse electron transfer (RET) reactions; however, knowledge of how exogenous stressors modulate site-specific ROS production is limited. We investigated the effects of anoxia-reoxygenation and cadmium (Cd) on H2O2 emission in fish liver mitochondria oxidizing glutamate-malate, succinate or palmitoylcarnitine-malate. We find that anoxia-reoxygenation attenuates H2O2 emission while the effect of Cd depends on the substrate, with monotonic responses for glutamate-malate and palmitoylcarnitine-malate, and a biphasic response for succinate. Anoxia-reoxygenation exerts a substrate-dependent inhibition of mitochondrial respiration which is more severe with palmitoylcarnitine-malate compared with succinate or glutamate-malate. Additionally, specific mitochondrial ROS-emitting sites were sequestered using blockers of electron transfer and the effects of anoxia-reoxygenation and Cd on H2O2 emission were evaluated. Here, we find that site-specific H2O2 emission capacities depend on the substrate and the direction of electron flow. Moreover, anoxia-reoxygenation alters site-specific H2O2 emission rates during succinate and glutamate-malate oxidation whereas Cd imposes monotonic or biphasic H2O2 emission responses depending on the substrate and site. Contrary to our expectation, anoxia-reoxygenation blunts the effect of Cd. These results suggest that the effect of exogenous stressors on mitochondrial oxidant production is governed by their impact on energy conversion reactions and mitochondrial redox poise. Moreover, direct increased ROS production seemingly does not explain the increased adverse effects associated with combined exposure of aquatic organisms to Cd and low dissolved oxygen levels.

Determination of Riboflavin by Nanocomposite Modified Carbon Paste Electrode in Biological Fluids Using Fast Fourier Transform Square Wave Voltammetry

Herein, fast Fourier transformation square-wave voltammetry (FFT-SWV) as a novel electrochemical determination technique was used to investigate the electrochemical behavior and determination of Riboflavin at the surface of a nanocomposite modified carbon paste electrode. The carbon paste electrode was modified by nanocomposite containing Samarium oxide (Sm2O3)/reduced graphene oxide (RGO) (2:1) to improve detection sensitivity of Riboflavin under optimal experimental conditions. Furthermore, the signal-to-noise ratio was significantly increased by application of discrete fast Fourier transformation analysis, background subtraction and two-dimensional integration of the electrode response over the selected potential range and the time window. Obtained cyclic voltammograms demonstrated a diffusion-controlled reversible electron transfer reaction for Riboflavin in phosphate buffer solution (pH=7.2). The peak potential values were pH-dependent, involving the same numbers of protons and electrons. To obtain the maximum sensitivity, some effective parameters such as scan rate (10 mV/s), accumulation time (0.2 s) and potential (+400 mV), frequency (1420 Hz) and amplitude (20 mV) were optimized. As a result, determination of Riboflavin using FFT-SWV showed a linear range of response from 10 to 400 nM (R2=0.9993), with limit of detection of 0.86 nM. An acceptable recovery percent was also obtained for Riboflavin in human plasma samples as criteria of measurement applicability of the proposed modified electrode.

Reversible redox activity of {Mo72Fe30} nano-polyoxometalate cluster in three crystalline forms

The {Mo72Fe30} cluster is the basic unit of three crystalline materials rhombohedral [Mo72Fe30O252(CH3COO)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91]·150H2O (1), orthorhombic [H4Mo72Fe30O254(CH3COO)10{Mo2O7(H2O)}{H2Mo2O8(H2O)}3(H2O)87]·80H2O (2) and host guest system [HxPMo12O40 ⊂ H4MoVI72FeIII30(CH3COO)15-O254(H2O)98]·ca.60H2O (3). The {Mo72Fe30} Keplerate cluster in all the three crystalline compounds actively undergoes reversible redox cycles without any significant structural disintegration. Hydrogen peroxide/molecular oxygen and ascorbic acid/sodium dithionite are found to be suitable oxidizing and reducing agents, respectively. Compound 1 (reasonably soluble in water) shows reversible electron transfer reactions in a homogeneous aqueous medium, whereas, compounds 2 and 3 (having extended structures, thereby insoluble in water) undergo reversible electron transfer reactions in heterogeneous manner in solid-liquid interface reactions.

Calcium channel blocker lercanidipine electrochemistry using a carbon black-modified glassy carbon electrode.

Lercanidipine, a third-generation dihydropyridine calcium L-type channel blocker, redox behavior at different carbon electrode materials, in a wide pH range, using cyclic, square-wave, and differential pulse voltammetry, was studied. A comparison was made between unmodified glassy carbon electrode (GCE) and boron-doped diamond electrode (BDDE), and GCE and BDDE modified with a carbon black (CB) nanoparticle embedded within a dihexadecylphosphate (DHP) nanostructured film (CB-DHP/GCE and CB-DHP/BDDE). Lercanidipine oxidation, for 3.4 < pH < 9.5, is an irreversible, diffusion-controlled, pH-dependent process that occurs in two consecutive steps, with the transfer of one electron and one proton, at the N1 and C4 positions in the 1,4-dihydropyridine ring. For pH > 9.5, both oxidation processes are pH-independent and a pKa = 9.40 was determined. Lercanidipine reduction at pH = 7.0 is an irreversible process, and the lercanidipine reduction products are electroactive and follow a reversible electron transfer reaction. Lercanidipine electroanalytical determination, at a nanostructured GCE modified with a CB-DHP film (CB-DHP/GCE), with no need for N2 purging, with a detection limit of 0.058μM (3.58 × 10-5gL-1) and a quantification limit of 0.176μM (1.08 × 10-4gL-1), was achieved. Graphical abstract.

Effect of Molecular Structure of Quinones and Carbon Electrode Surfaces on the Interfacial Electron Transfer Process

Quinones can undergo thermodynamically reversible proton-coupled electron transfer reactions and are being applied as electroactive compounds in aqueous organic batteries. However, the electrochemi...

Photoelectrochemical sewage treatment by a multifunctional g-C3N4/Ag/AgCl/BiVO4 photoanode for the simultaneous degradation of emerging pollutants and hydrogen production, and the disinfection of E. coli

This study describes the photoelectrochemical (PEC) treatment of authentic sewage from Hong Kong for H2 production and degradation of emerging pollutants (EP’s) simultaneously, and disinfection of E. coli. The g-C3N4/Ag/AgCl/BiVO4 (CAB-1) coated thin film acted as the photoanode in a three-electrode configuration PEC cell and real sewage as the electrolyte. Electrochemical studies revealed the near reversible, diffusion-controlled and high electron transfer reaction at the electrode-electrolyte surface. For CAB-1, the achieved photocurrent density was 0.1–0.2 mA cm−2 at 1.23 V vs. RHE exhibiting the highest PEC degradation efficiency (11.15% h−1 cm−2) compared to other base materials like g-C3N4/BiVO4 (6.88% h−1 cm−2) or Ag/AgCl/BiVO4 (4.06% h−1 cm−2). During the same reaction, the evolved 118 μmol of H2 gas corresponds to a Faradic efficiency of 69.38%. The composition of sewage was found to influence the overall PEC efficiency. The higher amount of total suspended solids, turbidity, and anionic species decreased the efficiency while as the other parameters like alkaline pH increased the PEC efficiency. Photo-electrochemically, the CAB-1 also effectively disinfected the E. coli present in the sewage with a final discharge of ≤1000 CFU/mL which is within the permissible discharge limits (≤1500 CFU/mL), in Hong Kong.

Further investigation of the equivalence of staircase and linear sweep voltammograms. IV - Averaged-current staircase voltammetry applied to electrochemical reactions involving soluble species

This article focuses on the sampled-current and averaged-current staircase voltammetry techniques compared to linear potential sweep/cyclic voltammetry for the investigation of electrochemical reactions involving soluble species. First, based on analytical solutions of the relevant voltammetric models, theoretical investigation is carried out assuming reversible electron transfer reactions and different mass transport conditions in the electrolyte, i.e. semi-infinite or finite-length planar diffusion, and diffusion to an inlaid disk electrode. Next, solving numerically the appropriate integral-equation-based model, further investigation takes into account the electron transfer kinetics, the uncompensated resistance of the electrolyte, and the interfacial double-layer charging, under one-dimensional mass transport conditions. Main conclusion is that the averaged-current staircase voltammetry technique should provide nearly the same current data as the linear potential sweep/cyclic voltammetry technique under a variety of experimental conditions.

Polyoxometalate Heterogeneous Nanostructures As Cathodes for Mg2+ Ion Storage

As global energy demands continue to rise each year, current state-of-the-art Li-ion battery (LIB) systems are predicted to reach the limit in the amount of energy that they can supply. In addition to this, LIBs are also limited by the low resource availability of Li metal. One proposed solution is to move away from LIBs to multivalent ion systems; of these alternatives, magnesium (Mg) is considered a promising material for the next generation of rechargeable batteries. Unlike Li, Mg metal does not form dendritic structures during cycling which would allow it to be employed as an anode which has a specific capacity of 2205 mAh/g compared to 777 mAh/g of the graphite anode that is currently used in LIBs. Mg also has a very high elemental abundance in the earth’s crust (2.44x104 ppm) which would drive down the production cost while simultaneously ensuring the longevity of these batteries in terms resource availability. Most importantly, the divalent nature of the Mg-ion means that it can carry twice the amount of charge per ion compared to Li. This is largely related to the high volumetric capacity (3833 mAh/ml) of Mg which is superior to even that of Li metal. While there is potential for Mg to replace LIBs, commercialization of these batteries has been hindered by sluggish insertion kinetics into cathode host materials as a direct result of the strong coulombic interactions experienced by the divalent Mg-ion. Due to this drawback, conventional metal oxide or sulfide insertion cathodes for Mg batteries tend to exhibit low capacities and operating voltages. In response to this, a large portion of Mg battery research is currently focused on the development of novel materials capable of functioning as cathodes for fast and efficient Mg-ion insertion. The idea proposed in this work is to depart from the conventional intercalation mechanism of LIBs and move towards a molecular cluster battery (MCB) based on polyoxometalate (POM) metal oxygen cluster molecules of early transition metals (Mo, W, V, or Nb). The unique redox activity of POMs are due to their intrinsic ability to form highly stable reduced and oxidized species allowing them to partake in fast reversible electron transfer reactions. Although POMs are also able to function as electron reservoirs, POMs themselves have negligible electronic conductivity as well as high solubility in both aqueous and organic media. Therefore, in order for these materials to be used as electrodes for electrochemical energy storage, they must first undergo hybridization with highly conductive insoluble substrates such as conductive organic polymers (COPs) or multi-walled carbon nanotubes (MWCNTs). The fabrication of heterogenous cathodes provide a “wiring” effect by electrically connecting the POM molecules allowing them all to take part in the redox chemistry while simultaneously anchoring them to a substrate, thus preventing any loss of active material to electrolyte dissolution during cycling. By taking advantage of the synergistic effect of pairing the ionically conductive POM molecule with the electrically conductive substrate; the resulting cathode material will thus be capable of fast electron transfer reactions with high ionic mobility. In this work, hybrid nanostructured electrodes of poly-3,4-ethylenedioxythiophene (PEDOT) and a phosphomolybdic acid (H3PMo12O40) POM have been fabricated electrochemically and applied as cathodes for Mg-ion storage. Preliminary cyclic voltammetry and galvanostatic cycling data have demonstrated an enhancement in the capacity of the PEDOT cathode after integration of the POM molecules throughout the polymer matrix. The initial cycling studies have also shown that the PEDOT-POM redox peaks are still present after 7 days of soaking in the organic electrolyte which suggests that the POM molecules do not readily dissolve out of the PEDOT matrix. This work highlights the potential of redox active POM inorganic clusters to function as cathodes with the capability of advancing the current state of Mg batteries.

Further investigation of the equivalence of staircase and linear scan voltammograms. I- Sampling conditions for reversible reactions involving soluble species

Since the pioneering work by Osteryoung et al., J. Electroanal. Chem. 222 (1987) 69, the discussion about the equivalence of staircase and linear scan voltammograms is based on the ‘Abelian’ or ‘non-Abelian’ feature of the integral equation used for modelling the voltammetric response of redox systems. In practice, further investigation is required for prediction of the optimal value of current sampling parameter (γopt) that guarantees the equivalence of voltammetric and staircase voltammetric data. This first article focuses on reversible electron transfer reactions involving soluble species. The discussion is based on integral-equation-based models and the use of local/global criteria for the comparison of staircase and linear scan voltammograms. Main results in the article and the Supporting information joined should concern the dependence of γopt on the electrode potential, the potential step amplitude of staircase signal, the reaction scheme, and the mass transport process involved.

Organic Ion-Pair Charge-Transfer (IPCT) Nanoparticles: Synthesis and Photoinduced Electrochromism.

We report fabrication of photoinduced-electrochromic (or photochromic) organic nanoparticles that can be regarded as a new class of photoswitchable nanomaterials. Ion association between dicationic benzyl viologen (BzV2+) and tetraphenylborate anion (TPB-) in water produces organic ion-pair charge-transfer-type (IPCT) nanoparticles with a mean diameter of 15-20 nm. Electrostatic binding of BzV2+ with TPB- results in the prominent appearance of a new broad absorption band at 400-550 nm, which can be assign to the CT transition between these species. The IPCT nanoparticles show an interesting photoinduced electrochromic behavior caused by the electron transfer (ET) from TPB- to BzV2+, giving an intense blue-color dispersion. The feed charge stoichiometry (= [TPB-]/(2 × [BzV2+])) does not influence the kinetics of the photoinduced electrochromism, but it remarkably controls the reverse ET reaction (or retention time) in the nanoparticles; in the case of neutral stoichiometry, a very long-lived ET state can be observed, which is mainly due to decomposition of the oxidized TPB (sacrificial donor) and the resultant absence of the counterpart of benzyl viologen radical cations (BzV+•) for back ET reaction. On the other hand, the excess presence of TPB- does not cause the decomposition of oxidized TPB in the nanoparticle, making the reverse ET reaction faster, but a moderately long-lived ET state is still observable, which is probably originated from efficient electron diffusion or transport between molecules inside the nanoparticle.

Polyoxometalate Modified Biomass Carbon Composites for Supercapacitor Electrodes

Polyoxometalates (POMs), nanoscale transition metal-oxide clusters, have emerged as promising building blocks for the fabrication of pseudocapacitive electrodes.[i] These POM clusters undergo fast reversible electron transfer reactions and have multiple stable redox states, ideal characteristics for energy storage applications.[ii] In order to leverage these properties for use in electrochemical capacitor (EC) electrodes, these POM clusters must be immobilized on a stable carbon substrate to create a composite electrode. There is synergy in this combination as the POMs contribute faradaic redox processes, while the carbon provides stability, high conductivity, and electrochemical double layer capacitive (EDLC) contributions. Porous carbon derived from biomass is an excellent potential substrate for these POM-carbon composites owing to its low cost, simple synthesis procedure, and high specific surface area. Here, we will report on our synthesis of porous carbon substrates derived from pine cone biomass via a two-stage carbonization and chemical activation procedure. These pine cone carbon samples are highly porous with specific surface areas over 2500 m2 g-1. In a sulfuric acid electrolyte, the high surface area of these samples results in a double layer capacitance of 265 F g-1. In order to further enhance this already large capacitance, the biomass carbons were modified with Keggin POM clusters, PMo12O40 3- and PW12O40 3- via a single step chemisorption. We have discovered that the intrinsic porosity and surface conditions of the pine cone biomass carbon are particularly well suited to the immobilization of Keggin POMs. Additionally, by adjusting the activation conditions, the carbon porosity can be tuned to further enhance POM chemisorption. The result is biomass carbon hybrids with exceptionally high loading of POM clusters. The redox activity of these immobilized POMs leads to significantly enhanced area and volume specific capacitance compared to the bare carbon substrate (Figure 1). In this talk, we will present the full characterization of the POM-biomass carbon hybrids as well as discuss the activation conditions and resulting substrate porosity necessary for superior POM adsorption. The POM chemistry that results in the optimal pseudocapacitive performance will also be presented and discussed. [i] M. Genovese, K. Lian. Current Opinion in Solid State and Materials Science. 19 (2015) 126-127 [ii] B.B Xu, L. Xu, G.G. Gao, W.H. Guo, S.P. Liu. J. Colloid Interface Sci. 330 (2009) 408 Figure 1

Diagnostic Criteria for Identifying Electrode Reaction Mechanisms By Cyclic Square Wave Voltammetry

This presentation will demonstrate the utility of cyclic square wave voltammetry for determining the mechanism of an electrode reaction. The impact of theoretical and empirical parameters on the shape of the current-voltage curve was evaluated computationally. Simulations were conducted for single and consecutive reversible electron transfer reactions as well as those that are kinetically controlled and/or chemically coupled. The simulation involved systematic variation in alpha, k0, Keq, kf + kb, amplitude, increment, period and switching potential. Trends in peak potentials, currents, and widths with variation in each of these parameters were elucidated. From these trends, diagnostic criteria for assigning each mechanism was identified and, in many cases, experimentally verified. Our goal is to facilitate the use of cyclic square wave voltammetry as a mechanistic tool by both experts and non-experts in electrochemistry. These criteria enable accurate diagnosis of the electrode reaction mechanism and measurement of pertinent kinetic and thermodynamic quantities.

A novel enzymatic glucose biosensor and sensitive non-enzymatic hydrogen peroxide sensor based on graphene and cobalt oxide nanoparticles composite modified glassy carbon electrode

In the present study, we have demonstrated the fabrication of novel enzymatic glucose biosensor using glucose oxidase (GOD) as a model enzyme which has been immobilized onto the graphene (GF) and cobalt oxide nanoparticles (Co3O4-NPs) composite modified electrode. The GF/Co3O4-NPs composite was prepared by hydrothermal method and characterized by using scanning electron microscopy, X-ray diffraction and elemental analysis. The GOD immobilized GF/Co3O4-NPs modified electrode shows a well defined redox behaviour indicating the reversible proton and electron transfer reaction of GOD. A heterogeneous electron transfer rate constant (Ks) of immobilized GOD has been calculated to be 3.52s−1 which is much higher than that of GOD immobilized GF supports. The fast electron transfer of GOD is attributed to the excellent biocompatibility of Co3O4-NPs and high conductivity of the GF. The fabricated glucose biosensor exhibits a wider linear response for glucose from 0.5mM to 16.5mM with the sensitivity of 13.52μAmM−1cm−2. In addition, a non-enzymatic H2O2 sensor has been further developed using GF/Co3O4-NPs composite modified electrode. The GF/Co3O4-NPs composite electrode shows an excellent electrocatalytic activity towards H2O2 with the response time of <10s. The H2O2 response at GF/Co3O4-NPs composite modified electrode displays a linear response ranging from 0.2 to 211.5μM with a limit of detection of 0.06μM.