Rotating Disk Electrode Voltammetry Research Articles

Experiments and Calculation on New N,N-bis-Tetrahydroacridines.

Tetrahydroacridines arouse particular interest due to the potential possibilities of application in the medical field and protection against corrosion. Bis-tetrahydroacridines were newly synthesized by Pfitzinger condensation of 5,5'-(ethane-1,2-diyl) diindoline-2,3-dione with several cyclanones. NMR, MS, and FT-IR were used to prove their molecular structure. In addition, a computer-aided study was performed for the lowest energy conformers of each structure, in vacuum conditions, at ground state using DFT models to assess their electronic properties. UV-Vis and voltammetric methods (cyclic voltammetry, differential pulse voltammetry, and rotating disk electrode voltammetry) were used to investigate their optical and electrochemical properties. The results obtained for these π-conjugated heteroaromatic compounds lead to the conclusion that they have real potential in applications in different fields such as pharmaceuticals and especially as corrosion inhibitors.

Direct Comparisons of Oxygen Electro-Reduction across Molecular and Extended Oxides

Our work is focused on understanding hydrogen transfer in redox-active metal oxides as candidates for next-generation catalytic architectures, using oxygen electro-reduction as a model reaction. We are specifically studying the interrelationships between hydrogen transfer electrocatalysis across what we term the “molecules-to-materials design continuum” by directly comparing electrochemical properties of molecular tungsten-based polyoxometalates (polyoxotungstates) and extended tungsten oxides.The goal of this study was to critically compare trends of activity and selectivity towards the two-electron oxygen reduction reaction using a series of three catalyst composites derived from molecular polyoxotungstates: (1) the intact molecule adsorbed on a conductive carbon support; (2) the same composite after thermal decomposition of the molecule to bulk WO3; and (3) an intermediate state comprising the partially decomposed molecule.Catalyst composites were synthesized by wet impregnation of the polyoxotungstate (TBA)4W10O32 (TBA = tetrabutylammonium) from acetonitrile on Vulcan carbon, targeting catalyst loadings that yield well-dispersed molecular units. We then used thermal treatments over a range of temperatures associated with progressive thermal decomposition to the intermediate and fully decomposed states. Thermal decomposition reactions and products were further characterized using thermogravimetric analysis and in-situ powder X-ray diffraction. Electrocatalytic measurements were made using standard analytical protocols comprising rotating-disk electrode voltammetry of carbon-supported catalysts deposited as thin films on glassy carbon substrates.On thermal treatment, we observed that the polyoxotungstate loses stabilizing counterions with progressive rearrangement into disordered clusters and ultimately crystalline nanoparticles of orthorhombic WO3. Each of these various forms exhibit broadly similar reactivity towards the oxygen reduction reaction. Electroanalytical results suggest all three tungsten-based composites are poor oxygen reduction catalysts with activities comparable to that of the carbon support. Nonetheless, Levich analysis suggests high selectivity for 2-electron conversion to H2O2 and catalytic onsets that correlate well with distinct voltametric features corresponding to H-activation and, in the case of extended oxides, bulk proton insertion. Ongoing work is focused on extending these studies toward more tractable hydrogen transfer reactions and identifying alternative catalysts with more thermodynamically accessible mechanisms for H activation.More broadly, we hypothesize that these types of apples-to-apples comparisons between molecular and extended catalysts will reveal vital information about the impact of active site composition and electronic structure on H-transfer catalysis.

Scalable Synthesis and Characterisation of a Liquid 2,3,5,6-tetraallylbenzene-1,4-diol Quinone

Organic redox species are finding uses in numerous research and development applications, such as electrochemical sensors, batteries, and production of chemicals. This paper presents a synthesis pathway of a redox-active liquid of 2,3,5,6-tetraallylbenzene-1,4-diol. The synthesis of 2,3,5,6-tetraallylbenzene-1,4-diol was found repeatable at approximately 60 g scale, with a total conversion of 92% across four synthesis steps. High purity was achieved with no further purification. The intermediates and compounds were characterized using attenuated total reflectance infrared spectroscopy, proton nuclear magnetic resonance, differential scanning calorimetry, thermogravimetric analysis, cyclic voltammetry, rotating disk electrode voltammetry, density, and viscosity measurements. The structural characterization verified the structure of 2,3,5,6-tetraallylbenzene-1,4-diol. Electrochemical characterization revealed a quasi-reversible response, a diffusion coefficient similar to the diffusion coefficient of hydroquinone.

Kinetics of Electrocatalytic Oxygen Reduction Reaction over an Activated Glassy Carbon Electrode in an Alkaline Medium

Hydrogen peroxide is a promising substitute for fossil fuels because it produces non-hazardous by-products. In this work, a glassy carbon GC was anodized in sulphuric acid at +1.8 V to prepare the working electrode. It was utilized to investigate the oxygen reduction reaction (ORR) in a basic medium containing 0.1 M NaOH as a supporting electrolyte. The objective of this investigation was to synthesize hydrogen peroxide. X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), linear polarization, cyclic voltammetry (CV), and rotating disk electrode voltammetry (RDE) were performed for characterization and investigation of the catalytic properties. The RDE analysis confirmed that oxygen reduction reactions followed two electrons’ process at an activated GC electrode. Hence, the prepared electrode generated hydrogen peroxide from molecular oxygen at a potential of around −0.35 V vs. Ag/AgCl (sat. KCl), significantly lower than the pristine GC surface. The transfer coefficient, standard reduction potential, and standard rate constant were estimated to be 0.75, −0.27 V, and 9.5 × 10−3 cm s−1, respectively.

Co-Catalyzed Hydrofluorination of Alkenes: Photocatalytic Method Development and Electroanalytical Mechanistic Investigation.

The hydrofluorination of alkenes represents an attractive strategy for the synthesis of aliphatic fluorides. This approach provides a direct means to form C(sp3)-F bonds selectively from readily available alkenes. Nonetheless, conducting hydrofluorination using nucleophilic fluorine sources poses significant challenges due to the low acidity and high toxicity associated with HF and the poor nucleophilicity of fluoride. In this study, we present a new Co(salen)-catalyzed hydrofluorination of simple alkenes utilizing Et3N·3HF as the sole source of both hydrogen and fluorine. This process operates via a photoredox-mediated polar-radical-polar crossover mechanism. We also demonstrated the versatility of this method by effectively converting a diverse array of simple and activated alkenes with varying degrees of substitution into hydrofluorinated products. Furthermore, we successfully applied this methodology to 18F-hydrofluorination reactions, enabling the introduction of 18F into potential radiopharmaceuticals. Our mechanistic investigations, conducted using rotating disk electrode voltammetry and DFT calculations, unveiled the involvement of both carbocation and CoIV-alkyl species as viable intermediates during the fluorination step, and the contribution of each pathway depends on the structure of the starting alkene.

Deconvoluting the Role of Electrolyte pH, Structural Sensitivity, and Electric Field Effects on the Electrochemical Hydrogenation of Phenol

Traditional thermochemical hydrogenation (TCH) methods that are used in the U.S. chemical and petroleum industries to produce value-added fuels are highly energy intensive. To achieve hydrogenation, they require high temperature and pressure, along with an external source of hydrogen that usually comes from steam methane reformation. Electrochemical hydrogenation (ECH) is an attractive alternative that replaces the thermal driving force with an applied electrical potential, allowing ECH to operate near ambient conditions. The participating protons come from the aqueous electrolyte solution rather than externally produced hydrogen. These features of ECH lower its energy demand compared to TCH and result in less greenhouse gas emissions. ECH is also promising for the processing of biomass feedstocks and could be powered directly by renewable energy, further minimizing the environmental impact.The addition of an aqueous electrolyte and electric field means that insights from TCH should not be directly translated to ECH systems, however, this is often the case in the literature. Fundamental studies on ECH of aromatic hydrocarbons (AHs) are necessary to address current limitations including: competition with the hydrogen evolution reaction (HER) resulting in lower faradaic efficiency, low rates compared to TCH, and little control over selectivity and degree of hydrogenation. For instance, the role of electrolyte pH on phenol ECH remains poorly understood. While some groups have reported negligible phenol turnover rates in electrolytes of pH 10 and above on Pt/C and Pd/C catalysts [1], Song et al. have shown that turnover rates and efficiency are highest on Rh/C at pH 10 [2]. Yet, the idea that low pH (3-5) is best has persisted and the source of the pH dependence remains unknown.In this work we use phenol as a simple representative AH for lignocellulosic bio-oil. We have shown with rotating disk electrode voltammetry that the presence of phenol in electrolytes of pH ~10 enhances HER rates on Pt, Pd, and Au catalysts. Considering that the pKa of phenol is also 10.0, we propose that interfacial phenol molecules channel protons to the catalyst surface by way of facile proton dissociation/reassociation, lowering the barrier for adsorbed H formation in alkaline electrolytes. While this may explain, in part, the low phenol turnover rates observed at higher pH, we further investigate why the opposite is observed on Rh/C catalysts. The role of atomic surface structure is also critical to the adsorption geometry and coverage of AHs. We use well-defined, low-index Pt single crystals to identify the true structural sensitivity for the ECH of AHs. We show with select stepped single crystal surfaces that there is a synergetic role between terrace width/step density that defines activity, balancing coverage of AH molecules, formation of surface adsorbed H, and transfer of that H to AH reactants. We use a low-volume, membrane-separated flow cell for chrono-amperometry followed by product analysis to correlate pH, structural sensitivity, and applied potential to phenol ECH rates and faradaic efficiency. With an understanding of the role of atomic surface structure and the true source of pH dependence, we propose strategies for enhancing phenol turnover rates at lower overpotentials, improving faradaic efficiency, and controlling selectivity.

Breaking Down the Performance Losses in O2-Evolution Stability Tests of IrO2-based Electrocatalysts

Understanding the deactivation mechanisms affecting the state-of-the-art, Ir oxide catalysts employed in polymer electrolyte water electrolyser (PEWE-) anodes is of utmost importance to guide catalyst design and improve PEWE-durability. With this motivation, we have tried to decouple the contributions of various degradation mechanisms to the overall performance losses observed in rotating disk electrode (RDE) tests on three different, commercial Ir oxide catalysts (pure or supported on Nb2O5). Specifically, we investigated whether these performance decays stem from an intrinsic deactivation of the catalysts caused by alterations in their oxidation state, crystalline structure, morphology and/or Ir-dissolution, and also assessed possible decreases in the catalyst loading caused by the delamination of the materials over the course of these OER-stability tests. Additionally, we also examined recently reported artifacts related to the use of RDE voltammetry for such measurements and found that neither these nor the above mechanisms (or combinations thereof) can cause the totality of the observed performance losses. Beyond these uncertainties, complementary PEWE-tests showed that this apparent RDE-instability is not reproduced in this application-relevant environment.

Redox properties of N-hydroxyimides in sulfuric acid-acetonitrile mixed solution as a HAT mediator for alcohol oxidation

Two hydroxyimides, N-hydroxysuccinimide and N-hydroxy-1,8-naphthalimide, showed chemically reversible redox responses in a sulfuric acid-acetonitrile mixture. In the mixed solution containing benzyl alcohol, catalytic oxidation of alcohol using N-oxyl radicals generated by the oxidation of hydroxyimide as a mediator was observed. The reaction between the mediator and alcohol was quantitatively evaluated from measurements by rotating disk electrode voltammetry.

Electrocatalytic Hydrogen Evolution Reaction from Acetic Acid over Gold Immobilized Glassy Carbon Surface

A hydrogen fuel cell is a highly promising alternative to fossil fuel sources owing to the emission of harmless byproducts. However, the operation of hydrogen fuel cells requires a constant supply of highly pure hydrogen gas. The scarcity of sustainable methods of producing such clean hydrogen hinders its global availability. In this work, a noble Au-atom-decorated glassy carbon electrode (Au/GCE) was prepared via a conventional electrodeposition technique and used to investigate the generation of hydrogen from acetic acid (AA) in a neutral electrolyte using 0.1 M KCl as the supporting electrolyte. Electrochemical impedance spectroscopy (EIS), open circuit potential measurement, cyclic voltammetry (CV), and rotating disk electrode voltammetry (RDE) were performed for the characterization and investigation of the catalytic properties. The constructed catalyst was able to produce hydrogen from acetic acid at a potential of approximately −0.2 V vs. RHE, which is much lower than a bare GCE surface. According to estimates, the Tafel slope and exchange current density are 178 mV dec−1 and 7.90×10−6 A cm−2, respectively. Furthermore, it was revealed that the hydrogen evolution reaction from acetic acid has a turnover frequency (TOF) of approximately 0.11 s−1.

Electrochemistry and Mass Transport of Ytterbium(III) in Bis(trifluoromethylsulfonyl)imide-Based Room-Temperature Ionic Liquids: Effects of Temperature, Viscosity, and Electrode Materials

Cyclic staircase voltammetry, rotating disk electrode voltammetry, controlled potential coulometry, and electrochemical impedance spectroscopy were used to probe the electrochemistry and mass transport of Yb3+ in the six room temperature ionic liquids based on the bis(trifluoromethylsulfonyl)imide (Tf2N−) anion with, 1-(1-butyl)−3-methylimidazolium (BuMeIm+), 1-(1-butyl)−1-methylpyrrolidinium (BuMePyro+), 1-(1-butyl)pyridinium (BuPy+), 1-butyltrimethylammonium (BuMe3N+), 1-ethyl-3-methylimidazolium (EtMeIm+), and tri(1-butyl)methylammonium (Bu3MeN+) cations. These investigations were carried out at glassy carbon as well as polycrystalline gold, platinum, and tungsten electrodes. The heterogeneous electron transfer rate of the quasireversible Yb3+/2+ redox couple was found to depend strongly on the electrode materials with the fastest rate observed at gold and the slowest rate found at tungsten, but was independent of the physicochemical properties of the various ionic liquids, in particular, the absolute viscosity. However, the mass transport of Yb3+ was dependent on the viscosity, and the temperature dependence of the diffusion coefficients was well represented by a Vogel-Tammann-Fulcher type expression for glass-forming ionic liquids. Analysis of the diffusion coefficient data with the Stokes-Einstein equation indicated that the solvodynamic radius of the diffusing Yb3+ was constant and independent of the structure and properties of the ionic liquid cations. The solvodynamic radius of Yb3+ was estimated from the “stick model” for the Stokes-Einstein equation. Application of the Random Closest Packing (RCP) model for spheres in consideration of the solvodynamic radius of the diffusing Yb3+ and the ionic radii of Yb3+ and Tf2N−, indicated that the former must diffuse in association with ∼5–6 of the anions.

Electrochemical and spectral studies of rhodanine in view of heavy metals determination

AbstractThe electrochemical study of 2‐Sulfanylidene‐1,3‐thiazolidin‐4‐one (rhodanine, R) was performed on a glassy carbon working electrode by using three methods: differential pulse voltammetry (DPV), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) at rotating disk electrode voltammetry (RDE). The CV, DPV, and LSV at RDE curves for R were recorded at different concentrations in 0.1 M TBAP/CH3CN. Polymeric films were formed by successive cycling at different potentials and by controlled potential electrolysis. The film formation was proved by recording the CV curves of the chemically modified electrodes (CMEs) in transfer solutions containing ferrocene in 0.1 M TBAP/CH3CN. The obtained CMEs were used for the detection of heavy metal ions. Synthetic samples of heavy metal ions (Cd (II), Pb (II), Cu (II), Hg (II)) of concentrations between 10−7 and 10−5 M were analyzed using CMEs prepared in different conditions. The most intense signal was obtained for Pb(II) ion (estimated detection limit = 10−7 M), which shows that these CMEs can be used for Pb(II) ion detection. The ability of R to form complexes with Pb(II) ion was also tested by UV‐Vis spectrometry. The obtained results showed the formation of Pb(II)R2 as the most stable complex.

PH Driven Pathways to Promote the Electrochemical Hydrogenation of Phenol and Other Aromatic Hydrocarbons

The electrochemical hydrogenation (ECH) of bio-mass derived compounds is an attractive alternative to traditional thermochemical hydrogenation (TCH) methods that are used in the U.S. chemical and petroleum industries to produce value-added fuels and chemicals. TCH uses high pressures and temperatures, along with an external source of hydrogen gas typically produced via methane reformation; these requirements make it an energy intensive process. ECH has the advantages of operating near ambient conditions and sourcing the participating hydrogen from the aqueous electrolyte solution, resulting in reduced energy costs and CO2 emissions compared to TCH. The applied potential provides an additional parameter for controlling selectivity, which makes ECH more suitable to handle the wide chemical variability of biomass-derived feedstocks.Aromatic hydrocarbons are of interest as model compounds for lignocellulosic bio-oil [1]. The ECH of aromatic hydrocarbons proceeds with high faradaic efficiency (FE) at low overpotentials, however, the ECH turnover rate remains low at these potentials. There is no simple fix to this, as any increase in overpotential, to increase ECH rate, will reduce the reaction FE due to competition with the hydrogen evolution reaction (HER). In this work we address the need for a more fundamental understanding of ECH systems to promote high turnover rates at low overpotentials. Specifically for phenol TCH, it is well known that the hydrogenation is limited by the formation/addition of surface adsorbed hydrogen. The current ECH literature draws on these TCH studies and assumes that phenol ECH is also limited by surface adsorbed hydrogen [2]. Thus, most ECH work is done is acidic media, where the kinetics of surface adsorbed hydrogen formation are fastest on platinum [3]. HER, however, is also faster on platinum in acidic media [4], making it more difficult to achieve high faradaic efficiency.Because of this limited scope of investigation, the impact of electrolyte chemistry, i.e. pH, on ECH kinetics has only been sparingly investigated. In this work, we investigate a new pathway for enhanced rates at low overpotentials, driven by the acid-base chemistry of reactants and using electrolyte pH to promote dissociative adsorption. By tailoring the electrolyte pH based on the pKa of the reactant molecule, we can lower the barrier associated with the first hydrogenation step, improving overall reaction kinetics. We demonstrate this effect with phenol ECH at various pH electrolyte on low-index single crystal electrodes using rotating disk electrode voltammetry and chrono-amperometry with product analysis. The ECH of acetophenone and benzaldehyde are also included to compare the effect of different functionalities on the phenyl ring. We report on the structural sensitivity, influence of pH and resulting electric field effects, and present new mechanistic insights for phenol ECH. With these insights we propose methods to promote higher ECH rates at lower overpotentials.

Insights into the Electrochemical Hydrogenation of Phenol

Traditional thermochemical hydrogenation (TCH) methods that are used in the U.S. chemical and petroleum industries to produce value-added fuels are highly energy intensive. To achieve hydrogenation, they require high temperature and pressure, along with an external source of hydrogen that usually comes from methane reformation. Electrochemical hydrogenation (ECH) is an attractive alternative that replaces the thermal driving force with an applied electrical potential, allowing ECH to operate near ambient conditions. The participating hydrogen comes from the aqueous electrolyte solution rather than externally produced hydrogen. These features of ECH lower its energy demand compared to TCH and result in less greenhouse gas emissions. ECH is also promising for the utilization of biomass feedstocks and could be powered directly by renewable energy, further minimizing its environmental impact.Aromatic hydrocarbons are of interest as model compounds for lignocellulosic bio-oil [1]. The ECH of aromatic hydrocarbons proceeds with high faradaic efficiency (FE) at low overpotentials, however, the ECH turnover rate remains low at these potentials. There is no simple fix to this because any increase in overpotential to increase ECH rate will reduce the reaction FE due to competition with the hydrogen evolution reaction (HER). In this work we address the need for a more fundamental understanding of ECH systems to promote high turnover rates at low overpotentials. In phenol TCH, it is well known that the hydrogenation is limited by the formation/addition of surface adsorbed hydrogen. The current ECH literature draws on these TCH studies and assumes that phenol ECH is also limited by surface adsorbed hydrogen [2]. Thus, most ECH work is done is acidic media, where the kinetics of surface adsorbed hydrogen formation are fastest on platinum [3]. HER, however, is also faster on platinum in acidic media [4], making it more difficult to achieve high FE.Because of this limited scope of investigation, the impact of electrolyte chemistry, i.e. pH, on ECH kinetics has only been sparingly investigated. In this work, we investigate a new pathway for enhanced rates at low overpotentials, driven by the acid-base chemistry of reactants and using electrolyte pH to promote dissociative adsorption. By tailoring the electrolyte pH based on the pKa of the reactant molecule, we can lower the barrier associated with the first hydrogenation step, improving overall reaction kinetics. We demonstrate this effect with phenol ECH at various pH electrolyte on low-index single crystal electrodes using rotating disk electrode voltammetry and chrono-amperometry with product analysis. We report on the structural sensitivity, influence of pH and resulting electric field effects, and present new mechanistic insights for phenol ECH. With these insights we propose methods to promote higher ECH rates at lower overpotentials.

Electrochemical Hydrogenation of Aromatic Hydrocarbons

Electrochemical hydrogenation (ECH) of bio-mass derived compounds is an attractive alternative to traditional thermochemical hydrogenation (TCH) methods that are used in the U.S. chemical and petroleum industries to produce value-added fuels and chemicals. TCH uses high pressures and temperatures, along with an external source of hydrogen gas typically produced via methane reformation, in order to achieve hydrogenation; these requirements make it an energy intensive process. ECH has the advantages of operating near ambient conditions and sourcing the participating hydrogen from the aqueous electrolyte solution, resulting in reduced energy costs and CO2 emissions compared to TCH. Furthermore, the applied potential provides an additional parameter for controlling selectivity, making ECH more suitable to handle the wide chemical variability of biomass-derived feedstocks.Aromatic hydrocarbons are of interest as model compounds for lignocellulosic bio-oil [1]. The ECH of aromatic hydrocarbons proceeds with high faradaic efficiency (FE) at low overpotentials, however, the ECH turnover rate remains low at these potentials. There is no simple fix to this, as any increase in overpotential in an attempt to increase the degree hydrogenation will reduce the reaction FE, due to competition with the hydrogen evolution reaction (HER). In this work we address the need for a more fundamental understanding of ECH systems to promote high turnover rates at low overpotentials. In phenol TCH, it is well known that the hydrogenation is limited by the formation/addition of surface adsorbed hydrogen. The current ECH literature draws on these TCH studies and assumes that phenol ECH is also limited by surface adsorbed hydrogen [2]. Thus, most ECH work is done is acidic media, where the kinetics of surface adsorbed hydrogen formation are fastest on platinum [3]. HER, however, is also faster on platinum in acidic media [4], making it more difficult to achieve high faradaic efficiency.We have investigated the ECH of phenol in aqueous electrolyte at varying pH (1, 3, 11, and 13) on low-index single crystal platinum electrodes using rotating disk electrode voltammetry. We have also included the ECH of acetophenone and benzaldehyde to compare the effect of different functionalities on the phenyl ring. The conversion and faradaic efficiency have been determined for these molecules at pH 1 and pH 11 at selected potentials. In this poster we will present new insights on the ECH reaction mechanism of aromatic hydrocarbons along with methods to promote higher ECH rates at low overpotentials.[1] J. Yan et al., "Characterizing Variability in Lignocellulosic Biomass: A Review," ACS Sustainable Chemistry & Engineering, vol. 8, no. 22, pp. 8059-8085, 2020, doi: 10.1021/acssuschemeng.9b06263.[2] N. Singh et al., "Aqueous phase catalytic and electrocatalytic hydrogenation of phenol and benzaldehyde over platinum group metals," Journal of Catalysis, vol. 382, pp. 372-384, 2020, doi: 10.1016/j.jcat.2019.12.034.[3] S. Intikhab, J. D. Snyder, and M. H. Tang, "Adsorbed Hydroxide Does Not Participate in the Volmer Step of Alkaline Hydrogen Electrocatalysis," ACS Catalysis, vol. 7, no. 12, pp. 8314-8319, 2017, doi: 10.1021/acscatal.7b02787.[4] I. Ledezma-Yanez, W. D. Z. Wallace, P. Sebastián-Pascual, V. Climent, J. M. Feliu, and M. T. M. Koper, "Interfacial water reorganization as a pH-dependent descriptor of the hydrogen evolution rate on platinum electrodes," Nature Energy, vol. 2, no. 4, 2017, doi: 10.1038/nenergy.2017.31.

Size and Charge Effects on Organic Flow Battery Crossover Evaluated By Quinone Permeabilities through Nafion

Organic and metalorganic reactants have become promising for long-lifetime flow batteries. Synthetic chemistry unlocks a wide design space to tailor reactant redox potential, solubility, chemical and electrochemical stability, redox kinetics, and transport properties. Minimizing the crossover of reactants through the membrane or separator is one crucial design goal. To that end, this work contributes a systematic evaluation of size- and charge-based effects on small molecule permeability through Nafion. These results inform the design of flow battery electrolytes that improve the transport selectivity of ion exchange membranes.Some recent flow battery designs have included crossover suppression strategies based on size and charge of reactants. One option is to leverage size-exclusion, for example by tethering redox-active moieties to polymer backbones,1,2 or by oligomerizing redox-active monomers.3-5 A charge-based strategy has been employed to decrease viologen crossover: sulfonate6 or phosphonate7 solubilizing groups were attached to the redox active core and paired with a cation exchange membrane, reducing crossover compared to previous iterations of this chemistry. Crossover rates of some organic-based flow battery molecules have been estimated to be very low, but other considerations must be balanced for designing viable battery technology. For example, electrolyte cost and solubility may be in direct tension with a crossover suppression strategy based on increasing redox mediator size.8 Untangling the effects of different membrane-molecule selectivity mechanisms is a valuable step on the path to advancing redox active molecule design.This work evaluates a set of quinones in which size is varied by the number of aromatic rings (e.g. hydroquinone, anthraquinone) and charge number is varied almost independently through sulfonation. Each sulfonate moiety contributes a -1 charge, increasing the magnitude of the molecule charge number with the same sign as the fixed charges in Nafion. Effective size of solvated species is accessed through rotating disk electrode voltammetry: Stokes radii are calculated from measured diffusion coefficients. We found over an order of magnitude permeability reduction per sulfonate, emphasizing the importance of charge-based exclusion for ion exchange membranes. In comparison, size-exclusion effects are less impactful. For example, the Stokes radius of anthraquinone 2,6-disulfonate (AQDS) is twice that of hydroquinone 2,5-disulfonate but their permeabilities fall within the same order of magnitude.1. T. Hagemann, J. Winsberg, M. Grube, I. Nischang, T. Janoschka, N. Martin, M. D. Hager, and U. S. Schubert, Journal of Power Sources, 378, 546 (2018).2. T. Janoschka, N. Martin, U. Martin, C. Friebe, S. Morgenstern, H. Hiller, M. D. Hager, and U. S. Schubert, Nature, 527, 78 (2015).3. M. J. Baran, M. N. Braten, E. C. Montoto, Z. T. Gossage, L. Ma, E. Chenard, J. S. Moore, J. Rodrıguez-Lopez, and B. A. Helms, Chemistry of Materials, 30, 3861 (2018).4. K. H. Hendriks, S. G. Robinson, M. N. Braten, C. S. Sevov, B. A. Helms, M. S. Sigman, S. D. Minteer, and M. S. Sanford, ACS Central Science, 4, 189 (2018).5. S. E. Doris, A. L. Ward, A. Baskin, P. D. Frischmann, N. Gavvalapalli, E. Chenard, C. S. Sevov, D. Prendergast, J. S. Moore, and B. A. Helms, Angewandte Chemie, 129, 1617 (2017).6. C. Debruler, B. Hu, J. Moss, J. Luo, and T. L. Liu, ACS Energy Letters, 3, 663, (2018).7. S. Jin, E. M. Fell, L. Vina-Lopez, Y. Jing, P. W. Michalak, R. G. Gordon, and M. J. Aziz, Advanced Energy Materials, 10, (2020).8. M. L. Perry, J. D. Saraidaridis, and R. M. Darling, Current Opinion in Electrochemistry, 21, 311 (2020).

Electrochemical and Spectral Studies on Benzylidenerhodanine for Sensor Development for Heavy Metals in Waters

Electrochemical and spectral studies of benzylidenerhodanine (BR) were performed in order to develop new sensors for heavy metals (HMs) based on chemically modified electrodes (CMEs). CMEs were obtained by cycling and by controlled potential electrolysis at different potentials and charges. Film formation was demonstrated by recording the CV curves of CMEs in transfer solutions containing ferrocene in 0.1 M TBAP/CH3CN. BR-CMEs were used for the analysis of HMs. Samples of Cd(II), Pb(II), Cu(II), and Hg(II), each possessing concentrations between 10−7 and 10−5 M, were analyzed by using CMEs prepared in different conditions. The most intense signal was obtained for the Pb(II) ion. These BR-CMEs can be used for the analysis of Pb(II) in monitored waters. An electrochemical study was performed at different concentrations of BR in 0.1 M TBAP/CH3CN on a glassy carbon electrode by differential pulse voltammetry, cyclic voltammetry, and rotating disk electrode voltammetry. The complexation ratio in the homogeneous solution has been established by the Mollard method in acetonitrile solutions.

Structure‐Performance Relationship of LaFe1‐xCoxO3Electrocatalysts for Oxygen Evolution, Isopropanol Oxidation, and Glycerol Oxidation

AbstractMitigating high energy costs related to sustainable H2production via water electrolysis is important to make this process commercially viable. Possible approaches are the investigation of low‐cost, highly active oxygen evolution reaction (OER) catalysts and the exploration of alternative anode reactions, such as the electrocatalytic isopropanol oxidation reaction (iPOR) or the glycerol oxidation reaction (GOR), offering the possibility of simultaneously lowering the anodic overpotential and generating value‐added products. A suitable class of catalysts are non‐noble metal‐based perovskites with the general formula ABO3, featuring rare‐earth metal cations at the A‐ and transition metals at the B‐site. We synthesised a series of LaFe1‐xCoxO3materials with x=0–0.70 by automated co‐precipitation at constant pH and subsequent calcination at 800 °C. X‐ray diffraction studies revealed that the phase purity was preserved in samples with x≤0.3. The activity towards the OER, iPOR, and GOR was investigated by rotating disk electrode voltammetry, showing a relation between structure and metal composition with the activity trends observed for the three reactions. Additionally, GOR product analysis via high‐performance liquid chromatography (HPLC) was conducted after 24 and 48 h electrolysis in a circular flow‐through cell setup, pointing out a trade‐off between activity and selectivity.

Correction to: Electrocatalytic Kinetics of N-hydroxynaphthalimide as a Redox Mediator for Benzyl Alcohol Oxidation Using Rotating Disk Electrode Voltammetry

Correction to: Electrocatalytic Kinetics of N-hydroxynaphthalimide as a Redox Mediator for Benzyl Alcohol Oxidation Using Rotating Disk Electrode Voltammetry

Electrocatalytic Oxygen Reduction Reaction at Silver Nanoparticles (AgNPs) Electrode in Neutral Solution: 5-amino-2-naphthalene-sulfonic acid (ANS) as a Reducing Agent for AgNPs

We report electrocatalytic oxygen reduction reaction (ORR) at silver nanoparticle (AgNPs) electrodes. The AgNPs was obtained in a general one-pot synthesis using 5-amino 2-naphthalene-sulfonic acid (ANS) as a reducing agent in aqueous and room-temperature conditions. The simultaneous formation of AgNPs and oxidation of ANS were monitored by UV–vis spectroscopy. The surface morphology of AgNPs was characterized by transmission electron microscopy, which revealed that AgNPs appeared as a sphere. The average size of AgNPs was found to be 16 ± 2 nm. Furthermore, the chemical identity of the nanostructures was established using X-ray photoelectron spectroscopy and X-ray diffraction. The prepared AgNPs showed electrocatalytic activity for the reduction of oxygen in neutral pH. Rotating disk electrode voltammetry was used to elucidate the kinetics of ORR at the AgNPs electrode. These results reveal that oxygen reduction reaction at AgNPs-PANS electrode involved direct four-electron pathways.

Electrocatalytic Kinetics of N-Hydroxynaphthalimide as a Redox Mediator for Benzyl Alcohol Oxidation Using Rotating Disk Electrode Voltammetry

Electrocatalytic Kinetics of N-Hydroxynaphthalimide as a Redox Mediator for Benzyl Alcohol Oxidation Using Rotating Disk Electrode Voltammetry