Cyclic Voltammetry Experiments Research Articles

Synthesis of N,N‐Disubstituted Hydrazines by Electrocatalytic Addition of Hydrazines to α,β‐Unsaturated Carbonyl Compounds

AbstractA strategy for the synthesis of N,N‐disubstituted hydrazines via the electrocatalytic addition of hydrazine to α,β‐unsaturated carbonyl compounds is reported. The reaction was carried out under constant current electrolytic conditions in an undivided cell. Using this methodology, various N,N‐disubstituted hydrazines were prepared in 57–94% yield in 40 minutes. By adding cyclohexanone and acetic acid to the reaction mixture of N,N‐disubstituted hydrazines and heating for 2 hours, a one‐pot synthesis of N‐substituted indoles was also developed. Furthermore, based on cyclic voltammetry and control experiments, a plausible mechanism involving a radical pathway is proposed.

Characterization of melanin from Exophiala mesophila with the prospect of potential biotechnological applications

IntroducionFungal melanin is an underexplored natural biomaterial of great biotechnological interest in different areas. This study investigated the physical, chemical, electrochemical, and metal-binding properties of melanin extracted from the metallotolerant black fungus Exophiala mesophila strain IRTA-M2-F10.Materials and methodsSpecific inhibitory studies with tricyclazole and biochemical profiling of whole cells by synchrotron radiation-based Fourier-transform infrared spectral microscopy (SR-FTIRM) were performed. An optimized extraction protocol was implemented, and purified fungal melanin was characterized using an array of spectrophotometric techniques (UV-Vis, FTIR, and EPR) and by cyclic voltammetry (CV) experiments. The metal-binding capacity of melanin extracts was also assessed by using Cr(VI) as a model heavy metal.ResultsInhibitory studies indicated that 1,8-dihydroxynaphthalene may be the main precursor molecule of E. mesophila melanin (DHN-melanin). The biochemical characterization of fungal melanin extracts were benchmarked against those from two melanins comprising the precursor molecule L-3,4-dihydroxiphenylalanine (DOPA-melanin): extracts from the ink of the cephalopod Sepia officinalis and DOPA-melanin synthesized in the laboratory. The CV results of melanin extracts incubated with and without cell suspensions of the electroconductive bacterium Geobacter sulfurreducens were indicative of novel semiquinone/hydroquinone redox transformations specific for each melanin type. These interactions may play an important role in cation exchange for the adsorption of metals and in microbial interspecies electron transfer processes.DiscussionThe obtained results provided further evidence for the DHN-nature of E. mesophila melanin. The FTIR profiling of melanin extracts exposed to Cr(VI), compared to unexposed melanin, resulted in useful information on the distinct surface-binding properties of fungal melanin. The parameters of the Langmuir and Freundlicht isotherms for the adsorption of Cr(VI) were determined and compared to bibliographic data. Altogether, the inherent properties of fungal melanin suggest its promising potential as a biomaterial for environmental applications.

Electrode Spacing Effects on the Capacitance of Glassy Carbon Electrodes in Aqueous Electrolytes

Abstract Matched glassy carbon electrodes in aqueous K2SO4 electrolytes were used to examine the effects of opposing electrode spacing on capacitive performance. Planar non-porous glassy carbon electrodes were used to avoid complications with porosity and roughness. Electrode spacing effects were examined in terms of device and individual electrode performance, using cyclic voltammetry, coupled with its deconvolution into residual, diffusional, and capacitive processes. Decreasing the spacing between electrodes led to a decrease in capacitive contributions, and a relative increase in diffusional and residual contributions, implying that individual electrodes were influencing the behaviour of each other. This is also consistent with the use of more dilute electrolytes. Electrode behaviour was modelled using the Poisson-Boltzmann equation, together with its integrated outputs of electric field and potential difference. For electrodes with the same amount of charge and a similar diffuse layer thickness, the electric field and potential drop was diminished because of their charge interaction. Conversely, it is shown that for a similar potential drop across the electrodes, the variable controlled in a cyclic voltammetry experiment, more charge accumulation is needed at the electrode-electrolyte interface to compensate for the counter charge generate from the opposing electrode.

Voltammetric Sensing of Chloride Based on a Redox-Active Complex: A Terpyridine-Co(II)-Dipyrromethene Functionalized Anion Receptor Deposited on a Gold Electrode.

A redox-active complex containing Co(II) connected to a terpyridine (TPY) and dipyrromethene functionalized anion receptor (DPM-AR) was created on a gold electrode surface. This host-guest supramolecular system based on a redox-active layer was used for voltammetric detection of chloride anions in aqueous solutions. The sensing mechanism was based on the changes in the redox activity of the complex observed upon binding of the anion to the receptor. The electron transfer coefficient (α) and electron transfer rate constant (k0) for the modified gold electrodes were calculated based on Cyclic Voltammetry (CV) experiments results. On the other hand, the sensing abilities were examined using Square Wave Voltammetry (SWV). More importantly, the anion receptor was selective to chloride, resulting in the highest change in Co(II) current intensity and allowing to distinguish chloride, sulfate and bromide. The proposed system displayed the highest sensitivity to Cl- with a limit of detection of 0.50 fM. The order of selectivity was: Cl- > SO42- > Br-, which was confirmed by the binding constants (K) and reaction coupling efficiencies (RCE).

Synthesis and Characterization of Palladium/Silver Modified Reduced Graphene Oxide–Nanocomposite Platform for Electrochemical Sensors

AbstractMetal nanoparticles incorporated into carbon nanostructures have tremendous applications in the field of nanosensors and other technologies. Herein, a nanohybrid of reduced graphene oxide modified with silver and/or palladium nanoparticles (Ag/Pd/rGO) was prepared by impregnation of Pd and Ag into the rGO platform and deposited on a glass carbon electrode. Palladium and silver nanoparticles improve the stability and durability of the sensor platform by preventing the agglomeration of graphene oxide sheets and providing chemical stability against environmental factors. This ensures long‐term reliability and repeatability of the sensor performance. The morphologies and microstructures of the as‐prepared nanohybrid were characterized by X‐ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, UV–visible and infrared spectroscopy. The average crystallite size of PdAgNPs was found to be between 12 and 15 nm and demonstrated good dispersion across reduced graphene oxide sheets with high‐loading capacities. Thorough investigation of the electrochemical properties of the nanomaterial surfaces through cyclic voltammetry (CV) experiments, revealed distinct redox peaks for Ag+/Ag0 and Pd2+/Pd0 processes and demonstrated the excellent electrochemical properties of the prepared nanocomposites. The rGO‐PdAgNPs‐GCE had a diffusion coefficient value of 1.14×10−14 cm2 s−1 which is acceptable for electrochemical sensors as it is indicative of a fast response time and enhanced sensitivity to changes in gas concentration. The results obtained through thorough characterizations contributes to the novelty of the research by offering a deeper understanding of the material properties and the potential of the nanohybrid material for a broad application scope.

Multiwalled-Carbon-Nanotube-Modified Li2ZnTi3O8 as Anode with Improved Cycling Stability and Rate Capability for Lithium-Ion Batteries

Due to its better electronic conductivity and larger lithium intercalation capacity, a multiwalled-carbon-nanotube (MWCNT)-modified Li2ZnTi3O8 (LZTO) has significant potential for use as an anode material for Li-ion batteries. The rapid and affordable ball-mill-aided solid state approach is used to synthesize LZTO with MWCNT-modified Li2ZnTi3O8 (LZTO@MWCNTs). Electrochemical performance tests of the anode material were carried out using cyclic voltammetry (CV), galvanostatic charge-discharge measurement, and electrochemical impedance spectroscopy (EIS). The CV experiments reveal that the LZTO@MWCNT electrode has a lower anodic and cathodic peak potential difference (0.184 V) than the LZTO electrode (0.211 V) and LZTO@MWCNT electrode has better electrochemical reversibility than that of pristine electrode after five cycles utilizing the same procedure. LZTO@ MWCNTs anode material has a higher charge-discharge capacity than LZTO anode material at 0.1–5 C rates. After 100 cycles, the initial discharge capacities of LZTO@MWCNT electrode are 227 and 142 mAh g−1 at the 1C–5C rate, respectively, whereas the initial discharge capacities of LZTO electrode are only144 and 28 mAh g−1 in the same condition. The charge transfer and SEI resistance of the LZTO anode are 19.31 and 62.74 ohms, respectively, after 30 cycles at 1C, according to the EIS data. Additionally, the values for the LZTO@MWCNTs anode are 7.93 and 12.06 ohms for charge transfer and SEI resistance, respectively.

A comprehensive examination of structural modifications, optical characteristics, and electrochemical analysis of magnesium‐doped dysprosium chromite

AbstractBackgroundThis study focuses on the synthesis of magnesium‐doped dysprosium chromite via a sol‐gel method. The investigation aims to understand the morphological and structural properties of the synthesized nanochromates. Key techniques employed include x‐ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy.AimsThe primary aim is to analyze the structural characteristics of MgxDy1−xCr2O4 nanoparticles with varying Mg doping concentrations (ranging from 0.2 to 0.8). Special attention is given to the crystallinity of the synthesized materials, with the goal of assessing the reliability and reproducibility of the sol‐gel synthesis method.MethodsXRD analysis is employed to identify major diffraction peaks associated with the chromate nanoparticles, providing insights into their crystallinity. SEM imaging allows for the examination of the morphological features of the synthesized materials. Additionally, Raman spectroscopy aids in further understanding the structural properties of the nanochromates.ResultsThe XRD analysis reveals average crystallite sizes for MgxDy1−xCr2O4 nanoparticles at different Mg doping concentrations. Notably, an improvement in crystalline quality is observed with an increase in Mg doping from 0.2 to 0.8, indicating a high level of control achieved in the synthesis process. Cyclic Voltammetry (CV) experiments conducted using a 1M KOH electrolyte and varying scan rates (3 mV/s to 50 mV/s) demonstrate enhanced electrochemical performance of the synthesized nanoparticles.ConclusionThe study concludes that the sol‐gel synthesis method effectively produces MgxDy1−xCr2O4 nanoparticles with controlled morphological and structural properties. The observed improvement in crystalline quality with increasing Mg doping concentration suggests potential applications in fields such as photo‐catalysis, where enhanced crystallinity correlates with improved photo‐catalytic potential for visible light absorption.

Synthesis, spectroscopic, electrochemistry and antioxidant properties of benzofuroxan and 2H-benzimidazole 1,3-dioxide derivatives: Effects of conjugation with electron-acceptor 1,2,3-triazolyl-1,2,4-oxadiazole

A series of novel benzofuroxan and of 2,2-dimethyl-2H-benzimidazole 1,3-dioxide derivatives conjugated to the strong electron-withdrawing 1,2,4-oxadiazole ring and to the amide isostere 1,2,3-triazole were synthesized. NHeterocycle-N-oxide-bearing carboxylic acids and 1,2,3-triazole-4-carbamidoximes served as convenient reactants for the obtention of the 1,2,4-oxadiazoles. By employing O-(benzotriazol-1-yl)-N,N,N’,N’-tetramethyluronium tetrafluoroborate (TBTU) as coupling reagent and 1,8-diazabicyclo[5.4.0]undec‑7-ene (DBU) as base in acetonitrile, in a one-pot sequence, at room temperature, products were obtained in generally high yields (64 – 93 %) after two 30 min steps and a simple purification process. NMR spectroscopy, X-Ray diffraction and DFT calculations helped to access the preferential tautomeric structures of selected compounds. UV–Vis spectroscopy revealed characteristic absorption peaks for 1,2,3-triazolyl-1,2,4-oxadiazoles 11aa-be, noteworthy an intramolecular charge transfer (ICT) band around 500–650 nm for benzimidazole-1,3-dioxide derivatives 11ba-be, while low fluorescence quantum yields and Stokes shifts were observed for all compounds. Both oxidation and reduction peaks were observed in Cyclic Voltammetry experiments, including irreversible reduction peaks for all 11aa-be compounds. TD-DFT calculations enabled comprehension of the molecular orbitals participation in the UV–Vis transitions, which depend on the N-oxide, the heterocycles and the substituted phenyl ring. Also, some compounds with electron withdrawing groups (Cl and CF3) also displayed good antioxidant activity in DPPH assays.

Electrochemical Characterization of Diffusion in Polymeric vs. Monomeric Solvents.

Polymer electrolyte was used as a medium for testing the performance of microband electrodes under conditions of linear diffusion. Cyclic voltammetry (CV) and chronoamperometry (CA) experiments were performed in a highly viscous medium, where diffusion rates are much slower than in fluid solutions. The log i vs. log v (CV) or log i vs. log t (CA) relationships with the current equation confirmed the existence of such conditions, yielding slope values that were lower than the expected 0.5. This could indicate an impure linear diffusion profile, i.e., some contribution from radial diffusion (edge effects). However, the desired value of 0.5 was obtained when performing these tests in monomeric solvents of similar viscosities, such as glycerol or propylene glycol. These results led to the conclusion that the current equations, which are based on Fick's laws, may not be applicable for polymer electrolytes, where various obstructions to free diffusion result in a more complicated process than for monomeric solvents.

Use of Suspended Particles as a New Approach to Increase the Active Electrode Area in Water Electrolysis Experiments

AbstractThe development of base metal electrodes that can act as active and stable oxygen generating electrodes in water electrolysis systems, especially at low pH levels, remains a challenge. The use of suspensions as electrolytes for water splitting has until recently been limited to photoelectrocatalytic approaches. A high current density (j=30 mA/cm2) for water electrolysis has been achieved at a very low oxygen evolution reaction (OER) potential (E=1.36 V vs. RHE) using a SnO2/H2SO4 suspension–based electrolyte in combination with a steel anode. More importantly, the high charge–to–oxygen conversion rate (Faraday efficiency of 88 % for OER at j=10 mA/cm2 current density). Since cyclic voltammetry (CV) experiments show that oxygen evolution starts at a low, but not exceptionally low, potential, the reason for the low potential in chronoamperometry (CP) tests is an increase in the active electrode area, which has been confirmed by various experiments. For the first time, the addition of a relatively small amount of solids to a clear electrolyte has been shown to significantly reduce the overpotential of the OER in water electrolysis down to the 100 mV region, resulting in a remarkable reduction in anode wear while maintaining a high current density.

Electrochemical Oxidative Ring‐Opening Reactions of 2H‐Indazoles with Alcohols to Obtain Ortho‐alkoxycarbonylated Azobenzenes

AbstractA strategy for synthesis of azo‐derived compounds by electrochemical oxidative ring‐opening reactions of 2H‐indazoles with alcohols is reported. The reactions are carried out under galvanostatic electrolysis conditions in an undivided cell without the use of transition metal catalysts. On the basis of cyclic voltammetry and control experiments, a plausible mechanism for this ring‐opening reaction involving the radical pathway is proposed. Furthermore, various 2H‐indazoles and alcohols are suitable in this system, giving the desired ortho‐alkoxycarbonylated azobenzenes in 9–84% yields.

Coumarin based glyoxylate photoinitiators for free radical and cationic Photopolymerizations with UV-Visible LED irradiation

High-performance photoinitiators (PIs) play a crucial role in ultraviolet–visible (UV–Vis) photopolymerization. In this study, three coumarin-3-oxoacetic acid methyl esters (COAEs) which demonstrate significant UV–Vis absorption within the 300–500 nm range were synthesized and studied. Real-time fourier transform infrared (RT-FTIR) and photo-differential scanning calorimetry (photo-DSC) experiments demonstrated that these PIs can function as Type I and Type II PIs for initiating free radical polymerization (FRP) of acrylate monomers. Additionally, they can serve as photosensitizers for iodonium salts and sulfonium salts, enabling cationic photopolymerization (CP) of epoxy and oxetane monomers. Remarkably, even at low concentrations of 0.01 wt%, they can effectively initiate the deep curing of Tri-(propylene glycol) diacrylate (TPGDA) to a depth of approximately 9 cm after 5 min of irradiation with a 415 nm or 450 nm LED light source. Furthermore, the COAEs exhibit satisfactory photobleaching properties, making them suitable for colorless applications in photopolymerization. The photochemical and photophysical properties of the COAEs were thoroughly investigated using absorption spectroscopy, electron spin resonance, cyclic voltammetry experiments, and photoinduced decarboxylation experiments to elucidate the photoinitiation mechanism. Cytotoxicity experiments revealed that COAE-N exhibited good cytocompatibility. Therefore, the exceptional polymerization properties of COAEs offer promising prospects for FRP and CP applications. Additionally, their efficient photobleaching characteristics make them highly suitable for deep photopolymerization applications. Moreover, the low cytotoxicity of COAEs suggests significant potential for biomedical applications such as dental restoration.

A Sustainable Combustion Process for Green Synthesis of TiO2 Nanoparticles: Applications in Photocatalytic Degradation and Electrochemical Sensing for Environmental Remediation

AbstractHerein, a sustainable approach to combustion has been presented, utilizing Aloe Vera latex as a reducing agent in synthesizing titanium dioxide (TiO2) nanoparticles. The phase and composition of TiO2 have been confirmed using X‐ray diffraction, while the band gap has been determined as 3.17 eV using the Kubelka‐Monk plot. The photocatalytic potential of the TiO2 has been explored by assessing their effectiveness in degrading AR‐88 dye, demonstrating significant activity at 500 nm. Remarkably, in a span of 120 min of UV radiation, AR‐88 dye could reach an impressive photodegradation rate of 98.6 %, rendering the dye nearly colorless. TiO2 NPs have also been investigated as an electrode material in sensing paracetamol and D‐glucose by coating them onto a carbon paste electrode and immersing them in a 1 M KOH solution. The cyclic voltammetry experiments reveal that the TiO2 NPs possess excellent electrochemical characteristics, with a calculated proton diffusion coefficient of 5.651×10−4 cm2 s−1. These findings underscore the potential of TiO2 as a highly desirable electrode material with remarkable electrochemical properties. This research opens new avenues for utilizing TiO2 NPs in various electrochemical applications, particularly in the detection of pharmaceutically important compounds, highlighting its versatility.

Ultrafast Sunlight-Induced Polymerization: Unveiling 2-Phenylnaphtho[2,3-d]Thiazole-4,9-dione as a Unique Scaffold for High-Speed and Precision 3D Printing.

A series of 15 dyes based on the 2-phenylnaphtho[2,3-d]thiazole-4,9-dione scaffold and 1 compound based on the 2,3-diphenyl-1,2,3,4-tetrahydrobenzo[g]quinoxaline-5,10-dione scaffold are studied as photoinitiators. These compounds are used in two- and three-component high-performance photoinitiating systems for the free radical polymerization of trimethylolpropane triacrylate (TMPTA) and polyethylene glycol diacrylate (PEGDA) under sunlight. Remarkably, the conversion of TMPTA can reach ≈60% within 20s, while PEGDA attains a 96% conversion within 90s. To delve into the intricate chemical mechanisms governing the polymerization, an array of analytical techniques is employed. Specifically, UV-vis absorption and fluorescence spectroscopy, steady-state photolysis, stability experiments, fluorescence quenching experiments, cyclic voltammetry, and electron spin resonance spin trapping (ESR-ST) experiments, collectively contribute to a comprehensive understanding of the photochemical mechanisms. Photoinitiation capacities of these systems are determined using real-time Fourier transformed infrared spectroscopy (RT-FTIR). Of particular interest is the revelation that, owing to the superior initiation ability of these dyes, high-resolution 3D patterns can be manufactured by direct laser write (DLW) technology and 3D printing. This underscores the efficient initiation of free radical polymerization processes by the newly developed dyes under both artificial and natural light sources, presenting an avenue for energy-saving, and environmentally friendly polymerization conditions.

A rational study of transduction mechanisms of different materials for all solid contact-ISEs

The new era of solid contact ion selective electrodes (SC-ISEs) miniaturized design has received an extensive amount of concern. Because it eliminated the requirement for ongoing internal solution composition optimization and created a two-phase system with stronger detection limitations. Herein, the determination of venlafaxine HCl is based on a comparison study between different ion- to electron transduction materials (such as; multiwalled carbon nanotubes (MWCNTs), polyaniline (PANi), and ferrocene) and illustrating their mechanisms in their applied sensors. Their different electrochemical features (such as bulk resistance (Rb**), double-layer capacitance (Cdl), geometric capacitance (Cg), and specific capacitance (Cp)) were evaluated and discussed by using the Electrochemical Impedance Spectroscopy (EIS), Chronopotentiometry (CP), and Cyclic Voltammetry (CV) experiments. The results indicated that each transducer's influence on the proposed sensor's electrochemical characteristics is determined by their unique chemical and physical properties. The electrochemical features vary for different solid contact materials used in transduction mechanisms. The results confirm that the MWCNT sensor revealed the best electrochemical behavior with the potentiometric response of a near-Nernestian slope of 56.1 ± 0.8 mV/decade with detection limits of 3.8 × 10−6 mol/L (r2 = 0.999) and a low potential drift (∆E/∆t) of 34.6 µV/s. Also, the selectivity study was performed in the presence of different interfering species either in single or complex matrices. This demonstrates excellent selectivity, stability, conductivity, and reliability as a VEN-TPB ion pair sensor for accurately measuring VEN in its various formulations. The proposed method was compared to HPLC reported technique and confirmed no significant difference between them. So, the proposed sensors fulfill their solutions' demand features for VEN appraisal.

An efficient synthesis for Cd(II), Cu(II), and UO2(II) complexes with N-ethyl-2-(1-(naphthalen-1-yl)ethylidene)hydrazine-1-carbothioamide under solvent-free condition using ball milling as green protocol

In this study, the potent ligand of N-ethyl-2-(1-(naphthalen-1-yl)ethylidene)hydrazine-1-carbothioamide (H2AN) was synthesized by condensation reaction between 1-(naphthalen-1-yl)ethan-1-one and N-ethylhydrazinecarbothioamide. Subsequently, a series of Cd(II), Cu(II), and UO2(II) complexes were prepared via the green ball milling method and characterized using various instrumental techniques like (IR, UV-Visible,1H-NMR,13C-NMR, SEM, EDX, elemental analysis & magnetic measurements). Molecular modeling and DFT studies were carried out to confirm the proposed binding manner. Also, both electron localization function (ELF) and localized orbital locator (LOL) methods were used to approximate the concentration of electron density in the compounds. Moreover, MIC as well as the colorimetric assay for isolated solid compounds were tested. Moreover, molecular property and drug-likeness prediction of prepared compounds were estimated for conformity to the Lipinski rule of five. Furthermore, docking studies were applied for ligand and complexes on the active site of E. coli (PDB ID: 6F86), S. aureus (PDB ID: 3BL6) and C. albicans (PDB ID: 1IYL) receptors. Finally, cyclic voltammetry experiments were done in both absence/presence of H2AN in 0.1M KCl at fixed temperature (298.15 K) and a potential window (1 to -1v). Various concentrations of Cu(II) were used in 0.1M KCl to study the electrochemical behavior and calculate some thermodynamic parameters.

Electrochemical C–H phosphorothiolation of indolizines with thiocyanate and phosphite in one pot

A facile and practical protocol for C–H phosphorothiolation of indolizines using thiocyanate as the sulfur source and phosphite as the phosphorylated reagent has been developed. A broad range of substrates were well tolerated and the desired products were obtained in moderate to excellent yields. Moreover, the reaction involved electrochemical thiocyanation of indolizines and a chemical process to construct the S–P bond in the presence of DBU. A plausible EC mechanism for this reaction has been revealed by cyclic voltammetry and control experiments. This method provided a green pathway to synthesize S-(hetero)aryl phosphorothioates by electrochemical oxidation at room temperature without external oxidants and transition metal catalysts.

Neutral Red as a Redox Probe for Comparative Evaluation of Electrochemical Performance of Bismuth Modified Electrodes

For the first time, Neutral Red (NR) has been used as a redox probe for comparative evaluation of the electrochemical performance of screen-printed carbon electrodes (SPCEs) modified with bismuth under different potentiostatic pre-plating conditions (Bi/SPCEs). It was shown that protonated NR undergoes quasi-reversible redox transformations at bare-SPCE and Bi/SPCEs in the pH range 5–6 in phosphate buffer solutions (PBS) in the potential range of (−0.2)–(−0.8) V, where bismuth is not electroactive. Bi/SPCEs have been characterized morphologically by scanning electron microscopy (SEM) and electrochemically by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) employing NR as a redox probe. The obtained SEM, CV, and EIS data are in good agreement. The highest charge transfer resistance (Rct) values (3.9 and 3.3 kΩ) were obtained at bare-SPCE and Bi/SPCE having low degree of bismuth coverage. Contrarily, the lowest Rct value (8 Ω) was recorded at Bi/SPCE, with the highest degree of bismuth coverage. CV experiments showed a significant increase in the electrochemical performances of Bi/SPCEs, whose surface is half or more covered with bismuth, in comparison to the bare-SPCE. Nickel (II) ions and formaldehyde (FM), in the form of formaldehyde hydrazone (FAH), were used as model analytes to determine the electroanalytical performance of Bi/SPCEs. A comparison of roughness factor and sensitivity toward both analytes for Bi/SPCEs with two-tailed Pearson’s criterion showed a high degree of correlation between their electrochemical and electroanalytical characteristics. The data acquired indicates that the use of NR as a redox probe may be quite helpful to control modification processes when developing novel bismuth-containing sensors.

Understanding the Interplay of the Brønsted Acidity of Catalyst Ancillary Groups and the Solution Components in Iron-porphyrin-Mediated Carbon Dioxide Reduction.

The rapid and efficient conversion of carbon dioxide (CO2) to carbon monoxide (CO) is an ongoing challenge. Catalysts based on iron-porphyrin cores have emerged as excellent electrochemical mediators of the two proton + two electron reduction of CO2 to CO, and many of the design features that promote function are known. Of those design features, the incorporation of Brønsted acids in the second coordination sphere of the iron ion has a significant impact on catalyst turnover kinetics. The Brønsted acids are often in the form of hydroxyphenyl groups. Herein, we explore how the acidity of an ancillary 2-hydroxyphenyl group affects the performance of CO2 reduction electrocatalysts. A series of meso-5,10,15,20-tetraaryl porphyrins were prepared where only the functional group at the 5-meso position has an ionizable proton. A series of cyclic voltammetry (CV) experiments reveal that the complex with -OMe positioned para to the ionizable -OH shows the largest CO2 reduction rate constants in acetonitrile solvent. This is the least acidic -OH of the compounds surveyed. The turnover frequency of the -OMe derivative can be further improved with the addition of 4-trifluoromethylphenol to the solution. In contrast, the iron-porphyrin complex with -CF3 positioned opposite the ionizable -OH shows the smallest CO2 reduction rate constants, and its turnover frequency is less enhanced with the addition of phenols to the reaction solutions. The origin of this effect is rationalized based on kinetic isotope effect experiments and density functional calculations. We conclude that catalysts with weaker internal acids coupled with stronger external acid additives provide superior CO2 reduction kinetics.

In Situ Electrochemistry of Formate on Cu Thin Films Using ATR-FTIR Spectroscopy and X-ray Photoelectron Spectroscopy.

Formate (HCOO-) is the most dominant intermediate identified during carbon dioxide electrochemical reduction (CO2ER). While previous studies showed that copper (Cu)-based materials that include Cu(0), Cu2O, and CuO are ideal catalysts for CO2ER, challenges to scalability stem from low selectivity and undesirable products in the -1.0-1.0 V range. There are few studies on the binding mechanism of intermediates and products for these systems as well as on changes to surface sites upon applying potential. Here, we use an in situ approach to study the redox surface chemistry of formate on Cu thin films deposited on Si wafers using a VeeMAX III spectroelectrochemical (SEC) cell compatible with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Spectra for surface species were collected in real time as a function of applied potential during cyclic voltammetry (CV) experiments. Results showed the reproducibility of CV curves on freshly prepared Cu/Si wafers with relatively high signal-to-noise ATR-FTIR absorbance features of surface species during these electrochemical experiments. The oxidation reaction of HCOO- to bicarbonate (HCO3-) was observed using ATR-FTIR at a voltage of 0.27 V. Samples were then subjected to reduction in the CV, and the aqueous phase products below the detection limit of the SEC-ATR-FTIR were identified using ion chromatography (IC). We report the formation of glycolate (H3C2O3-) and glyoxylate (HC2O3-) with trace amounts of oxalate (C2O42-), indicating that C-C coupling reactions proceed in these systems. Changes to the oxidation state of surface Cu were measured using X-ray photoelectron spectroscopy, which showed a reduction in Cu(0) and an increase in Cu(OH)2, indicating surface oxidation.