Cavity Microelectrode Research Articles

Innovative electrochemical sensor based on platinum group metal complexes for determination of nitrite: Application for simultaneous detection of nitrite and tartrazine

In the context of this experimental study, new palladium and ruthenium complexes based on a symmetric ligand, named 2E-Peaemp ((3E,3’E)-3,3’-(((piperazine-1,4-diyl bis (ethane-2,1-diyl)) bis (azanediyl)) bis (ethan1-yl-1-ylidene)) bis (6-methyl-2H-pyran-2,4(3 H)-dione), and their hybrid compounds with carbon nanotubes were prepared and characterized. The sensors prepared using a cavity microelectrode (MEC) modified with a mixture of graphite (CG), carbon nanotubes (MWCNT) and the synthesized complexes (Pd-2E-Peaemp and Ru-2E-Peaemp) were applied to detect the pollutants such as Nitrites and Tartrazine separately and simultaneously in aqueous solutions and real samples (Tap water, wastewater and bottled commercial spring water). The detection limits (LODs) determined for nitrites and tartrazine are obtained using MEC/CG-MWCNT-Pd-2E-Peaemp electrode, and the electrochemical measurements demonstrated a sensitive and rapid response in the analysis of these species. LODs are 0.39 µM and 0.11 µM, respectively, within the concentration range of 0–909 µM for nitrites and 0–97 µM for tartrazine. This electrode modified by the palladium complex is also used to simultaneously detect nitrite and tartrazine analytes using the differential pulse voltammetry (DPV) technique, indicating that the proposed sensor can be an interesting alternative tool to measure these species in real samples. The application of this electrode in these natural environments reveals that the developed sensor can detect low concentrations of nitrite (NO2-; trace) without any interference from other ions substances as acetate (CH3COO-), borate (BO3−3), phosphate (PO4−3), dihydrogen ( 2 H+), sulfate (SO4−2), sodium (Na+), hydroxide (OH-), potasium (K+), chloride (Cl-), magnesium (I) ( Mg+), nitrate (NO3-), calcium (Ca2+), carbonate (CO3−2).

(Invited) Degradation and Poisoning of Proton-Exchange Membrane Water Electrolyzer Anode Catalysts

Hydrogen production through water electrolysis is a crucial technology to enable the transition to a carbon neutral, hydrogen-based economy. One of the primary types of electrolyzers is the low-temperature proton-exchange membrane water electrolyzer (PEMWE). As with the analogous proton-exchange membrane fuel cells, platinum group metal electrocatalysts are utilized due to their activity and stability in acidic environment. Electrocatalysis R&D efforts for PEMWEs primarily focus on the oxygen evolution reaction (OER) since it is several orders of magnitude kinetically slower than the hydrogen evolution reaction (HER).1 Iridium-based metal oxides (IrOx) are regarded as the best PEM electrolyzer electrocatalysts as they balance activity and stability.2 However, improvements are needed in both areas to enable minimization of Ir loading to meet system cost targets while also meeting challenging performance and lifetime targets.3 An understanding of the factors affecting both the activity and stability of Ir-based OER catalysts is needed to develop strategies to enable both high OER activity and long-term stability of the PEMWE anode catalyst.This presentation will describe our studies of the effects of perfluorosulfonic acid (PFSA) binder on the OER kinetics and the factors influencing the stability of two commercial Ir-based OER catalysts, one comprised of IrOx only and the other also containing TiOx. Measurements of OER kinetics as a function of ionomer to catalyst ratio utilizing rotating disc electrode and cavity microelectrode methods in an acidic aqueous electrochemical environment will be described. Dissolution and loss of Ir under the operating conditions of the PEMWE anode is considered to be one of the main PEMWE anode degradation mechanisms.4 To understand the factors affecting this phenomenon, the potential and time-dependence of Ir (and Ti) were determined using an electrochemical flow cell system connected to an inductively-coupled plasma-mass spectrometer (ICP-MS) capable of detecting trace concentrations (<ppb) of dissolved elements in solution. The electrochemical data combined with the ICP-MS data have been used to evaluate the influence of various factors such as potential, potentiodynamic profile parameters (e.g., scan rate, upper and lower potential limits) on the dissolution processes in acidic aqueous electrolyte at room temperature.AcknowledgementsThis research is supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the H2NEW Consortium. Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.References A. Raveendran, M. Chandran, and R. Dhanusuraman, RSC Adv., 13 (2023) 3843.J. Ouimet, J.R. Glenn, D.D. Porcellinis, A.R. Motz, M. Carmo, K.E. Ayers, ACS Catalysis, 12 (2022) 6159."Technical Targets for Proton Exchange Membrane Electrolysis", U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, March, 2023.Zeng, R. Ouimet, L. Bonville, A. Niedzwiecki, C. Capuano, K. Ayers, A.P. Soleymani, J. Jankovic, H. Yu, R. Maric, et al., J. Electrochem. Soc., 169(5) (2022) 054536.

A micro-electrochemical sensor based on a nanostructured carbon paste electrode as an original tool for selective detection of ultra-traces of 17α –ethinylestradiol in environmental water samples and in biologic fluids

A new electrochemical micro-sensor has been designed for the sensitive detection of ultra-traces of 17α – ethinylestradiol (EE2). A carbon paste cavity micro-electrode modified by carbon black nanoparticles (GC-nCB)-µCPE was used with an electrochemical preconcentration (EP) step of EE2 on (GC-nCB)-µCPE at 0.0 V during 300 s in a 0.01 mol.L-1 phosphate buffer solution (pH = 7.4) before voltammetric determination. The results demonstrate that two line calibrations were obtained in the concentration ranges of 0.005 to 0.2 μmol.L-1 and 0.2 to 1 μmol.L-1. The detection and quantification limits are estimated at 1.4 nmol.L-1 and 4.9 nmol.L-1, respectively. Moreover, a high sensitivity of 4.16 µA.mol−1.L and good selectivity for the quantification of EE2 in the presence of different interfering organic and inorganic compounds were observed. Based on the results (satisfactory recovery (less than 3.5 %) and relationship standard deviation (less than 2.5 %)),the designed micro-sensor can be successfully applied to the analysis of EE2 in environmental water samples and in biologic fluids.The modified microsensor presented an efficient and inexpensive tool for the quantification of EE2.

Cation desolvation-induced capacitance enhancement in reduced graphene oxide (rGO)

Understanding the local electrochemical processes is of key importance for efficient energy storage applications, including electrochemical double layer capacitors. In this work, we studied the charge storage mechanism of a model material - reduced graphene oxide (rGO) - in aqueous electrolyte using the combination of cavity micro-electrode, operando electrochemical quartz crystal microbalance (EQCM) and operando electrochemical dilatometry (ECD) tools. We evidence two regions with different charge storage mechanisms, depending on the cation-carbon interaction. Notably, under high cathodic polarization (region II), we report an important capacitance increase in Zn2+ containing electrolyte with minimum volume expansion, which is associated with Zn2+ desolvation resulting from strong electrostatic Zn2+-rGO interactions. These results highlight the significant role of ion-electrode interaction strength and cation desolvation in modulating the charging mechanisms, offering potential pathways for optimized capacitive energy storage. As a broader perspective, understanding confined electrochemical systems and the coupling between chemical, electrochemical and transport processes in confinement may open tremendous opportunities for energy, catalysis or water treatment applications in the future.

Understanding Ion Charging Dynamics in Nanoporous Carbons for Electrochemical Double Layer Capacitor Applications

The electric double layer (EDL) is one of the key concepts in electrochemistry, and understanding its charging kinetics is of key importance. Significant progress has been made via theoretical methods; however, it is challenging to study the ion dynamics experimentally in porous carbon electrodes under realistic conditions because of fast charge relaxation. In this work, the charging kinetics of porous carbon electrodes with different pore sizes in an aqueous electrolyte was experimentally investigated in electrolytes with various concentrations by using a cavity microelectrode. We were able to observe electrolyte depletion, and we systematically studied the key parameters that will affect the electrolyte depletion, resulting in major changes in the charging kinetics. Results showed that low concentration, high overpotential, and small carbon pore size triggered the electrolyte depletion, decreasing the charging kinetics. These findings further push our understanding of the ion dynamics of the EDL at the charged porous carbon/electrolyte interface.

Iron redox behavior and oxygen reduction activity of Fe-N-C electrocatalysts in different electrolytes

The iron redox behavior and oxygen reduction reaction (ORR) activity of Fe-N-C ORR electrocatalysts synthesized by a variety of techniques were investigated as a function of the identity of the electrolyte anion (bisulfate/sulfate or perchlorate) at a constant pH. In situ X-ray absorption spectroscopy data support the assignment of the redox peaks in the voltammograms to the Fe3+/Fe2+ redox couple. It was found that for a given Fe-N-C catalyst, there is a correlation between the Fe redox couple peak potential and the ORR activity in perchloric acid electrolyte, but not in sulfuric acid electrolyte. While a higher Fe redox couple potential (≥ 110 mV higher) was observed in perchloric acid electrolyte, a higher ORR activity was obtained in sulfuric acid electrolyte. The higher ORR activity observed in sulfuric acid than perchloric acid was correlated with the higher peak current and larger faradaic charge for the Fe redox couple. A study of the Fe redox behavior using a cavity microelectrode, eliminating the impact of ionomer, showed that the interaction of H2SO4 with Fe-N-C is stronger than that of HClO4 and that Fe redox in both electrolytes is a reversible surface electrochemical reaction.

A new highly sensitive micro-sensor for the ultra-traces analysis of paracetamol directly in water

In the present work, a simple, inexpensive and highly sensitive electrochemical micro-sensor was developed for trace detection of paracetamol (PAR) directly in water, using electrochemical preconcentration technique (EP) on a cavity microelectrode modified with carbon black nanoparticles (nCB/ CME). The results demonstrate that with an EP of PAR on nCB/ CME at 0 V for 900 s in BRS 0.04 M at pH = 7, the new proposed micro-sensor show two large linear response in ranges of 5 × 10-10 to 9 × 10-8 mol.L-1 and from 1 × 10-7 to 1 × 10-6 mol.L-1. The detection and quantification limits are estimated to be 1.4 × 10-10 and 4.3 × 10-10 mol.L-1, respectively. The performances of the new proposed nCB/ CME for the determination of PAR were compared to its performances without EP and the results reveal the importance of the application of EP in improving the electroanalytical characteristics. The applicability of the designed micro-sensor was successfully applied for the direct analysis of local tap water and treated wastewater samples spiked with trace PAR compounds with a satisfactory recovery (less than 4 %) and a relation standard deviation less than 5 %. It indicates that the electrochemical micro-sensors are an effective device for monitoring PAR concentrations directly in water without any pretreatment.

A novel hybrid carbon materials-modified electrochemical sensor used for detection of gallic acid

Novel hybrid carbon materials such as activated carbon-carbon nanotubes (AC-CNTs) and carbon spheres/activated carbon-carbon nanotubes (CSs/AC-CNTs) based on activated carbon (AC) derived from the pits of Algerian date palm have been prepared and characterized. In addition, the carbon paste electrodes based on graphite carbon (GC) and cavity microelectrode (CME) modified with these hybrid materials were used to detect gallic acid at pH = 7 using square wave voltammetry method (SWV). The conductivity measurements revealed that CSs/AC-CNTs is more conducting than AC-CNTs. SWV measurements showed that the oxidation current was directly proportional to the concentrations of gallic acid (from 0 to 0.00536 M) with the lowest limit of detection (LOD), reaching 6.43 µM and 3.64 µM using GC/CSs/AC-CNTs electrode and CME/GC/CSs/AC-CNTs sensor, respectively. The reproducibility and the stability of the studied sensor were confirmed by the relative standard deviation of the oxidation current response of gallic acid (RSD Reproducibility = 1.44% and RSD Stability = 3.7%).

Effect of the residual silver and adsorbed lead anions towards the electrocatalytic methanol oxidation on nanoporous gold in alkaline media

Nanoporous gold (NPG) obtained by potentiostatic dealloying of an AuAg master alloy was pulverized, filled into a cavity microelectrode and its surface electrochemistry was investigated in NaOH and KOH solutions. This method yielded highly resolved undistorted voltammograms of this polycrystalline material with clear evidences for surface segregation of Ag during storage in air. One cycle in 0.1 M H2SO4 can remove most of the residual Ag from the surface as evidenced by voltammetry after back transfer to alkaline solution and by X-ray photoelectron spectroscopy (XPS). After removal of residual Ag from the surface, the surface undergoes rephasing forming wider {111} and {110} terraces as evidenced by Pb underpotential deposition (UPD). By adjustment of the bulk concentration of PbII species, a selective partial coverage of the high internal surface area of NPG could be intentionally adjusted. Lead species remain attached to the NPG surface at potentials positive of the UPD regions either as plumbates or PbIV species as evidenced by XPS. Those tools enable to disentangle effects on the electrocatalysis of the methanol oxidation reaction (MOR) in different potential regions for 1 M methanol in different concentrations of NaOH and KOH. The MOR commences at lower potentials in the presence of residual Ag. At very high potential, the presence of Ag species promotes the oxidation to CO2/CO32-. Tafel analysis after selective blocking of specific facets shows that the {110} terraces promote especially the first step of MOR while the {111} terraces enhance the rate of further steps that are rate-limiting at higher potentials. While high coverages by Pb UPD layers or adsorbed plumbate anions inhibit electrooxidation, the behavior of NPG electrodes with low coverages of Pb species is reminiscent to NPG electrodes with residual Ag. This could be caused by promoting the methoxide and/or OH- adsorption at low overpotentials and catalyzing complete oxidation by a surface bound PbIV species at higher potentials. The catalytic currents increase with base concentration and are higher for KOH compared to NaOH. Comparable effects of base concentration on the parameters of the Tafel lines suggest that this effect is a result of slightly stronger deprotonation of methanol in bulk KOH solutions.

Poly(benzoquinonyldisulfide) as organic positve electrode for Mg and Li batteries

The study of innovative solutions to replace current lithium technology is being carried out at a rapid pace. One of the proposed solution is the development of magnesium batteries, especially organic positive electrode which can exhibit high capacity and capacity retention. In this field, the electrochemical responses of poly(benzoquinonyldisulfide) (PBQDS) in lithium and magnesium cells were investigated in diglyme and sulfolane based electrolytes. Using cavity micro-electrode, similar response was obtained by cyclic voltammetry with the presence of a reversible redox system at 3.5 V vs. Li+/Li or 2.2 V vs. Mg2+/Mg. Using sulfolane + LiTFSI (bis(trifluoromethane)sulfonamide lithium salt) electrolyte, the PBQDS active material achieves a stable capacity of 140 mAh g−1 at C/20. In Mg cell, even if the starting capacity is high, a capacity decrease is noticed along time presumably due to the progressive Mg2+ trapping within the quinone structure. The addition of solvating additive permits to partially mitigate this drawback.

Restructuring of Nanoporous Gold Surfaces During Electrochemical Cycling in Acidic and Alkaline Media

AbstractThe electrochemical behavior of nanoporous gold (NPG) obtained by dealloying a AgAu alloy has been investigated by means of cyclic voltammetry (CV) in 0.1 M H2SO4 and 0.1 M KOH solutions supplemented by X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) in order to understand different effects of the electrochemical treatment on the development of the surface structure of NPG. In order to reduce the IR drop caused by the high surface area of the bicontinuous network of pores and ligaments in NPG, NPG was transformed to a powder, from which a small portion was filled into a cavity microelectrode (CME). Additionally, this avoided sample‐to‐sample variation from the dealloying process because many fillings could be made from one NPG monolith. The cycling in 0.1 M H2SO4 led to restructuring of the surface to a more faceted one, only after the residual silver on the surface had been removed in the initial scan. The same cycling program in 0.1 M KOH did not cause restructuring. However, a transfer of the sample to 0.1 M H2SO4 could start the process. The ligament size did not change during restructuring. Additionally, it was found that residual Ag in NPG stabilizes the highly curved surfaces of the ligaments containing a high density of surface defects. The dissolution of the residual Ag in acid electrolytes lifts the blockage towards surface restructuring. These findings form a basis for understanding the electrochemical behavior of NPG and to devise appropriate treatments, for instance for their use in electrocatalysis.

Electrochemical study of carbon dioxide reduction at copper–palladium nanoparticles: Influence of the bimetallic composition in the CO poisoning tolerance

A study of the CO2 electrochemical reduction reaction (CO2RR) at Pd100−xCux solid solution type nanoalloys is presented. Cyclic voltammetry and chronoamperometry are used in combination with a cavity microelectrode (CME) for the first time. Low-distorted voltammetric signals obtained with the CME evidence that for alloys with low or moderate Cu content (up to 50 at%) the typical CO2RR inhibition peak, related to CO blocking Pd active sites, becomes a current plateau. Interestingly, the plateau height matches the theoretical value corresponding to the steady state current of a microdisc. This fact indicates a better tolerance of Pd100−xCux towards CO poisoning and also the attainment of a pseudo-steady state where mass transport should be controlled by diffusion. The synergy between Cu and Pd is thus established for the first time at the level of the voltammograms. The chronoamperometric responses exhibit three well defined regions corresponding to (1) double layer charging and diffusion/reaction establishment, (2) beginning of CO poisoning by formation of a CO adlayer and (3) final collapse of the catalytic activity at a critical time, tc, which depends directly on the bimetallic composition. A plot of tc vs. Pd content exhibits a clear volcano shape, from which ~ Pd72Cu28 is identified as a close to optimal composition in terms of CO tolerance and Pd35Cu65 as the composition from which the advantage of alloying Pd with Cu is lost. An in-depth analysis of the I/V response and its evolution with composition and time is performed in the CO2RR and CO stripping regions. As a result, the possibility of developing a method to further increase the catalyst lifetime based on periodical releasing of “CO-like” intermediates by CO stripping is proposed.

Organic Cathode Based on Quinone-Sulfide Polymer for Both Li and Mg Batteries

The undeniable benefit of lithium-ion (LIB) batteries for the development of a more environmentally friendly economy was recognized by the 2019 Nobel Prize in Chemistry. However, relying only on LIBs to energy storage will put considerable strain on lithium and cobalt resources used in these batteries. Therefore, alternative battery technologies other than LIBs are desirable to satisfy our growing demand for energy. Magnesium-ion batteries offer many distinct advantages over LIBs, including the high earth-abundance of magnesium, its high energy density and reversible dendrite-free Mg deposition1. In parallel, organic materials are receiving an increasing amount of attention as electrode materials for future post lithium-ion batteries due to their versatility and sustainability2. In order to propose organic cathode with both high potential and specific capacity, new polymer based on hydroquinone sulfide, poly(benzoquinone disulfide) (PBQDS), were prepared in view to be applied in both lithium and magnesium batteries. Diglyme and sulfolane solvents associated with both LiTFSI (lithium bistrifluomethane sulfonimide) and Mg(TFSI)2 salts were selected, as electrolytes, in order to evaluate the potentiality of the active material3. First of all, the electrochemical responses of PBQDS in lithium and magnesium based electrolytes was performed in a cavity micro-electrode. Whereas in both case the cyclic voltammetry exhibit a close to reversible redox stem (Fig. 1a), The electrochemical characteristics of the material are very similar in term of potential and ΔEpeak in both lithium and magnesium systems at a relative high scan rate i.e. 1 mV s-1. An improvement of the redox couple reversibility seems to be observed in Mg form, with a ΔEpeak= 400 mV at E° of 0.3 V vs Fc+/Fc (3.5 vs Li+/Li). Given this interesting behavior, PBQDS in a coin cell configuration using glyme + LiTFSI electrolyte, was analyzed. . A stable capacity of 160 mAh g-1 was obtained at C/10 after 70 cycles, whereas a value of 120 mAh g-1 was maintained at C rate (Fig. 1b). In order to improve, the electrochemical performances, especially at high C-rate, the impact of the particle sizes (controlled grinding) of the cathodic material is in progress in view to approach its theoretical capacity value. In addition, the electrochemical investigations in both Mg and Li based electrolytes will be presented in regard to the electrolyte nature and the PBQDS morphology. 1. H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, D. Aurbach, Energy Environ. Sci., 2013, 6, 2265–2279.2. P. Poizot, F. Dolhem, Energy Environ. Sci., 2011, 4, 20033. H. Dong, Y. Liang, O. Tutusaus, R. Mohtadi, Y. Zhang, F. Hao, Y. Yao, Joule 2019, 3, 1–12 Figure 1

Electrochemical reduction of europium(iii) using tetra-n-octyl diglycolamide functionalized ordered mesoporous carbon microelectrodes

This work investigates the one-electron reduction of Eu(iii) to Eu(ii) by ordered mesoporous carbon (OMC), with and without tetra-n-octyl diglycolamide (TODGA) functionalization, in cavity microelectrode (CME) systems.

Bimetallic Cu–Rh Nanoparticles on Diazonium-Modified Carbon Powders for the Electrocatalytic Reduction of Nitrates

4-Benzenethiol-functionalized high-surface-area graphite powder was prepared and decorated with bimetallic Cu100-xRhx nanoparticles (NPs) to serve as electrocatalysts for the reduction of nitrates. In the first step, the HSAG powder was grafted with in-situ-generated diazonium compounds from 4-aminothiophenol (ATP) in an acidic medium using NaNO2 for the diazotization process. The surface composition was tuned using different initial quantities of ATP. The surface XPS-determined S/C atomic ratio was found to increase stepwise with the initial quantity of amine. In a second step, the grafted and untreated HSAG powders were decorated with Cu100-xRhx NPs by a wet chemical method and the elemental composition of the end composites was assessed by EDS-SEM and ICP, whereas TEM and EDS-TEM served to characterize the NP morphology and their composition on the nanometer scale. In all cases, the NP size was invariably found to be ∼1.7 nm but with a size distribution becoming narrower under an increasing grafting rate and the global composition enriched in copper. Voltammetry was performed with a cavity microelectrode to evaluate the electrocatalytic performance of the composites for nitrate reduction. Increasing diazonium grafting led to a progressive reduction of the peak current intensity and a shift of the peak potentials toward cathodic values. The maximum intensity was obtained for 0.005 μmol of diazonium salt per mg of HSAG, with a gain of 40% in comparison to the best untreated sample. This improvement and a change in the voltammogram characteristics after grafting seem to result from modifications of the local composition at the level of NPs that differ from the global composition. This work conclusively shows that diazonium surface modification is important not only in attaching electrocatalytic NPs to carbon supports but also in providing a narrower size distribution of the electrocatalysts together with finely tuned catalytic properties.

Anisotropic Nanoporous Nickel Obtained through the Chemical Dealloying of Y2Ni7 for the Comprehension of Anode Surface Chemistry of Ni‐MH Batteries

AbstractFor the first time, the nickel layer formed during the corrosion of intermetallic alloys with a stacked structure has been isolated. This nickel layer has been produced by chemical dealloying of Y2Ni7 through a corrosion process in alkaline medium. This anisotropic and nanoporous phase has been fully characterized regarding its morphology, chemical and structural properties, as well as its electrochemical behavior. The metallic phase is made of interconnected nanocrystalline cubic nickel, showing preferential orientation and nanopores. A cavity microelectrode has been used in addition to classical methods using bulk electrodes for electrochemical investigations of the layer. This full characterization is of primary importance to better understand the behavior of metallic anodes in Ni‐MH batteries upon cycling and to ensure a longer lifetime.

Direct Electrochemical Desulfurization of Solid Sb2S3 to Antimony Powders in Deep Eutectic Solvent

Antimony (Sb) powders and sulfur nanoparticles have been prepared by direct electroreduction of solid Sb2S3 in ChCl-EG DES at 353 K. Cyclic voltammogram of Sb2S3 on Pt-powder cavity microelectrode demonstrates that the electrochemical desulfurization of Sb2S3 to metallic Sb is a one-step process through three-electron transfer. Constant voltage electrolysis indicates that Sb2S3 can be completely transformed into metallic Sb and sulfur for 16 h, and the cathodic current efficiency is about 50.64%. Besides, ESI-MS analysis implies that four-coordinated complex anions [SbCl4]− are formed and the electrodeposition of [SbCl4]−→Sb0 also exists simultaneously except for the mainly direct desulfurization process. Dissolved Sb(III) ions can be reduced and deposited at Sb grains to form larger hemispherical particles in a more stable state, which looks like a snail shell to encapsulate these Sb grains. In addition, amorphous sulfur powders are densely agglomerated with each other to establish a network structure and the morphology is irregularly globular with diameters of 14–25 nm. The electro-desulfurization process of Sb2S3 powders has been analyzed and a schematic illustration is also proposed. This finding provides a possible way for green extraction of Sb from stibnite resources in DESs at near room temperature with short process and emission-free SO2.

Electrochemical oxidation of urea on nickel-rhodium nanoparticles/carbon composites

Ni100-xRhx/C composites consisting in bimetallic nanoparticles (10 wt.%) dispersed in high surface area graphite were synthesized and their electrocatalytic performances for urea oxidation tested in alkaline media by cyclic voltammetry using a cavity microelectrode. The composites are synthesized by impregnation of a graphite powder with an aqueous solution of nickel and rhodium salts, followed by drying and reduction under H2/Ar at 500 °C. TEM observations reveal that the Rh fraction influences the average nanoparticle size which varies from 15 nm for pure Ni to 2 nm for pure Rh. XRD analysis indicates that solid solutions are obtained for all compositions.Ni100-xRhx with up to 30 at.% of rhodium have a higher electrocatalytic activity than pure Ni and their voltammograms exhibit two urea oxidation peaks rather than one, the additional peak being at a potential 50 mV less positive than that of pure nickel. When the rhodium content increases above 30 at.%, the current of urea oxidation decreases and becomes almost zero for pure rhodium. These variations in current as the fraction of rhodium increases are only related to the decrease in nanoparticle size and in nickel content (within a surface layer of ∼1 nm). Hence, there is no synergistic effect between nickel and rhodium for the oxidation of urea in alkaline media.

Synthesis, characterization and molecular modeling of binuclear Pd(II) and Ir(IV) complexes with bis [4-hydroxy-6-methyl-3-{(1E)-N-[2-(ethylamino)ethyl]ethanimidoyl}-2H-pyran-2-one]: Application to detection of glucose

Two binuclear Pd (II) and Ir(IV) complexes with new bis [4-hydroxy-6-methyl-3-{(1E)-N-[2-(ethylamino) ethyl] ethanimidoyl}-2H-pyran-2-one] ligand (Schiff base: L) have been prepared and characterized by elemental analysis, ESI-MS, conductivity, NMR (1H NMR, 13C NMR, COSY-NMR, HMBC-NMR and HSQC-NMR), EPR, FT-IR, ATR, UV–Visible spectra and cyclic voltammetry. Both antioxidant and antimicrobial activities were studied; the stability constants of the metal complexes and their interactions with glucose were estimated using spectrophotometric method. In addition, the detection of glucose using Pd(II) and Ir(IV) complexes was investigated using cavity microelectrode (CME) by chronoamperometric method.The characterization results and the molecular parameters were determined using DFT technique; a square planar geometry around Pd (II) and an octahedral geometry around Ir(IV) was found.The antioxidant measurements showed that the ligand and its complexes exhibited remarkable activity, and the antimicrobial studies revealed that all compounds are biologically active for some bacteria and fungi.Electrochemical measurements showed the presence of sensitive responses towards glucose using both Pd(II) and Ir(IV) complexes; these results were found to be higher than other materials around glucose concentration range of 0–4 mM.

Advanced analytical techniques to characterize materials for electrochemical capacitors

This review covers recent developments in advanced analytical techniques to characterize materials for electrochemical capacitors. For double layer capacitors, examples of the use of in situ X-ray photoelectron spectroscopy (XPS), pulsed electrochemical mass spectrometry (PEMS) technique, temperature-programmed desorption coupled with mass spectroscopy (TPD-MS) technique, in situ NMR spectroscopy, and in situ dilatometry measurement are presented, for studying carbon/electrolyte interface with a focus onto electrolyte ions confinement in nanopores and changes during ageing. For the pseudocapacitive system, in situ X-ray (neutron) diffraction or scattering, in situ dilatometry technique, cavity micro-electrode, in situ Raman spectroscopy, TPD-MS technique, and electrochemical quartz crystal microbalance (EQCM) technique have been employed for studying materials structure, electrochemical kinetic, interface interaction, and ions adsorption/desorption. These advanced analytical techniques probe insight into charge storage mechanisms, and guiding the fast development of supercapacitors.