The purpose of this study is to evaluate the surface activity of silicon by evaluating a voltammetric profile of the substrate in an electrolytic medium. Since the electrical current flowing through the circuit is a measure of the rate at which a redox process occurs at the interface, higher current values will indicate more active substrates. For this study, hydroxyl radicals were generated by photochemical decomposition of H2O2. For this purpose, a H2O2 solution was irradiated with a UV lamp. The experimental conditions that were varied in the process were: illumination time, H2O2 concentration. The presence of the hydroxyl radicals generated through the methodology employed was qualitatively confirmed by fluorescence, using for this purpose (i) a 2 ',7 '-dichlorodihydrofluorescein diacetate (DCFH-DA) probe and (ii) a "radical scavenger", which corresponds to an antioxidant species, in this case ascorbic acid. On the other hand, for the voltammetric measurements of the semiconducting substrate after interaction with hydroxyl radicals, a 0,1 M KCl solution was used as electrolyte solution. The experimental conditions studied were: influence of the pH of the medium and influence of different chemical treatments applied to the substrates used after interaction with hydroxyl radicals. From the results obtained, an increase in both(H2O2) concentration and immersion time produces an increase in current in the interphase electrode processes, indicating an activation of the semiconductor electrode surface. Indeed, in the anodic hemicycle, the signal of substrate oxidation appears at -0,75 V, and then from -0,45 V onwards, the oxidation of water. This is an indication that the semiconductor/electrolyte interface is ohmic, since in the absence of illumination (absence of minority carriers, h(+)) there are oxidation processes. On the other hand, for pH values in the intervals between 2 > pH > 5 and 7 > pH > 13, the slopes are approximately 0 mV/pH and for the interval between 5 > pH > 7, of the order of 60 mV/pH, this being an indication of a change in the nature of the surface functional groups of silicon.

The detection and control of glucose (Glu) levels in both food and biological samples have gained importance in recent decades, as imbalances in glucose levels can lead to health complications such as diabetes mellitus. Consequently, this study focused on synthesizing thin films of Cu2O and evaluating their application as a non-enzymatic amperometric glucose sensor. The Cu2O films were obtained on FTO at a constant potential (-0.575 V vs. SMSE), in an inert atmosphere and at room temperature. The electrolyte solution consisted of 0.02 M of copper acetate (Cu(OOCCH3)(2)) and 0.1 M of sodium acetate (NaOOCCH3) at pH 5.79, in a three-electrode cell. The films obtained were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). On the other hand, the electrocatalytic activity was studied using linear potential sweep (LPS) and chronoamperometry (CA) techniques. From these techniques, it was possible to determine the sensitivity (228.1 mu A mM(-1) cm(-2)), limit of detection (LOD 2.49 x 10(-3) mM), limit of quantification (LOQ 7.54 x 10(-3) mM) and linear range (0.10 mM <=[Glucose] <= 15 mM). In this concentration interval the response time was between 1.4 and 14 s. It was established that the sensor exhibits minimal response to various electroactive interferences and demonstrates reproducibility and stability over time. In this way, the proposed Cu2O electrode is a good candidate to be used as a non-enzymatic amperometric glucose sensor.

Ion-intercalation electrochemistry under quasi-equilibrium conditions is described in terms of a logistic approximation. The theoretical model assumes that the differential capacitance can be expressed as a logistic relationship between the transferred charge and the applied potential. This semiempirical model provides analytical solutions for the constitutive equations, including a simplified account of uncompensated resistive and capacitive effects in the cell. The model is applied to describe the Fe- and Cu-centered voltammetry of a synthetic potassium-copper hexacyanoferrate in contact with Li+-, Na+-, and K+-containing DMSO electrolyte solutions with satisfactory results.

El premio Nobel 2023 en el área de química, fue concedido a 3 investigadores: Alexei Ekimov, Luis Brus y Moungi Bawendi, por sus aportes al descubrimiento, caracterización y control de la producción de los puntos cuánticos. Los puntos cuánticos son nanoestructuras semiconductoras que exhiben propiedades cuánticas, i. e., propiedades dependientes del tamaño. De acuerdo a estos aportes al conocimiento, es que desde mediados de los años 90’s estas nanopartículas tienen diversas aplicaciones tecnológicas, tales como en la industria de la electrónica y la óptica, así como en la medicina, producción de sustancias, sensores, conversión de energía, entre otras. Este manuscrito busca dar una mirada general a las propiedades químicas y físicas de los puntos cuánticos, a los aportes de los investigadores galardonados en este campo, y a una experiencia propia en la utilización de estas partículas con fines de sensor de sustancias reactivas.

A CdCO3/CdO/Co3O4 composite has been prepared on nickel foam through a combined hydrothermal-annealing method. An asymmetric hybrid supercapacitor (SC) device was assembled with this composite as the positive electrode and activated carbon was the negative electrode. The SC exhibited a high specific capacitance of 84 F g(-1) @ 1 mA cm(-2), a maximum energy density of 26.3 W h kg(-1), and a power density of 2290 W kg(-1), along with a wide potential window of 1.5 V and long cycle life (92% after 6000 cycles). SCs assembled in series powered various light-emitting diodes and moved an electrical mini-motor.

The Cover Feature shows an idealized representation of the processes of electrochemically-assisted cation intercalation processes occurring in copper hexacyanoferrates. Cover design by María Teresa Doménech-Carbó, Universitat Politècnica de València. More information can be found in the Research Article by Antonio Doménech-Carbó, Silvana López, Eduardo Muñoz and co-workers.

The cation-insertion solid state electrochemistry of a potassium copper(II) hexacyanoferrate in contact with LiClO4 /DMSO, NaPF6 /DMSO, and KPF6 /DMSO electrolytes has been theoretically and experimentally studied using the voltammetry of immobilized particles methodology. Voltammetric data, combined with SEM/EDS analysis permit to determine a K0.876 CuII1.328 FeIII0.049 [FeIII0.318 FeII0.682 (CN)6 ] stoichiometry for the synthesized solid. Separation of electronic and ionic contributions to Gibbs energy changes can be made based on cyclic voltammetric and open circuit potential measurements. These parameters can be combined to measure values of the Gibbs energy of cation-independent electron transfer of 7.2±0.4 (K+ ), 7.1±0.5 (Na+ ) kJ mol-1 , in close agreement with the expected independence of this parameter on the electrolyte cation. The reduction Fe(III) centers bound to cyano groups exhibit a cation-dependent, essentially Nernstian character which can be described in terms of Na+ and K+ insertion/deinsertion while in the case of Li+ electrolytes there is significant co-cation diffusion. Chronoamperometric data provide estimates of the diffusion coefficients of Na+ , and K+ ions through the solid around 10-9 cm2 s-1 .

Rechargeable lithium-ion batteries are among the most promising battery technologies to meet energy conversion and storage requirements. However, this technology is still limited due to its high cost, which prevents its use on a large scale. Therefore, cheaper energy storage systems with long cycle life, high power/efficiency, and safety are in great demand and interest. Prussian blue analogs are promising candidates for use in large-scale energy storage applications due to their long-life cycles, high power density, and high energy efficiency [1]. Along with the change of the transition metal, some structural parameters and some fundamental properties of these compounds can be changed, affecting some parameters such as the battery's storage capacity. This work studied the electrochemical insertion of lithium ions into Copper Hexacyanoferrate (CuHCF). This compound was synthesized by a hydrothermal process using a factorial design for determining the significance variables, i. e., precursor concentrations, temperature, and reaction time, on the electrochemical performance of the battery. The samples obtained were characterized by FESEM, TEM, XRD, and TGA. The results show cubic structures with a high degree of crystallinity and an evident dependence of the crystallite size (50 - 140 nm) with the variation of the synthesis conditions. Finally, lithium-ion batteries were measured using a CuHCF cathode (theoretical charge 85.1 mAhg-1). The capacity values depended on the crystallite size, obtaining the best results in the synthesis under lower concentrations, reaction time, and temperature. This sample was submitted to deep charge/discharge cycles at a rate of C/20, where the capacity value was close to 60 mAhg-1 (right image). This demonstrates the influence of the crystallite size on the material's performance, managing to find the optimal synthesis conditions to maximize the battery capacity. References. [1] 1. Marzhana Omarova, Aibolat Koishybay, Nulati Yesibolati, Almagul Mentbayeva, Nurzhan Umirov, Kairat Ismailov, Desmond Adair, Moulay-Rachid Babaa, Indira Kurmanbayeva, Zhumabay Bakenov, Electrochim. Acta, 184 (2015) 58-63. Figure 1

In this work, the influence of the synthesis parameters (concentration, temperature, and reaction time) on the electrochemical performance of potassium-cobalt(II) octacyanomolybdate (KCoOCM) as a cathode material for its application in lithium-ion batteries was studied. The compound was synthesized hydrothermally using a chemometric approach and characterized by different techniques (FESEM, XRD, TGA). The KCoOCM showed a change in its morphology from prismatic structures to nanorods according to the synthesis conditions. Additionally, there was an influence on the specific capacity as a function of the synthesis parameters, i.e., precursor’s concentrations, temperature, and reaction time. The capacity values reached by the material was 50 mAh g−1, which is close to the theoretical value of the KCoOCM (60 mAh g−1). The statistical method employed would allow finding a condition where it is possible to maximize the capacity value of the material, which has been scarcely studied in this area. Finally, the performance of a lithium-ion battery based on a cathode of KCoOCM is reported for the first time in literature. Figure 1

Erratum&amp;mdash;Novel Rechargeable Lithium-Ion Battery Based on a Cathode of Potassium-Cobalt(II) Octacyanomolybdate [J. Electrochem. Soc., 168, 100543 (2021)]

A binder-free CdCO3/CdO/Co3O4 compound with a micro-cube-like morphology onto a nickel foam (NF) via a facile two-step hydrothermal + annealing procedure has been developed. The morphological, structural and electrochemical behavior of both the single compounds constituting this final product and the final product itself has been studied. The synergistic contribution effect of the single compounds in the final compound resulting specific capacitance values are presented and discussed. The CdCO3/CdO/Co3O4@NF electrode exhibits excellent supercapacitive performance with a high specific capacitance (CS) of 1759.2 F g-1 at a current density of 1 mA cm-2 and a CS value of 792.3 F g-1 at a current density of 50 mA cm-2 with a very good rate capability. The CdCO3/CdO/Co3O4@NF electrode also demonstrates a high coulombic efficiency of 96% at a current density as high as 50 mA cm-2 and also exhibits a good cycle stability with capacitance retention of ca. 100% after 1.000 cycles at a current density of 10 mA cm-2 along with a potential window of 0.4 V. The obtained results suggest that the facilely synthesized CdCO3/CdO/Co3O4 compound has great potential in high-performance electrochemical supercapacitor devices.

Based on three-phase electrode models, we study to access the Gibbs energy contributions for the transfer of ions and electrons in Prussian blue analogs since they have long life cycles and high energy efficiency. Ni[Fe(CN) 6 ] (HCFNi) and Cu[Fe(CN) 6 ] (HCFCu) were preliminarily synthesized by a hydrothermal process. The obtained HCFNi powders were supported on a paraffin-impregnated graphite electrode in contact with an organic electrolyte, producing solid-state oxidation-reduction electrochemical reactions, which have been monitored by cyclic voltammetry and open circuit potential measurements in the presence of potassium as intercalating ion. The results show a behavior according to the Nernst equation as the potassium ion concentration varies, with a slope of 61.2 mV/dec. These experiments make it possible to access Gibbs free energy values for both transfers separately and replicate them for different insertion ions, such as Na + and Li + . Figure: (Left) Open circuit potential measurements; (center) mid-peak potential measurements; and (right) cyclic voltammetry for Ni[Fe(CN)6] in potassium media. Figure 1

The optical properties of ZnO nanorod (NR) arrays were investigated by optical total transmittance (TT) and diffuse reflectance (DR) spectroscopy in the visible region. The NRs were grown electrochemically in a three-electrode cell over a glass/fluorine-doped tin oxide (FTO) substrate. The mean length, radius, and density of NR samples were characterized by scanning electron microscopy. The results were correlated with the observed optical properties. Since light scattering for these NR arrays is highly dependent on their morphology, therefore, a model for light scattering based in the Mie theory for cylinders was implemented to understand the observed spectra. The mean scattering and extinction cross sections were calculated from the morphology of the samples. They were used to fit the DR spectra. From the fittings, the TT spectra of the samples could be calculated. A good agreement with the experimental results was obtained. This indicates that the implemented model represents well the observed scattering phenomena.

In this work, the influence of the electrochemical insertion of different alkali ions, e.g., lithium, sodium, and potassium, on the electrochromic properties of copper(II) hexacyanoferrate(III) (CuHCF) was addressed. CuHCF was electrochemically synthesized on FTO substrates, and a nucleation and growth analysis was shown that follows a 3D progressive nucleation with diffusion-controlled growth, which was confirmed by SEM analysis. The spectroelectrochemical study demonstrated that spectral changes were centered into three regions: a green band (506 nm) associated with a charge transfer (Fe III → Cu II ), a violet band (413 nm) associated with d-d orbital transition for Cu +2 ions, and an ultraviolet band (354 nm) associated with a ligand-metal charge transfer (CN - → Fe III ). This electronic transfer, along with the calculated electrochromic efficiency averages, indicates a relationship between the ionic radius of insertion ions and the deformation generated in CuHCF. An increase in the ionic radius decreases the interatomic charge transfer, which produces a low electrochromic efficiency.

The present work reports the changes in CdTe quantum dots' size and optical properties (CdTe QDs) after interaction with hydroxyl radicals (center dot OH). Through characterization by UV-vis spectroscopy, fluorescence spectroscopy, and transmission electron microscopy, it was possible to observe the reduction in the size of the nanoparticles when exposed to Fenton's reagent (source of center dot OH radicals) under constant exposure to UV light. Furthermore, the results show shifts in the emission peak values at lower wavelengths, dependent on the initial size of the QD and the radical's concentration.

In this work, an assembly of FTO/α-Fe 2 O 3 /PB|M + electrolyte|PB/α-Fe 2 O 3 /FTO (M +  = Li + , Na + , K + ) secondary photocell was done to improve the charge capacity in the presence of illumination. Our previous results with these electrodes demonstrated the possibility of transferring photogenerated carriers from hematite to Prussian blue. This cell was characterized by incident photon-to-current efficiency (IPCE) and galvanostatic charge/discharge measurements under illumination and compared in darkness. A higher IPCE when potassium ions are employed in the cell was founded, which suggests an easy insertion/desertion of these ions inside/outside of the hexacyanometallate framework, related to the more compact water coordination sphere for this ion. The voltage cell increased when the system was charged under illumination, indicating an increase in the oxidation/reduction of iron centers in the hexacyanometallate structure due to the increase of photogenerated carriers in hematite. The cell’s specific capacity reaches around 12% of the theoretical capacity, with a voltage close to the theoretical (1.5 V) and about 95% of coulombic efficiency when the cell was charged and discharged at longer times (8 h).

Iron pyrite micro- and nano-sized crystals are desirable as active materials in lithium ion batteries and photovoltaics, and are particularly suitable for nanocrystal inks for roll-to-roll deposited or ink-jet printed solar cells. In this paper we report the synthesis of iron pyrite micro- and nano-sized crystals via simple and convenient green one-step microwave-assisted hydrothermal (M - H) process at relatively low growth temperatures, using commonly used precursors such as FeCl3, Na2S and S-8 and. The structural, morphological and optical properties of the resulting nanostructured materials have been thoroughly investigated for two typical M - H growth temperatures. X-ray diffraction (XRD) pattern and Raman data revealed good crystalline quality for the as synthesized pyrite NCs. Typical XRD patterns show the dominant peaks which can be indexed as a pure cubic phase of FeS2, with lattice constant values close to the lattice parameters reported for FeS2, and in agreement with a stoichiometric pyrite phase. XRD and Raman analysis also confirm that no other impurities phases such as hexagonal FeS2, marcasite, pyrrhotite, greigite, S or Fe-O compounds were detected, confirming the high purity of the synthesized iron pyrite nanocrystals. Various shapes of pyrite like quasi-cubic, cubic and flower-like FeS2 nanocrystals have been observed, which can be modulated by using different synthetic conditions. The sizes of the pyrite micro- and nanostructures were in the range of 150 nm to 1 mu m as obtained. The present study indicates that the M - H method is a facile one-step way to obtain phase pure iron pyrite micro- and nano-sized crystals. Optical characterization confirms direct bandgap transitions (values of 2.61 eV and 2.55 eV for iron pyrite NCs samples hydrothermal grown at 130 degrees C and 160 degrees C, respectively), and indirect bandgap transitions (values of 1.19 eV and 1.52 eV for samples hydrothermal grown at 130 degrees C and 160 degrees C, respectively). Optical studies show high absorbance in the entire UV-Vis wavelength range making the as-synthesized pyrite nanocrystals potential candidate as absorber in nanoscale photovoltaic solar cells.

The initial transient, or running-in, period during abrasive wear has been largely overlooked in the literature, with the focus instead being on steady-state conditions. However, the running-in period of abrasion might determine the evolution to steady-state wear behaviour, as is known to occur in sliding wear conditions. To this end, the running-in period during the abrasive wear of the austenitic stainless steel AISI 316L and Hadfield (15%Mn-1.5%C) steel was analysed through the testing pin (flat-ended)-abrasive paper wear configuration. The effects of the normal load, the size of the abrasive, and the type of material were evaluated, and the wear rate and the strain hardening of the matrix were recorded. The steady-state wear might be influenced by the phenomena occurring during the running-in period. Thus, the hardening, roughness, friction coefficient and wear micromechanisms were correlated with the wear rate to elucidate these possible relationships.

Cadmium telluride quantum dots (CdTe-QDs) can be deposited from colloidal solutions on glassy carbon (GC) electrodes potentiostatically. The immobilization of QDs can be performed at potentials positive and negative from the potential of zero charge (PZC = 0.45 V vs. Ag/AgCl), including the open circuit potential. The surface coverage of QDs depends on the deposition potential and time. The amount of QD layers was determined by following the redox process of cadmium by cyclic voltammetry and chronoamperometry. Additionally, the QD layers were characterized by scanning electrochemical microscopy (SECM) indicating a decrease of the surface conductivity of GC electrodes.