Mol Dm Research Articles

Simple and convenient preconcentration procedure for the isotopic analysis of uranium in seawater.

The demand for monitoring anthropogenic U isotopes, 236U and 233U, in seawater will continue to increase due to radioecological issues and the need for tools for environmental dynamics research. In response to this growing demand, herein, a novel and simple method was developed for the collection of U isotopes in seawater, both in the laboratory and field, using a fabric-like amidoxime adsorbent. The results from the adsorption studies showed that the optimum conditions for processing seawater in a glass beaker were as follows: seawater pH 4, amidoxime adsorbent 0.20 mmol per 500 g seawater and an adsorption time of 9 hours. Alternatively, when using a closed polyethylene container in experiments on-board a ship and using the same ratio of adsorbent to seawater as in the beaker experiment in the laboratory, the optimum conditions were as follows: seawater pH 8 and an adsorption time of 24 hours. Under the above-mentioned conditions, more than 95% of the U underwent adsorption in both the beaker and the polyethylene container experiments. In the case of analyte desorption, more than 80% of U in seawater was recovered using 2-3 mol dm-3 HCl or HNO3 as the eluent. Thus, it was concluded that the amidoxime adsorbent can serve as a simple and effective pre-concentration method for the ultra-trace monitoring of U isotopes in seawater.

Kinetics and oxidation of thiocarbohydrazide by hexacyanoferrate(III) in aqueous perchloric acid medium

Hexacyanoferrate(III) [HCF(III)] was used to oxidize thiocarbohydrazide (TCH) in an aqueous perchloric acid (HClO4) medium, and the reaction kinetics were studied spectrophotometrically at 420 nm while keeping a constant ionic strength of 1.0 mol dm−3 and modulating the temperature between 298K–318K. The stoichiometry of the reaction among TCH and HCF in the HClO4 medium is 1:2. The reaction has a lower than unit order in both TCH and HClO4 and is of the first order in HCF. The impact of varying the ionic strength and dielectric constant of the medium on the rate has been investigated. The effect of temperature on the reaction rate was studied, and different activation parameters of reaction Ea, ΔH#, ΔS#, ΔG#, and log10 A were calculated. The products of oxidation were analyzed by simple qualitative analysis. On the basis of the collected data, the rate law has been derived, and a probable mechanism has been proposed.

Phase Transition Behavior of Biphasic Systems Affected By the Charge-Transfer Process

Lithium-ion batteries have attracted attention with the development of electric vehicles and the introduction of renewable energy. For use in these applications, lithium-ion batteries with fast charge and discharge acceptability are particularly important. The charge and discharge reactions of lithium-ion batteries are limited by several factors such as ion and electron transfer in the electrode and electrolyte, charge transfer at the electrode-electrolyte interface, and reaction rates during phase transitions. It has been reported that the rate limiting factor of the biphasic materials is the phase boundary rearrangement, and the activation energy of such phase transition has been investigated in previous studies. However, there are variations in the reported activation energy values even for the same electrode material. Since there are many unexplored factors that affect the phase transition rate, we have examined the effect of these factors on the phase transition rate using LiFePO4as model electrodes. In our previous presentation, we showed that the phase transition behavior of LiFePO4 electrode changes depending on the electrolyte, suggesting the influence of the electrode/electrolyte interface. (1) In this presentation, we report the relationship between the activation energy of the biphasic reaction and that of the solvation/desolvation of the electrolyte measured using a four-probe cell (2), and the effect on the phase transition behavior when the transferred ion species is changed from Li+ to Na+. A non-aqueous-type three-electrode cell was composed of the LiFePO4 as a working electrode, lithium foils as a counter and reference electrodes, and a 1 mol dm–3 solution of LiPF6 in ethylene carbonate and diethyl carbonate (1:1 v/v) as an electrolyte solution and was constructed in an Ar-filled glove box. An aqueous-type three-electrode cell was composed of the LiFePO4 as a working electrode, a Ni wire as a counter electrode, Ag/AgCl/sat’d KCl aq as a reference electrode, and a 0.5 mol dm–3 Li2SO4 aqueous solution as an electrolyte solution. The charging–discharging behavior was firstly measured to confirm the cell characteristics and then the potential step measurement was employed. The Avrami plots based on the potential step results (3) were used to obtain the reaction rate constant k. Further experiments at different temperatures were performed and the Arrhenius plots were drawn to calculate the activation energy of the phase transition. (3) The activation energy for solvation/desolvation of the electrolyte was calculated by making a four-probe cell with the counter electrode and reference electrode symmetrically arranged across the solid electrolyte Li2OAl2O3SiO2P2O5TiO2 (OHARA) and measuring AC impedance spectra at different temperatures. For the Na+ system, the LiFePO4 electrode was electrochemically delithiated to produce FePO4, and then Na+ was inserted into FePO4 to obtain NaFePO4 in the aqueous electrolyte. Electrochemical measurements were performed with the obtained electrode. The potential step measurements were performed with the aqueous and non-aqueous electrolyte cells. Their activation energies were obtained from the Arrhenius plots with the k values and compared. The activation energy measured in the aqueous electrolytes was smaller than that measured in the nonaqueous electrolyte. The activation energy for the solvation/desolvation processes was also smaller for the aqueous electrolytes system, suggesting that the charge transfer process between electrode and electrolyte is involved in the rate-determining process of the phase transition. Next, we performed the same experiment by changing the mobile ion species from Li+ to Na+. The activation energy for Na+extraction was nearly zero, suggesting very fast phase transition. If the volume change corresponding to the phase transition limits the rate, large Na+ extraction would lead to high activation energy than Li+ extraction. The tendency was the opposite, suggesting that the weak interaction of Na+ and water affects the whole phase transition.References(1) C. Yamamoto, A. Ikezawa and H. Arai, The 242nd Electrochemical Society Meeting, A02-0130 (2022).(2) Z. Ogumi., Electrochemistry, 78, 319 (2010).(3) J. Allen, T.R. Jow, and J. Wolfenstine, Chem. Mater., 19, 2108-2011 (2007).(4) Y. Orikasa, T. Maeda, Y. Koyama, T. Minato, H. Murayama, K. Fukuda, H. Tanida, H. Arai, E. Matsubara, Y. Uchimoto, and Z. Ogumi, J. Electrochem. Soc. 160, A3061-A3065 (2013). Figure 1

Quantitative Analysis of CO2 Evolution in an Alkaline Electrolyte Solution By Differential Electrochemical Mass Spectroscopy

CO2 is involved in various main and side reactions of electrochemical energy devices, such as carbon corrosion reactions and alcohol oxidation reactions. Differential electrochemical mass spectroscopy (DEMS) has been intensively applied in acidic electrolyte solutions to analyze these reactions. DEMS is the in-situ electrochemical measurement technique to analyze volatile species with the mass spectrometer (MS). However, the applications of DEMS to alkaline electrolyte solutions have been limited due to the high solubility of CO2 in alkaline solutions. While "conventional DEMS cells," where porous thin-film working electrodes are formed onto polytetrafluoroethylene (PTFE) membrane interface, can quantitatively analyze CO2 that has not dissolved into the electrolyte yet [1], the working electrode materials are limited to those that can be deposited on porous PTFE membrane as porous thin-films. Recently, Möller et al. have developed the DEMS system, which can detect CO2 from general planer electrodes coated by catalyst powders by combining a neutralizer and "dual thin-layer flow cell" [2]. However, due to the relatively low detection limit, quantitative analysis of evolved CO2 has not been accomplished. In this study, we attempt to use high surface area electrodes to enhance the MS signal of CO2 to enable quantitative analysis of evolved CO2. To suppress the in-plane reaction distribution in the flow cell, we integrated an anion exchange membrane into the cell and arranged the counter electrode opposing the working electrode [3] (Fig. 1 (a)).CO-stripping voltammetry was performed to evaluate the CO2 detectability of the constructed DEMS system. The DEMS cell was composed of a commercial Pt/C electrode as the working electrode, a commercial Hg/HgO electrode as the reference electrode, a Pt mesh as the reference electrode, 1 mol dm–3 KOH aq as the electrolyte solution, and 1 mol dm–3 H2SO4 aq as the neutralizer. Figure 1 (b) shows the CO-stripping voltammogram and corresponding MS signal of CO2 (m/z = 44). MS signal of CO2 accompanied by the anodic CO oxidation current is clearly observed from 0.6 to 1.2 V vs. RHE. The calibration constant, which correlates the MS signal of CO2 to partial current for CO2 evolution reaction, is successfully obtained as 2.2 × 10–10, which shows that the DEMS system established in this study can quantitatively analyze CO2. Applications to the carbon corrosion reactions are also presented at the site.

Electrochemical Reduction from CO2 to CH4 By Electrodeposited Cu/L-Histidine Hybrid Materials

The electrochemical reduction technology of carbon dioxide (CO2) is attracting attention due to it can convert CO2 into a useful resource with zero emissions by using surplus electricity and renewable energy. For achieving efficient electrolytic reduction of CO2, the development of a high active electrocatalysts is required. Copper (Cu) is the only metal that is capable of electrochemically converting CO2 to hydrocarbons, but the high overpotential of hydrocarbon formation and the low selectivity of the reduction products have been problems. One of the solutions to these problems is the hybridization of metal and organic materials, in which the metal serves as the CO2 reduction reaction sites and the organic material stabilizes the intermediates [1]. In the present study, we have demonstrated electrochemical reduction of CO2 by electrodeposited Cu loading L-Histidine (L-His) which is expecting stabilization of CO2 reductive intermediates hybrids.The electrodeposited Cu/L-His hybrids was obtained by a constant current electrolysis at -1.0~-4.5 mA cm-2 for 1 C cm-2 from the aqueous solutions containing 10 mmol dm-3, CuSO4･5H2O, 0.1 mol dm-3 Na2SO4, and 0.5~20 mmol dm-3 L-His in a three-electrode cell with carbon paper (CP) as the working electrode, platinum wire as the counter electrode, and Ag/AgCl as the reference electrode. The pH of electrolytic bath was controlled between 1.10 and 4.07 by adding H2SO4. The electrochemical reduction of CO2 has been carried out by a constant potential electrolysis at -1.27 V vs. RHE of 0.5 mol dm-3 KHCO3 aqueous solutions saturated with CO2. The amount of reductive gas products was quantified by GC-MS and GC-TCD.The changing the color from pale blue to deep blue was observed by adding L-His into electrolytic bath containing Na2SO4 and CuSO4･5H2O. As increasing concentration of L-His, absorption peak measured by UV-Vis was shifting from around 800 nm originated [Cu(H2O)4]2+ to around 630 nm. The shift was not observed above Cu2+ : L-His = 1 : 2 for molar concentration ratio, therefore, it was considered that Cu2+ and L-His form a complex of [Cu(L-His)2]2+ in aqueous solution. Thus, electrodeposition of Cu/L-His has been tried from Cu2+ : L-His = 1 : 2 aqueous solutions but electrodeposited Cu/L-His cannot achieve. As decreasing pH of electrolytic bath with fixing Cu2+ : L-His = 1 : 2, the absorption peak originated [Cu(L-His)2]2+ was shifting to [Cu(H2O)4]2+ absorption peak. Below pH = 1.7, the absorption peak had been shifted to [Cu(H2O)4]2+ completely and the precipitate was obtained in this condition. The hybridization Cu and L-His was confirmed by Raman spectra. Not only Cu, L-His peaks but also new peak originated L-His adsorbs to Cu were observed. CP has fiber like structure but electrodeposited Cu and Cu/L-His were precipitated such coating CP fiber. The particle size of Cu/L-His hybrids was more homogeneous, and the particles were more densely packed together compared to the pure Cu. However, changing diffraction patterns and peak broadening due to loading organic components in XRD were not observed.The electrochemical reductive reaction of CO2 on ED Cu has been conducted and the faradic efficiency (FE) of CO2 reductive gas product were calculated (Figure). Electrodeposited Cu (ED Cu) showed dramatically improvement of FE from CO2 to CH4 compared to copper foil (Cu foil). Furthermore, the L-His loading electrodeposited Cu (ED Cu/L-His) was more improved than ED Cu. Worthy of a special mention, the amount of hydrogen generation was reduced dramatically by introducing L-His. It can be considered that a reaction field was formed in which the CO2 reduction reaction preferentially takes place over hydrogen evolution. As increasing the concentration of L-His between 0.5~20 mmol dm-3, the FE from CO2 to CH4 goes high until 1.0 mmol dm-3 and then goes down, therefore, it can be observed that high L-His loading inhibits CO2 electrochemical reduction.[1] S. Jia et al., Angew. Chem. Int. Ed. 2021, 60, 10977–10982. Figure 1

Liquid Structure and Anti-Corrosion Effect of Super-Concentrated Electrolyte Solution

For realizing sustainable world, Lithium-ion batteries are required to have higher energy density. Aluminum metal have been dominantly used as a current collector of positive electrode. A mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) containing 1 mol dm-3 Lithium hexafluorophosphate (LiPF6) has been used as an electrolyte solution. Aluminum forms thin passivation layer on its surface, preventing the corrosion. However, aluminum corrosion may occur due to this electrolyte solution under high voltage condition. Recently, super-concentrated electrolyte solution (SCES) [1], which consists of only two or three times as much solvent as lithium salt, has been attracting attention as a new electrolyte solution of high-voltage lithium-ion battery. Motsumoto et al. proposed that aluminum corrosion was remarkably suppressed in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based SCES [2]. To clarify the corrosion-inhibiting factor of SCES, we investigated aluminum corrosion in the several lithium salts based SCESs [3]. And we found that lithium perchlorate (LiClO4)-based SCES could suppress corrosion of Aluminum current collector. Liquid structure of the SCES may plays an important role in corrosion suppression. In the present work, we demonstrated Raman spectroscopy and Quantum chemical calculations to reveal the liquid structure of the LiClO4-based SCES.The LiClO4 based SCES was prepared by dissolving LiClO4 into DMC as the molar ratio of 1 : 2. For comparison, DMC solution containing 1 mol dm-3 LiClO4 and neat DMC was also prepared. Raman spectroscopic experiments were conducted using Laser Raman spectrophotometer (NRS-5100, JASCO) installed a laser at 532 nm. Quantum calculations were performed using the Gaussion 9 program suite (Gaussian, USA). Geometry optimization were conducted at the B3LYP/6-311+G(d,p) level. An intensive peak is observed at approximately 915 cm-1 for neat DMC. When a small amount of LiClO4 is added to DMC (corresponding to 1 mol dm-3 LiClO4 solution), new peak is observed at approximately 932 cm-1. This peak can be assigned to ClO4 - anion. A new peak appears at approximately 950 cm-1 with increasing LiClO4 (corresponding to the SCES). According to the Quantum calculations, the new peak is assigned to aggregate in which the ClO4 - cross-links Li+. In addition, HOMO energy of a contact ion pair (CIP), in which ClO4 - coordinates to Li+, is lower than that of free ClO4 - anion. The oxidative stability of ClO4 - increases by forming CIP and aggregate. The decomposition products of ClO4 - may affect the Aluminum corrosion. The high oxidative stability of LiClO4-based SCES may prevent the Aluminum corrosion.

Potassium Vanadium Fluorides as Positive Electrode Materials for K-Ion Batteries

Potassium-ion batteries (KIBs) have attracted much attention as a potential high-voltage and high-power secondary batteries due to a low standard electrode potential of K+/K in carbonate ester-based electrolytes and weak Lewis acidity of K+ (1). We reported the K+ ion extraction/insertion reactions in polyanionic compounds at a high average working potential of > 4 V vs. K+/K, which should be attributed to the inductive effect of anion(2)(3). However, the specific capacity of polyanionic compounds is often limited by the high mass of the redox-inactive polyanion framework. In this study, we focused on potassium-containing vanadium fluorides, which have high theoretical capacity.We first created a triangle phase diagram of K-V-F systems considering with their theoretical capacities, as shown in Fig. 1a. Based on the theoretical capacity and valence of V, K3VF6 was selected and synthesized, and its electrode behavior and structural changes associated with potassium extraction were investigated as a positive electrode material for KIBs.K3VF6 was synthesized through a mechanochemical method after mixing stoichiometric ratios of KF and VF3 with 10 wt% Ketjen black (KB) and calcined to enhance crystallinity. The calcination was performed in an argon atmosphere at 300 °C. The working electrodes were prepared by mixing the synthesized sample with conductive carbon (KB) and binder (PVdF) at a weight ratio of 8 : 1 : 1 and applying it to an Al foil. The charge-discharge tests were conducted using coin cells with the prepared positive electrode, K metal counter electrode, and 1.0 mol dm-3 KPF6/EC : PC = 1 : 1 (v/v) or 5.6 mol kg-1 KFSA/G3 electrolyte (4).The Rietveld refinement of the synchrotron XRD pattern of K3VF6 is shown in Figure 1b. All of the diffraction peaks, except for VO peaks, could be indexed to the tetragonal space group I4/m. The refinement showed good fitting with a low R wp value of 6.18 %. The diffusion barrier of K+ ions in K3VF6 was calculated to 0.77 and 0.89 eV along b-axis and c-axis, respectively, by the BVEL method.Figure 1c shows the initial charge/discharge curve of K3VF6 electrode. The electrode exhibited a plateau at about 3.7 V and an initial discharge capacity of about 95 mAh g-1, which corresponds to a one-electron reaction of V4+/3+ (Figure 1c).Figure 1d shows ex-situ XAFS measurements to investigate the variation of V valence state during charge/discharge. After being charged to 4.3 V, the white line peak shifted to the higher energy and the pre-edge peak became stronger than the pristine spectra, indicating oxidation of V from trivalent to tetravalent during charge. The white line and the pre-edge peaks of K3VF6 discharged to 2.0 V are almost identical to that of the pristine, showing reversible V3+/4+ redox. We will further discuss the structural changes during the K+ ion extraction/insertion process and the redox behavior of V in the presentation.

Insights into the Complex Oxidation Behaviour of Aqueous H3PO3 through in Situ P K- Edge XANES

High-temperature electrolyte membrane fuel cells (HT-PEMFCs) using H3PO4-doped membranes are an enticing choice for electrochemical energy sources at elevated temperatures [1]. Yet, one of the challenges concerning these systems is the reduction of H3PO4 to lower valency phosphorus compounds, such as H3PO3, during operation [2,3,4]. H3PO3 can strongly adsorb on the Pt catalysts, hence poisoning it and thereby lowering the fuel cell performance [5,6]. Interestingly, the presence of Pt may, under certain conditions, catalyze the chemical (re-)oxidation of aqueous H3PO3 back to H3PO4, illustrating the complexity of the H3POx – Pt interaction. Therefore, to optimize the performance of HT-PEMFCs by rational design of the catalyst/electrolyte interface, further insight into H3PO3 oxidation behaviour and Pt/H3PO3 interaction under conditions relevant to HT-PEMFCs operation is required.In this study, in situ P K- edge XANES (x-ray absorption near edge structure) spectroscopy was conducted to shed light on the oxidation behaviour of aqueous H3PO3 by investigating the impact of (i) different temperatures (25°C vs 75°C), (ii) varying electrode roughness (flat planar Pt vs rough Pt black), (iii) different electrode potentials (open circuit potentials vs more positive potentials [+0.8, +0.9, and +1.0 VRHE]), and (iv) varying molar concentrations of H3PO3 (0.1 , 1 , and 5 mol dm-3). Initially, XANES coupled with electrochemical characterization (e.g. OCP, cyclic voltammetry) of the system was performed under different radiation doses (i.e.: photon fluxes, exposure time) to determine the effect of radiolysis and/or radiation damage during experiments that may lead to misinterpretations of XANES results. Under high radiation dose, we find evidence of H2 presence in the vicinity of the Pt electrode, likely generated by water radiolysis. We have developed experimental procedures to suppress these undesirable effects during the collection of the XANES data, enabling an accurate determination of H3PO3 oxidation behaviour and minimizing the radiolysis contribution to the process. It was found that higher temperature facilitates the oxidation of aqueous H3PO3 to H3PO4, presumably because H3PO3 exists in the thermodynamically preferred “active” pyramidal form at elevated temperatures, which is more prone to react with H2O, forming H3PO4 and H2. In aqueous H3PO3 solutions with higher H2O contents, also more pronounced oxidation of H3PO3 is observed, indicating that oxidation of H3PO3 to H3PO4 in aqueous solutions proceeds via the presence of H2O. The experiments using rough Pt black electrodes additionally hint at the observation of electrochemical oxidation of H3PO3 to H3PO4 during the application of positive potentials. This work provides insights into the underlying chemical processes that occur at conditions relevant for HT-PEMFCs operation and thus it paves the way for possible strategies to mitigate H3PO3 poisoning of the Pt electrode during operation.

Enhanced Kinetics of Oxygen Reduction Reactions in Alkaline Solutions inside Mesoporous Electrodes

Oxygen reduction reactions (ORR) in alkaline solutions attract increasing attention for their use as the cathodic reaction in metal-air batteries and alkaline fuel cells. However, the commercialization of these systems is impeded by high activation and concentration overpotentials of ORR, which originate from the sluggish kinetics on the catalyst surface and oxygen transport in the electrolyte, respectively. Although the practical electrode enables a decrease of the overpotentials with the porous structure, the effect of inner pores has not been understood. Among various pore sizes, it is crucial to investigate an electrochemical behavior in mesopores with a size of a few nm since such confined structures possibly change the intrinsic catalytic kinetics.1 In this study, we evaluated the ORR activity in the mesopore using Pt model electrodes with arrays of cylindrical pores with uniform pore sizes (Fig. a). We investigated the activity dependence on the electrode thickness to separate activation and concentration overpotentials, and found that the activation overpotential inside the mesopore with a size of 1.8 nm is smaller than that measured with the planer electrode. Pt model electrodes were electrodeposited from platinum salt in a liquid crystalline phase of a surfactant.2 The liquid crystalline phase was obtained by mixing 29 wt% of H2O, 29 wt% of hexachloroplatinic acid, and 42 wt% of octaethylene glycol monododecyl ether. The three-electrode cell consisted of an Au disk (φ 4 mm) working electrode, a Pt wire counter electrode, and an Ag|AgCl|sat’d KClaq reference electrode. The deposition was conducted at –0.055 V and 25 °C, and the charge densities were adjusted to obtain the electrode thickness of ca. 45, 100, 380, and 900 nm. Transmission electron microscopy (TEM) was performed to observe the pore structure. Electrochemical surface area (ECSA) and ORR activities were evaluated by cyclic voltammetry in N2/O2-saturated 0.1 mol dm–3 KOH solutions with a rotating disk electrode system, consisting of the porous model or a polished planar Pt working electrode, a Pt wire counter electrode, and a Hg|HgO reference electrode. The scan rate and rotation speed were 20 mV s–1 and 2000 rpm, respectively. TEM image exhibits the honeycomb arrays of mesopores with a pore size of 1.8 nm and a pore distance of 4.9 nm (Fig. a). The model electrodes possessed polycrystalline facets, and ECSA was calculated from the hydrogen adsorption peak area in blank voltammetry (Fig. b). The ECSA matched closely with the geometrically calculated surface area, suggesting that the cylindrical pores are uniformly distributed on the electrodes with defined pore lengths (Fig. c). ORR activities were evaluated with the Tafel plots (Fig. d), with current densities corrected for ECSA and concentration overpotential outside the mesopores. Since the oxygen transport resistance or the concentration overpotential is higher in longer pores, the electrodes with longer pore lengths caused smaller ORR current densities. In contrast, the concentration overpotential was suppressed enough to extract the activation overpotential when the pore length was 45 nm and 100 nm, and these electrodes led to higher ORR current density than the planar electrode. The result indicates that the activation overpotential inside the mesopore with a size of 1.8 nm is smaller than that measured with the planer electrode. We will report the origin of the enhanced kinetics inside the mesopore from the viewpoint of the electronic structure change.

Tracking Oxygen Evolution Activities of Perovskite Oxide Catalysts By 3D Electrochemical Impedance Spectroscopy

IntroductionPromoting the oxygen evolution reaction (OER) is important for more efficient electrochemical water splitting because its sluggish reaction kinetics degenerate the overall efficiency. Perovskite oxides (ABO3) are known as promising electrocatalysts for the OER, which have a flexibility of composition and structure. Among these electrocatalysts, Ba0.5Sr0.5Co0.8Fe0.2O3–δ (BSCF) exhibits good OER activities in an alkaline solution1. One of its specific properties is the change of the surface structure and composition during the OER in alkaline solutions, leading the improvement of the OER activity2. In general, the OER activities of metal oxides significantly depend on electrochemical surface area (ECSA) and activity per surface area (specific activity). However, it is not easy to decouple these two factors when the surface structure and composition change continuously during the OER.Electrochemical impedance spectroscopy (EIS) has been used as a useful tool, which provides information related to electrode/electrolyte interface3. Here, in order to reveal the origin of the OER activities behavior, we used 3D EIS including time axis and tracked the ECSA and specific activity of perovskite oxides during the OER in alkaline solutions.Experimental methodsPerovskite oxides used in this study (BSCF, La0.5Sr0.5Co0.8Fe0.2O3–δ (LSCF) and LaCoO3–δ (LCO)) were synthesized by the sol–gel method.The OER activities of obtained perovskite oxides were evaluated using a three-electrode electrochemical cell with a rotating disk electrode (RDE) in 1.0 mol dm–3 KOH solution. A working electrode was prepared by drop-casting an ink suspension with perovskite oxides (0.25 mg cm–2), acetylene black (0.05 mg cm–2), and Nafion (0.05 mg cm–2) on glassy carbon. Pt wire and a reversible hydrogen electrode (RHE) were used as the counter and reference electrodes, respectively. 3D EIS was obtained in the following steps: First, cyclic voltammetry (CV) was performed at certain cycles (1, 5, 10 ,30, and 50 cycles). Second, the electrode was left at open circuit potential for 5 min. Finally, potentiostatic EIS (PEIS) was recorded 5 times (approximately 10 min), and then Nyquist plots at 5 min from the beginning of the first PEIS were compared.Results and discussionFrom CV measurements of perovskite oxides, while the OER activities of BSCF increased, those of LSCF and LCO slightly decreased with increasing CV cycles. Figure shows Nyquist plots of perovskite oxides after certain CV cycles. The impedance spectra show a semicircle in the high- and mid-frequency regions, respectively. While a semicircle in the high-frequency region was independent on the direct current (DC) potential, the mid-frequency region semicircle was dependent on DC potential. The contrasting behavior indicated that the semicircle in the mid-frequency region corresponds to the charge transfer resistance, which contains the information of double-layer capacitance for the OER. Therefore, we tracked the semicircle in the mid-frequency region during the OER.A semicircle in the mid-frequency region of BSCF gradually decreased with CV cycles, indicating that the BSCF surface changed to a preferred structure during the OER cycles. As a result of the equivalent circuit fitting, the charge transfer resistance decreased and the double-layer capacitance increased with CV cycles. On the other hand, a semicircle in the mid-frequency region of LSCF and LCO remained unchanged or slightly increased.More detailed evaluation of their ECSA and specific activities during OER will be discussed at the conference.Reference[1] J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough and Y. Shao−Horn, Science, 334, 1383 (2011).[2] K. J. May, C. E. Carlton, K. A. Stoerzinger, M. Risch, J. Suntivich, Y.-L. Lee, A. Grimaud and Y. Shao-Horn, J. Phys. Chem. Lett., 3, 3264 (2012)[3] V. A. Alves, L. A. da Silva, and J. F. C. Boodts, Electrochim. Acta, 44, 1525 (1998). Figure 1

P'2-Na2/3[Mn1-X Sc x ]O2 Electrode in Sodium-Batteries

In recent years, Na-ion batteries (SIB) are expected to be an alternative to Li-ion batteries. One of the cathode materials for SIB is transition metal layered oxides Na x TMO2 (TM = transition metal). In order to improve their capacity, efforts have been made to utilize the redox process(es) of not only TM ions but also oxide ions (oxygen redox). In addition, partial replacement of TMs with electrochemically inactive elements has been investigated to enhance cycle stability. Our group reported P2-type Na x MnMeO2 (Me = Li, Mg) exhibit higher capacity than existing materials via using additional redox of oxide ions (1, 2). Another example delivering high capacity reported in our group is P’2-type Na2/3MnO2, where the average oxidation states of Mn is about +3.37 and a co-operative Jahn-Teller distortion (CJTD) of Mn3+ (t2g 3-eg 1) is shown (3). In this study, we synthesized P’2-Na2/3Mn1-x Sc x O2 and studied the effect of Sc substitution on the electrochemical properties of P’2-Na2/3MnO2. P’2-Na2/3Mn1-x Sc x O2 (x = 0, 0.08, 0.11) samples were synthesized using Na2CO3, Mn2O3, and Sc2O3 as starting materials, based on the synthesis method of the non-doped P’2-Na2/3MnO2 as we previously reported (3). For galvanostatic cycling tests, a working electrode consisted of active materials, acetylene black, and PVdF in 80:10:10 wt.% on Al foil. Na metal was used as a counter electrode, and an electrolyte used was 1.0 mol dm-3 NaPF6 PC solution. XRD patterns of P’2-Na2/3Mn1-x Sc x O2 are shown in Fig. 1 (a). Major diffraction peaks can be indexed as orthorhombic Na2/3MnO2 with space group of Cmcm, confirming P’2-type layered oxides. Note that non-substituted Na2/3MnO2 shows a superstructure peak at 23.9º in 2θ attributed to in-plane superstructure (3). At x = 0.11, impurity of Sc2O3 is observed, indicating that Sc is substituted for Mn up to about 8% in P’2-Na2/3MnO2. Sc3+ ions which has a large ionic radius than Mn3+ ions and no Jahn-Teller distortion, resulted in the enlarged lattice constant a (Figure 1 (a), inset) and the reduced lattice distortion (4). Fig. 1 (b) shows the discharge capacity and the coulombic efficiency of P’2-Na2/3Mn1-x Sc x O2 Electrode in Na cell. The capacity retention after 50 cycles for the non-substituted x = 0 (non-sub) and Sc-substituted x = 0.08 (Sc-sub) in the voltage range of 1.5 – 4.4 V was 66.4% and 85.4%, respectively. In-situ XRD data can support better cycling life. The Sc-sub exhibited better rate characteristics than the non-sub, indicating that there is an optimal amount of Sc to improve the electrochemical properties. Looking at the initial charge/discharge curves at different cutoff voltages (Fig. 1 (c)), setting the upper cutoff voltage beyond 3.47 V, causes a significant polarization due to the phase transition from P’2 to OP4. From the cycle stability tests at different upper cutoff voltages (Fig. 1 (d)), the upper cutoff limit of 4.0 V demonstrates notable capacity fade than that of 4.4 V. One possible reasons should be changing the surface chemistry of electrode by applying higher voltage than 4.0 V. We will further discuss the effects of Sc substitution and charge/discharge voltage range on the electrochemical properties.References Yabuuchi, S. Komaba, et al., J. Mater. Chem., 2, 16851 (2014).Yabuuchi, S. Komaba, et al., Adv Energy Mater., 4, 1301453 (2014).Kumakura, S. Komaba, et al., Angew. Chem. Int. Ed., 55, 12760 (2016).S. Kumakura, S. Komaba, et al., Chem Mater., 29, 8958 (2017). Figure 1

Attempts to Electrochemically Synthesize Palladium Superhydrides By High Pressure Method – Combination of Electrolytic Hydrogen Charging and Electroplating of Protective Coatings –

IntroductionIncited by the possibility of room-temperature superconductors in superhydrides, numerous them have been synthesized using a diamond anvil cell under high pressures up to several hundred GPa. Although palladium has widely researched for a long time as a prototype hydrogen-absorbing metal, the palladium superhydrides has not yet been obtained under such high pressures. A recent theorical calculation has predicted that the palladium superhydrides (e.g., PdH10) may be synthesized by combing electrolysis and high pressure1), but it is not certain whether it can be achieved. In this study, we attempted to synthesize the palladium superhydrides by using electrolytic hydrogen charging under high pressures, and subsequently applied protective coatings to suppress the hydrogen desorption from the palladium hydrides at ambient pressure.ExperimentalFigure shows a schematic illustration of the high-pressure apparatus. The high-pressure apparatus can apply the pressure of up to 400 MPa to the electrolyte in the electrolytic cell by pumping water into a sealed high-pressure vessel using a plunger pump and pressure multipliers. A cold-rolled palladium foil of 30 ~ 40 μm in thickness was used as a cathode, and a zinc plate was utilized as a soluble anode. Hydrogen was electrochemically loaded into the palladium foil at 0 V vs. Zn in an electrolyte consisting of 0.1 mol dm-3 sulfuric acid and 4.6 mmol dm-3 zinc sulfate under various pressures for 6 hours. Subsequently, the palladium foil was coated with the zinc film at constant current density 25 mA cm-2 for 120 seconds under the high pressure. The specimen was removed from the electrolytic cell in the high-pressure vessel at ambient pressure, and the hydrogen concentration of the palladium hydride PdH x was determined by thermal desorption spectroscopy. Structural analysis was conducted using X-ray diffraction and scanning electron microscopy.Results and discussionA number of bubbles were observed on the palladium foil surface during the electrolytic charging at ambient pressure. On the other hand, no bubbles were observed at 300 MPa. The zinc film with approximately 1.4 μm thick was coated on the PdH x surface after the electrolytic hydrogen charging. The hydrogen concentration of the PdH x was approximately x = 0.7 immediately after synthesis, which decreased to x = 0.2 without the zinc coating. On the other hand, the hydrogen concentration of the PdH x was maintained at least 1 week with the zinc coating. This result indicates that the zinc film acts as a barrier to hydrogen desorption from PdH x , and suggests that if the palladium superhydrides could be synthesized by electrolytic hydrogen charging under high pressure, it could be taken out to ambient pressure while maintaining its concentration.Reference1) W. Guan, R. J. Hemley, and V. Viswanathan, PNAS, 118, e2110470118 (2021) Figure 1

The study on distribution coefficient of polonium between tri-octylphosphine oxide (TOPO) and tri-butylphosphate (TBP) in toluene and cyclohexane and selected inorganic acids

In this work the distribution coefficients (D) of polonium between 0.1 mol dm−3 TOPO/toluene; TOPO/cyclohexane; TBP/toluene and TBP/cyclohexane and aqueous solutions of inorganic acids (HCl, HNO3, H2SO4 and H3PO4) were determinated. The molarities of inorganic acids were between 0.5 and 12.0 mol dm−3. The activity of extracted Po-209 was measured by means of liquid scintillation counting. The best result was obtained for TOPO/toluene and 2 mol dm−3 H2SO4 system (D = 62 ± 9). The most stable conditions of extraction were found for TOPO/toluene-HCl system.

A Spectroscopic Approach on Permanganate Oxidation of 1-[(4-Chlorophenyl)methyl]piperidin-4-amine in Presence of Ruthenium(III) Catalyst with DFT Analysis on Reaction Mechanism Pathway

The kinetic oxidation of 1-[(4-chlorophenyl)methyl]piperidin-4-amine (CMP) using alkaline potassium permanganate in presence of Ru(III) as catalyst was conducted spectrophotometrically at 303 K. The Pseudo first-order reaction was maintained with regard to oxidant and substrate during the reaction at an ionic strength of 0.01 mol dm-3. The first-order kinetics has been depicted with respect to catalyst Ru(III) chloride and less than unit order with substrate and medium. For the slow step, different activation parameters including ΔH# (kJ mol-1), Ea (kJ mol-1), ΔG# (kJ mol-1) and ΔS# (J K-1 mol-1) were calculated. The effect of temperature, variation of substrate concentration, oxidant, ionic strength were studied. The stoichiometry ratio of the reaction to the substrate and oxidizing agent was found to be 1:4. The products of reaction were isolated and identified as chlorobenzene and L-alanine, N-(2-aminomethylethyl)-carboxylic acid by LC-MS spectra, a suitable mechanism has been proposed and the rate laws are derived. The frontier molecular orbital (FMO) and frontier electron density (FED) of piperidiamine and the oxidative products were studied using density functional theory (DFT). The results of the theoretical calculations supported the suggested reaction pathways.

Development of an SPRi Test for the Quantitative Detection of Cadherin 12 in Human Plasma and Peritoneal Fluid

A new method for the determination of cadherin 12 (CDH12)—an adhesive protein that has a significant impact on the development, growth, and movement of cancer cells—was developed and validated. The method is based on a biosensor using surface plasmon resonance imaging (SPRi) detection. A quartz crystal microbalance was used to analyze the characteristics of the formation of successive layers of the biosensor, from the linker monolayer to the final capture of CDH12 from solution. The association equilibrium constant (KA = 1.66 × 1011 dm3 mol−1) and the dissociation equilibrium constant (KD = 7.52 × 10−12 mol dm−3) of the anti-CDH12 antibody–CDH12 protein complex were determined. The determined analytical parameters, namely the values determining the accuracy, precision, and repeatability of the method, do not exceed the permissible 20% deviations specified by the aforementioned institutions. The proposed method is also selective with respect to possible potential interferents, occurring in up to 100-fold excess concentration relative to the CDH12 concentration. The determined Limit of Quantification (LOQ = 4.92 pg mL−1) indicates the possibility of performing quantitative analysis in human plasma or peritoneal fluid without the need to concentrate the samples; however, particular attention should be paid to their storage conditions, as the analyte does not exhibit high stability. The Passing–Bablok regression model revealed good agreement between the reference method and the SPRi biosensor, with ρSpearman values of 0.961 and 0.925.

AN ELECTROMETRIC METHOD FOR THE DETERMINATION OF IMPACT OF DMSO-WATER MIXTURES ON pKa VALUES OF SALICYLIC ACID DERIVATIVES

Objective: The main objective of this present study is to conduct an experiment to analyze the variation of protonation-deprotonation equilibria with regards to the dielectric constants of an organic medium, influence of errors on protonation constants and effect of pH on the percentage of species. Methods: The present investigation was carried out by using pH meter at a temperature of 303 K and ionic strength of 0.16 mol dm-3 in Dimethyl sulfoxide (DMSO)-water mixtures. The processing of data was done by using Gran plot titration. The advanced principles of mathematics and fuzzy logic have been employed to correlate chemical problems, known as chemometrics. To obtain best-fit chemical models, a modelling strategy such as SCPHD is used and a computer program MINIQUAD 75 is also employed for the refinement of results. Results: In the present study, we found the influence of dielectric constants of a medium Dimethyl sulfoxide (DMSO)-water on protonation constants of 5-Sulfosalicylic acid and 5-Hydroxysalicylic acid has been studied. The species distribution diagrams were presented and understood the effect of pH on the percentage of species. The obtained skewness values are ranging from 0.11-0.36 and–0.56-0.38, for 5-Sulfosalicylic acid (5-SSA) and 5-Hydroxysalicylic acid (5-HSA), respectively, which describes the distribution curves are right skewed and left skewed. The kurtosis values are ranging from 2.12-3.56, which indicates the peak of the distribution curve exhibits both platykurtic and leptokurtic pattern. The changes in the concentrations of some influential parameters such as log F, acid, alkali, volume of titrands, ligand causes variation of stability constants and the order of the effect of influential parameters on stability constants are as alkali>acid>ligand>volume of titrand>log F. Conclusion: It is observed that the significant influence of co-solvent Dimethyl sulfoxide (DMSO)-Water mixtures on the protonation constants of ligands also studied how some factors such as changes in concentrations of ligand, acid, base log F and volume of the solution have influence on the protonation constants.

Exploring the Impact of DAHP Impregnation on Activated Carbon Fibers for Efficient Charge Storage and Selective O2 Reduction to Peroxide

Understanding the properties and behavior of carbon materials is of paramount importance in the pursuit of sustainable energy solutions and technological advancements. As versatile and abundant resources, carbon materials play a central role in various energy conversion and storage applications, making them essential components in the transition toward a greener and more efficient future. This study explores the impact of diammonium hydrogen phosphate (DAHP) impregnation on activated carbon fibers (ACFs) for efficient energy storage and conversion applications. The viscose fibers were impregnated with varying DAHP concentrations, followed by carbonization and activation processes. The capacitance measurements were conducted in 6 mol dm−3 KOH, 0.5 mol dm−3 H2SO4, and 2 mol dm−3 KNO3 solutions, while the oxygen reduction reaction (ORR) measurements were performed in O2-saturated 0.1 mol dm−3 KOH solution. We find that the presented materials display specific capacitances up to 160 F g−1 when the DAHP concentration is in the range of 1.0 to 2.5%. Moreover, for the samples with lower DAHP concentrations, highly selective O2 reduction to peroxide was achieved while maintaining low ORR onset potentials. Thus, by impregnating viscose fibers with DAHP, it is possible to tune their electrochemical properties while increasing the yield, enabling the more sustainable and energy-efficient synthesis of advanced materials for energy conversion applications.

Comparison of different preparation methods for oxygen isotope determination of phosphate in mammal tooth enamel

AbstractWe tested several sample pre-treatment protocols for the study of oxygen isotope ratios in the phosphate phase of mammalian enamel of ten different fossil samples. We investigated the effect of different pre-treatment methods and the duration of the hydrogen fluoride treatment on enamel samples from skeletal phosphate with known δ18O values. The samples had been measured previously, so we could compare the ratios measured in our laboratory with the previous values to choose the best chemical preparation procedure. Four pre-soaking methods and two different time intervals of 2 mol dm−3 hydrogen fluoride treatment were compared during our experiments. In our experimental conditions, the distilled water wash and the 6 h of soaking in hydrogen fluoride gave the closest results to the expected δ-values. The steps of the tested preparation processes were repeated at least three times on each sample, so the reproducibility of the process could be also investigated.

Protonation equilibria of the tryptophan metabolite 8-hydroxyquinoline-2-carboxylic acid (8-HQA) and its precursors: A potentiometric and calorimetric comparative study

The protonation constants of quinaldic acid (QA), 8-hydroxyquinoline (8-HQ) and 8-hydroxyquinoline-2-carboxylic acid (8-HQA) were determined potentiometrically in KCl(aq) at I = 0.2 mol dm−3 at different temperatures (288.15 ≤ T/K ≤ 318.15). Their temperature dependence was modeled by the van't Hoff equation, which allowed the calculation of other thermodynamic parameters, such as ΔH0 and ΔS0. Protonation enthalpy changes were also experimentally determined by isothermal titration calorimetry (ITC) at T = 298.15 K in the same medium and ionic strength conditions. From the obtained results, it emerged that all stepwise protonation reactions for the three ligands are exothermic, with protonation constants decreasing with increasing temperature. Then, thermodynamic protonation parameters obtained by both approaches were critically analyzed and compared, evidencing that protonation enthalpy changes obtained experimentally by direct calorimetry are more accurate than those derived by the van't Hoff equation. However, the latter approach proved useful to evidence possible variability of this thermodynamic parameter with temperature, thus allowing the eventual calculation of the corresponding ΔCp. Furthermore, on the basis of both the analysis of the obtained parameters and the results of detailed 1D and 2D 1H NMR studies, it was possible to unequivocally determine the protonation sequence of the different functional groups of 8-HQA (as well as QA and 8-HQ): from basic to acidic pH, the first group to undergo protonation is the phenolate, followed by the quinolinic nitrogen and, finally, by the carboxylate.

A new potentiometric method of determining the ionization constant of water based on the ionic liquid salt bridge consisting of N-ethyl-N-heptylpyrrolidinium bis(pentafluoroethanesulfonyl)amide

The ionization constant of water, KW, has been determined potentiometrically by use of an ionic liquid salt bridge (ILSB) consisting of a moderately hydrophobic N-ethyl-N-heptylpyrrolidinium bis(pentafluoroethanesulfonyl)amide at 25°C. The value obtained for pKW = -log10(KW) on the assumption that the liquid junction potential across the ILSB inserted between aqueous ca. 0.001 mol dm−3 solutions of HCl and NaOH is negligible was 13.81 ± 0.01(STDEV), which is smaller than 13.9965, reported about 90 years ago [1,2], based on potentiometry of the cells claimed to be without liquid junction. The present results seem to challenge the unproven assumption of no liquid junction in the so-called Harned cells in that if our Ecell value were greater by 10 mV, pKW would have been in perfect agreement with their 13.99, although it is very difficult to expect such a substantial magnitude of potential difference across the ILSB; logically, one may expect the opposite case, that is, that their value bears ca. 10 mV surplus possibly due to the hidden liquid junctions in the Harned cell.Relevant physicochemical properties of N-ethyl-N-alkylpyrrolidinium+ (alkyl = pentyl, hexyl and heptyl) and its ionic liquids formed in combination with bis(pentafluoroethanesulfonyl)amide− at 25°C are also reported.