EIS Measurements Research Articles

Microwave assisted activation of silkworm excrement for fast adsorption of methylene blue and high performance supercapacitor.

The activated carbon (AC) with an exceptionally high surface area was made of silkworm excrement (SE) by microwave-assisted KOH activation (MAKA). It was investigated for the potential applications in methylene blue (MB) adsorption and a supercapacitor electrode. The effect of activation time on the AC properties and performance was studied. The physical and chemical properties of the as-prepared samples were analyzed by FE-SEM, TEM, N2 adsorption, and Raman spectroscopy. Remarkably, the AC with the largest specific surface area (SAs) of 2530.3m2g-1 was produced by partial carbonization of SE at 400°C (SE400-5) and then activated for only 5min. The large SAs is attributed to the abundance of micro-pores, leading to the enhanced MB absorption performance, as equilibrium was reached within 10min at 25ppm of MB concentration. The maximum MB adsorption capacity for SE400-5 was 902.56mg g-1. The adsorption isotherms revealed that the Langmuir model best fits the empirical data (R2 ≥ 0.9813), indicating monolayer adsorption. The kinetic model fitted well to the Pseudo-second-order (PSO) (R2 ≥ 0.9691). CV, GCD, and EIS measurements also evaluated the electrochemical properties of all samples. The electrodes were made without the addition of conductive material. The SE400-5 also had the lowest total resistance and highest total effective capacitance, which resulted in its highest specific capacitance (Cs) of 322F g-1 at 0.5A g-1. The capacitive retention of SE400-5 remained as high as 98% even after 10,000 cycles at 10A g-1. These results demonstrate that SE is a viable source of AC for MB adsorption and a supercapacitor electrode.

Silver doping effect on the electrochromic performance of the WO3 thin films produced by thermal evaporation in vacuum

Ag doped WO3 thin films are successfully fabricated by thermal evaporation method in vacuum as precursor, and then annealed at 450 °C in nitrogen gases atmosphere. Cyclic voltammetry, repeating chronoamperometry, chronocolumetry and optical transmittance are recorded in 1 M LiClO4/propylene carbonate electrolyte. The color of the WO3 thin films changes from transparent to the blue under the applied potential of -1.8 and +1.9 V. XRD studies show that all the films have a polycrystalline structure of WO3. The molecular formation is also confirmed by Raman and X-Ray photoelectron spectroscopy (XPS). The EDS elemental mappings clearly confirm the homogeneous distribution of Ag, W and O elements into the WO3 network. From the optical studies, indirect band gap energy of the WO3 decreases as Ag doping level increases. The best coloration and bleaching times (2.33 and 1.25 s) are obtained for the Ag(2%):WO3 thin films, compared to the pure WO3 (3.79 and 1.96 s). The produced WO3 films exhibit high reversibility (39.6/69.1%), high coloration efficiency values (26.3/141.2 cm2/C), and good cycling stability. From the EIS measurements, the charge-transfer resistance is Ag(2%):WO3 < the pure WO3 < Ag(5%):WO3 < Ag(8%):WO3, which means that Ag(2%):WO3 has the biggest electrochemically active surface area. Electronic energy levels of the pure WO3 and the Ag:WO3 thin films are also given. From the Mott-Schottky studies, it is determined that the donor concentration of the materials is of the order of 1014-1015 cm−3. In the literature, there are very limited studies related to electrochromic thin films by thermal evaporation in vacuum. In this sense, the reported results in this study are promising for the electrochromic applications.

Tuning Supercapacitive Behavior of Eri Silk (Philosamiaricini)‐Polyanilne Nanocomposite for Electrodes Applications

ABSTRACTHerein, the synthesis of Polyaniline‐Eri nanosilk fibroin (PANI/ENSF) composite supercapacitor electrode material by utilizing Eri silk (Philosamiaricini) as a raw material and polyaniline (PANI) with H2SO4 as doping acid and (NH4)2S2O8 as an oxidant, via a simple in situ oxidative polymerization technique, with good performance characteristics is reported. The chemical composition of the composites have been studied by using XRD, FT‐IR, UV–vis spectroscopy, Raman spectroscopy, and morphology is studied by SEM. BET analysis reveals that the surface area of composite is 712.10 m2g−1, and BJH analysis shows that the pore size is mainly concentrated between 1.5 and 15.7 nm. The composite shows electrical conductivity of 17.33 × 10−2 Scm−1 (Keithley Model 2000). The electrochemical performances are evaluated by using CV, GCD, and EIS measurements. The three‐electrode system composite shows specific capacitance of about 310.12 Fg−1 at 0.1 Ag−1, which is the highest value being reported, compared to already available polyaniline‐silk composites. Further the studies have been extended to assemble a symmetrical two‐electrode supercapacitor device which also exhibits a high value of specific capacitance of 35 Fg−1 at 5 Ag−1 and 96.12% capacity retention over 5000 cycles. For the first time, this study reports using a Polyaniline‐Eri nanosilk composite to design an efficient supercapacitor electrode.

Ag3PO4 anchored SnWO4 Z-scheme heterojunction for reactive blue 21 degradation: Performance analysis and mechanism insights

The Ag3PO4–SnWO4 heterostructured nanocomposites have been prepared by the chemical precipitation process. The prepared nanocomposites were examined through XRD, TEM, UV–visible NIR, PL, BET, Mott Schottky, EIS, and ESR measurements. The diffraction peaks of Ag3PO4–SnWO4 nanocomposite showed the peaks of SnWO4 nanoparticles that are orthorhombic in the Ag3PO4 tetragonal structure, which suggested that they are present in the mixed phase of the composite. Photoluminescence spectra displayed efficiency in charge separation of e−-h+ pairs in Ag3PO4–SnWO4-1 nanocomposite. The Ag3PO4–SnWO4 nanocomposites have been examined for degrading the aqueous solution of reactive blue (RB 21) under natural sunlight irradiation. The superior photoactivity of Ag3PO4–SnWO4-1 could be ascribed to the existence of a heterostructure between Ag3PO4 and SnWO4 nanoparticles that improved the light absorption ability of the heterostructure. Also, a low rate of recombination of electron and hole pairs between Ag3PO4 and SnWO4 nanoparticles was observed. The Mott–Schottky plot revealed both Ag3PO4 and SnWO4 as n type semiconductor with flat-band potential values as 0.34 and −0.54 eV respectively. The photocatalytic rate reached the fastest on the incorporation of 100 mg SnWO4 compared to pristine Ag3PO4 and SnWO4 particles with 91.4% degradation efficiency and a rate constant of 0.257 min−1. The photogenerated O2∙−, h+ and ∙OH radicals indicated by the radical trapping experiment were mainly liable for the RB 21 degradation.

Alkali surface modification of titanium for biomedical implants

AbstractNanostructures were successfully created on titanium (Ti) substrates through alkali treatment. By varying the concentration, temperature, and duration of the alkali treatment, different nanostructure surfaces were achieved on Ti. FE‐SEM analysis revealed a transition from a smooth to a nanoporous surface structure. The alkali treatment notably decreased the contact angle of Ti from 64° to 48°. Raman spectroscopy of Ti treated with 5 M NaOH at 80 °C for 24 h showed distinct titanate peaks at 188, 190, and 270 cm−1, confirming the formation of titanate compounds on the Ti surface. EIS measurements further demonstrated that the treated Ti exhibited reduced chemical activity, increased surface roughness, and porosity of approximately 40–50% compared to untreated Ti. In vitro biocompatibility tests using baby hamster kidney cells indicated positive cell attachment and proliferation after 72 h of culturing on the alkali‐treated Ti. These modifications enhance the surface properties and expand the potential applications of titanium in biomedical, industrial, and environmental technologies.

Low-frequency EIS interpretation with the potential to predict the durability of protective coatings

Obtaining impedance response with predictive value for coating durability is central to meeting today's protective coatings end-user requirements. Here we present a novel approach to interpreting the low-frequency impedance of industrial coatings that takes into account the relevance of the coating properties that determine their barrier and adhesion durability. Modern, high adhesion, low VOC polymer coatings utilize cross-linking chemistry with polar or hydrogen bonding materials, leading to the apparent paradox that coatings exhibit corrosion creep values that are very low and inversely related to the barrier effect derived from the EIS response. In practice, once the corrosion creep rate is negligible, the ability of a coating to act as a long-term effective barrier, especially at edges and welds, becomes a major concern, and the improvement in durability relies on the improvement of the barrier. In the present study, we investigated the barrier effect of conventional partial and full offshore coating systems with epoxy and epoxy mastic layers applied without and with zinc-rich or zinc phosphate primers and polyurethane topcoats. The panels were aged for two years in an atmospheric offshore-like conditions and subsequently exhibited defects due to inadequate coating thickness, number of layers, surface preparation and inadequate application practice. EIS measurements were performed on the panels in the laboratory in dry and wet state. EIS provided a quantitative rating of the barrier effect that can serve as a basis for informed upgrading of coating solutions, application practices or workmanship quality, particularly in structures with limited access where high durability is an imperative.

Facile synthesis of spherical-shaped CeC2–TiO2 nanocomposite electrocatalyst with boosted alkaline OER

Developing noble metal-free multifunctional electrocatalysts to catalyze water oxidation is vital for future renewable energy systems. Herein, through several defect modifications, the CeC2–TiO2 nanocomposite on the strength of enriched oxygen vacancies was successfully fabricated by facile hydrothermal method on SS (stainless steel) substrate, attributed to the conductive ability for fast electron transportation. A well-defined phase growth, vibrational bonding of metal atoms, morphological determination, and elemental composition for synthesized heterostructured electrocatalysts were revealed by XRD, FTIR, TEM, and EDX, respectively. XPS has complied to understand the moderate binding energies of CeC2–TiO2 for OER intermediates, which signifies the strong interactions between electronic states of Ce, C, Ti, and O atoms. With the plentiful catalytic active sites, the resultant CeC2–TiO2 entails low overpotentials of only 169 mV and 108.8 mV/dec Tafel slope to afford 10 mA cm−2 for OER in 1.0 M KOH are tested through cyclic and linear sweep voltammogram measurements, thereby exhibit promising activity in alkaline water electrolysis. EIS measurements revealed a decreased polarization resistance for the composite dominated by the small semicircle diameter, corresponding to the adsorption of intermediates. Finally, observed results strongly recommended that the CeC2–TiO2 catalyst exhibited superior OER performance due to excellent electrical chemical coupling between CeC2 and TiO2.

Ta-ions doping impact on structural modifications and bandgap tuning of NiCo2O4 hexagonal nanosheets for high rated pseudocapacitor electrodes

Getting higher activity, lower cost and especially better stability at the same time is still one of the biggest problems in the supercapacitors research. Morphology tailoring and crystal imperfections induce d due to doping based defects in ternary transition metal oxides at the nano-scale level is crucial for enhancing the performance of supercapacitors. This research investigates of the utilization of Ta-doped NiCo2O4 (Ta-NCO) hexagonal nano-sheets for supercapacitor electrodes. The structural and morphological study of pristine and Ta-doped samples has been determined using XRD, SEM, TEM and HRTEM. The enhanced inherent conductivity and diffusion at the interface are also confirmed using electrochemical measurements study. The NCO-5 material exhibits a notable enhancement in capacitance and cycling retention. The NCO-5 electrode demonstrates a high specific capacitance (Cs) of 2445.7 F/g at 1 A/g. The pseudocapacitive behavior by power law (b = 0.67) and an increase in capacitive contribution with the scan rate reaching a value of 47.2 % at 100 mV/s by Dunn method exhibits it suitability of pseudocapacitors. The low Rct value signifies it improved capacitive performance as deduced from EIS measurements. Crucially, it maintains around 95.3 % of its capacitance after undergoing 10,000 GCD cycles. The high specific capacitance, remarkable capacitive characteristics and high stability of NCO-5 make it an excellent contestant for supercapacitor applications. The fabricated asymmetric supercapacitor (NCO-5//AC) shows exceptional energy density (ED) of 96.35 Wh/kg with power density (PD) of 825.03 W/kg.

Experimental and Quantum Chemical Studies of a Green Corrosion Inhibitor for Mild Steel in Acidic Chloride Solution

AbstractA green corrosion inhibitor was prepared from the bio‐based platform compound 5‐hydroxymethylfurfural through a green synthetic route, which avoid the use of toxic reagent. The inhibition performance and mechanism of this compound for the corrosion of mild steel in 0.1 M HCl was investigated by using the weight loss experiments, polarization measurements, EIS measurements and quantum chemical calculations. The corrosion inhibition efficiency by weight loss measurement (ηWLM%) of this inhibitor can reach up to 90.3 % at 303 K with 1.2 mM concentration. Moreover, the electrochemical experiments revealed that this corrosion inhibitor acts as a mixed‐type inhibitor. Thermodynamic studies gave the values of the standard Gibbs free energy , fall within the range of −20 kJ/mol to −40 kJ/mol, suggested the adsorption of this compound is a spontaneous process involving both physisorption and chemisorption. In addition, quantum chemical calculations were conducted to further validate the formation of an effective absorption layer by this inhibitor on metal surfaces, which showed that the electron density iso‐surfaces of HOMO was mainly distributed on chloride ions, while LUMO tended to be distributed on furan rings and aldehyde groups. Besides, the other quantum chemical parameters of this inhibitor were also calculated to explore the molecular activity, such as, the molecular volume (ν, 333.105 Å), global hardness (η, 4.706 eV), global softness (σ, 0.2125 eV), electronegativity (χ, 4.93 eV), dipolemoment (μ, 13.1429 D) and vertical ionization energy (VIE, 7.2646 eV).

Studying the Effect of Operating Conditions and NO2 Cathode Contamination on PEM Fuel Cells Using Distribution Function of Relaxation Times Analysis.

The effect of NO2, an air pollutant, on the durability of polymer electrolyte membrane fuel cells (PEMFCs) and the affected electrochemical processes in the PEMFC following the contamination were investigated. In-situElectrochemical Impedance Spectroscopy (EIS) measurements were conducted on PEMFCs under different operating conditions of temperature and relative humidity (RH). NO2 was introduced to the cathode inlet flow. Analyses of the EIS measurements were performed using a genetic algorithm called ISGP (Impedance Spectroscopy by Genetic Programming) to obtain the distribution function of relaxation times (DFRT, a.k.a. DRT) models. Utilizing ISGP enabled us to differentiate the various phenomena in PEMFC and study how they are affected by NO2 contamination. Moreover, the experiments demonstrate the effectiveness of the mitigation method to flush the PEMFC and regenerate its performance after being contaminated, particularly at low operating temperatures. Energy-dispersive X-ray spectroscopy (EDS) technique is performed on the contaminated PEMFC to detect the presence of any nitrogen components in the FC's gas diffusion layer and the catalyst layer post the mitigation step. Cyclic Voltammetry is also performed on the contaminated cell to determine the effect of the contamination on the electrochemically active surface area of the cathode by evaluating the double-layer capacitance.

A novel photoelectrochemical based water splitting and uric acid biosensing using PLD grown In2Se3 thin films

By altering the deposition pressure during the film growth process using the pulsed laser deposition (PLD) technology, indium selenide (In2Se3) thin films have been optimized to produce their distinct phases. The phase purity, optical and morphological studies were carried out using XRD, Raman spectroscopy, XPS, UV–visible spectroscopy, AFM and FESEM measurements. A high absorption in the visible region is observed for In2Se3 thin films with suitable band edges for hydrogen evolution. Photoelectrochemical (PEC) activity for In2Se3 photoelectrodes having various phases was analyzed based on CV and I-t response. A good charge transport characteristics were observed using the EIS measurements on PLD grown In2Se3 thin films. The Mott–Schottky analysis for the charge carrier density, flat band potential, and depletion layer width was performed for the deposition pressure dependent phase formation and high performance for PEC water splitting conversion efficiency of 0.48 %, 0.57 % and 0.98 % corresponding to α-In2Se3, β-In2Se3 and γ-In2Se3 were observed, respectively. The as prepared In2Se3 thin films were employed for the detection of Uric Acid (UA) using the cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry. The high sensitivity (0.38 mA/mM), selectivity and repeatability of the prepared biosensor demonstrates In2Se3 as potential candidate for the PEC based water splitting and biosensing application without the presence of an external mediator and can work in the self-powered mode.

Unveiling the potency of tetrahydropalmitine as a green anticorrosion material for 2024 aluminum alloy in acid-chloride environments

2024 aluminum alloy has garnered attention from researchers because of its numerous applications in the oil and gas, aerospace, and marine sectors. However, its constituent high Cu content (the primary alloying element) poses a significant challenge to its use, particularly in applications that demand high corrosion resistance. This is particularly troubling in oxygen-containing chloride systems. Herein, we developed a protection strategy for 2024 Al alloy in an acid-chloride environment (composed of 0.5 M NaCl and 0.25 M H2SO4) using natural tetrahydropalmitine (THP) isolated from Corydalis yanhusuo. THP was effectively characterized from its 1H NMR, 13C NMR, and FTIR spectra, and its anticorrosion potentials were methodically investigated by electrochemical, gravimetry and theoretical experiments. Upon the addition of THP to the test system, EIS measurements revealed a steady increase in the Nyquist semicircles, as well as the Bode impedance and phase angle plots, attaining an optimum inhibition efficiency of 91.5 % at 2.0 g/L THP. Tafel plots manifested mixed-type anticorrosion effects with dominant cathodic properties, ascribed to the ordered shielding effect of both the hydrogen evolution reaction and the oxidation of oxide-free ions. According to gravimetric corrosion assessment, the 2024 Al alloy mainly retained its protection over time in the presence of THP, exhibiting only minor decline in its protectability. This is attributed to the combined effect of stable oxide film formation and the adsorbed THP on the alloy surface. SEM afforded the proof of THP adsorption on 2024 Al while XPS offered clarity into its anticorrosion mechanism. Conceptual DFT parameters, molecular electrostatic potential and molecular dynamics simulation were used to comprehend the inhibition process of THP on Al surface. Generally, THP was proven to be a viable and sustainable bio-based anticorrosion material for the protection of 2024 Al alloy.

Synthesis and Characterizations of Novel Copolymers with Zwitterionic Moiety-Based Solid Polymer Electrolytes for Solid-State Lithium Metal Battery

Electric vehicles (EVs) have become the dominant choice in the automotive industry, displacing internal combustion engine vehicles (ICEVs) to some extent. The development of high-efficiency batteries is essential to meet these market demands. Conventional lithium-ion batteries (LIBs), which consist of a cathode, anode, separator, and liquid electrolyte (such as 1M LiPF6 in carbonate solvents), have been widely utilized in portable electronic devices, hybrid electric vehicles (HEVs), and EVs. This popularity is attributed to their relatively high energy density and extended cycle life [1]. However, LIBs with energy density exceeding 240 Wh kg-1 face challenges in terms of thermal stability, potentially leading to fire and explosions by overcharging or accidental cell penetration. This drawback significantly hinders their application in automotive settings [2, 3]. In response to these safety concerns, there is a shift towards incorporating solid-state electrolytes (SSEs) as a replacement for liquid electrolytes. SSEs include solid polymer electrolyte (SPE), inorganic solid electrolyte (ISE), and composite polymer electrolyte (CPE).Solid-state lithium metal batteries (SSLMBs) incorporating SPE hold significant promise for advancing energy storage technologies due to their high energy density and improved safety features. However, the low ionic conductivity and ionic transference number of SPEs present challenges in their application for solid-state batteries. This work focuses on designing novel copolymers with polar soft unit and zwitterionic unit to address these challenges.In this study, poly(ethylene glycol) methyl ether acrylate (PEGMEA) and sulfobetaine methacrylate (SBMA) were selected as the polar soft segment and zwitterionic unit, respectively. Various ratios of PEGMEA/SBMA in copolymers were synthesized and characterized, and the resultant SPEs consisting of resultant copolymers and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were prepared. Subsequently, their electrochemical, thermal, mechanical, and morphological properties were systematically investigated. The copolymers-based SPEs exhibited improved electrochemical properties. The optimized SPE comprising the copolymer with the molar ratio of PEGMEA/SBMA = 1/3 and 50 wt% LiTFSI exhibited the ionic conductivity of approx. 2×10–4 S cm–1, lithium-ion transference number of approx. 0.3, Li+ diffusion coefficient of 15×10-12 cm² s-1, and oxidation stability of 5.2 V (vs. Li/Li+) at 25 oC. Additionally, the mechanical properties of such SPEs were assessed, showing improved tensile strength (up to approx. 6 MPa) and Young’s modulus (up to approx. 83 MPa) with increasing SBMA content. The selected SPE with the best electrochemical properties was sandwiched between a Li metal electrode and a LiFePO4 electrode to assemble a SSLMB. As a result, the discharge capacity (DC) at 0.1 C-rate and room temperature was approx. 170 mA h g–1. Furthermore, the DC at a 0.5 C-rate was approx. 146 mA h g–1, and the capacity retention of 70% obtained after 470 cycles. In summary, this work demonstrates the potential of tailored copolymers with zwitterionic moiety-based SPEs for SSLMB. The comprehensive characterization and performance assessments provide valuable insights into the design and optimization of polymer electrolytes for next-generation energy storage systems.The copolymers and corresponding SPEs underwent characterization through various techniques such as DSC, SEM, XRD, and FTIR. The Ionic conductivity of the SPEs was determined by analyzing the results obtained from EIS measurement. The lithium-ion diffusion coefficient (DLi+) for SPE in a symmetric SSLMB cell, Li/SPE/Li, was also calculated based on the EIS results [4]. The oxidation stability window of the SPE was measured using the linear sweep voltammetry technique, and the ion transfer number was determined using the Evans-Vincent-Bruce method [5].

Investigation and Characterization of Interfacial Transport Phenomena in the Catalyst Layer Using Rheo-Impedance Measurement

Electrodes or catalyst layers (CLs) are the heart of fuel cell and electrolyzer cell devices. They are mainly heterogeneous porous electrodes composed of catalyst particles, ion-conducting polymer material, and void spaces that make up the triple-phase boundary (TPB). It is important to tailor the CL’s microstructure such that there are abundant TPBs where reactions take place to maximize catalyst utilization and improve cell performance. However, this is a critical challenge due to lack of fundamental understanding of the interfacial transport within the CL. Understanding how catalyst ink parameters affect ink properties and how ink components interact, and ultimately, their relationship with CL microstructure formation and cell performance, are essential to designing electrodes. Electrode morphology is important and is controlled by the ionomer/catalyst interactions formed in precursor inks that evolve during mixing and electrode fabrication.In this study, we probe interactions in catalyst inks with different formulations (ionomer-to-carbon ratio and IPA/water) using a new experimental method to unravel the complexities of ionomer/catalyst particle interactions. The new experimental method is a combination of rheological and electrical impedance spectroscopy measurements (rheo-EIS) that takes advantage of the dynamic nature of catalyst ink and the fact that the rheological and electrical behaviors of the ink are coupled to the microstructure of the material. Using rheo-EIS tool, in combination with zeta (ζ) potential and dynamic light scattering (DLS) measurements, we were able to systematically study how the level of agglomeration of the inks and microstructures evolve with respect to different I/C ratios, solvent formulation, and external shear forces. Results from the three-phase rebuilt test designed to simulate the ink coating condition with single-frequency EIS measurement give information on how the ionomer/catalyst particle interactions form and recover during the coating process. In addition, the full frequency range EIS measurements provide complementary data of the ionic and electrical resistance of the ink before and after high shear applications. Furthermore, the observations of the effect of I/C and IPA/water ratios from this study provide insights on how to better engineer suitable catalyst inks and how to control specific CL microstructure without the need for time-consuming optimization and empirical studies.

EIS Investigation of a Single Pit on Cantor Alloy in Acidic Environment

High-entropy alloys (HEA) are an emerging class of materials with promising properties such as high strength and ductility, improved fatigue resistance, fracture toughness, and thermal stability. They show considerable potential for use as corrosion resistant alloys to support our infrastructure especially for use in extreme environments. In this work, we mainly focused on the typical Cantor alloy, which consists in a mixture of 5 elements CrMnFeCoNi in equimolar proportion. A huge amount of works has already been devoted to the study corrosion resistance of alloys in sulfuric acid [1] or in chloride containing solutions [2,3]. For the latter, the study of the pitting propagation remains challenging since this kind of corrosion initiates as a stochastic process.Electrochemical impedance spectroscopy (EIS) is intensively used as a tool for corrosion research and is well suited for the identification of complex mechanisms. However, data analysis remains difficult in the case of pitting studies, which can be described schematically as n anodic sites in parallel at different states of evolution. In this work we report on EIS analysis performed on a single pit (Fig. 1a) in order to describe the various step of its evolution as a function of time, but also as a function of various parameters such as the chloride ion concentration or the corrosion potential. Single pits were obtained by studying the breakdown of the passive film using the pumped-micropipette delivery/substrate collection (Pumped-MD/SC) mode of scanning electrochemical microscopy (SECM). A detailed mechanism is proposed to account for EIS results obtained on a single pit (Fig. 1b) in order to explain results on usuals EIS measurements.[1] J. Yang, J. Wu, C. Y. Zhang, S. D. Zhang, B. J. Yang, W. Emori et J. Q. Wang, « Effects of Mn on the electrochemical corrosion and passivation behavior of CoFeNiMnCr high-entropy alloy system in H2SO4 solution », Journal of Alloys and Compounds, 819, avril 2020, p. 152943, https://doi.org/10.1016/j.jallcom.2019.152943[2] Camila Boldrini Nascimento, Uyime Donatus, Carlos Triveño Ríos et Renato Altobelli Antunes, « Electronic properties of the passive films formed on CoCrFeNi and CoCrFeNiAl high entropy alloys in sodium chloride solution », Journal of Materials Research and Technology, 9, no 6, novembre 2020, p. 13879-92, https://doi.org/10.1016/j.jmrt.2020.10.002[3] Mengjiao Li, Qingjun Chen, Xia Cui, Xinyuan Peng et Guosheng Huang, « Evaluation of corrosion resistance of the single-phase light refractory high entropy alloy TiCrVNb0.5Al0.5 in chloride environment », Journal of Alloys and Compounds, 857, mars 2021, p. 158278, https://doi.org/10.1016/j.jallcom.2020.158278 Figure 1

On the Correlation of Kramers-Kronig (KK) Analysis and Non-Linear Harmonic Analysis (NHA)

Primary lithium batteries are known for their elevated volumetric and gravimetric energy densities and production cost efficiency. Within this category, lithium thionyl chloride (Li/SOCl2) batteries exhibit a constant discharge voltage (~3.6 V) and a broad operational temperature range (-50ᵒC to 80ᵒC). Moreover, forming a LiCl passivation layer on the metallic Li anode can extend its shelf-life up to 20 years at optimal storage temperature. These characteristics render lithium thionyl chloride batteries applicable in military and security applications, microcomputers, measurement devices, and medical instruments. Therefore, the characterization of lithium thionyl chloride batteries accurately has the utmost importance. Understanding the critical electrochemical processes that occur inside the battery without damaging or disassembling the cell requires delicate techniques.EIS has emerged as a non-destructive and in-situ measurement technique with increasing popularity. Essential battery properties can be derived from EIS data. The credibility of EIS data, considering linearity, causality, and stability, can be verified through Kramers-Kronig relations. The obtained spectrum is fitted with an optimal number of Voigt elements (RC components in parallel)[1]. Given the linearity and stability of these individual Voigt elements, the entire spectrum should exhibit linearity if it is Kramers-Kronig compatible[2].Non-linear harmonic analysis (NHA) is a complementary technique to EIS, wherein the response signal undergoes conversion from the time domain to the frequency domain through Fast Fourier Transformation (FFT). While EIS employs a single-phased pure sinusoidal signal as the input, the response includes a fundamental frequency and harmonics at integer frequencies of this fundamental response signal. NHA can be utilized in the diagnosis of non-linear, non-stationary situations alongside the identification of drift and initial transients.This study first explains a new EIS measurement method for Li/SOCl2 batteries and Li/SOCl2/SO2Cl2 mixture batteries. The new method describes the solid electrolyte interface (SEI) stability of the batteries and the modifications needed to get KK-compatible results. After that, the equivalent circuit fits applied to the acquired spectra. Essential battery parameters such as solution resistance, charge transfer resistance, and double-layer capacitance were calculated. Kramers-Kronig analysis of the batteries was conducted, and the residuals of the fits were investigated. Subsequently, the NHA of the batteries was examined and compared to the Kramers-Kronig residuals. A correlation between the residuals and NHA of the batteries was extended based on the terms "KK-compatible" and "non-KK-compatible" in comparing KK-residuals and NHA results.[1] Boukamp, B. A. , Journal of the Electrochemical Society 142.6 (1995): 1885.[2] Agarwal, et al., Journal of the Electrochemical Society 142.12 (1995): 4159. Figure 1

Impact of Mechanical Stimuli on PEO-Litfsi Stiffness and Ionic Conductivity

Recently a large emphasis has been placed on developing safer electrolytes for lithium-ion batteries as a response to an increase in battery demand. Solid polymer electrolytes, such as those based on polyethylene oxide (PEO) show good resistance to mechanical loading, and when coupled with ceramic fillers demonstrate enhance ionic conductivity as well. Prior to this work, efforts have been made to determine the effects mechanical stimuli have on the stiffness and ionic conductivity of the electrolyte.1–3 However, while previous research has primarily focused on bulk EIS measurements of the electrolyte, here we leverage atomic force microscopy (AFM) to modulate the tip-substrate contact force from a few piconewtons to tens of millinewtons to study the correlation between mechanical loading and ionic conductivity, along with measuring the evolution of the substrate stiffness as a function of mechanical cycling.In this study, we contact the PEO-LiTFSI surface with an electrically conductive Pt-coated tip and mechanically cycle the sample by applying a pre-determined contact force a set number of times. By keeping the contact force and time constant, we extracted the cycle-dependent evolution of the sample stiffness. Results show that stiffness is reduced 30% within the first ten cycles, and then minimally changes with subsequent cycling, matching the results from bulk measurements. Changes in ionic conductivity as a function of mechanical cycling are then measured using electrical characterization techniques. To gain a better understanding of how conductivity and stiffness are evolving, we conducted a parametric study by varying tip size, contact force, and number of mechanical cycles. From early results, we found that electrical resistance increases by ~3% (from 2985 Ohm to 3075 Ohm) after 100 cycles of mechanical force ranging between ~ 0 nN to 450 nN with a 5 µm radius tip. The change in the electrical resistance is believed to originate from the local amorphization of PEO-LiTFSI induced by the mechanical stimuli and resulting change of the local conductivity. These results can be leveraged to further understand how mechanical stimuli affects the mechanical and electrical characteristics of solid electrolytes and help establish a model to predict long-term stability and performance of batteries.This work was supported by the National Science Foundation (#2125640).(1) Yoon, D. et al., ACS Appl. Energy Mater, 6 (18), 9400, 2023(2) Li, X. et al., ACS Appl. Mater. Interfaces, 11 (25), 22745, 2019(3) Liu, L. et al., Nano Energy, 69, 104398, 2020

Investigating Ion-Coupled Electron Transfer of Conducting Polymers

After years of basic and applied studies of electron transfer in redox active films, the fundamentals of ion transfer during the exchange remain to be understood. Empirically, the processes are ion-transport limited. Using a conducting polymer as a model system, we aim to study the relationship between electron and ion transfer during redox switching.We work on electrochromic conducting polymers because of their observable and detectable color changes in addition to the current during the redox switching. Tracing optical signals can enhance the understanding of electrical signals from redox reactions. When a potential is applied to the electroactive polymer, its color will change from lighter to darker or vice versa. Keeping in mind that absorbances are additive, the ratio of the contents that make up the overall color of the polymer changes. This ratio change is directly proportional to the amount of matter under inter-conversion during the redox reaction.This study aims to explore the ion-electron mechanism in conductive polymers using the simultaneous Spectro-CV method. To achieve this, we conducted cyclic voltammetry at exceptionally high scanning rates, leveraging the conductive polymer's color-changing property. At these high rates, ion movement was restricted due to limited time for forward and backward motion, potentially reaching a point of stagnation. The investigation focused on whether the polymer would continue changing color, providing insights into ion-electron transfer. In addition, we are conducting EIS measurements alongside simultaneous Spectro-CV measurements and attempting to fit the impedance response of the polymer with an appropriate model. We aim to track the time constants provided by the polymer at different voltage values and understand the corresponding physical processes associated with these time constants. Additionally, we aim to use our EIS model to validate the desired redox current information obtained from optical data. We mathematically reach the faradaic portion of the total current with EIS and compare the results obtained from optical data.

Surface dynamics and electrochemical examination of Co3O4 films by iron doping

This study focused on Co3O4 films, which were prepared by cost-effective chemical bath deposition on In:SnO2 (ITO) substrates with iron doping concentrations ranging from 2 to 6 mol %. Structural properties were investigated by XRD as well as nanotexture of Fe: Co3O4 films was captured via SEM and detailed fractal analysis was analyzed in each prepared film. Effective using of prepared Fe: Co3O4 electrodes for electrochemical charge storage applications has been examined by using CV and EIS. From x-ray patterns, spinel cubic structure of Co3O4 was observed in all samples, while peaks with Co2O3 and substrate indexed peaks were also shown. Pure and iron doped Co3O4 surfaces have spherical agglomerative forms while porous structures were observed in 4% Co3O4 samples. Redox peaks induced by Faradaic reactions in the CV plots present pseudo- capacitive nature for all electrodes and improves charge transfer process in 4% Co3O4 and 6% Co3O4 from EIS measurements. Additionally, using scaling theory, the coverage ratio, fractal dimensions, cluster sizes and interface critical exponent values of the superficial hetero morphology of the samples are calculated. While the coating rate decreases according to the iron concentration, fractal dimensions increase. However, as the number of clusters increases, the average cluster size decreases. The interface critical exponent value shows an irregular change.

Photoactive Donor–Acceptor Covalent Organic Framework Material for Synergistic Cyclization Approach to Imidazole Derivatives

ABSTRACTAs one of the most potential platforms for heterogeneous catalysis, two‐dimensional porphyrin‐based covalent organic frameworks (COFs) have attracted great research interests. In this work, following the correlation of COF structure and their performance, a type of donor–acceptor 2D COF (Por‐COF‐Zn) based on porphyrin and thiophene units was designed and easily constructed by one‐pot method using 5,10,15,20‐tetra‐(4‐aminophenyl)porphyrin (TAPP), thieno[3,2‐b]thiophene‐2,5‐dicarbaldehyde, and zinc acetate. The as‐synthesized COF material is tested to show high crystallinity and good thermal and chemical stability. The Brunauer–Emmett–Teller (BET) measure results show that the specific surface area of Por‐COF‐Zn is 413.6 m2g−1, and the pore volume is 0.279 cm3g−1. Transient photocurrent response and EIS measurement also demonstrate that Por‐COF‐Zn exhibits an efficient separation of photogenerated electron/hole pairs. The photocatalytic performance of the resulted COF was further evaluated by using intramolecular cyclization of N‐phenyl‐o‐phenylenediamine and benzaldehyde to form benzimidazole derivative. The catalyst system exhibited good to high conversion efficiency, moderate substrate applicability, and excellent stability and recyclability for the catalytic cyclization approach of benzimidazoles. The catalytic mechanism should be contributed to the synergistic effect of organic framework and metallic zinc. Our current work also provides valuable information for understanding COF‐based photocatalytic systems and further highlight new insights to meet new challenges of heterogeneous photocatalysis.