Potentiostatic Electrochemical Impedance Spectroscopy Research Articles

What Limits the Stability Performance of Polymeric Carbon Nitride Photoanode for Photoelectrochemical Water Splitting?

Although many researches have been reported about the high performance of polymeric carbon nitride (PCN) photoanode, but it is still limited by poor stability. In this work, PCN nanosheets photoanode is used as a platform to investigate the sources of this issue. Through a combination of photoelectrochemical, X-ray Photoelectron Spectroscopy (XPS), and Potentiostatic Electrochemical Impedance Spectroscopy (PIES) measurements, it is shown that amounts of C═O bonds will form on the surface of PCN photoanodes, which limited the separation of the photogenerated carriers. To solve this problem, the TiO2 is deposited on PCN photoanode (named as PCN/TiO2) to improve the stability. And the PEC water splitting studies revealed that the stability of PCN/TiO2 photoanode is improved significantly as its photocurrent density can still maintain 90% after 3 h of reaction. This study provides a new way to understand the mechanism for the performance decrease of PCN photoanode and hope to inspire more powerful strategies to improve PCN photoanode stability.

Electroanalytical detection of fruit ethylene by a novel electroactive biosensing membrane

Purpose This study aims to present an innovative approach to detect and monitor ethylene gas during fruit ripening. Design/methodology/approach It uses a specialized composite membrane in conjunction with a solid-state electrochemical method. This unique electroactive membrane, composed of polyvinyl alcohol (PVA), chitosan (CHT), lithium chloride (LiCl) and ammonium molybdate (AMO), exhibits synergistic behavior when applied to a microelectrode chip surface. This composite enhances the sensitivity of electrochemical ethylene detection. Empirical experiments were conducted to elucidate the ripening kinetics in various fruit specimens, including apples, pears and mangoes. These fruits released ethylene, which was analyzed using the molybdenum-permeated electroactive biopolymer composite membrane, a critical determinant of ethylene levels. Findings Characterization of the synthesized composite through techniques such as X-ray diffraction and Fourier-transform infrared spectroscopy revealed reduced crystallinity and decreased hydrogen bond interactions upon activation with Mo ions. Field emission scanning electron microscopy images exhibited a distinctive porous surface morphology with spherical microgranules. Energy dispersive X-ray analysis indicated a significant change in the mass or atomic composition of Mo in the composite membrane after Mo ion activation. Electrochemical measurements, including cyclic voltammetry and potentiostatic electrochemical impedance spectroscopy, validated the efficiency of the Mo-activated PVA-CHT-LiCl-AMO membrane, manifesting an impressive 87.79% increase in sensitivity compared to the nonactivated membrane. Practical implications This research work represents a significant advancement in the field of ethylene detection and fruit ripening monitoring. The Mo-activated PVA-CHT-LiCl-AMO membrane offers a reliable and effective solution for real-time ethylene detection, providing an invaluable tool for the horticultural industry to optimize fruit ripening processes, extend shelf life and ensure the delivery of high-quality produce to consumers. Social implications The findings of this study hold great promise for fostering sustainability and efficiency within the global fruit supply chain, ultimately benefiting both producers and consumers alike. Originality/value The implications of this research extend to the fabrication of a sensor based on a solid-state electroactive PVA-CHT-LiCl-AMO composite membrane, which upon Mo-activation exhibits robust electrochemical fruit ethylene detection when exposed to different fruits.

Synthesis and electrochemical studies of 1,1’-binaphthyl-2,2’-diol for aqueous rechargeable lithium-ion battery applications

The constant increase in the utilization of lithium-ion batteries (LIBs) in various field applications, including electrical vehicles and electronic devices, has led researchers to focus on their multiple path developments to obtain new electrode materials. The practical development of these electrode materials, based on organic and inorganic moieties, is challenging for various groups of LIB scientists. The concept of organic electrode materials is highly competitive with inorganic electrode materials because of the accessibility of more active sites with structural diversity, high energy and power density, environmental friendliness potential sustainability, and low cost. Herein, 1,1’-binaphthyl-2,2’-diol (BINOL) is investigated as an organic electrode material that contains two hydroxyl groups that act as active centers. The oxidative coupling process is employed to synthesize BINOL and so obtained product was characterized by using FT-IR, 1H-NMR and MASS techniques. The electrochemical investigations were carried out using sat. Li2SO4 electrolytic medium at three-electrode cell system. The Cyclic voltammetry (CV) has provided information on the anodic behavior of the material and its stability studied at different scan rates. The battery performance of the cell BINOL | Sat. Li2SO4 | LiMn2O4 by galvanostatic charge-discharge potential limit (GCPL) shows 197/171mAhg−1 specific capacity and 90% columbic efficiency. The electrochemical kinetic obtained by potentiostatic electrochemical impedance spectroscopy (PEIS) shows a semi-infinite diffusion process.

Measurement of Enthalpy and Entropy of a Model Electrocatalyst for the Oxygen Evolution Reaction

AbstractExperimentally determined thermodynamic parameters are rarely reported for electrocatalytic reactions including the oxygen evolution reaction (OER). Yet, they contain unique and valuable mechanistic insight and present a missing link to theoretical investigations. Herein, a protocol for determining thermodynamic properties of the rate determining state and intermediate (RDSI) of the OER is presented. Cobalt oxide is investigated at pH 7 as a case study. Two different approaches are employed: steady state polarization (SSP) that uses chronopotentiometry at different temperatures and current values, and potentiostatic electrochemical impedance spectroscopy (PEIS) at different DC voltages and temperatures. The data is used to fit a 3D plane from which entropy and enthalpy of the RDSI are obtained. The data analysis requires an appropriate filtering of the data. Hence, we discuss suitable figures of merit for establishing appropriate filtering criteria. The values obtained are 0.72 and −0.39 eV (at 298 K) for enthalpic and entropic contributions, respectively. The obtained values are reproducible for both approaches and consistent with literature.

Electrochemical Analysis of Charge Overpotentials in Non-Aqueous Lithium and Sodium Oxygen Batteries

Aprotic metal-oxygen batteries, especially Li-O2 and Na-O2 batteries, could afford theoretical specific energies of more than 500 Wh/kg. However, while not compromising on rechargeability, the practical realization of the theoretically possible high specific energies has been elusive. A better understanding of the differences and similarities between Li–O2 and Na–O2 battery systems in terms of charge-discharge mechanisms and parasitic chemistry will be meaningful in solving these challenges. Here, we explore the differences between the two systems using a combination of galvanostatic charge-discharge measurements, Differential Electrochemical Mass spectrometry (DEMS), and Potentiostatic Electrochemical Impedance Spectroscopy (PEIS) analysis. The discharge profiles of these battery chemistries are similar in terms of overpotential and have been widely studied. But the origins of the differences in charge overpotentials are not clear. Using in-situ pressure decay measurements during discharge, we calculated the number of electrons/oxygen (e-/O2) to be 2.02 and 1.01 for Li-O2 and Na-O2 cells, respectively. Further, DEMS analysis during charge has shown that the ideal 2 e-/O2 is attained only during the initial phases of charging for Li-O2 cells. However, for Na-O2, the ideal 1 e-/O2 is achieved during a signification portion of the galvanostatic charge step. We corroborate these findings with PEIS and distribution of relaxation times (DRT) analysis to develop a mechanistic view of the processes that lead to poor coulombic and oxygen evolution efficiencies in metal-oxygen cells. Based on DRT analysis, we identify a lower time constant process that is common to both Li-O2 and Na-O2 cells. Interestingly, we observed that voltage polarization is preceded by the observation of this lower time constant peak. In the case of Li-O2 cells, this lower time constant process was observed at the end of discharge and throughout the recharge process, while for the Na-O2 cells, this was only observed after about 70% of recharge. We discuss the possible origins of this low time-constant process and its implications for recharging metal-oxygen batteries. We will also discuss the role of singlet oxygen, if any, in the recharge efficiencies of these two aprotic metal-oxygen batteries. Our results imply that the identification of the origins of this lower time constant process and possible suppression of this process will be key for rechargeable metal-oxygen batteries.

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

Investigation of Heteroatom Doped Graphene Anode for High-Capacity Alkali Metal-Ion Batteries

The drastic growth of Li-ion batteries (LIBs) in global electronic market and low crustal abundance of Li demands for more abundant alternatives such as sodium and potassium having similar electrochemical properties. Sodium-ion battery (SIB) and potassium-ion battery (PIB) can be used “side-by-side” to LIB which can help battery technology progress efficiently. 1Graphite has been a commercial anode in LIB due to its low cost, high abundance, high electrical conductivity, with a theoretical storage capacity (LiC6) of 372 mAh g-1. In contrast the utilization of graphite in SIBs and PIBs is challenging. This is due to the large radius and unstable graphite-intercalation compounds (NaC64) giving very low theoretical capacity of 30 mAh g-1. In PIBs, graphite exhibits a theoretical capacity of 279 mAh g-1 but suffers from poor stability due to huge volume expansion (60%) in fully potassiated state (KC8). Thus, focus is now shifted on to class of amorphous carbon materials such as hard carbon, soft carbon, graphene etc. with variations in micro-structures, larger interlayer spacing, and defect rich sites promoting enhanced capacity and stability even at high current densities. 2 In my presentation I will be discussing about the synthesis of heteroatom doped graphene with high charge storage and stability for LIB, SIB and PIB compared to graphite. The heteroatom doped graphene exhibits nearly 1000 mAh g-1 (LIB), 380 mAh g-1 (SIB) and 379 mAh g-1 (PIB) at a low current density of 25 mAg-1. Additionally, the elastic nature of ultrathin graphene nanosheets aids in attaining long term cyclability at 1 A g-1 with high-capacity retention of 83% for 300 cycles (LIB), 73% for 400 cycles (SIB) and 91% for 600 cycles (PIB). The enhanced stability in case of PIB, is attributed to optimizing solid electrolyte interphase (SEI) components and improving interfacial reaction kinetics at high current densities. Choice of high concentrated electrolyte (HCE) over conventional KPF6 in EC:DEC determines the nature of SEI and thereby helps in achieving cycling stability. The stability in SEI is characterized via voltage profile and understanding chemical composition by ex-situ X-ray photoelectron spectroscopy. Robust SEI in HCE is due to difference in anion structure studied by Raman spectroscopy.Furthermore, the charge-discharge mechanism, alkali ion diffusion kinetics and structure-activity relationship of electrode materials was investigated using various techniques like cyclic voltammetry profiles at different scan rates and Galvanostatic intermittent titration technique (GITT). Additionally, deeper insights into the fundamental understanding of interfacial and bulk behavior were provided with the help of in-situ Raman spectroscopy and in-situ potentiostatic electrochemical impedance spectroscopy (PEIS) analysis. The investigation of peak area and shift in D (defect) and G (graphitic) band analyzed from in-situ Raman studies helped in understanding the evolution and reversibility of alkali ion storage behavior during charging and discharging. PEIS analysis gave us a thorough understanding of the evolution of stable SEI on charging-discharging and after cycling, which helps us to understand the long-term stability in LIB, SIB and PIB.

The Impact of Intergrain Phases on the Ionic Conductivity of the LAGP Solid Electrolyte Material Prepared by Spark Plasma Sintering.

Li1.5Al0.5Ge1.5(PO4)3 (LAGP) is a promising oxide solid electrolyte for all-solid-state batteries due to its excellent air stability, acceptable electrochemical stability window, and cost-effective precursor materials. However, further improvement in the ionic conductivity performance of oxide solid-state electrolytes is hindered by the presence of grain boundaries and their associated morphologies and composition. These key factors thus represent a major obstacle to the improved design of modern oxide based solid-state electrolytes. This study establishes a correlation between the influence of the grain boundary phases, their 3D morphology, and compositions formed under different sintering conditions on the overall LAGP ionic conductivity. Spark plasma sintering has been employed to sinter oxide solid electrolyte material at different temperatures with high compacity values, whereas a combined potentiostatic electrochemical impedance spectroscopy, 3D FIB-SEM tomography, XRD, and solid-state NMR/materials modeling approach provides an in-depth analysis of the influence of the morphology, structure, and composition of the grain boundary phases that impact the total ionic conductivity. This work establishes the first 3D FIB-SEM tomography analysis of the LAGP morphology and the secondary phases formed in the grain boundaries at the nanoscale level, whereas the associated 31P and 27Al MAS NMR study coupled with materials modeling reveals that the grain boundary material is composed of Li4P2O7 and disordered Li9Al3(P2O7)3(PO4)2 phases. Quantitative 31P MAS NMR measurements demonstrate that optimal ionic conductivity for the LAGP system is achieved for the 680 °C SPS preparation when the disordered Li9Al3(P2O7)3(PO4)2 phase dominates the grain boundary composition with reduced contributions from the highly ordered Li4P2O7 phases, whereas the 27Al MAS NMR data reveal that minimal structural change is experienced by each phase throughout this suite of sintering temperatures.

Lignin-Derivative Ionic Liquids as Corrosion Inhibitors.

Corrosion is a significant problem that negatively affects a wide range of structures and buildings, resulting in their premature failure, which causes safety hazards and significant economic loss. For this reason, various approaches have been developed to prevent or minimize the effects of corrosion, including corrosion inhibitors. Recently, biobased inhibitors have gained a certain interest thanks to their unique properties, eco-friendliness, and availability. Among all the green precursors, lignin is of particular interest, being a natural polymer that can be obtained from different sources including agricultural residues. Corrosion inhibitors based on ionic liquids (ILs) also present interesting advantages, such as low volatility and high tunability. If combined, it may be possible to obtain new lignin-based ILs that present interesting corrosion inhibitor properties. In this work, the inhibition properties of new biobased lignin ILs and the influence of anions and cations on the corrosion of mild steel in an aqueous solution of 0.01 M NaCl were investigated by Potentiostatic Electrochemical Impedance Spectroscopy (PEIS) and Cyclic Potentiodynamic Polarization (CPP). Moreover, the surface was characterized using SEM, EDS, and optical profilometry. The IL choline syringate showed promising performance, reducing the corrosion current after 24 h immersion in 0.01 M sodium chloride, from 1.66 µA/cm2 for the control to 0.066 µA/cm2 with 10 mM of the IL present. In addition to its performance as a corrosion inhibitor, both components of this IL also meet or exceed the current additional desired properties of such compounds, being readily available, and well tolerated in organisms and the environment.

Vanadium-doped magnesium oxide nanoparticles as electrodes in supercapacitor devices

Vanadium (V)-doped MgO nanoparticles were used as electrode materials in all-in-one solid-state supercapacitor applications. The prepared samples’ structural and morphological properties were thoroughly analyzed using XRD, Raman spectroscopy, TEM, PL, and BET. EPR spectroscopy was employed to analyze the paramagnetic centers induced in the host material and showed that all V-doped samples displayed a V4+ characteristic EPR signal. The electrochemical analysis of the assembled symmetric supercapacitors was done using cyclic voltammetry, galvanostatic cycling with potential limitation technique, and potentiostatic electrochemical impedance spectroscopy. The results reveal that the novel V-doped MgO material displayed excellent capacitance performance between 0 and 1 V, delivering a specific capacitance of 50 F/g at a 10 mV/s scan rate. It also exhibits a maximum energy density of 4.17 Wh/kg, comparable to values obtained from other symmetric supercapacitor configurations. When a booster material like carbon black was added, the specific capacitance value increased dramatically to 1200 F/g, values that were never reported before in the literature for MgO-based materials.

Effect of Zinc on electrochemical corrosion behaviour of Mg-1Sn alloy as anode for Mg batteries

Magnesium and its alloys are widely used for various aerospace, biomedical, energy storage, and automobile applications. Magnesium alloys are favored due to their high specific strength. Now a days Magnesium act as a promising material for energy storage. Magnesium possesses high energy density than lithium. So, Mg can also be used as an anode for batteries. But corrosion resistance is the major drawback of Mg batteries. The deficiency can be overcome by alloying or coating with various metals. Different metals like Zinc and Tin act as promising alloy elements against corrosion resistance and also Zinc increases the ductility of the Mg. In this study, Zn is added to Mg-1Sn to analyze the corrosion characteristics between Mg-1Sn and Mg-1Sn-1Zn samples. Electrochemical tests like Potentiostatic Electrochemical impedance spectroscopy and Tafel were conducted to study the difference between the two alloys in 3.5 wt% NaCl solution. The results conclude that adding zinc with Mg-1Sn improves the anodic efficiency and shows a comparatively high Corrosion Potential [Ecorr] and the Mg-1Sn-1Zn alloys have a lower corrosion rate than Mg-1Sn.

Diffusion Controlled Features of Microwave Assisted ZnS/ZnO Nanocomposite with Reduced Band Gap

ZnS and ZnO are both wide band gap semiconductors. Their nanocomposites have high potential for photocatalytic activity and useful for different applications such as optical sensor, photoconductor, catalysts and anode material for solar cells. In the present investigations an effort has been made to synthesize ZnS/ZnO nanocomposites by inducing microwave treatment before hydrothermal process in order to increase the reaction rate of ZnS/ZnO and to reduce the optical band gap and particle size of the material. X-ray diffraction data revealed the formation of ZnS as well as ZnO phases. W-H plot and Size-Strain plot revealed information of size and strain present in the material. UV–vis spectroscopy analysis showed a reduced band gap of 3.14 eV and the refractive index of 2.36 for the material. Microstructural and morphological investigations as carried out by TEM and FESEM showed spherical shaped particles having average crystallite size of about 26 nm. Elemental compositional analysis of the material depicted the presence of zinc, oxygen and sulphur. FTIR study revealed the formation of Zn-S bond and presence of adsorbed oxygen in the as-synthesized material. The electrochemical studies include cyclic voltammetry (CV) and Potentiostatic Electrochemical Impedance Spectroscopy (PEIS). Cyclic voltammetry depicted the diffusion-controlled behaviour of the ZnS/ZnO nanocomposites and the reduction in specific capacitance with increasing scan rate. PEIS studies were analyzed by Nyquist and Bode plot which also confirmed the diffusion behaviour of material by Randle’s Circuit and its parameters. ZnS/ZnO showed diffusion controlled features indicating that the excitons control the current in the material and thus has a good prospect for solar cell applications.

Investigation on corrosion inhibitors for zinc batteries: Sodium sulphate

To store energy rechargeable batteries had developed widely. Over the concern of safety and cost-efficient, rechargeable aqueous metal-ion batteries are mostly favored. Various studies have been performed on different aqueous metal-ion batteries. Out of them, zinc-ion batteries have some unique and outstanding benefits. The aqueous electrolytes give assurance against exploding by their non-flammable nature. The zinc anodes are being used as it benefits the stability and redox reversibility. Zinc anodes have a higher theoretical capacity (820 mAh g−1) and low redox potential [−0.76 V vs. SHE (standard hydrogen electrode)]. As a measure to increase corrosion resistance, sodium sulphate is being used as an inhibitor. The zinc anode is being analyzed at different concentrations of the inhibitor and the best concentration is being identified for the battery applications. Potentiostatic EIS (Electrochemical Impedance Spectroscopy) and Tafel analysis are done to determine the corrosion behavior of the zinc with the addition of the inhibitor.

Impedance response of aluminum alloys with varying Mg content in Al-Mg systems during exposure to chloride corrosion environment

This research discusses the corrosion behavior of as-cast Al alloys with different Mg content by potentiostatic electrochemical impedance spectroscopy (PEIS). The complex plane spectra of all samples feature a high-frequency loop, followed by semi-infinite diffusion impedance characteristics at low frequencies, with the corrosion-induced formation of a defined porous structure of a layer making finite diffusion through the pores dominant upon prolonged exposure. The most compact layer causes the most pronounced and well-resolved finite diffusion features in the impedance spectra of the sample with the highest Mg content, while the sample with the lowest Mg content has a highly porous layer unable to slow down the corrosion rate at the layer/ /sample interface. The highest layer capacitance and diffusion admittance are found in the sample with the highest Mg content, with a more adherent protective film expected to form. However, the growth rate of the layer was not adequate for the remarkable closing of the pits, indicating the weakness of this sample towards pit activity. The results show that increasing Mg content improves corrosion resistance and clearly separates bulky corrosion from localized pitting corrosion, but it also increases the thickness of a more compact, poorly adhesive layer.

Internal Resistance Analysis of Na/NiCl2 Cells using Electrochemical Impedance Spectroscopy

A pulsed discharge regime (GITT) was used to investigate the ohmic internal resistance of Na/NiCl2 cells, also known as ZEBRA Cells. Two ways were chosen to determine the internal resistance, on the one side the voltage response of the corresponding current enables a calculation. On the other side the potentiostatic electrochemical impedance spectroscopy (EIS) was used to measure cell spectra including the ohmic internal resistance. By comparing both methods the feasibility of ohmic internal resistance (IR) calculation can be evaluated. The cells were investigated within five different operating temperatures (300 °C–180 °C with 30 K steps). Results show that the ohmic internal resistance of a Na/NiCl2 is increasing when the operating temperature is decreasing, mainly due to the decrease of ionic conductivity of separator and the secondary electrolyte NaAlCl4. As a direct consequence, there is a significant capacity loss. Therefore, the operating temperature can be identified as capacity limiting factor.

Rare Earth Based Nanocomposite Materials for Prominent Performance Supercapacitor: A Review

Rare-earth-based nanocomposites are currently attracting extensive research interest in biology, medicine, physics, chemistry and material science owing to their optical, electrical and electronic properties, their stability and novel applications. Rare-earth based nanomaterials, especially rare earth oxides (Yttrium oxide, Gadolinium oxide, lanthanum oxide, cerium dioxide, etc.) have fascinated people's devotion owing to their good environmentally friendly and redox properties characteristics. Rare-earth based nanomaterials with exceptional electrochemical properties can be attained by simple, low-cost, environmentally friendly approaches such as hydrothermal/solvothermal method, electrodeposition method, atomic layer deposition method, etc. The electrochemical and microstructures properties of the samples were characterized by X-ray diffraction, scanning electron microscopy, galvanostatic charge/discharge cycling, potentiostatic electrochemical impedance spectroscopy and cyclic voltammetry, in this review, we present a wide-ranging explanation of synthesis methods, morphology and electrochemical performance of numerous rare-earth based nanomaterials used in supercapacitors. We present in this review a brief overview of the recent and general progresses in their functionalization and synthesis.

(Digital Presentation) Effects of Surface Finish on the Corrosion Performance of Additively Manufactured Metals

Metal additive manufacturing (AM) is becoming a transformative technology in the manufacturing industry. The as-built surfaces produced by metal AM are very different compared to wrought material, typically resulting in very rough surfaces that have different corrosion properties. There are a large number of studies that have attempted to understand the corrosion response of metal AM. However, these studies are typically performed on materials that have been printed on a single machine. As a result, there are significant inconsistencies in the literature due to the high variability in the quality of parts manufactured on different machines. We will present work that compares the corrosion response of AM 316L stainless steel (SS) that has been printed on multiple machines. Our results have shown there is significant variability observed in the corrosion performance of metal AM parts built on different machines and within a single build plate. The observed corrosion performance is likely affected by the stability of the passive film, chemical segregation, and microstructure of the surface. We also propose that surface finishing of AM 316L SS reduces the part-to-part variations observed in the corrosion performance of the material printed on different machines and within a single build plate.This talk will discuss the corrosion properties of AM 316L SS, A20x (AM aluminum alloy), and Ti-6Al-4V parts produced by direct metal laser sintering (DMLS). The majority of our work focused on understanding the susceptibility to localized corrosion of metal additively manufactured materials with respect to build machine, surface roughness, and build angle. As a result, we also examined the corrosion performance of 316L SS built on a single instrument as we varied the build parameters. Conventional electrochemical corrosion experiments were used to characterize corrosion performance, including open circuit potential, potentiostatic electrochemical impedance spectroscopy, and potentiodynamic polarization scans. White light interferometry, optical profilometry, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were utilized to characterize the surface of the samples.

From Powder to Sheets – a Comparative Study for Solution-Cast Solid Electrolyte/Binder-Sheets As Separators in All-Solid-State Batteries

Sulfidic all-solid-state batteries (ASSBs) are considered as one of the next-generation energy storage systems.[1,2] Most of the previous research studies have investigated ASSBs that are based on a pellet-type separators, i.e., a highly compressed solid electrolyte (SE) powder, with thicknesses of several hundreds of microns.[3] However, their applicability is limited to small electrode area single-layer lab-scale cells, as large-format cells would require separator pellets with a large area that are difficult to produce. Furthermore, in order to be competitive or superior to state-of-the-art lithium-ion batteries based on liquid electrolytes, the thickness of the solid electrolyte separator in ASSBs should be less than 100 μm.[4] Consequently, a key for the industrialization of large-format and high energy density ASSBs is the development of sheet-type cell components. Up to date, only a few publications focus on sheet-type SE separators, investigating appropriate solvents and binders for wet-processed SE/binder composites.[4-7] In the present study, we report on the preparation of composite sheet-type separators for ASSBs by a slurry-based process, investigating three different sulfidic solid electrolyte systems (Li6PS5Cl, Li7P3S11 and Li10SnP2S12) in combination with different volume fractions of hydrogenated nitrile butadiene rubber (HNBR, φHNBR = 1.7 – 16.0 vol.-%) binder.By means of the analysis of top-view and cross-sectional scanning electron microscopy (SEM) images of the prepared sheet-type separators, combined with energy dispersive X-ray spectroscopy (EDX), we characterize the influence of the slurry-coating process conditions as well as of the binder volume fraction on their morphology. Densification of the obtained separator sheets is easily possible by uniaxial compression at room temperature, resulting in residual pore volume fractions of ≈ 3 – 12 %, depending on the respective solid electrolyte. While increasing fabrication pressures lead to a reduction of void volume and an increasing contacting between the solid electrolyte particles, very high fabrication pressures (> 200 MPa) lead to a fusing of the SE particles and to nearly pore-free separator sheets.Besides the micromorphology and porosity of the SE/HNBR separator sheets, we investigate the dependence of binder content and processing conditions on their ionic conductivity by means of potentiostatic electrochemical impedance spectroscopy (PEIS) measurements that are performed using a novel, in-house designed cell setup. As one would expect, the Li+-ion conductivity of the SE/HNBR separator sheets decreases with increasing binder volume fraction (see Figure 1a). Interestingly, however, the relationship between Li+-ion conductivity and binder volume fraction (φ HNBR) is essentially identical for the three different sulfidic electrolytes that are examined in our study (see Figure 1b). To obtain mechanically stable and free-standing SE/HNBR separator sheets, an HNBR volume fraction of approximately 8 vol.-% is required for all three SEs, yielding in a separator sheet conductivity of ≈ 0.5 mS/cm at 70 MPa, which is ≈ 3-fold lower than that of the pure, binder-free SE powder conductivity measured at the same conditions. Nevertheless, by considering the currently achievable thicknesses of these solution-cast separator sheets of ≈ 50 µm, their overall areal resistance (in unit of Ω·cm2) is equal or even lower than that of the typically substantially thicker pellet-type separators, so that these separator-sheets can be used for the assembly of large-format cells with competitive separator resistances.[1] J. Janek and W. G. Zeier, Nature Energy, 1, 16141 (2016).[2] W. Zhang, D. A. Weber, H. Weigand, T. Arlt, I. Manke, D. Schroder, R. Koerver, T. Leichtweiss, P. Hartmann, W. G. Zeier and J. Janek, ACS Appl Mater Interfaces, 9, 17835 (2017).[3] M. R. Busche, D. A. Weber, Y. Schneider, C. Dietrich, S. Wenzel, T. Leichtweiss, D. Schröder, W. Zhang, H. Weigand, D. Walter, S. J. Sedlmaier, D. Houtarde, L. F. Nazar and J. Janek, Chemistry of Materials, 28, 6152 (2016).[4] N. Riphaus, P. Strobl, B. Stiaszny, T. Zinkevich, M. Yavuz, J. Schnell, S. Indris, H. A. Gasteiger and S. J. Sedlmaier, Journal of the Electrochemical Society, 165, A3993 (2018).[5] K. Lee, S. Kim, J. Park, S. H. Park, A. Coskun, D. S. Jung, W. Cho and J. W. Choi, Journal of the Electrochemical Society, 164, A2075 (2017).[6] A. Sakuda, K. Kuratani, M. Yamamoto, M. Takahashi, T. Takeuchi and H. Kobayashi, Journal of the Electrochemical Society, 164, A2474 (2017).[7] F. Shen, M. B. Dixit, W. Zaman, N. Hortance, B. Rogers and K. B. Hatzell, Journal of the Electrochemical Society, 166, A3182 (2019). Acknowledgements: This work was carried out as part of the research project “Industrialisierbarkeit Festkörperelektrolyte”, funded by the Bavarian Ministry of Economic Affairs, Regional Development and Energy. This work was also supported by the BMW Group. Figure 1

Changing the grain size of FeSiAl powders to improve corrosion resistance and wave absorbing property

FeSiAl (FSA) is easily corroded by corrosive media in marine environment, which can reduce the microwave absorption performance. Therefore, it is necessary to improve the corrosion resistance of FSA. In this work, Cr atoms replace part of Si atoms in FSA to obtain FeSiAlCr flaky powders via rapid quenching and ball milling. The X-ray diffractometer test results show that the average grain size of the flaky powders was decreased from 12.21 nm to 11.16 nm with the increase of Cr content. The electrochemical corrosion behavior of FeSiAlCr was measured by potentiodynamic and potentiostatic electrochemical impedance spectroscopy (EIS) in 5 wt% NaCl solution. The results show that the free corrosion potentials of FeSiAlCr move towards positive values, the corrosion currents are reduced, and therefore the corrosion rates become slower with the increase of Cr content. In addition, FeSiAlCr possesses enhanced microwave absorption performance with a minimum reflection loss (RLmin) of −6.58 dB at 2.19 GHz with a matching thickness of 1.5 mm. Therefore, FeSiAlCr flaky powders are promising microwave absorbing materials in terms of low frequency absorption and corrosion resistance.

EPR investigation of point defects in HfB2 and their roles in supercapacitor device performances

Boron-based materials have various attractive properties and gained increased attention in recent years as promising materials for energy storage applications. Despite vast literature on structural and mechanical properties of transition metal diborides, hafnium diboride (HfB2) in particular, research that addresses the use of HfB2 as an electrode for supercapacitor devices is lacking. Herein, we report both the synthesis and characterization of HfB2 and its electrochemical performance as the electrode for all-in-one symmetric and asymmetric supercapacitor devices. HfB2 powders were synthesized by mechanical activation assisted carbothermal reduction of hafnium oxide and boron oxide precursors. To improve the electrochemical energy storage performance of the electrodes, point defects (either Hf or B vacancies/interstitials) were formed in HfB2 through annealing at different temperatures (1450 and 1650 °C) under a flowing Ar atmosphere. The origin of point defects and their localization on the surface in HfB2 were identified using electron paramagnetic resonance (EPR) spectroscopy and discussed both from chemical and materials point-of-view. The defective HfB2 electrode exhibited higher performance than that of the non-defective one with specific energy and power densities of 0.144 W h kg−1 and 33.3 W kg−1; specific charge–discharge capacities of 0.32 and 0.31 mA h g−1; and 115.5%, 106.2%, and 84.1% retention of the initial capacitances, respectively. The relation between the defect content and the improved supercapacitor performances was explained by employing several structural (x-ray diffractometer and x-ray fluorescence), electronic (EPR), and electrochemical (potentiostatic electrochemical impedance spectroscopy, cyclic voltammetry, galvanostatic cycling with potential limitation) characterization tools.