Ex-situ Methods Research Articles

In-situ investigation of the time-temperature dependent lattice and microstructure of Sn-Bi alloys

Alloys based on the Sn-Bi system are widely considered as the most promising candidates for low temperature solders (LTS) in the electronics industry due to their low liquidus temperature, non-toxicity and relatively low cost. However, implementation of LTS is complicated as they exhibit different characteristics from conventional Pb-free solders. While the solid solubility of alloying additions in Sn is typically <1 wt% in the current generation of Pb-free solders, the solubility of Bi in Sn ranges from less than 3 wt% at room temperature to 21 wt% at the eutectic temperature of 139 °C. In consequence, the microstructure and properties of Sn-Bi solders change significantly under varying temperature during normal service, affecting reliability. Since these changes are time and temperature dependent, interpreting results obtained using ex-situ methods requires assumptions about the stability of the alloy during transitions from the test environment to the observation environment, leading to an incomplete understanding of these changes. To address this, in-situ synchrotron powder X-ray diffraction (PXRD) and in-situ scanning electron microscopy (SEM) techniques were developed to investigate the time-temperature dependent lattice and microstructure of hypo-eutectic Sn-37wt%Bi and near-eutectic Sn-57wt%Bi solder alloys. This made possible for the first time the observation of changes during temperature fluctuations. The study revealed that lattice and microstructure are highly sensitive to factors like temperature ramp rate and isothermal holding time, not previously considered. The results will impact the design of electronic circuitry and process parameters during electronics assembly to enhance reliability and performance.

Comparison of In-situ Nondestructive Testing and Ex-situ Methods in Additive Manufactured Specimens for Internal Feature Detection

ABSTRACT The effectiveness and repeatability of Additive Manufacturing (AM) technologies has been often measured through rigorous testing, both in-situ and ex-situ. In-situ nondestructive testing (NDT) has been used to understand the AM process and detect anomalies during the build. Ex-situ testing has been used for material characterization and internal defect detection. In this work, in-situ NDT and ex-situ testing methods are compared as applied to a Fused Filament Fabrication (FFF) process to detect defects that have formed internally in the part. Intentionally embedded features and defects are monitored and analyzed in-situ and ex-situ. Results from an automated image-based real-time defect detection system, an ultrasound ex-situ system, and a tensile testing system are compared to detect defects and their effects on mechanical properties. Real-time image-based defect detection is found to effectively spot defects as they form and allow the potential for implementing defect correction methods, while ex-situ tensile testing can be used as a form of validation to in-situ results.

In-Situ Polymerized Solid-State Polymer Electrolytes for High-Safety Sodium Metal Batteries: Progress and Perspectives

The practical usage of sodium metal batteries is mainly hampered by their potential safety risks caused by conventional liquid-state electrolytes. Hence, solid-state sodium metal batteries, which employ inorganic solid electrolytes and/or solid-state polymer electrolytes, are considered an emerging technology for addressing the safety hazards. Unfortunately, these traditional inorganic/polymer solid electrolytes, most of which are prepared via ex-situ methods, frequently suffer from inadequate ionic conductivity and sluggish interfacial transportation. In light of this, in-situ polymerized solid-state polymer electrolytes are proposed to simplify their preparation process and simultaneously address these aforementioned challenges. In this review, the up-to-date research progress of the design, synthesis, and applications of this kind of polymer electrolytes for sodium batteries of high safety via several in-situ polymerization methods (including photoinduced in-situ polymerization, thermally induced in-situ free radical polymerization, in-situ cationic polymerization, and cross-linking reaction) are summarized. In addition, some perspectives, opportunities, challenges, and potential research directions regarding the further development of in-situ fabricated solid-state polymer electrolytes are also provided. We expect that this review will shed some light on designing high-performance solid-state polymer electrolytes for building next-generation sodium batteries with high safety and high energy.

Phase transformation kinetics in a coarse-grain Ti17 alloy determined by laser ultrasonics and dilatometry

Different methods are used to determine the phase transformation titanium alloys. While ex-situ methods require a large number of samples and accurate quantification of the phases, in-situ methods can provide the kinetics of transformation continuously and with less samples. However, the results are based on the changes of physical properties, and the interpretation of the results in terms of phase transformation are not direct. This study compares two in-situ methods to measure the kinetics of phase transformation for a Ti17 alloy, namely: laser ultrasonics for metallurgy (LUMet) and dilatometry. While LUMet is coupled to a Gleeble® 3500 thermo-mechanical simulator with ohmic resistance heating, the dilatometer device uses induction heating. We performed two types of experiments by heating the specimens above the β-transus temperature (∼ 865 °C) and 1) and then fast cooled below the β-transus temperature and held at different temperatures, or 2) continuously cooled at different rates. The β→α + β phase transformation is inferred by the evolution of the longitudinal wave speed with the LUMet method and by the change in the length of the specimen by dilatometry. We obtained the information about the isothermal phase transformation using the normalized changes in length for the dilatometric data and in longitudinal ultrasonic velocity. In the investigated isothermal temperature range (580 – 700 °C), the β →α + β transformation is completed within one hour of holding with the fastest transformation rates at 580 °C. For the continuous cooling treatments, the small change in length measured by dilatometry makes it impractical to use the lever rule to accurately determine the relative transformation fraction. However, we could successfully apply the lever rule to the LUMet data. Furthermore, the derivatives of the change in length and ultrasonic velocity are used to estimate the transformation temperatures as a function of the cooling rates. Further, the in-situ measurements are supplemented with ex-situ characterization of the microconstituents after heat treatments using scanning electron microscopy.

Enhanced detection of viruses for improved water safety

Human viruses pose a significant health risk in freshwater environments, but current monitoring methods are inadequate for detecting viral presence efficiently. We evaluated a novel passive in-situ concentration method using granular activated carbon (GAC). This study detected and quantified eight enteric and non-enteric, pathogenic viruses in a freshwater recreational lake in paired grab and GAC passive samples. The results found that GAC passive sampling had a higher detection rate for all viruses compared to grab samples, with adenovirus found to be the most prevalent virus, followed by respiratory syncytial virus, norovirus, enterovirus, influenza A, SARS-CoV-2, and rotavirus. GAC in-situ concentration allowed for the capture and recovery of viral gene copy targets that ranged from one to three orders of magnitude higher than conventional ex-situ concentration methods used in viral monitoring. This simple and affordable sampling method may have far-reaching implications for reducing barriers associated with viral monitoring across various environmental contexts.

Iridium Deposited on Niobium-Doped Titanium Dioxide (NbTiO) for High-Stability and Effective Oxygen Evolution Reaction (OER) Catalyst in Acidic Environment

The state-of-the-art iridium-based catalyst, which is the trade-off between activity and durability during acidic OER, needs to be distributed on low-cost effective support materials for the economical utilization of electrolyzers.1 Normally, dopant is introduced into the oxide lattice structure in order to improve the conductivity of the support, which in turn can diminish the Iridium loading content. In this talk, niobium doped titanium dioxide (NbTiO), which is proved to have promising durability in acidic OER conditions, is applied for supported Ir-based catalyst. Based on the powder compression method for conductivity measurement,2 the resistivity of synthesized Nb-doped TiO2, with niobium content of 10 at. % (NbTiO10), is about tens times lower than the resistivity of anatase TiO2 (a.TiO2). Which, in turn brings to the 40 wt. % Ir/NbTiO10 the resistivity of millions times lower than 40 wt.% Ir/a.TiO2 and hundreds times lower than 50 wt.% Ir/a.TiO2. Moreover, by introducing an organic framework to the synthesis, support's surface area can be enlarged and its macroporous morphology can be modified. Various ex-situ methods, e.g. HR-STEM, XRD, and RDE, are used to investigate the influence of the distribution and oxidation state of the Ir-active phase on doped TiO2 support onto the performance of catalysts, before and after the acceleration stress test (AST). And in-situ methods, including ICP-MS coupling scanning flow cell and XAS, are also applied, in order to reveal the alternating of every single component in the catalytic system during OER and after the AST. The catalyst was then tested in electrolyzer to compare its performance with the commercial Elyst Umicore Catalyst. Reier, T.; Oezaslan, M.; Strasser, P., Electrocatalytic Oxygen Evolution Reaction (OER) on Ru, Ir, and Pt Catalysts: A Comparative Study of Nanoparticles and Bulk Materials. ACS Catalysis 2012, 2 (8), 1765-1772. Karimi, F.; Peppley, B. A., Metal Carbide and Oxide Supports for Iridium-Based Oxygen Evolution Reaction Electrocatalysts for Polymer-Electrolyte-Membrane Water Electrolysis. Electrochimica Acta 2017, 246, 654-670.

Evaluation of Phosphoric Acid Leaching in PBI Membranes for High-Temperature PEM Fuel Cells By Ex-Situ and Operando Characterization Methods

High-Temperature PEM Fuel Cells (HT-PEMFCs) based on PA-doped-PBI membranes have become a promising sustainable power generation system due to their high proton conductivity, high tolerance to hydrogen impurities, thermal stability and high utilization of waste heat [1]. Unlike low-temperature fuel cells based on perfluorosulfonic acid polymers (Nafion), HT-PEMFCs do not need water to act as a proton conductor, instead a hydrogen-bonded matrix is established between PA and PBI, negating the need for humidification in the system. As a result, the proton conductivity of the PA-doped PBI membrane is related to its PA loading. When PA is added to the PBI membrane, each PBI repeat unit can only bond with two PA molecules, leading to higher doping levels due to PA distributed in the PBI matrix in a free state. This extra PA leaches from the membrane to the electrodes during cell operation [2] resulting in several problems, the reduction of the proton conductivity of the membrane, blocking of the pathway for the gases to and from catalytically active sites and drive the migration of Pt-based catalyst, resulting in an increase in both mass and charge transfer resistances [3].To prevent acid leaching out of the membrane and the subsequent negative effects on the fuel cell performance, Single Layer Graphene (SLG) has been incorporated as barrier material between the PEM and cathode/anode. SLG acts as sieve material to block all atoms and molecules from passing through with the exception of protons improving the performance and the long-term of the HT-PEMFC [4]. However, although the electrochemical characterization proves this enhancement, the mechanism of the phosphoric acid migration and the effect of the SLG on the leaching is still unknown.In this work, different techniques, X-rat CT [4, 5]y, Raman microscopy [5] and µ-XRF, have been used to evaluate the PA leaching under ex-situ and in-operando conditions to study the mechanism of the migration of the acid and to prove that the electrochemical improvement is due to SLG has a positive effect in the HT-PEMFC.

Synchrotron High-Energy X-ray &amp; Neutron Diffraction, and Laser-Scanning Confocal Microscopy: &lt;i&gt;In-Situ&lt;/i&gt; Characterization Techniques for Bulk Nanocrystalline Metals

This report is aimed at giving an overview of the significance of the novel and innovative microstructural and microscopic characterization techniques for bulk nanostructured metals processed by severe plastic deformation, specifically high-pressure torsion (HPT). In practice, the microstructural relaxation behavior upon heating of nanostructured 316L stainless steel and CoCrFeNi high-entropy alloy was characterized by in-situ heating neutron diffraction measurements; the heterogeneous phase distribution of an HPT-bonded hetero-nanostructured Al-Mg alloy was examined using synchrotron high-energy X-ray diffraction; and the microstructural evolution upon heating of a nanostructured CoCrFeNiMn high-entropy alloy was examined by laser-scanning confocal microscopy. These novel techniques are complementary to each other and any other in- or ex-situ testing methods, especially when nanocrystalline metals are transforming microstructurally and compositionally with temperature and time in a hierarchical manner. The outcomes of the studies emphasize the importance of the methodologies and the development of characterization techniques for further in-depth exploration in the research field of severe plastic deformation.

Electrochemical NH3 production: In-situ evaluation of the activity and durability of nitrogen-reduction catalysis using scanning electrochemical microscopy (SECM)

Developing efficient electrochemical processes for ammonia (NH3) production is a significant challenge that needs to be met to realize a carbon-neutral chemical industry. Recently, electrocatalytic nitrogen-reduction has been actively investigated under ambient conditions. However, the evaluation of electrodes for NH3 production using ex-situ NH3 detection methods only provide time- and space-averaged catalytic information. When investigating the transient activity of electrodes with spatiotemporal information, the real-time detection of NH3 near the electrode with high analytical resolution is essential. In this study, in-situ detection of electrochemically generated NH3 was first demonstrated using scanning electrochemical microscopy. A low NH3 flux of 6.6 nmol cm−2 s−1 generated from an Fe-CuS/C electrode was detected using NH3 oxidation current detected at a polycrystalline Pt ultramicroelectrode. This observation provides invaluable information on catalysis, including transient activity and durability. The advantages and limitations of the proposed in-situ NH3 detection method are demonstrated in an evaluation of nitrogen-reduction electrolysis.

Quadruple modification for constructing ultra-stable lithium-rich cathodes

Lithium-rich layered oxides are considered as the next generation cathode materials for lithium-ion batteries due to their high capacity and operating voltage. However, O2 release, side reactions at the cathode-electrolyte interface, transition metal(TM) dissolution, and microcracking evolution severely limit the commercial application of Li-rich cathode materials. In this work, the Eu is used to modify the Li1.2Mn0.54Co0.13Ni0.13O2 for the lithium-rich cathode. The doping of Eu in the bulk phase greatly improves the redox activity of the material, and a large number of oxygen vacancies extremely alleviate the irreversible changes of lattice oxygen. The Eu2O3 modified layer at the interface and the heterogeneous structure of the rock-salt phase effectively ensure the structural integrity and stability of the CEI during long time cycling, disturbing the orientation of the non-bonded O 2p orbitals. The attenuation of specific capacity (0.04 mA h g−1/cycle) and voltage (0.31 mV/cycle) is greatly reduced by the quadruple modification of Eu. The charge compensation mechanism, phase structure transition pattern, anion behavior and CEI evolution are analyzed by a series of ex-situ methods. The simple modification method provides guidance for the overall improvement of the performance of lithium-rich cathode materials.

Sorption and Desorption of Vapor of n-Pentane by Porphyrin Aluminum Metal-Organic Framework: Mechanism of Bonding, Kinetics and Stoichiometry by Complementary In-Situ Time-Dependent and Ex-Situ Methods.

Metal-organic frameworks (MOFs) are highly nanostructured coordination polymers that contain metal cations and organic linkers and feature very large pore volumes and surface areas. The sorption and desorption of n-pentane vapor by porphyrin aluminum metal-organic framework Al-MOF-TCPPH2 where TCPPH2 is tetrakis(4-carboxyphenyl)porphyrin linker were studied by a novel method of in-situ time-dependent attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy in a controlled atmosphere and complementary in-situ and ex-situ methods. Sorption facilely occurs in the flow of dried air, and in the obtained adsorption complex the adsorbate molecules interact with phenyl and carboxylate groups of the linker and the O-H group. Sorption kinetics follows the pseudo-first-order rate law, as confirmed by in-situ time-dependent gravimetry. Further, an ex-situ (static) sorption of n-pentane vapor results in an adsorption complex with as much as 29.1 wt.% n-pentane with the stoichiometric formula [Al-MOF-TCPPH2]2(n-C5H12)7 and a distinct XRD pattern. Finally, in the flow of dried air, the adsorption complex gradually desorbed n-pentane, following the pseudo-first-order rate law. The reversibility of sorption and desorption makes porphyrin aluminum MOF promising for the separation of light hydrocarbons and chemo-sensing. In-situ time-dependent ATR-FTIR spectroscopy in a controlled atmosphere, in combination with in-situ time-dependent gravimetry, is a new approach for the determination of binding sites of sorbents with adsorbate molecules, the stoichiometry of complexes, and chemical kinetics of "solid-gas" interactions.

In-situ SEM characterization and numerical modelling of bainite formation and impingement of a medium- carbon, low-alloy steel

A novel in-situ scanning electron microscope (SEM) characterization technique for observing phase transformation is developed and its results studied and compared to well-founded experimental ex-situ methods as well as numerical modelling of bainite formation. Phase transformation kinetics are compared between the in-situ SEM, dilatometry test as well as mean field and Cellular Automata (CA) models. Microstructural evolution during phase transformation is compared between in-situ SEM, ex-situ EBSD and CA model results. The in-situ method allows for direct observation of bainite sheaf growth and impingement. The in-situ results in combination with EBSD data can be used to parameterize the CA model sheaf nucleation and growth equations.

Boosting kinetics of tellurium redox reaction for high-performance aqueous zinc-tellurium batteries

Aqueous zinc-ion batteries have attracted extensive attention due to their environmental friendliness, low cost and high theoretical capacity. Among them, the conventional cathode materials mainly rely on ion intercalation or surface redox mechanisms, which usually exhibit unsatisfactory specific capacity. Currently, aqueous zinc-tellurium (Zn-Te) batteries based on conversion mechanisms have shown great potential to provide greater specific capacity. However, the sluggish electrochemical reaction kinetics limits the further development of Zn-Te batteries. Herein, the hierarchical structure was prepared by in situ growing MoS2 on N, F co-doped porous carbon nanosheets (MoS2@NFC), which served as Te hosts to construct aqueous Zn-Te batteries. Benefitting from the hierarchical structure and unique catalytic property of the MoS2@NFC, the kinetics of Te redox reaction was remarkably enhanced for aqueous Zn-Te batteries. As a result, the aqueous Zn-Te batteries based the Te-MoS2@NFC electrode exhibited high specific capacity (483 mAh g−1 at 150 mA g−1), outstanding rate performance and excellent cycling stability. Furthermore, the catalytic conversion mechanism of Zn-Te batteries was systematically explored through various ex-situ characterization methods and density functional theory (DFT) calculations. Therefore, this work provides a novel idea to design high performance conversion-type aqueous zinc-ion batteries.

Multi-scale analysis for accelerated degradation mechanisms of cylindrical LiFePO4/graphite batteries under distinct positions of jelly roll

Lithium iron phosphate (LFP) batteries are widely used in the electric vehicle due to the great chemical stability and cost advantages. Fluctuations in the environment and driving conditions lead to a deterioration in battery performance that is inevitable. In addition, due to the winding manufacturing characteristics of cylindrical battery electrodes, the uneven distribution of current and temperature accelerates the aging process. In this paper, the cross-comparison aging test of cylindrical LFP batteries is designed, in which three kinds of constant current and two different dynamic working conditions are used for accelerated aging test at high temperature. The aging behavior and mechanism are investigated quantitatively by combination of in-situ electrochemical test and ex-situ Post-Mortem methods. During the long-term cycle of the battery, external characteristic parameters such as capacity, internal resistance, and open circuit voltage are periodically checked up. Until the capacity retention falls below 80%, the batteries are disassembled to sample the electrodes at the specified positions from the jelly roll. The material morphology changes of electrodes are observed by scanning electron microscopy. The half-cell tests were produced to obtain material-level aging information based on performance tests. This multi-scale analytical method enables the detailed process of performance loss, which guides performance prediction and safety diagnostics.

Towards the understanding of the Ti/Al ratio role in solid-state reaction for ohmic contacts on n-GaN

The fast-growing market of GaN-based power electronics requires the development of performing ohmic contacts. The Ti/Al stack, being one of the most popular, has been thoughtfully investigated over the years in terms of electrical performances but remains to be better understood in terms of contact formation and related solid-state reactions, especially when targeting small Ti to Al ratios (typically, down to lower than 5 at. %). In this paper, the influence of the deposited Ti layer thickness on the resulting contact is investigated using in-situ and ex-situ XRD methods as well as TEM imaging. It is found that a threshold exists, below which the diffusion phenomena ruling alloy formation during annealing are controlled, leading to a frozen Al3Ti/Al bi-layer morphology. Past this threshold, the erratic formation of non-textured Al3Ti grains is observed, which is detrimental to devices performances. The result interpretation is supported by an extended bibliography survey focused on material science, the first of the sort.

A new in-situ method to estimate fish target strength reveals high variability in broadband measurements

Fish Target Strength (TS) is a requirement for estimating abundance from surveys of pelagic fish using echosounders. This paper describes a novel in-situ method to estimate TS as a function of fish body length (L), according to the standard equation TS = 20 log (L) +b20, where b20 is the species-specific factor to be estimated. We made measurements of TS with a broadband scientific echosounder, which is becoming the new tool of choice in fisheries acoustics due to its enhanced signal-to-noise ratio, and higher range resolution and the ability to measure the frequency response. A split-beam 38 kHz broadband transducer was pole-mounted on a small boat in the fjords of Nuuk, Greenland. With the boat stationary, individual Atlantic cod Gadus morhua were detected as echotraces, caught with a fishing line, measured in length and then released. Video footage, from a camera attached to the line, was inspected to verify a single individual was attracted to the lure and caught. Fish echotrace tracking techniques were applied to estimate the tilt of the fish from each acoustic sample and the measured TS was adjusted accordingly with the use of a Kirchhoff-Approximation scattering model. The b20 parameter was estimated by linear regression. This method combines the benefits of associating TS from single fish of known length, which is typical of ex-situ methods, with the in-situ advantages of measuring TS of an undisturbed fish in its natural environment. Results yielded a b20 of − 65.6 dB ( ± 0.83 dB C.I.), which is within the range of previously published values for Atlantic cod measured with narrowband systems. Large variability of TS was observed within fish tracks (average s.d. of 5.55 dB). This is the first description of TS for Atlantic cod with broadband equipment. The high variability could not be attributed to variation in fish length nor tilt angle. Other physiological and behavioural aspects were also discarded. It is possible that this may be an intrinsic property of broadband acoustics, which indicates a need for re-evaluating TS to length relationships as fisheries science moves towards the wider application of broadband acoustics.

Oxygen activity excited thiophene-diketopyrrolopyrrole-based organic molecules as anode for lithium-ion batteries with enhanced interfacial storage capacity and long cycling capability

In this work, we synthesized various thiophene-diketopyrrolopyrrole-based (DPP-2T-based) molecules by Knoevenagel condensation and halogenation reaction, which applied DPP-2T-based small molecules as anode for lithium-ion batteries (LIBs) for the first time. We studied the different substituents on battery performance and explored the charge–discharge mechanism for DPP-2T-based molecules. DPP-2T-based molecules exhibit different electrochemical properties by substituting various groups at nitrogen positions, where DPP-2T-TA (tert-butyl acetate) electrode possesses better capacity and long-term cycle performance than that of DPP-2T-H (no substitution) and DPP-2T-C6 (hexane) electrode. DPP-2T-TA electrode present an unusual upward tendency for its discharge specific capacity during cycling, which displays that of 530 mAh/g (1000 mA g−1) after 2000 cycles and the capacity retention reaches up to 142.5 %. It is better than those of DPP-2T-H (439 mAh/g, 108.1 %) and DPP-2T-C6 (423 mAh/g, 113.1 %) electrode, which is ascribed to oxygen activity excitation in tert-butyl acetate. This moment, the energy density and power density of DPP-2T-TA electrode are 346 Wh kg−1 and 699 W kg−1, respectively. To further explain this phenomenon, we used many ex-situ measurgin methods such as differential specific capacity (dQ/dV) curves, scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectrometer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and natural bond orbital (NBO) analysis to characterize the detailed lithiation/delithiation process of DPP-2T-TA electrode. The results suggest that the unusual capacity amplification for DPP-2T-TA electrode attributed to lithium-ions inserted into unsaturated carbons and increases its interfacial storage capacity. We believe that the synthesis of DPP-2T-based organic molecules can provide a novel strategy for the development of organic electrode materials for LIBs.

Food and feeding habits of Tor tambra (Valenciennes, 1842) in Cibareno River, West Java, Indonesia

The Cibareno River in Sukabumi, West Java, is the habitat of Tor tambra, one of Indonesia's most highly valuable native freshwater fish species. The native fish population in this river may be threatened by the planned weir construction. The study aims to examine the food and feeding habits of Tor tambra in the Cibareno River. This study was carried out for four months (May, June, July, and September 2022) at six locations in the Cibareno River. A total of 61 individuals of T. tambra displayed an isometric growth pattern with good condition factor. Aquatic insects were the primary food, with nematodes and phytoplankton acting as supplements. Plant seeds were often eaten as an extra source of food. These results were supported by fish morphometric data such as relative mouthwidth and relative gut length, which showed that they are omnivorous and tend to be carnivorous. In addition, the relative eye diameter of the fish indicates that Tor tambra is a diurnal forager. The findings suggest that both in-situ and ex-situ conservation methods are viable options for the preservation of Tor tambra in the Cibareno River.

A voltage control strategy to improve the cycling stability of organic electrode materials: The case of para-dinitrobenzene

Small-molecule organic cathode materials (SMOCMs) with high energy density are promising for various energy storage devices including rechargeable lithium batteries, but it is a huge challenge to simultaneously satisfy the demand of cycling stability. Herein, by taking nitro-based para-dinitrobenzene (pDNB) as an example, we propose a simple but effective voltage control strategy to improve the cycling stability, without energy density decrease or cost increase of the system as for many other complicated solutions. The highly reversible two-electron redox reaction of pDNB provides it full utilization of the theoretical capacity (319 mAh g−1) and high discharge plateau at 2.65 V vs Li+/Li, and thus an outstanding energy density of 850 Wh kg−1. Different voltage windows of 1.8/2.4–3.4/3.8 V are applied to test the cycling performance, and 2.4–3.8 V is selected as the optimized one endowing a high capacity retention of 86 % after 100 cycles (as a contrast, only 8 % within 1.8–3.4 V). Various electrochemical analyses and ex-situ characterization methods reveale that the influence is not in the depth of discharge/charge, but in the dissolution–redepostion behavior of active material and thus the electrode structure evolution. This work provides not only a novel strategy to improve the cycling stability of SMOCMs, but also a new perspective to understand the capacity fading mechanism of them.

Elucidating the charge storage mechanism of high-performance vertical graphene cathodes for zinc-ion hybrid supercapacitors

Aqueous zinc-ion hybrid supercapacitors (ZHSs) are gaining enormous attention due to intrinsic safety, low cost and potential for acquiring both high energy density and high power density, but their electrochemical properties are realistically restricted by improper physicochemical characteristics and ambiguous charge storage mechanism of carbon cathodes. Herein, we report an advanced carbon cathode of activated vertical graphene (A-VGN) for high-performance ZHSs. For the A-VGN cathode, vertical graphene array morphology and hierarchically porous structure effectively shorten ion diffusion distance, and meanwhile, large specific surface and oxygen doping offer abundant active sites for ion adsorption. Consequently, the A-VGN cathode-based ZHS presents exceptional electrochemical performance such as a high capacity of 246 mAh/g, fast charge/discharge capability, superior cycling stability with 97.4% capacity retention over 10,000 charge/discharge cycles, as well as preponderant energy density among various carbon cathode-based ZHSs. Furthermore, in-operando Raman spectroscopy and in-operando pH monitoring techniques, being supplemented by ex-situ methods, are applied to investigate the charge storage mechanism of the A-VGN cathode. Dynamic adsorption/desorption behaviors of different ions on the carbon cathode during charge/discharge processes are elucidated. This work is expected to facilitate the development of ZHSs by providing new insights into the design and charge storage mechanism of carbon cathodes.