Cycling Endurance Research Articles

Enhanced electrochemical behavior of naturally derived Eu3+: PEG/CaCO3 nanocomposite for supercapacitor application

The nano CaCO3 (nC) and various concentrations (0.02, 0.04, 0.06, and 0.08 M) of Eu3+ doped CaCO3/PEG nanocomposites (respectively represented as nCE1, nCE2, nCE3, and nCE4) were prepared through the biomimetic method. The functional groups, purity, and phase of the prepared products were assessed by FTIR and XRD. The prepared products were CaCO3/PEG and Eu3+ doped CaCO3/PEG with rhombohedral structures. The chemical state of the sample was studied using XPS, which revealed the presence of Ca, C, O, and Eu. No secondary phase was detected. FE-SEM and HR-TEM images of nCE4 show the distinct rhombohedral and spherical-like morphologies. The electrochemical performance of nC, nCE1, and nCE4 was investigated using a three-electrode system with Na2SO4 as the electrolyte. The prepared electrode materials behaved as pseudocapacitors, and the nCE4 electrode exhibited a specific capacitance value which is three times higher than that of the nC electrode. The present study suggests that nCE4 can be used as an electrode in supercapacitor applications. The cyclic stability of the CaCO3/PEG: Eu (0.08 M) nanocomposite after 1000 cycles at 3 A g−1 showed better cycle endurance, with a high retention of 97 %.

Growth and characterization of sputter-deposited Ga2O3-based memristive devices

In the last few years, there has been significant interest in gallium oxide devices for resistive switching technologies due to its remarkable sensitivity to oxygen. In this study, we present the growth and resistive switching of a (2¯01) oriented (75 ± 3) nmβ-Ga2O3 thin film on a Ru/Al2O3 substrate using magnetron radio frequency sputtering. The observed resistive switching was attributed to the formation and rupture of conductive filaments constituted by oxygen vacancies in the β-Ga2O3 film as confirmed by x-ray photoelectron spectroscopy and energy-dispersive x-ray spectroscopy. The electrical conduction was found to be of Ohmic nature in the low-resistance ON state, while the high-resistance OFF state was governed by the Poole–Frenkel transport mechanism. Exhibiting stable endurance cycles, long retention times, and ON/OFF ratios of up to 104, the devices can be considered as promising prototypes for future nonvolatile resistive switching random access memory with respect to both switching performance and device stability.

How sintering temperature affects the electrochemical performance of ultra-high nickel (Ni > 0.9) cathode material

The burgeoning demand for electric vehicles with extended driving ranges has propelled ongoing development efforts for ultra-high nickel (Ni > 0.9) cathode materials. Despite significant ongoing research focused on Ni-rich cathode materials, a more comprehensive foundational understanding of ultra-high nickel cathode materials is essential. In our research, we employed LiNi0.94Co0.06O2 as a model ultra-high nickel cathode material to systematically delve into the interplay between sintering temperature, structural features, and electrochemical behavior. Within a sintering temperature spectrum of 660–720 °C, we discerned that specimens produced at diminished temperatures manifest a reduced initial discharge capacity yet excel in cycling endurance. In stark contrast, their counterparts produced at augmented temperatures behave inversely. Identifying a singular sintering temperature that achieves equilibrium between initial discharge capacity and cycling performance proves elusive. Through X-ray diffraction and high-resolution transmission electron microscopy, it became evident that samples synthesized at lower temperatures exhibit pronounced lithium-nickel mixing and develop a thicker NiO layer on the surface, leading to compromised initial discharge performance and capacity. Utilizing focused ion beam scanning electron microscopy, differential capacity analysis, and in-situ X-ray diffraction, we confirm that samples synthesized at lower temperatures possess smaller particle sizes, enabling them to withstand volumetric expansion stress during cycling, resulting in enhanced cycling performance. In the realm of ultra-high nickel cathode materials, elevating the sintering temperature is a conduit to superior initial discharge efficiency and capacity. Yet, the imperative of preserving diminutive particle dimensions, as a stratagem to bolster cycling performance, stands out as a pivotal research frontier.

Promoting homogeneous lithiation of silicon anodes via the application of bifunctional PEDOT:PSS/PEG composite binders

Polymeric conducting binders have increasingly become a subject of significant research interest due to their dual roles as both a binder and a conducting agent. This dual functionality not only increases the proportion of active materials in the electrode but also elevates the volumetric energy density of current Li-ion batteries. In this study, we explore the potential of a composite of PEDOT:PSS and polyethylene glycol (PEG) as a high-performing binder for silicon anodes. This highly conductive PEDOT:PSS, enhanced by the addition of PEG polymer, displays exceptional electrochemical characteristics, including superior C-rate, Li-ion diffusivity performance, and extended cycle endurance. Of particular interest are the enhanced mechanical properties bestowed by the plasticizing effect of the PEG polymer. This improvement aids the Si anode in resisting pulverization during successive discharge and charge cycles. As a result, this enables extended cyclability without the creation of anode cracking. Additionally, the use of operando optical microscopy allows for the direct observation of lithiation kinetics within the PEDOT:PSS/PEG binder. This revealed a uniform color change with restrained volume expansion, demonstrating the successful operation of the binder. Consequently, the bifunctional PEDOT:PSS/PEG binder shows promise as a robust strategy for the next generation of high-performance lithium-ion battery binders.

High-performance energy storage in BNST-based lead-free ferroelectric ceramics achieved through high-entropy engineering

The utilization of a high entropy approach for the design of high-performance perovskite dielectric capacitors has been gaining much attention for the development of next-generation pulse power capacitors. Despite this, there are still challenges to further enhance their energy storage density and efficiency. To address this, a high-entropy strategy is proposed to significantly improve the energy storage characteristics of ceramics by increasing the configurational entropy and delaying saturation polarization. This approach has resulted in an ultra-high recoverable energy storage density (Wrec) of 7.16 J/cm3 and a high efficiency (η) of 93.3 % for 0.8[0.65(Bi0.5Na0.5)TiO3-0.35SrTiO3)]-0.2[Ba(Zr0.2Ti0.2Sn0.2Hf0.2Nb0.2)O3] (abbreviated as 0.8BNST-0.2Ba(5 M)O) ceramic. The inclusion of Ba(5 M)O high entropy oxides has resulted in slender polarization–electric field hysteresis loops with delayed polarization saturation. The increase in atomic configuration entropy, degree of atomic disorder and lattice distortion due to the Ba(5 M)O high entropy oxides, has led to an increase in breakdown field, improved energy storage density and efficiency. Furthermore, excellent thermal stability (30–150 ℃), superior frequency stability (5–1000 Hz), and robust fatigue (100–105 cycles) endurance were achieved. The high entropy strategy has been demonstrated to be an effective method for the design of novel capacitors with superior energy storage performance.

High-intensity non-invasive ventilation during exercise-training versus without in people with very severe COPD and chronic hypercapnic respiratory failure: a randomised controlled trial

BackgroundPeople with very severe chronic obstructive pulmonary disease (COPD) using nocturnal non-invasive ventilation (NIV) for chronic hypercapnic respiratory failure (CHRF) experience reduced exercise capacity and severe dyspnoea during exercise training...

Strong atom capture ability and pinning effect by doping an element with large electronegativity difference in Sb2Te3 phase change material

The ultimate goal of memory researchers and developers is to devise a universal memory to replace all memories in complex hierarchies of memory systems. Phase change memory is considered by the International Semiconductor Industry Association as the most likely emerging storage technology to achieve this ambitious goal due to its excellent performance. However, the relatively slow operation speed and poor cycle endurance are stumbling blocks for this purpose. Here, we propose a new doping strategy to construct stable bonding by introducing atoms with large electronegativity differences from the matrix Te atoms enhancing the capture ability and the pinning effect to Te atoms, which facilitates fast nucleation and suppresses migration of Te atoms to achieve significant performance improvement. Using ab initio molecular dynamics simulations, we explore and compare the atomic structures, chemical bonding, and dynamics properties of Hf doped Sb2Te3 (HfST), La doped Sb2Te3 (LaST), Rb doped Sb2Te3 (RbST) and Sr doped Sb2Te3 (SrST). In the XST (X refers to Hf, Rb, La and Sr atoms) systems, the increase of the more stable ring structure fluctuation and the stronger atom capture capability of rings enable more and faster formation of nuclei during crystallization. Higher Peierls-like distortions suggest better thermal stability. The motility of Te atoms is suppressed due to the pinning effect. High coordination of atoms and the concentration reduction of the lone-pair electron and void enable small density difference. Our results show that fast universal memory with good endurance can be achieved by the construction of strong bonding by doping atoms with large electronegativity differences, providing an important guidance for experiments and industries.

Improved oxygen ion migration efficiency and resistive switching properties in SrFeOx memristor with vertical superlattice-like structure

The resistive switching (RS) behaviour between high and low resistance states in SrFeOx memristors originates from topological phase transition (TPT) induced by the migration of oxygen ions. Accelerating the migration of oxygen ions in the anisotropic crystal structure of SrFeO2.5 is of great importance for improving the RS properties and promoting the application for this TPT memristor. In this study, SrFeOx TPT memristors with different superlattice-like (SLL) structures were fabricated and the prepared devices with a vertical-type SIL structure display an ultra-low operation voltage of only 0.6 V, excellent cycling stability, data retention, and endurance performance. Moreover, the microstructures of vertical and horizontal SLL SrFeO2.5 were characterized with X-ray diffraction and transmission electron microscope. Furthermore, the differences in oxygen ion migration rate in the two structures were also tested by in-situ X-ray photoelectron spectroscopy. Finally, the optical band gaps and oxygen ion migration barriers of the two structures were calculated using first principles. All the characterizations and simulation results prove that the vertical type SrFeOx shows a higher oxygen ion migration efficiency. More encouragingly, the vertical SLL devices exhibit up to 96 % recognition accuracy for the Mixed National Institute of Standards and Technology image recognition task.

System-based Monitoring of Muscular Fatigue in Lower-Extremity Movement

Physical fatigue accounts for many injuries in the workplace, sports arena, or battlefield. The traditional approaches to monitor fatigue rely on detecting and measuring shifts in the person’s muscular surface electromyography (sEMG) signals. However, assessing neuromuscular fatigue based purely on sEMG signals fails to account for the changing muscle dynamics during long dynamic physical tasks. To combat this dilemma, a system-based methodology has been recently developed and applied to several upper-extremity tasks. In this paper, we validate the efficacy of this novel methodology on the lower extremities during a dynamic activity. Specifically, the system-based monitoring methodology was applied to a cycling endurance task. It was statistically demonstrated that the system-based methodology resulted in a more-sensitive and less noisy metric, in comparison with an EMG-based methodology. The efficacy of the methodology was further illustrated by analyzing the inter-segmental recovering and fatiguing trends, which aligned with each muscle’s expected inter-muscle synergistic relationship.

Hybrid Dry and Wet Etching of LiNbO3 Domain-Wall Memory Devices with 90° Etching Angles and Excellent Electrical Properties.

Ferroelectric domain walls, agile nanoscale interfaces of polar order, can be selectively controlled by electric fields for their position, conformation, and function, which is ultimately the key to realizing novel low-energy memory and computing structures. LiNbO3 single-crystal domain wall memory has the advantages of high operational speed, high integration density, and virtually unlimited endurance cycles, appearing as a good solution for the next generation of highly miniaturized low-energy memories. However, the etching process poses significant challenges in the nanofabrication and high-density integration of LiNbO3 domain-wall memories. Here, we employed a hybrid etching technique to achieve smooth sidewalls with a 90° inclined angle, leading to a 24% reduction in the coercive field and a 2.5-fold increase in the linear domain wall current density with a retention time of more than 106 seconds and endurance of over 105 writing cycles. Combined with the results of X-ray diffraction patterns and X-ray photoelectric spectra, it is concluded that the excellent electrical performance is related to the formation of an oxygen-deficient LiNbO3-x layer on the sidewall surface during the wet chemical etching process, which is a conductive layer that reduces the thickness of the "dead" layer between the side electrodes and the LiNbO3 cell and rectifies the diode-like wall currents with an onset voltage reduced from 1.23 to 0.28 V. These results prove the high-density integration of ferroelectric domain-wall memories at the nanoscale and provide a new strategy applicable to the development of LiNbO3 photonic devices.

Synergistic integration of Bi2O3||CoWO4 for asymmetric supercapattery: A binder-free approach ensuring high endurance cycling stability

Supercapatteries are becoming increasingly popular as energy storage devices due to their remarkable electrochemical characteristics, which combine a high energy storage capacity, similar to batteries, and a high-power output, similar to supercapacitors. In this study, the assembly of Bi2O3/Carbon cloth (anode) and CoWO4/Nickel foam (cathode) electrodes was carried out using a PVA-KOH gel electrolyte. The device operated within a potential range of 1.55 V and exhibited a specific capacity of 423 C/g at a 1 A/g current density. Additionally, the prepared solid-state device showed remarkable electrochemical stability, retaining over 96 % coulombic efficiency and 90 % capacity after 10,000 GCD cycles. Furthermore, the fabricated asymmetric supercapattery demonstrated an energy density of 115.11 Wh/kg and a specific power density of 6005 W/kg. The ability of the fabricated adaptable supercapacitor to power an LED highlights its potential in flexible applications without compromising functionality. This presents a promising outlook for the advancement of electrochemical energy storage devices.

Between-Seasons Variability of Cyclists' Peak Performance: A Longitudinal Analysis of "Real-World" Power Output Data in Male Professional Cyclists.

The record power profile (RPP) has gained popularity as a method of monitoring endurance cycling performance. However, the expected variation of cyclists' performance between seasons remains unknown. We aimed to assess the between-seasons variability of peak performance (assessed through the RPP) in male professional cyclists. The study followed a longitudinal observational design. Sixty-one male professional cyclists (age 26 [5]y) with power output data from both training sessions and competitions were analyzed for a median of 4 consecutive seasons (range 2-12). The highest mean maximum power values attained for different durations (from 10s to 30min), as well as the resulting critical power, were determined for each season. Within-cyclist variability between seasons was assessed, and the upper threshold of expected changes (ie,twice the normal coefficient of variation) was determined. All mean maximum power values showed an overall high agreement and low variability between seasons (intraclass correlation coefficient [ICC]= .76-.88 and coefficient of variation [CV]= 3.2%-5.9%), with the lowest variability observed for long efforts (>1min). Critical power showed an ICC and CV of .79 (95% CI, .70-.85) and 3.3% (95% CI, 3.0%-3.7%), respectively. Upper thresholds of expected variation were <12% for short efforts (≤1min) and <8% for long efforts. "Real-world" peak performance assessed through the RPP shows a low variability between seasons in male professional cyclists-especially for long efforts-with expected variation being around 6% and 3% for short (≤1min) and long efforts, respectively, and with changes >12% and >8%, respectively, being infrequent for these effort durations.

Improving bifunctional catalytic activity of biochar via in-situ growth of nickel-iron hydroxide as cathodic catalyst for zinc-air batteries

Expanding the application scenarios of wood-derived biochar guided by the conversion of traditional energy to new energy shows great promise as a field. As thrilling energy conversion apparatus, zinc-air batteries (ZABs) require cathode catalysts with high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities and stability. Herein, two-dimensional nickel-iron hydroxide nanosheets were creatively assembled in N-doped wood-derived biochar (NiFe-LDH@NC) by an in-situ growth method. The categorized porous organization in wood-derived biochar facilitates the rapid seepage of electrolytes and rapid diffusion of reaction gases. The unique interfacial structure of biochar and NiFe-LDH accelerates electron transfer during oxygen electrocatalysis, and endows NiFe-LDH@NC with first-class catalytic activity and durability for ORR and OER. The ZAB derived from NiFe-LDH@NC showed elevated discharge productivity and cycle endurance, making it promising for viable applications. This work provided a convenient way for the conversion of wood-derived biochar to high-value added electrocatalysts.Graphical

Maintenance of internal load despite a stepwise reduction in external load during moderate intensity heart rate clamped cycling with acute graded normobaric hypoxia in males

ObjectivesTo investigate the acute effects of graded hypoxia on external and internal loads during 60 min of endurance cycling at a clamped heart rate. DesignRepeated measures. MethodsOn separate visits, 16 trained males cycled for 60 min at a clamped heart rate corresponding to 80 % of their first ventilatory threshold at sea-level and 2500 m, 3000 m, 3500 m and 4000 m simulated altitudes (inspired oxygen fractions of 20.9 %, 15.4 %, 14.5 %, 13.6 % and 12.7 %, respectively). Markers of external (power output) and internal (blood lactate concentration, tissue saturation index, cardio-respiratory and perceptual responses) loads were measured every 15 min during cycling. Neuromuscular function of knee extensors was characterised pre- and post-exercise. ResultsCompared to sea-level (101 ± 22 W), there was a stepwise reduction in power output with increasing hypoxia severity (−17.9 ± 8.9 %, −27.1 ± 10.7 %, −34.2 ± 12.0 % and − 44.6 ± 15.1 % at 2500 m, 3000 m, 3500 m, and 4000 m, respectively, all p < 0.05). Blood lactate and tissue saturation index were not different across hypoxia severities, and perceptual responses were exacerbated at 4000 m only, with increased breathing difficulty. Knee extensor torque decreased post-exercise (−14.5 ± 9.0 %, p < 0.05), independent of condition. ConclusionsIncreasing hypoxia severity reduces cycling power output and arterial oxygen saturation in a stepwise fashion without affecting exercise responses between sea-level and simulated altitudes up to 3500 m despite breathing difficulty being elevated at 4000 m.

Coconut Water: A Sports Drink Alternative?

Coconut water is used as an alternative to conventional sports drinks for hydration during endurance cycling; however, evidence supporting its use is limited. This study determined if drinking coconut water compared to a sports drink altered cycling performance and physiology. In a randomized crossover trial, 19 experienced male (n = 15) and female (n = 4) cyclists (age 30 ± 9 years, body mass 79 ± 11 kg, V̇O2 peak 55 ± 8 mL·kg-1·min-1) completed two experimental trials, consuming either a commercially available sports drink or iso-calorific coconut water during 90 min of sub-maximal cycling at 70% of their peak power output, followed by a simulated, variable gradient, 20 km time trial. Blood glucose, lactate, sweat loss, and heart rate were monitored throughout the 90 min of sub-maximal cycling, as well as the time trial performance (seconds) and average power (watts). A repeated measures analysis of variance and effect sizes (Cohen's d) analysis were applied. There were no significant differences (p ≥ 0.05) between the treatments for any of the measured physiological or performance variables. Additionally, the effect size analysis showed only trivial (d ≤ 0.2) differences between the treatments for all the measured variables, except blood glucose, which was lower in the coconut water trial compared to the sports drink trial (d = 0.31). Consuming coconut water had a similar effect on the cycling time trial performance and the physiological responses to consuming a commercially available sports drink.

Recent Advances in Cerium Oxide-Based Memristors for Neuromorphic Computing.

This review article attempts to provide a comprehensive review of the recent progress in cerium oxide (CeO2)-based resistive random-access memories (RRAMs). CeO2 is considered the most promising candidate because of its multiple oxidation states (Ce3+ and Ce4+), remarkable resistive-switching (RS) uniformity in DC mode, gradual resistance transition, cycling endurance, long data-retention period, and utilization of the RS mechanism as a dielectric layer, thereby exhibiting potential for neuromorphic computing. In this context, a detailed study of the filamentary mechanisms and their types is required. Accordingly, extensive studies on unipolar, bipolar, and threshold memristive behaviors are reviewed in this work. Furthermore, electrode-based (both symmetric and asymmetric) engineering is focused for the memristor's structures such as single-layer, bilayer (as an oxygen barrier layer), and doped switching-layer-based memristors have been proved to be unique CeO2-based synaptic devices. Hence, neuromorphic applications comprising spike-based learning processes, potentiation and depression characteristics, potentiation motion and synaptic weight decay process, short-term plasticity, and long-term plasticity are intensively studied. More recently, because learning based on Pavlov's dog experiment has been adopted as an advanced synoptic study, it is one of the primary topics of this review. Finally, CeO2-based memristors are considered promising compared to previously reported memristors for advanced synaptic study in the future, particularly by utilizing high-dielectric-constant oxide memristors.

Highly compatible and reliable ZrN interfacial layer between TiN top electrode and antiferroelectric ZrO2 thin film to boost the electrocaloric behavior

A highly compatible and reliable ZrN interfacial layer with different cycles of atomic layer deposition was inserted between the TiN top electrode and antiferroelectric (AFE) ZrO2 thin film to achieve low oxygen vacancies and high crystallinity of the ZrO2 thin film, boosting the AFE and electrocaloric (EC) characteristics of TiN/ZrO2/TiN metal–insulator–metal (MIM) capacitors. An outstanding adiabatic temperature change (ΔT) of − 21 K was realized for devices with a ZrN interfacial layer of nine cycles, which can be ascribed to the reduction in redox between the TiN and ZrO2 for the suppression of interfacial dead layer during annealing as confirmed via high-angle annular dark field images and interfacial capacitance measurement. Hence, the reliability of ZrO2 MIM capacitors with a nine-cycle ZrN interfacial layer was examined with a negligible change in AFE and EC behaviors after a cycling endurance test of 106 cycles, exhibiting great potential for future applications in solid-state cooling.

Facile one-pot electropolymerization of novel Cu complexed conducting polymer for Resistive Random Access Memory

An innovative one-pot electrochemical method has been studied for the Polypyrrole-Cu (PPy-Cu) composite films synthesis as the active layer of the Resistive Random Access Memory (ReRAM). Cu has been uniformly distributed in PPy-Cu composite films and exhibits two valence states of Cu (0) and Cu (II). The existence of Cu (II) is beneficial for keeping stable resistive switching performance. The Pt/PPy-Cu/Pt ReRAM device exhibits excellent memory performance with a low threshold voltage, a long retention time and good endurance cycles. The resistive switching mechanism is dominated by the Space Charge Limited Current (SCLC) effect accompanied by Schottky emission.

A Novel Hybrid Multifunctional Compound: (CMQ)BiCl5 Showing Enhancement in Physical Properties by Halogen Substitution

AbstractOrganic‐inorganic hybrid multifunctional materials have received significant attention due to their potential applications in smart devices such as phase‐change memory (PCM), resistive random‐access memory (ReRAM). Yet, devices application requires achieving a balance between fast switching speeds, long‐term stability, and high cycling endurance in materials still facing difficulties. Herein, we report two hybrid phase transition compounds: (CMQ)BiCl5(CMQ=Chloromethyl Quinuclidin‐3‐one) (1) and (FMQ)2SbBr5(FMQ=Fluoromethyl Quinuclidin‐3‐one) (2), both two compounds exhibit high phase transition temperature, dual‐stable behavior in dielectric during reversible phase transition process. Notably, 1 exhibit small dielectric change after multiple dielectric state switching. Furthermore, investigate the influence of halogen substitution (F to Cl) for compound properties, which show an Increasing transition temperature (9 K) and raising structural dimension (0D to 1D). Additionally, using first principles, analyze the electronic structure of 1 and find that it has a 3.4 eV wide bandgap, closing to GaN semiconductor (3.4 eV). This work provides a new insight into developing the next‐generation phase transition compounds and chemical modification enhances material performance.

Enhanced resistive switching characteries in HfOx memory devices by embedding W nanoparticles

Resistive random access memory (RRAM) has lots of advantages that make it a promising candidate for ultra-high-density memory applications and neuromorphic computing. However, challenges such as high forming voltage, low endurance, and poor uniformity have hampered the development and application of RRAM. To improve the uniformity of the resistive memory, this paper systematically investigates the HfOx-based RRAM by embedding nanoparticles. In this paper, the HfOx-Based RRAM with and without tungsten nanoparticles (W NPs) is fabricated by magnetron sputtering, UV lithography, and stripping. Comparing the various resistive switching behaviors of the two devices, it can be observed that the W NPs device exhibits lower switching voltage (including a 69.87% reduction in Vforming and a reduction in Vset/Vreset from 1.4 V/-1.36 to 0.7 V/-1.0 V), more stable cycling endurance (&gt;105 cycles), and higher uniformity. A potential switching mechanism is considered based on the XPS analysis and the research on the fitting of HRS and LRS: Embedding W NPs can improve the device performance by inducing and controlling the conductive filaments (CFs) size and paths. This thesis has implications for the performance enhancement and development of resistive memory.