Capacitation Process Research Articles

Belbin’s Team Role Theory and Shared Leadership for Universities Employment Services: New Bridges Between Graduates and Employers

Nowadays, higher education institutions are required to have a more significant role in society, especially by leading mediation among stakeholders and transferring their research results. In Spain, universities still do not have a substantial role in linking potential employers and graduates. In this indispensable context of transferability and collaboration, The University of Extremadura and the state Employment Office of the region of Extremadura signed an agreement with the aim of becoming bridges between students, former students and employers. To do so, the Internship and Employment Office (SEPYE) was launched to develop actions and projects that will increase the employability of students. In order to optimize the SEPYE, a diagnosis and capacitation process that allowed the training of the service’s staff was developed. This process was designed under a shared leadership perspective using Belbin’s team roles theory as a diagnosis tool. In this article, the description of the creation of the service, the training of its staff and the results of the strategy using Belbin’s theory will be described with the idea that this common leadership collaboration can be transferred to similar contexts.

Chicken Feathers-Derived Carbon Electrodes for Capacitive Deionization

Capacitive deionization (CDI) is an emerging technology which is being developed as a promising desalination alternative for charged species from salt water, being electrode materials as key drivers for highly efficient process. In this study, we report sustainable, scalable and stable carbon electrodes for CDI. Electrodes were synthesized from poultry chicken feathers waste using pyrolysis followed by chemical activation with potassium hydroxide at a 1:4 ratio to produce highly porous carbon. Poultry chicken feathers-activated carbon (CF-AC) were prepared and fabricated into electrodes using poly(vinyl alcohol) (PVA) binder and later crosslinked with glutaraldehyde (GA) to produce a PVA-GA polymer due to its hydrophilicity by acetylation reaction to improve the resistance of carbon material. Prepared materials were characterized using scanning electron microscopy, Fourier transform infrared, X-ray diffraction, Brunauer-Emmett-Teller and cyclic voltammetry. Fabricated CDI electrodes were used to investigate their performance for desalination, and exhibited different electrosorption capacity at different applied potentials. Modified electrode possessed good stability in shear conditions and CDI process was stable and reproducible around 16 electrosorption cycles. Salt removal capacity of PVA-GA-bonded CF-AC (PVA-GA-CF-AC) electrodes was found to be 3.89 mg g-1. The obtained outcomes offer important considerations of ions electrosorption and help advancing CDI system for water treatment and desalination.

Pinnwall: Heterogeneous Electrode Models from Integrating Machine Learning and Atomistic Simulation

Electrochemical energy storage always involves the capacitive process. The prevailing electrode model used to study such polarizable electrode-electrolyte systems is the Siepmann-Sprik model, which has been recently extended to study the metallicity in the electrode model by including the Thomas-Fermi screening length. Nevertheless, a further extension to heterogeneous electrode models is required. Here, we address this challenge by integrating the atomistic machine learning code (PiNN) [1] for generating the base charge [2] and response kernel [3] and the classical molecular dynamics code (MetalWalls). This leads to the development of the PiNNwall [4] interface. Apart from the cases of chemically doped graphene and graphene oxide electrodes as shown in this study, the PiNNwall interface also allows us to probe polarized oxide surfaces in which both the proton charge and the electronic charge can coexist. Therefore, this work opens the door for modelling heterogeneous and complex electrode materials often found in energy storage systems.[1] Shao, Y.; Hellström, M.; Mitev, P. D.; Knijff, L.; Zhang, C. PiNN: A python library for building atomic neural networks of molecules and materials. J. Chem. Inf. Model. 2020, 60, 1184.[2] Knijff, L.; Zhang, C. Machine learning inference of molecular dipole moment in liquid water. Mach. Learn.: Sci. Technol. 2021, 2, 03LT03.[3] Shao, Y.; Andersson, L.; Knijff, L.; Zhang, C. Finite-field coupling via learning the charge response kernel. Electron. Struct. 2022, 4, 014012.[4] Dufils, T., Knijff, L., Shao, Y. and Zhang, C. PiNNwall: heterogeneous electrode models from integrating machine learning and atomistic simulation. arXiv preprint arXiv:2303.15307. 2023.*This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (Grant Agreement No. 949012). We also acknowledge the support from the Centre for Interdisciplinary Mathematics (CIM) and the AI4Research initiative at Uppsala University.

Enhancing U(VI) removal by using biomass-derived hierarchical porous carbon/α-MnO2 nano fiber composites as high hybrid capacitance electrodes for capacitive deionization

The radioactive pollution caused by uranium containing wastewater generated during the nuclear fuel cycle seriously threatens human health and environmental safety. The electrosorption (or capacitive deionization, CDI) separation of U(VI) from wastewater has the advantages of high efficiency, low energy consumption, convenient operation, and no secondary pollution, making it a promising new separation technology. By combining double layer capacitive materials with pseudo capacitive materials, the specific capacitance and ion storage capacity of the composites can be significantly improved, thereby improving the electrosorption performance. This work used natural biomass as raw material to prepare hierarchical porous biocarbon through high-temperature pyrolysis and chemical activation, and then it was incorporated with hydrothermally synthesized α-MnO2 nanofibers to obtain novel composites (BC/α-MnO2) with high hybrid capacitance for U(VI) removal in CDI. The electrochemical characteristics of the composites and their electrosorption performances for U (VI) were respectively investigated in a three electrode system and a CDI device. The results suggested that BC/α-MnO2 exhibited an ideal capacitive behavior, and theoretical calculations indicated the synergistic effect of capacitive and diffusion control processes on ion storage. Among different BC/α-MnO2 electrodes, BC/α-MnO2-2 had the highest specific capacitance (130.48 F/g) and also the highest adsorption capacity for U (VI) (280.20 mg/g at 0.9 V and pH 4.0). The isotherms and kinetics of U (VI) electrosorption were consistent with the Langmuir and PFO models, respectively. The electrosorption mechanism was mainly related to the contribution of pseudocapacitance and EDL adsorption. Overall, BC/α-MnO2-2 exhibited ideal electrochemical properties and excellent electrsorption performance for U (VI) (high electrosorption capacity, fast kinetic rate, and good cycling stability), facile fabrication and environmentally friendly, and thus it has promising application in CDI treatment of radioactive wastewater.

A review on the distribution of relaxation times analysis: A powerful tool for process identification of electrochemical systems

The Distribution of Relaxation Times (DRT) analysis gained considerable attention for its ability to reveal detailed information about complex electrochemical processes without requiring a priori knowledge. This review provides a comprehensive insight into different methods of the DRT analysis, their mathematical bases, and the latest approaches to acquiring and analyzing frequency and time domain data. The analysis is based on the deconvolution of frequency domain data into a distribution function of gains at (pre-specified) relaxation times in the time domain, which improves the spectral resolution and separability of electrochemical processes. It provides valuable information about different electrochemical processes on different time scales, making it particularly useful for the characterization of both materials and electrochemical systems. The DRT analysis can be applied to arbitrary spectra containing electromagnetic effects, resistive–capacitive processes, and solid-state diffusion. To enhance process identification, a post-processing step involving peak analysis with Gaussian or RQ-distribution peaks is presented and the assignment of peak patterns induced by distributed processes like solid-state diffusion is discussed. In addition, a step-by-step workflow for the DRT analysis is provided to guide researchers from data acquisition and validation techniques to calculation and interpretation of the distribution function.

Analysis of voltametric data from electrochemical capacitor electrode materials: Method refinement for improved outcomes

A revised model is proposed to improve analysis outcomes from the voltametric analysis of electrochemical capacitor materials and electrodes at different sweep rates (v). Conventional analysis involves breaking down the voltametric current (i) into contributions from capacitive processes (i∝v) and diffusional processes (i∝v1/2). The proposed model introduces a resistance or residual current term, improving the goodness of fit and the quality of data interpretation. This is demonstrated by application of the revised model to artificial voltametric data, electrical double layer capacitor data, as well as pseudo-capacitive electrode data. Analysis with this model also demonstrates the importance of understanding resistive processes in electrode systems, in particular differentiating resistance in the act of charge storage (double layer and redox processes), and ohmic electrode resistance.

The compound YK 3-237 promotes pig sperm capacitation-related events

Before fertilization of the oocyte, the spermatozoa must undergo through a series of biochemical changes in the female reproductive tract named sperm capacitation. Spermatozoa regulates its functions by post-translational modifications, being historically the most studied protein phosphorylation. In addition to phosphorylation, recently, protein acetylation has been described as an important molecular mechanism with regulatory roles in several reproductive processes. However, its role on the mammal’s sperm capacitation process remains unraveled. Sirtuins are a deacetylase protein family with 7 members that regulate protein acetylation. Here, we investigated the possible role of SIRT1 on pig sperm capacitation-related events by using YK 3-237, a commercial SIRT1 activator drug. SIRT1 is localized in the midpiece of pig spermatozoa. Protein tyrosine phosphorylation (focused at p32) is an event associated to pig sperm capacitation that increases when spermatozoa are in vitro capacitated in presence of YK 3-237. Eventually, YK 3-237 induces acrosome reaction in capacitated spermatozoa: YK 3-237 treatment tripled (3.40 ± 0.40 fold increase) the percentage of acrosome-reacted spermatozoa compared to the control. In addition, YK 3-237 induces sperm intracellular pH alkalinization and raises the intracellular calcium levels through a CatSper independent mechanism. YK 3-237 was not able to bypass sAC inhibition by LRE1. In summary, YK 3-237 promotes pig sperm capacitation by a mechanism upstream of sAC activation and independent of CatSper calcium channel.

Fabrication of CH3NH3SnCl3 perovskite nanocrystal-based electrode for supercapacitor devices application

Lead-free halide perovskites nanocrystals (NCs) have been widely used not only in the field of optoelectronics but also in energy storage applications like electrochemical supercapacitors, which could replace electrochemical batteries due to their high power density and long cycle life. The low energy density of supercapacitors is one of the main reasons why they have limited commercial applications. Herein, we have reported synthesis of 3D methylammonium tin chloride perovskite (MASnCl3) nanocrystals (NCs) via a ligand-assisted re-precipitation process (LARP) and determined its performance as an electrochemical supercapacitor. The formation of MASnCl3 NCs is confirmed by different characterization tools. The supercapacitor performances of the synthesized NCs are studied by using three-electrode electrochemical measurements. The maximum specific capacitance, energy density, and power density are found to be 2050 Fg−1, 12 kWKg−1, and 102 WhKg−1, respectively. The charge storage mechanism is estimated from the power law equation by studying the diffusion-limited and capacitive processes and it has been found that the capacitance is 94.16 % capacitive to 5.84 % diffusive in nature. The supercapacitor performance of the synthesized MASnCl3 NCs are studied by fabricating a metal coin-based two-electrode system in which PVA-H2SO4 as solid state electrolyte and NCs act as an active material. The device has retained 80.7 % of its initial specific capacitance value even after 1000 GCD cycles. Interestingly, the developed device showed almost similar gravimetric capacitance value and is enabled to glow a light emitting diode (LED) smoothly.

Na+/H+ Exchangers (NHEs) in Mammalian Sperm: Essential Contributors to Male Fertility.

Na+/H+ exchangers (NHEs) are known to be important regulators of pH in multiple intracellular compartments of eukaryotic cells. Sperm function is especially dependent on changes in pH and thus it has been postulated that NHEs play important roles in regulating the intracellular pH of these cells. For example, in order to achieve fertilization, mature sperm must maintain a basal pH in the male reproductive tract and then alkalize in response to specific signals in the female reproductive tract during the capacitation process. Eight NHE isoforms are expressed in mammalian testis/sperm: NHE1, NHE3, NHE5, NHE8, NHA1, NHA2, NHE10, and NHE11. These NHE isoforms are expressed at varying times during spermatogenesis and localize to different subcellular structures in developing and mature sperm where they contribute to multiple aspects of sperm physiology and male fertility including proper sperm development/morphogenesis, motility, capacitation, and the acrosome reaction. Previous work has provided evidence for NHE3, NHE8, NHA1, NHA2, and NHE10 being critical for male fertility in mice and NHE10 has recently been shown to be essential for male fertility in humans. In this article we review what is known about each NHE isoform expressed in mammalian sperm and discuss the physiological significance of each NHE isoform with respect to male fertility.

Metal-organic framework-derived Nickel Diselenide grown in situ on carbon for high-performance Li storage

The creation of innovative anodes to replace graphite in lithium-ion batteries (LIBs) is necessary to meet the rising demand for energy storage devices. Based on the large Li storage capacity, transition metal selenides (TMSs) draw considerable interest for LIBs. However, volume expansion of TMSs during the cycling process hinders their large-scale commercial application for LIBs. Herein, the NiSe2 particle grown in situ on the porous carbon framework (NiSe2@C) is prepared by selenization of metal-organic frameworks (MOFs) in an argon atmosphere. NiSe2@C exhibits a high reversible Li storage capacity (770 mAh g−1 at 200 mA g−1after 100 cycles), long cycling life (308 mAh g−1 at 1 A g−1 after 1000 cycles), and good rate capability (214 mAh g−1 at 5.0 A g−1). The long cycling performance can be attributed to the fact that NiSe2@C can withstand volume expansion during the Li+ insertion and desertion process. Furthermore, cyclic voltammetry (CV) tests at various scan rates are conducted to investigate the kinetics of NiSe2@C for LIBs, indicating that the Li storage behaviour of NiSe2@C is primarily controlled by the capacitive process. The fabrication of the TMS@C composites by selenization of MOFs is a potential way to obtain anodes for high-performance Li storage.

Energy storage characteristics and mechanism of organic-conjugated polyanthraquinoneimide for metal-free dual-ion batteries

Organic materials have gained significant attention in the battery energy storage field due to their good reaction kinetics and designable properties. However, conventional organic materials typically exhibit poor cycling stability in dual-ion batteries because of their high solubility and low electron conductivity. Herein, an organic conjugated polyanthraquinoneimide (PAQI) with stacked layered porous nanosheet structures by a one-step solvothermal process. After polymerization, not only the solubility of PAQI in electrolytes was reduced, but also the utilization of the active site (C=O) was significantly increased to enhance the electronic conductivity. Moreover, PAQI also exhibited a high ion diffusion coefficient (0.946 × 10−10 ∼ 1.293 × 10−10 cm2 s−1) and showed excellent electrochemical performance as the anode for a metal-free dual-ion battery, with a discharge specific capacity of up to 128 mAh g−1 and a capacity retention rate of 80% after 200 cycles under a high rate of 2 C (1 C = 228 mA g−1). Meanwhile, cyclic voltammetry tests and reaction kinetic calculations revealed that PAQI was a pseudocapacitive storage mechanism combining diffusion control and surface capacitance processes (the capacitance contribution is 82.59 % at a scan rate of 0.9 mV s−1). These abundant stacked layered porous nanosheet structures provided a new route for research and development of the next-generation green metal-free dual-ion batteries.

On the role of inductive loops at low frequencies in PEM electrolysis

Inductive loops at low frequencies have been observed in the electrochemical impedance spectra (EIS) of various electrochemical cells. Although different physicochemical models for this phenomenon have been suggested in many other applications, this topic has not been widely discussed in the field of proton exchange membrane (PEM) electrolysis.In this article, low-frequency inductive loops in PEM electrolysis cells and their impact on cell performance are analyzed. We show that this phenomenon is reproducible and occurs with different cell materials and setups. Its impact increases with increasing current density and decreasing temperature. At extreme conditions (7 A∙cm−2, 40 °C) we show that the negative polarization resistance of the inductive process can exceed the capacitive polarization processes by a factor of three, resulting in a direct current resistance less than the high frequency series resistance of the cell.

Pseudocapacitive deionization of high concentrations of hexavalent chromium using NiFe-layered double hydroxide/polypyrrole asymmetric electrode

The wastewater polluted by high concentrations of aqueous hexavalent chromium (Cr(VI)) has serious adverse effects on ecological environment and human health. As a burgeoning, environmental-friendly, and promising wastewater treatment technology, capacitive deionization (CDI) process for efficient removal of aqueous Cr(VI) needs to be investigated. In this work, pseudocapacitive NiFe-layered double hydroxide/ polypyrrole (NiFe-LDH/PPy, denoted as NiFe/PPy) electrode was synthesized by the in-situ polymerization of PPy on the NiFe-LDH surface. Results of characterizations manifested that NiFe/PPy had the chain spherical structure of PPy. In particular, excellent PPy provides effective reversible capacitance and ion diffusion and improves the conductivity and pseudocapacitance performance of NiFe-LDH. Then, the NiFe/PPy anode and activated carbon (AC) cathode were assembled into the CDI cell for capacitive removal of high concentrations of aqueous Cr(VI). In 20 mL/min of flow velocity, 1.2 V, and 100 mL 100 mg/L of Cr(VI) solution, the Cr(VI) electrosorption capacity and removal ratio attained to 47.95 mg/g and 95.89%, respectively. The electrosorption of Cr(VI) slightly decreased under the common competing anions of Cl−, NO3−, SO42−, HCO3−, and CO32−. Based on Langmuir isotherm model, the maximum theoretical removal capacity of NiFe/PPy for Cr(VI) was 111 mg/g. The electrostatic attraction, reduction, and surface complexation played primary roles in the CDI system of NiFe/PPy//AC asymmetric electrodes. The outstanding electrosorption performance makes this CDI system have a favorable application prospect in the actual wastewater treatment containing high concentrations of Cr(VI).

Boosting capacitive deionization of monovalent and hardness ions using Ti3C2Tx MXene as an intercalation-type pseudocapacitive electrode

MXene is a promising electrode material for energy storage and capacitive deionization (CDI) applications. In this study, a viable approach was developed to synthesize Ti3C2Tx at different LiF/Ti3AlC2 mass ratios of 0.5 – 2.0 for the enhanced CDI to remove different cations including hardness (Mg2+ and Ca2+), salt (Na+), and ammonium (NH4+) ions. The Ti3C2Tx was fabricated using the hydrothermal method in the presence of LiF and HCl. The optimal mass ratio of 1.0 results in the formation of hydrophilic and well-delaminated nanosheets. Moreover, the Ti3C2Tx-1 shows an interconnected meso-macroporous structure with a specific surface area of 48.4 m2/g. The Ti3C2Tx MXene exhibits an exceptional electrochemical performance with a specific capacitance of 540 F g−1 at 5 mV s−1 in the presence of 1 M H2SO4. A remarkable desalination performance with the salt adsorption capacity (SAC) of 39.7 mg g−1 is obtained. The well-suited lattice fringe and inter-connected porous structure of the Ti3C2Tx nanosheets accelerate the electron transport, which can maintain the cyclability over 50 cycles. This enhanced electron transport leads to an improved deionization capability during the CDI process. Moreover, the Ti3C2Tx-based CDI device exhibits prominent selectivity for hardness ions with SACs of 43.8 and 39.5 mg g−1 for Ca2+ and Mg2+, respectively. The SAC of NH4+ can also be up of 39.7 mg g−1 at 1000 mg L−1. Results in this study clearly elaborate the promising potentiality for the utilization of MXene as an effective electrode material for desalination and other electrochemical applications.

Electrochemical Impedance Spectroscopy of Amorphous TiO2 Protected Photocathodes Under Hydrogen Evolution Conditions

Despite widespread use of electrochemical impedance spectroscopy (EIS) to study multi-layer photoelectrochemical (PEC) cells, the appropriate equivalent circuits describing these devices under hydrogen evolution conditions are not commonly investigated.1 This creates ambiguity with respect to the pathways of charge recombination and ionic movement within layers of the device during operation, therefore limiting rational development of future PEC devices. In this study, amorphous TiO2 (a-TiO2) protected silicon photocathodes have been investigated using EIS to show that these devices behave according to the Maxwell circuit during hydrogen evolution, which occurs when the semiconductor is in depletion. Therefore, there are two simultaneous processes occurring in parallel and on different timescales. While the high frequency component is the result of the depletion region in the semiconductor, the low frequency component of this circuit is found to originate from the a-TiO2 itself, implying a capacitive charging process of this protective overlayer during PEC cell operation. Studies to isolate the physical mechanism of capacitive charging in the a-TiO2 from a range of possibilities such as proton intercalation and vacancy migration have been carried out. This result is important for the development of future PEC devices using emerging semiconductors which heavily rely on the a-TiO2 overlayer in acidic electrolytes, such as Cu2O and Sb2Se3, where this low frequency process has previously been observed.1 Using the Maxwell circuit for a-TiO2 protected photocathodes under hydrogen evolution conditions, one can independently determine properties of the semiconductor, such as the depletion capacitance and doping density, and the protective overlayer in these PEC devices under hydrogen evolution conditions. With this baseline, EIS can continue to aid the development of PEC cells as additional overlayers are developed and tested for further performance improvements. Yang, W. et al. Operando Analysis of Semiconductor Junctions in Multi-Layered Photocathodes for Solar Water Splitting by Impedance Spectroscopy. Adv. Energy Mater. 11, 2003569 (2021). Figure 1

Two-step pyrolysis-hydrothermal synthesis of hierarchical nickel‑cobalt phosphate nanoflakes decorated on g-C3N4 nanosheets for high-performance hybrid supercapacitors

Ni-Co phosphate (NCP) nanoflakes and graphitic carbon nitride (g-CN) nanosheets are combined to fabricate a composite electrochemical electrode via a two-step pyrolysis-hydrothermal process. Physicochemical characterizations reveal the proper formation of the target material with highly porous morphology and crumpled nanostructures with highly active surface sites. The electrochemical properties of the NCP/g-CN composite in a three-electrode system depict excellent pseudocapacitive performance due to the faradaic behavior and redox activities of both NCP and g-CN with a very high capacitive value of 2000 F/g (242 mAh/g) @ 1 A/g current density. The charge storage behavior is mainly dominated by the surface-controlled (capacitive) process at higher scan rates, which is mostly dominated by surface pseudocapacitance, whereas, at low scan rates both surface-controlled and diffusion-controlled processes are equally active to provide a combined battery-capacitor behavior. Due to this, a hybrid supercapacitor device, fabricated with NCP/g-CN as positive and activated carbon (AC) as a negative electrode, showed excellent energy density (50 Wh/kg) along with exceptional cyclability (∼90 % capacity retention over 5000 cycles). Additionally, the redox-rich g-CN matrix within the composite dominates the sluggish diffusion-controlled process at higher scan rates to enhance the capacitive process without compromising the charge storage kinetics, thus enhancing the power density to ∼7.0 kW/kg. This excellent energy-power performance of the NCP/g-CN//AC hybrid supercapacitor cell (HSC) is better than some of the commercial devices like lead-acid, Ni-Cd, and Ni-MH batteries, indicating potential applications in next-generation charge storage devices.

Investigation of diffusivity in nanometer‐thick yttria‐stabilized zirconia by chronoamperometry and its formalism

AbstractThis work aims to demonstrate that chronoamperometry is a valuable tool for determining diffusivities in all‐solid‐state nanometer‐thick cells. The transient current in chronoamperometry of electrochemical cells under constant voltage is described by firstly considering purely capacitive processes, defined by RC circuit equations, and then purely diffusive processes, by Cottrell's equations. The physical meaning of the equations has been amply described in liquid cells with porous electrodes but scarcely in solid‐state cells. Thus, we studied Metal/Insulator/Metal nano‐cells with Ru and Au electrodes, Yttria Stabilized Zirconia (YSZ) electrolyte at temperatures between 50 and 170°C and voltages between 0.5 V and 1.5 V, where non‐Faradaic processes occur. The calculated diffusive and capacitive contributions at different temperatures obey the Arrhenius law. The activation energy was associated with vacancies, the major carrier during electrical transport. The analysis discusses other parameters, such as capacitance, effective concentration, and leakage current. The experimental diffusivity of YSZ electrolytes was compared with diffusivity values obtained by the statistical moment method.

SofTer: Theory, software, and video tutorial for simulating capacitive deionization with tertiary current distributions

Capacitive deionization (CDI) is a desalination method that has been expanding substantially in recent years. As processes are getting more complex, corresponding developments in theory and software are necessary to keep up and drive future research. In this work, we derive a new CDI theory based on a tertiary current distribution, meaning each ionic species is resolved individually in a unified framework in 1D/2D. The results show that this approach is ideal for simulations with multiple ionic species and materials that affect cations and anions differently. Direct examples include such as intercalation materials and membranes. It is also effective for incorporating electrode replenishment in flow-electrode CDI (FCDI). By benchmarking with traditional methods, we demonstrate that numerical stability is a central limitation of traditional methods for these applications. The results identify physical processes involving rapid changes to cause major instabilities. This can thus be handled by introducing specific numerically stabilizing factors. Finally, the theory is compiled into comprehensive software that researchers can straightforwardly apply in future studies without having to reconstruct methods from scratch. A corresponding video tutorial has also been deposited. In conclusion, the work pushes the limits of the simulation capabilities in a wide range of CDI processes.

In-situ fabricated copper-holmium co-doped cobalt ferrite nanocomposite with cross-linked graphene as novel electrode material for supercapacitor application

Recently, hybrid electrode materials based on cross-linked carbon analogues have gained significant consideration for their excellent cyclic stability and high specific capacities. This work presents the fabrication of copper and holmium co-doped cobalt ferrite with cross-linked graphene (denoted as CH-CoF/CLG) through one-step hydrothermal route, as novel electrode material for supercapacitor study. The electrochemical performance of CH-CoF/CLG along with its counterparts i.e., CoF, CH-CoF was evaluated through CV, GCD, and EIS analysis using three electrode system. The specific capacitance (Csp) of CoF, CH-CoF, and CH-CoF/CLG nanocomposite at a sweep rate of 5 mV/s is 458 F/g, 762 F/g, and 1258 F/g, respectively, within a potential range of 0.0 to 0.6 V. For CH-CoF/CLG, the calculated slope value (b = 0.84) using power law showed that the energy storage mechanism is based on both capacitive and diffusional processes. The GCD test showed that CH-CoF/CLG exhibited long discharge time (td = 615 s), as compared to CH-CoF (td = 409 s), and CoF (td = 264 s). Moreover, after the fabrication of CH-CoF with CLG, the value of equivalent series resistance (ESR) and charge transfer resistance (Rct) for CH-CoF/CLG were decreased to 0.74 Ω and 0.84 Ω, compared to CoF (1.18 Ω and 1.29 Ω) and CH-CoF (0.88 Ω and 1.0 Ω). When tested for cyclic stability, CH-CoF/CLG displayed insignificant loss in performance up to 3000 cyclic runs. The high supercapacitor performance of CH-CoF/CLG can be assigned to the combined effects arising from the co-doping of transition metal and rare earth metal ions (Cu+2 and Ho+3) into CoF lattice, porous cross-linked structure, high wettability, low intrinsic resistance, and easy accessibility of KOH ions into deep layers of active material. As obtained results deduce that the CH-CoF/CLG nanocomposite is a competent capacitive material for energy storage.

Three-Dimensional Nanoporous CNT@Mn3O4 Hybrid Anode: High Pseudocapacitive Contribution and Superior Lithium Storage

A composite electrode of carbon nanotube CNT@Mn3O4 nanocable was successfully synthesized via direct electrophoretic deposition onto a copper foil, followed by calcination. By uniformly depositing Mn3O4 nanoparticles on CNTs, a nanocable structure of CNT@Mn3O4 can be formed, where the CNT acts as a “highway” for electrons and ions to facilitate fast transportation. Moreover, capacitive energy storage processes play a crucial role in lithium (Li) storage, especially during high scan rates. The significant contribution of capacitance is highly advantageous for the rapid transfer of Li+ ions, which ultimately results in an improved reversible capacity and prolonged cycle stability of the battery. A high specific capacity of 1367 mAh g−1 was maintained over 300 charge–discharge cycles at a current density of 1 A g−1, indicating excellent capacity retention and an extended cycle life. Furthermore, the synthesis process was facile and cost-effective, obviating the need for complex procedures such as mixing and pasting. Additionally, no binder was required, thereby enhancing battery quality efficiency.