Electrochemical Storage Devices Research Articles

Screen-printed electrodes based on hybrids of poly(ortho-ethoxyaniline) and reduced graphene oxide

Screen-printed electrodes (SPEs) based on hybrids of the conducting polymer poly(ortho-ethoxyaniline) (POEA), graphene oxide (GO) and reduced graphene oxide (rGO) were produced and characterized. The SPEs were produced from conductive inks based on graphite and alkyd resin and were modified with hybrids of POEA with GO, and rGO. The hybrids POEA-GO and POEA-rGO were produced by chemical polymerization of o-ethoxyaniline (orthophenitidine) in 1.0 mol L−1 with GO or rGO dispersed into the monomer solution. The SPEs were modified by the replacement of 5 % in mass of graphite by 5 % in mass of POEA-GO or POEA-rGO hybrids. The hybrids were characterized by Raman and FT-IR spectroscopies and XRD analyses. The modified SPEs, SPE/POEA, SPE/POEA-GO, and SPE/POEA-rGO were characterized by scanning electron microscopy, and by cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The electrodes based on the rGO hybrid, SPE/POEA-rGO, showed a significant reduction of the charge transfer resistance obtained by EIS by a factor of 3 compared with SPE/POEA, from 4.62 kΩ to 1.48 kΩ, without changing the redox behaviour of POEA. The methodology used to produce SPE/POEA-rGO is a simple, effective, scalable, and low-cost alternative to produce POEA-based electrodes for applications such as in electrochemical sensors and charge storage devices.

Biopolymer blend composite films based on polyvinyl alcohol/ chitosan/ grape seed extract via green approach for flexible optoelectronic devices

The flourishing environmental concerns have grabbed the attention of researchers developing environmentally supportive materials in various fields. A green approach was used to create biopolymer blend composites based on polyvinyl alcohol (PVA) and chitosan (CS) doped with various concentrations of grape seed (GS). Various analytical techniques, such as Fourier-transform infrared spectroscopy (FTIR), UV–visible (UV) spectra, field emission scanning electron microscope (FE-SEM) and differential scanning calorimetry (DSC) were used to evaluate the optical, structural and thermal properties of the prepared blend composites. The optical properties of blend composites were determined by UV spectroscopy and the findings revealed that absorption intensity increased with increasing GS, while bandgap energy decreased from 4.18 eV for pure blend to 2.91 eV for blend/15 wt% GS. The homogeneous distribution of GS particles in the biopolymer blend was identified with FE-SEM images. DSC results showed that increasing the GS content increased the glass transition temperature of the blend composites. The AC conductivity and dielectric constant were measured using the LCR meter. The conductivity rises with increasing frequency and dosage of GS, with the greatest conductivity obtained at 15 wt% loading. In comparison to a pure blend, it was discovered that the inclusion of 15 wt% GS enhanced the tensile strength by 50%, hardness by 17% and the reduction in elongation at break by 19 %. As a consequence, environmentally friendly PVA/CS/GS biopolymer blend composites with excellent mechanical, thermal, electrical, and dielectric parameters might be a viable green option for flexible electronic, electrochemical and energy storage devices.

A high-performance asymmetric supercapacitor based on morphologically tuned CoB anode and heterostructured graphitic carbon nitride/MoSe2 cathode

Transition metal borides (TMBs) are among the fascinating electrode materials for supercapacitors. TMBs have high theoretical capacity, however the narrow potential window, structural deterioration during redox cycling, and fairly small surface area remains a major limitation. To resolve these, we synthesize cobalt boride (CoB) in different morphologies by initiating the reaction with different precursors namely, zeolitic imidazolic framework-67 (ZIF-67), Co layered hydroxide (SLH), and CoCl2. CoB synthesis from ZIF-67, SLH, and CoCl2 results in nanoflower, nanoplate, and nanowire morphology. CoB in nanowire morphology, shows highest charge storage of 273 F g−1 at 1 A g−1 due to 1D structure that endow plentiful surface area, high conductivity, ample electroactive sites and structural stability. We also engineer layer structure of molybdenum selenide (MoSe2) to favorably expand interlayer distance to enhance atomic surface exposure by successfully inserting graphitic carbon nitride (gCN) nanosheets into adjacent MoSe2 layers. Herein, asymmetric supercapacitor, CoB||gCN/MoSe2 displays a wide potential window of 1.5 V, remarkable energy density of 97.44 Wh kg−1 at 621.3 W kg−1 along with 93 % capacitance retention after 10 k GCD cycles. The research reported here demonstrates the great application potential for the asymmetric devices based on CoB||gCN/MoSe2 for the future of electrochemical charge storage devices.

Axial heteroatom (P, S and Cl)-decorated Fe single-atom catalyst for the oxygen reduction reaction: a DFT study.

An FeN4 single-atom catalyst (SAC) embedded in a graphene matrix is considered an oxygen reduction reaction (ORR) catalyst for its good activity and durability, and decoration on the Fe active site can further modulate the performance of the FeN4 SAC. In this work, the axial heteroatom (L = P, S and Cl)-decorated FeN4 SAC (FeN4L) and pure FeN4 were comparatively studied using density functional theory (DFT) calculations. It was found that the rate-determining step (RDS) in the ORR on pure FeN4 is the reduction of OH to H2O in the last step with an overpotential of 0.58 V. However, the RDS of the ORR for the axial heteroatom-decorated FeN4L is the reduction of O2 to OOH in the first step. The axial P and S heteroatom-decorated FeN4P and FeN4S exhibit lower activity than pure FeN4 since the overpotentials of the ORR on FeN4P and FeN4S are 1.02 V and 1.09 V, respectively. Meanwhile, FeN4Cl exhibits the best activity towards the ORR since it possesses the lowest overpotential (0.51 V). The main reason is that the axial heteroatom decoration alleviates the adsorption of all the species in the whole ORR, thus modulating the free energy in every elementary reaction step. A volcano relationship between the d band center and the ORR activity can be determined among the axial heteroatom-decorated FeN4L SACs. The d band center of the Fe atom in various FeN4L SACs follows the order of FeN4 > FeN4Cl > FeN4S > FeN4P, whereas the overpotential of the ORR on various catalysts follows the order of FeN4Cl > FeN4 > FeN4S ≈ FeN4P. ΔG(*OH) is a simple descriptor for the prediction of the ORR activity of various axial heteroatom-decorated FeN4L, although the RDS in the ORR is either the first step or the last step. This paper provides a guide to the design and selection of the ORR over SACs with different axial heteroatom decorations, contributing to the rational design of more powerful ORR electrocatalysts and achieving advances in electrochemical conversion and storage devices.

High load, long cycle and flexible zinc-ion hybrid supercapacitors

Zinc-ion hybrid supercapacitor (ZIHS) combines the advantages of both batteries and capacitors to achieve high operating voltage, high energy and high power density.It is considered as a novel sustainable electrochemical energy storage device, but the problems of poor cycling stability and low energy density in most ZIHS still need to be solved. In this work, MnO2@ carbon cloth cathode with high load of 17.2 mg cm−2 was fabricated by in-situ deposition and hydrothermal treatment, and the active carbon extracted from banana peel was used as the anode. The assembled flexible ZIHS device exhibits a remarkable combination of high energy density and high specific capacity, attributed to the synergistic effect achieved by employing two distinct morphologies of MnO2 composites. Notably, the energy density of 674 μWh cm−2 can be maintained at a power density of 999 μW cm−2 In addition, the aqueous ZIHS retention rate was 94.56 % in 80,000 cycles. Therefore, the research results are of great significance to develop a safe, reliable and high electrochemical performance storage device.

Redox Active Organic Liquids for Energy Storage

The necessity to move to renewable energy sources has increased over the last few years. However, to ensure a good transition and effective energy supply, efficient, cheap, and green technologies are required as grid-level storage.1 Redox-Active Organic Materials (ROMs) are a fast-growing research topic in different electrochemical storage devices. Their advantageous characteristics of being formed from highly abundant elements, having a high electrochemical tunability, ease of handling and device processing, and high versatility for a variety of energy storage applications make ROMs attractive.1–3 Redox-Active Liquids (RALs) are themselves a new trend within the category of ROMs because the physical properties of organic liquids are advantageous for some storage devices.4–6 Those advantages include no requirement for materials processing after synthesis, high miscibility and/or high solubility with battery electrolytes, the ability to be used as a solvent themselves without any additional additives,4,5 and the avoidance of surface-related changes e.g., dendrites.7 RALs have been studied as mediators or active materials in the context of different applications such as supercapacitors,6,8 conventional,4,5,9 and hybrid-flow batteries.10,11 In this work, we present the synthesis and physio-chemical characterization of different RALs that can be used in such energy storage devices. The characterization results supported by computational analyses were used to investigate the correlation between the chemical structure and the electrochemical properties of the compounds. The obtained information was then further used to inform the design of further compounds with enhanced electrochemical properties.(1) Schon, T. B.; McAllister, B. T.; Li, P. F.; Seferos, D. S. The Rise of Organic Electrode Materials for Energy Storage. Chem Soc Rev 2016, 45 (22), 6345–6404. https://doi.org/10.1039/c6cs00173d.(2) Kwon, G.; Ko, Y.; Kim, Y.; Kim, K.; Kang, K. Versatile Redox-Active Organic Materials for Rechargeable Energy Storage. Acc Chem Res 2021, 54 (23), 4423–4433. https://doi.org/10.1021/acs.accounts.1c00590.(3) Lee, S.; Hong, J.; Kang, K. Redox-Active Organic Compounds for Future Sustainable Energy Storage System. Advanced Energy Materials. Wiley-VCH Verlag August 1, 2020. https://doi.org/10.1002/aenm.202001445.(4) Zhao, Y.; Zhang, J.; Agarwal, G.; Yu, Z.; Corman, R. E.; Wang, Y.; Robertson, L. A.; Shi, Z.; Doan, H. A.; Ewoldt, R. H.; Shkrob, I. A.; Assary, R. S.; Cheng, L.; Srinivasan, V.; Babinec, S. J.; Zhang, L. TEMPO Allegro: Liquid Catholyte Redoxmers for Nonaqueous Redox Flow Batteries. J Mater Chem A Mater 2021, 9 (31), 16769–16775. https://doi.org/10.1039/d1ta04297a.(5) Robertson, L.; Udin, M. A.; Shlrob, I. A.; Moore, J. S.; Zhang, L. Liquid Redoxmers for Nonaqueous Redox Flow Batteries. ChemSusChem 2023, e202300043. https://doi.org/10.1002/CSSC.202300043.(6) Fontaine, O. A Deeper Understanding of the Electron Transfer Is the Key to the Success of Biredox Ionic Liquids. Energy Storage Mater 2019, 21, 240–245. https://doi.org/10.1016/J.ENSM.2019.06.023.(7) Bao, J.; Li, C.; Zhang, F.; Wang, P.; Zhang, X.; He, P.; Zhou, H. A Liquid Anode of Lithium Biphenyl for Highly Safe Lithium-Air Battery with Hybrid Electrolyte. Batter Supercaps 2020, 3 (8), 708–712. https://doi.org/10.1002/BATT.202000092.(8) Mourad, E.; Coustan, L.; Lannelongue, P.; Zigah, D.; Mehdi, A.; Vioux, A.; Freunberger, S. A.; Favier, F.; Fontaine, O. Biredox Ionic Liquids with Solid-like Redox Density in the Liquid State for High-Energy Supercapacitors. Nature Materials 2016 16:4 2016, 16 (4), 446–453. https://doi.org/10.1038/nmat4808.(9) Chen, H.; Niu, Z.; Zhao, Y. Redox-Active Binary Eutectics: Preparation and Their Electrochemical Properties. Electrochem commun 2021, 126. https://doi.org/10.1016/j.elecom.2021.107028.(10) Shimizu, A.; Takenaka, K.; Handa, N.; Nokami, T.; Itoh, T.; Yoshida, J.-I.; Shimizu, A.; Takenaka, K.; Yoshida, J.; Handa, N.; Nokami, T.; Itoh, T. Liquid Quinones for Solvent-Free Redox Flow Batteries. Advanced Materials 2017, 29 (41), 1606592. https://doi.org/10.1002/ADMA.201606592.(11) Chen, N.; Chen, D.; Wu, J.; Lai, Y.; Chen, D. Polyethylene Glycol Modified Tetrathiafulvalene for High Energy Density Non-Aqueous Catholyte of Hybrid Redox Flow Batteries. Chemical Engineering Journal 2023, 462. https://doi.org/10.1016/j.cej.2023.141996.

Improving the Electronic Conductivity of Alluaudite Na2.5Fe1.75(SO4)3 Cathodes for Na-Ion Batteries

The increasing dependency on batteries in modern technology has led to an ever-increasing demand that cannot be met by Li-ion batteries (LIBs) alone. The push towards using renewable energy and electric vehicles, coupled with the limited reserves of lithium resources is encouraging research into alternative options for electrochemical storage devices. Na-ion batteries (SIBs) are a promising alternatives due to the similarity of their chemistry to LIBs. This allows for utilisation of analogous materials and methods already in place for LIBs. Furthermore, SIBs are more economically viable and environmentally sustainable due to the abundance of the elements that can be utilised as electrode active materials. For example, SIB cathodes, such as Na2.5Fe1.75(SO4)3, can be synthesised from precursor materials that are widely available by-products of industry. The polyanionic framework of Na2.5Fe1.75(SO4)3 has three 3-dimensional vacancies within it, in which Na-ions de/intercalate.[1] However, the performance of Na-ion batteries is hindered by the low electronic conductivity of these polyanionic compounds, affecting the flow of electrons through the material and the reversible movements of the Na ions.[2] To address this issue, previous reports have shown that using a conductive additive such as carbon black and graphene oxides can increase the electronic conductivity of Na ion cathode materials and improving battery performance.[3]In this work, we investigate a non-stoichiometric alluaudite phase Na2.5Fe1.75(SO4)3 material (NFS), produced by a ball-milling-assisted solid-state synthesis. A study of the effects of variables on the ball milling process using the was carried out. A multi-step process involving a repetition of the ball milling and annealing was used to decrease particle size and eliminate impurities. The results were compared regarding particle size, impurities present, conductivity and battery performance. The obtained materials were characterised using X-ray diffraction, scanning electron microscopy and electrochemical impedance spectroscopy. The materials were tested as cathodes in sodium half-cells with 1 mol/L NaClO4 in ethylene carbonate (EC)/ propylene carbonate (PC) electrolyte. The additional ball milling and annealing steps saw a significant decrease in impurities present across all variations in methodology. All batteries show three redox peaks in their differential capacity plots, demonstrating that all three vacancies within the polyanionic framework of Na2.5Fe1.75(SO4)3 are active during charge and discharge. The best performing electrode achieved a capacity of 80 mAh/g using only C45 as a conductive additive. These are promising results that are expected to improve with further studies researching the addition of RGOs and MXenes into the ball milling process. These composite electrodes will be prepared by combining rGOs/MXenes with the NFS precursors during the synthesis process of Na2.5Fe1.75(SO4)3 to enhance battery performance further.

Lutetium Gallium Garnet (Lu3Ga5O12): A potential material for Supercapacitor and Pesticide detection applications

Rare earth gallium garnets possess numerous applications due to their excellent physical and chemical properties. The bifunctional applications from Lu3Ga5O12 can indeed open a new era for gallium garnets. The electrochemical storage devices and electrochemical detection of pesticides using Lu3Ga5O12 offer a unique perspective to the other nanocomposites. Herein, Lu3Ga5O12 was synthesized via a simple citrate gel-matrix method. Analytical techniques such as XRD, Raman, UV-Vis Spectroscopy, FE-SEM, XPS and BET examined the phase purity, crystallinity, optical properties, surface morphology, oxidation state, pore size etc. Electrochemical measurements, including CV, GCD, and EIS, validate that the as-prepared Lu3Ga5O12 exhibits a remarkable specific capacitance of about 658 Fg-1 at 1 Ag-1. It also provides a higher capacitive retention rate of 88.41% for 5000 cycles at 5 Ag-1. It is then employed to fabricate an asymmetric device for its practical applications and exhibits a capacitive retention rate of about 74.88% and 95.02% of coulombic efficiency for 5000 cycles at 4 Ag-1. A simple, biocompatible sensing platform for the detection of imidacloprid was proposed. It establishes a linear relationship between sensing current and concentration from DPV with imidacloprid concentration ranging from 0.1 to 26nM. The LOD obtained is 0.3nM, thus enabling as a suitable sensor for practical accessibility.

Inhibition of Corrosion in Alkaline Silicon–Air Batteries with Polyethylene Glycol

Silicon–air batteries (SABs) are attracting significant attention for their potential as high‐energy‐density electrochemical storage devices. One of the main limitations for the commercial use of alkaline SABs is the high corrosion, which results in a low conversion efficiency. Herein, the aim is to examine the influence of polyethylene glycol (PEG) on the conversion efficiency of SABs, shedding light on key factors affecting their performance. SABs using KOH as electrolyte at two concentrations, 0.5 and 2.0 mol L−1, are investigated. The results show that replacing part of the water in the alkaline electrolyte with PEG changes the etching behavior from anisotropic to polishing and increases the specific energy density by 53% and 123% in 0.5 and 2 mol L−1 KOH electrolytes, respectively.

Low-temperature green synthesis of few-layered graphene sheets from pomegranate peels for supercapacitor applications

Graphene presents practical applications in energy storage devices, especially supercapacitors. However, mainstream synthesis of graphene includes toxic chemical usage, which threatens the environment. With the recent attention shift to synthesizing nanomaterials from agro-waste due to their easy availability, cost-effectiveness, and, most importantly, their environmental friendliness, we present, in this work for the first time, a novel and green synthesis of few-layered graphene sheets using pomegranate peels as a precursor at a low temperature of 80 °C. The surface morphology and microstructural properties are determined by Transmission Electron Microscopy (TEM), Energy Dispersive X-Ray spectroscopy (EDX), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), UV–visible spectroscopy (UV–vis), and the electrical properties determined by Hall Effect Measurement. The application as a supercapacitor is also examined using Cyclic Voltammetry (CV), Charge–Discharge Cycling (GCD), and Electrochemical Impedance Spectroscopy (EIS). The resulting supercapacitor delivers an areal capacitance of 3.39 mF{cm}^{-2} at a current density of 15.6 μA {cm}^{-2}, making our synthesized graphene a good choice for electrochemical storage devices.

Bacterial assisted sustainable production of Three-Dimensional defective carbon from rice straw for supercapacitor

Defective carbon nanomaterials with three-dimensional (3D) structure are showing great potential for advanced electrochemical storage and conversion devices, but its application is restricted by the synthesis, which is usually involved with complicate and energy-intensive processes. Herein, pyrolysis of rice straw (RS) residue, of which is collected from the bacterial assisted hydrolysis, is proposed by us here, and the obtained bio-char is defective with 3D structure and rich in oxygen-containing functional groups. Compared to the pristine one, specific surface area of the representative RS carbon (RSC2) was increased from 428.8 to 1131.7 m2 g−1. The assembled supercapacitor with RSC2 showed a high specific capacitance of 331F g−1 at a charge–discharge current density of 0.5 A g−1, and a capacity retention of 97.6% was maintained at 5 A g−1 even after 10,000 cycles.

Improving Students' Understanding of Energy Conservation through Training on Making Electrochemical Storage Devices

This paper reports the activities aimed at teachers and high school students in Lubuk Linggau, which went smoothly, interspersed with questions and answers. Demo and presentation, which are program activities, also run smoothly. The theme of community service activities is making a supercapacitor and battery and explaining the material used to make both energy storage devices. In addition, the team also presented basic knowledge about potentiostats and multimeters as test instruments related to electrochemistry. The activity went smoothly, interspersed with questions and answers—the demo and training have run smoothly. The theme of program activities includes the demo and training of preparing supercapacitor - batteries, explaining the materials - tools employed to make the energy storage devices. In addition, the team also presented basic knowledge about supercapacitors, batteries, potentiostats, and other tools related to electrochemistry. The activities of teachers and students at school took place very enthusiastically in receiving direction and counseling from the team. The enthusiasm can be seen in the active discussions between the team and members of these community groups. Group members feel the positive value of the activities carried out by the team. Generally, the team and participant can work out the ideas contained in the patent well. The team recommends some extended programs to propose, such as (a) similar activities should be carried out continuously to increase acknowledgment. (b) collaborating with others, and (c) developing online lab work.

Imbibition and rheology of polymer-matrix nanoporous metal composites: Towards extrusion-based 3D printing

When combined with additive manufacturing, nanoporous metals can be shaped into multifunctional and interdigitated 3D circuits with hierarchical diffusional pathways, critical for optimizing electrochemical storage devices. In an attempt to develop a method for extrusion-based additive manufacturing of nanoporous metals and their composites, this paper examines a new polymer matrix composite reinforced with spherical nanoporous copper powders (PMC-NP-Cu) synthesized by dealloying at high fill fractions (>45 vol%), that can be integrated with fused filament fabrication (FFF). The role of capillary imbibition of the polymer into the metal's nanopores was investigated by examining their wettability, rheology, and density as a function of polymer's molecular weight (MW) particularly for a range of radius of gyration (Rg) between 2 and 20 nm comparable to its average pore size (22 nm). It was found that the melt viscosity of PMC-NP-Cu with the shortest Mw departed from classical viscosity scaling (i.e., η ∞ MW1) which is attributed to the polymer imbibition into nanopores and composite densification. For molecular weights equal to 5 and 200 kg/mol, it was found that the volume fraction of the reinforcing phase was 16% and 8% higher respectively when imbibition was accounted for, resulting in an increase of two orders of magnitude in its zero-shear viscosity. These results correlated to the extrudability tests of PMC-NP-Cu filaments at higher packing factors (i.e., 47 vol%) for FFF. The insight of this study might be beneficial to integrate nanoporous metals into binder-based 3D printing technology to fabricate interdigitated battery electrodes and multifunctional 3D printed electronics.

Crystal transformation engineering for effective polysulfides blocking layer for excellent energy density lithium–sulfur batteries

Lithium–sulfur batteries (LSBs) with ultra-high energy density are emerging as the best alternative for next-generation energy storage systems. Nevertheless, polysulfide (LiPS) shuttling induces rapid capacity diminution, and short battery lifespan, which seriously hinders their practical application. Herein, a solvothermal and controlled pyrolysis process was used to synthesize the metal-organic frameworks derived m–/c–ZrO2 heterojunction distributed on nitrogen-doped porous carbon (NC) and uniformly wrapped by graphene sheets. Electrochemical investigation demonstrates that the m–/c–ZrO2/NCG heterostructure modified separator can efficiently impede LiPSs shuttling and regulate the conversion reaction of long-chain LiPSs, which is further confirmed by first-principles theoretical calculations. The as-prepared m–/c–ZrO2/NCG-based LSBs showed remarkable cyclability with a decay rate of 0.023 % per cycle over 1000 cycles at a high rate of 2 C. Importantly, at very high sulfur loading of 6.8 mg cm−2, an excellent reversible specific capacity of 924.1 mAh g−1 at 0.2 C after 100 cycles is achieved, which is expected to obtain high energy performance. This work delivers a promised strategy for the rational design of multifunctional heterostructure for stable and safe LSBs, providing a means of narrowing the gap for the commercialization of high-energy next-generation electrochemical storage devices.

Ionic Liquid–Graphene Interface: Effect of Anions on the Fermi Level

Since energy conversion and storage processes take place at the electrolyte–electrode interface, it is important to develop experimental and theoretical procedures to understand the interfacial nanostructure in graphene-based electrochemical storage devices where ionic liquids (ILs) are used as electrolytes. In this contribution, the impact of the anions of imidazolium-based ILs on the IL–graphene interface as well as on the electronic structure of graphene is investigated. Raman spectroscopy unveils that 1-butyl-3-methylimidazolium ILs having smaller anions induce n-type doping, while ILs with larger anions have a negligible effect on the doping. Molecular modeling simulations reveal that changes in the electrostatic potential at the IL–graphene interface are responsible for the n-type doping.

NixCo1-x@NixCo1-xO/NCNT as Trifunctional ORR, OER, and HER Electrocatalysts and its Application in a Zn-Air Battery.

The efficient electrochemical conversion and storage devices can be boosted by the development of cost-effective and durable electrocatalysts. However, simultaneous in-depth understanding of the reaction mechanism is also required. Herein, we report the preparation, characterization, and electrochemical activities of bimetallic NixCo1-x NPs and core-shell NixCo1-x@NixCo1-xO NPs stabilized on N-doped carbon nanotubes (NCNTs). The electrocatalyst is derived from a bimetallic MOF {[Ni0.5Co0.5(bpe)2(N(CN)2)](N(CN)2)·(5H2O)}n (1) via pyrolysis followed by calcination. Pyrolysis of the bimetallic MOF gives rise to bimetallic nanoparticles stabilized on NCNTs, which, when subsequently calcined, leads to the formation of a core-shell structure with a semiconducting oxide shell (NixCo1-xO) encapsulating the NixCo1-x bimetallic NP core. Detailed evaluation of the electrocatalytic performance of NixCo1-x@NixCo1-xO/NCNT proves its worth as a bifunctional catalyst with 380 mV overpotential for oxygen evolution reaction at 10 mA cm-2 current density and 0.87 V (vs RHE) onset for oxygen reduction reaction in the alkaline medium. Additionally, the prepared electrocatalyst efficiently catalyzes the hydrogen evolution reaction with a nominal overpotential of 74 mV (vs RHE) for reaching 10 mA cm-2 current density in acidic medium. The practical applicability of this catalyst is further upheld in the fabrication of a zinc-air battery having high specific capacity with high round-trip efficiency and adequate cycle life. DFT calculations establish that the structure of NixCo1-x@NixCo1-xO/NCNT is crucial for its electrochemical activity since it has the threefold advantages of cooperative charge transfer from Co to Ni, synergistic relationship between the conductive alloy core and semiconducting oxide shell, and a highly conductive N-doped CNT matrix.

Lignin-based materials for electrochemical energy storage devices

Lignin is the most abundant aromatic polymer in nature, which is rich in a large number of benzene ring structures and active functional groups. The molecular structure of lignin has unique designability and controllability, and is a class of functional materials with great application prospects in energy storage and conversion. Here, this review firstly focuses on the concept, classification, and physicochemical property of lignin. Then, the application research of lignin in the field of electrochemical storage materials and devices are summarized, such as lignin-carbon materials and lignin-carbon composites in supercapacitors and secondary batteries. Finally, this review points out the bottlenecks that need to be solved urgently and the prospects for future research priorities.

Tuning the electrochemical properties of NiS2 2D-nanoflakes by one-zone sulfurization for supercapacitor applications

Nickel-based sulfides (particularly NiS2) are regarded as promising materials for highly efficient electrochemical generation and storage devices. The conventional fabrication methods of nanostructured NiSX electrodes involve several complex steps using multiple precursors and techniques. In this paper, the NiSX electrodes are prepared by a plain one-step process of one-zone sulfurization of Ni foam. The evolution of highly electroactive 2D-nanoflakes reliant on sulfurization temperature is studied. Scanning electron microscopy, x-ray diffractometry, and energy-dispersive x-ray spectroscopy confirmed the presence of NiSX (x = 1 and 2) in the prepared structures. A strong dependence of sample morphology and 2D-nanoflakes density on sulfurization temperature was demonstrated. The electrochemical properties of samples were characterized by cyclic voltammetry and electrochemical impedance spectroscopy measurements. Owing to the 2D-nanoflake structure, the NiS2 showed attractive electrochemical performance, including a high specific capacitance of 648 mF cm−2 and a capacitance retention rate of 90,7% after 3000 cycles. Our study shows that the composition and crystal growth of NiSX can be tuned by reaction temperature during the sulfurization and high perspective of sulfurization in the synthesis of highly electroactive large-scale electrodes for supercapacitors.

Material thermal extrusion of conductive 3D electrodes using highly loaded graphene and graphite colloidal feedstock

Evolution in the energy storage field requires the development of more sustainable and efficient high-performance electrochemical storage devices (EESDs). Additive manufacturing (AM) opens unique opportunities to improve the efficiency and the electrochemical response by the design of 3D electrodes and the increasing of exposed active surface area impossible to achieve by other processing techniques. In other to reach high-performance EESDs, carbonaceous species are well-established as electroactive materials owing to their electronic properties, low cost, and sustainable origin. Although the materials have been widely investigated, there is a lack of feedstock development for the fabrication of EESDs by AM technologies. This work presents the fabrication of metals free light conductive filaments for material thermal extrusion (MTE) by formulating PLA-based composites with a high content of colloidal graphite and graphene (15–25 vol%). By the colloidal characterization and surface modification of the carbonaceous species, an improved distribution and enhanced platelet/polymer bond were achieved, provoking the inorganic phase's orientation during the extrusion process. Prepared filaments were characterized to analyze the influence of the microstructural anisotropy on thermal, thermorheological, mechanical, and electrical properties. Subsequently, developed filaments were used to print complex electrodes by MTE, enhancing the electrochemical properties of the electrodes with superior control of the macrostructural design. The developed colloidal filaments with an oriented inorganic microstructure, not only allow a defined shaping of the outer structure of the electrodes but also let the design of completely different microstructures. Consequently, different microstructural configurations were printed increasing the number of conduction paths in the polymeric matrix to achieve high electric conductivities (22 S.m-1) in printed electrodes.

Resent Development of Binder-Free Electrodes of Transition Metal Oxides and Nanohybrids for High Performance Supercapacitors - A Review.

The entire world is aware of the serious issue of global warming and therefore utilizing renewable energy sources is the most encouraging steps toward solving energy crises, and as a result, energy storage solutions are necessary. The supercapacitors (SCs) have a high-power density and a long cycle life, they are promising as an electrochemical conversion and storage device. In order to achieve high electrochemical performance, electrode fabrication must be implemented properly. Electrochemically inactive and insulating binders are utilized in the conventional slurry coating method of making electrodes to provide adhesion between the electrode material and the substrate. This results in an undesirable "dead mass," which lowers the overall device performance. In this review, we focused on binder-free SCs electrodes based on transition metal oxides and composites. With the best examples providing the critical aspects, the benefits of binder-free electrodes over slurry-coated electrodes are addressed. Additionally, different metal-oxides used in the fabrication of binder-free electrodes are assessed, taking into account the various synthesis methods, giving an overall picture of the work done for binder-free electrodes. The future outlook is provided along with the benefits and drawbacks of binder-free electrodes based on transition metal oxides.