Flexible carbon cloth based solid-state supercapacitor from hierarchical holothurian-morphological NiCo2O4@NiMoO4/PANI

Polyoxometalate Etching of NMO@NF for Highly Efficient Oxygen Evolution Reaction in Water Splitting

In this study, PTA&PMA/NiMoO4@NF was synthesized on nickel foam through wet chemical etching to promote the kinetics of the oxygen evolution reaction (OER) effectively. OER benefits from two cationic (Ni and Mo) defects and the optimized electronic configuration of PTA&PMA/NiMoO4@NF. Thus, it only needs 200 mV to reach the current density of 10 mA cm-2 in 1.0 mol/L of KOH. This value is nearly 100 mV lower than the value needed by pure NiMoO4. After being used as an anode for water splitting in an alkaline solution, the as-obtained catalyst can operate at a current density of 10 mA cm-2 for 24 h of good stability. The synthesis strategy adopted in this study can provide an effective, low-cost, simple, and convenient strategy for improving the OER electrocatalytic performance of other transition metal oxides.

Organic-inorganic hybrid cathode enabled by in-situ interface polymerization engineering boosts Zn2+ desolvation in aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) have attracted considerable attention for application in large-scale energy storage systems. However, the progress of RAZIBs has been hindered by the sluggish reaction kinetics and poor structural stability, which are closely associated with the desolvation process of hydrated Zn2+. To overcome these issues, an in situ interfacial polymerization strategy is proposed to uniformly germinate a polyaniline (PANI) layer on α-MnO2 and form an organic-inorganic hybrid cathode (MnO2@PANI). Theoretical calculations and experimental characterizations disclose that the polyaniline layer equipped with hydrophilic functional groups can effectively trap the active water molecules to break the strong attraction between H2O and Zn2+, thereby facilitating the desolvation process of hydrated Zn2+, and regulating the Zn2+ diffusion kinetics and electrode reaction kinetics on the cathode/electrolyte surface. Meanwhile, the irreversible phase evolution and dissolution of active species are largely suppressed due to the PANI shell protecting the α-MnO2 from the attack of active water molecules. As a consequence, the organic-inorganic hybrid cathode exhibits 401.9 mAh/g after 200 cycles at a current density of 0.5 A/g and long-term durability over 1000 cycles at a current density of 2.0 A/g without irreversible phase transformation. This work provides insight into the regulation of the desolvation process for high performance aqueous energy storage systems.

Rational Design of Nanosheet Array-Like Layered-Double-Hydroxide-Derived NiCo2O4 In Situ Grown on Reduced-Graphene-Oxide-Coated Nickel Foam for High-Performance Solid-State Supercapacitors

The investigation of high-performance supercapacitors is essential for accelerating the development of energy storage devices. In this work, a 3D hierarchical nanosheet array-like nickel cobaltite/reduced graphene oxide/nickel foam composite (NiCo2O4/rGO/NF) was assembled via an aqueous coprecipitation-hydrothermal strategy assisted by citric acid. Benefiting from a NiCo layered-double-hydroxide precursor with an atomic-level lattice confinement effect of metal ions and effective hybridization with rGO, the NiCo2O4/rGO/NF composite is featured as thin NiCo2O4 nanosheets (∼113.6 nm × 11.2 nm) composed of NiCo2O4 nanoparticles (∼10.9 nm) vertically staggered on the surface of a rGO-modified NF skeleton, leading to high surface area, abundant mesoporous structure, and active site exposure. The as-obtained NiCo2O4/rGO/NF was directly used as a binder-free integrated electrode for supercapacitors, achieving an excellent specific capacitance of 2863.4 F g-1 (1503.3 C g-1) at 1 A g-1, a superior rate performance of 2335.2 F g-1 at 20 A g-1, and a stability retention of 91.7% after 5000 cycles. More impressively, a solid-state asymmetric supercapacitor assembled by the present NiCo2O4/rGO/NF integrated electrode as the positive electrode and commercial activated carbon as the negative electrode achieved a high energy density of 69.2 Wh kg-1 at a power density of 800 W kg-1, and the energy density at a peak power density of 20004 W kg-1 still remained at 48.9 Wh kg-1, also showing a good cycling stability of 87.2% retention over 10000 cycles. The present facile synthesis strategy of the as-obtained NiCo2O4/rGO/NF nanosheet array composite can be used for the design and construction of many other transition-metal oxide/graphene/NF composite materials with excellent structural stability and performance in energy storage and other related areas.

Self-sacrifice-template epitaxial growth of hierarchical MnO2@NiCo2O4 heterojunction electrode for high-performance asymmetric supercapacitor

Constructing three-dimensional (3D) hierarchical bimetallic pseudocapacitive materials with abundant opening channel and heterojunction structures is rather promising but still challenging for high-performance supercapacitors. Herein, a self-sacrifice-template epitaxial growth strategy was proposed for the first time to construct 3D hierarchical bimetallic pseudocapacitive material. By using this strategy, NiCo2O4 nanowires (NiCo2O4NW) arrayed randomly to form a porous shell via in-situ epitaxial growth fully enclosing a MnO2 tube core, forming multiple transport channels and nano-heterojunctions between MnO2 and NiCo2O4NW, which facilitates electron transfer, i.e. exhibiting high electronic conductivity than any single component. As a result of the self-sacrifice-template epitaxial growth method, special hollow tectorum-like 3D hierarchical structure with considerable inter-nanowire space and hollow interior space enables easy access of electrolyte to NiCo2O4NW surface and MnO2 core, thereby resulting in highly exposed redox active sites of MnO2 core and NiCo2O4NW shell for energy storage. Comprehensive evaluations confirmed MnO2@NiCo2O4NW was a supercapacitor electrode candidate, delivering a superior energy density of 106.37 Wh kg-1. Such performance can be ascribed to the synergistic coupling effect of 3D hierarchical tube and nano-heterojunction structures. The proposed self-sacrifice-template epitaxial growth strategy provides important guidance for designing high-performance energy storage materials.

A 3D stacked corrugated pore structure composed of CoNiO2 and polyaniline within the tracheids of wood-derived carbon for high-performance asymmetric supercapacitors

A novel 3D stacked corrugated pore structure of polyaniline (PANI)/CoNiO₂@activated wood-derived carbon (AWC) has been successfully constructed to prepare high-performance electrode materials for supercapacitors. AWC functions as a supporting framework that provides ample attachment sites for the loaded active materials. The CoNiO₂ nanowire substrate, consisting of 3D stacked pores, not only serves as a template for subsequent PANI loading, but also acts as an effective buffer to mitigate the volume expansion of the PANI during ionic intercalation. The distinctive corrugated pore structure of PANI/CoNiO₂@AWC facilitates electrolyte contact and significantly enhances the electrode material properties. The PANI/CoNiO₂@AWC composite materials exhibit excellent performance (14.31F cm^-2 at 5 mA cm^-2) and superior capacitance retention (80% from 5 to 30 mA cm^-2), owing to the synergistic effect among their components. Finally, PANI/CoNiO₂@ AWC//reduced graphene oxide (rGO)@AWC asymmetric supercapacitor is assembled, which has a wide operating voltage (0 ∼ 1.8 V), high energy density (4.95 mWh cm^-3 at 26.44 mW cm^-3) and cycling stability (90.96% after 7000 cycles).

Electrolyte-Wettability Issues and Challenges of Electrode Materials in Electrochemical Energy Storage, Energy Conversion, and Beyond

The electrolyte-wettability of electrode materials in liquid electrolytes plays a crucial role in electrochemical energy storage, conversion systems, and beyond relied on interface electrochemical process. However, most electrode materials do not have satisfactory electrolyte-wettability for possibly electrochemical reaction. In the last 30 years, there are a lot of literature have directed at exploiting methods to improve electrolyte-wettability of electrodes, understanding basic electrolyte-wettability mechanisms of electrode materials, exploring the effect of electrolyte-wettability on its electrochemical energy storage, conversion, and beyond performance. This review systematically and comprehensively evaluates the effect of electrolyte-wettability on electrochemical energy storage performance of the electrode materials used in supercapacitors, metal ion batteries, and metal-based batteries, electrochemical energy conversion performance of the electrode materials used in fuel cells and electrochemical water splitting systems, as well as capacitive deionization performance of the electrode materials used in capacitive deionization systems. Finally, the challenges in approaches for improving electrolyte-wettability of electrode materials, characterization techniques of electrolyte-wettability, as well as electrolyte-wettability of electrode materials applied in special environment and other electrochemical systems with electrodes and liquid electrolytes, which gives future possible directions for constructing interesting electrolyte-wettability to meet the demand of high electrochemical performance, are also discussed.

Nanostructured Conducting Polymers and Their Applications in Energy Storage Devices

Due to the energy requirements for various human activities, and the need for a substantial change in the energy matrix, it is important to research and design new materials that allow the availability of appropriate technologies. In this sense, together with proposals that advocate a reduction in the conversion, storage, and feeding of clean energies, such as fuel cells and electrochemical capacitors energy consumption, there is an approach that is based on the development of better applications for and batteries. An alternative to commonly used inorganic materials is conducting polymers (CP). Strategies based on the formation of composite materials and nanostructures allow outstanding performances in electrochemical energy storage devices such as those mentioned. Particularly, the nanostructuring of CP stands out because, in the last two decades, there has been an important evolution in the design of various types of nanostructures, with a strong focus on their synergistic combination with other types of materials. This bibliographic compilation reviews state of the art in this area, with a special focus on how nanostructured CP would contribute to the search for new materials for the development of energy storage devices, based mainly on the morphology they present and on their versatility to be combined with other materials, which allows notable improvements in aspects such as reduction in ionic diffusion trajectories and electronic transport, optimization of spaces for ion penetration, a greater number of electrochemically active sites and better stability in charge/discharge cycles.

Interfacial engineered PANI/carbon nanotube electrode for 1.8 V ultrahigh voltage aqueous supercapacitors

Flexible three-dimensional interconnected carbon nanotubes on the carbon cloth (3D-CNTs/CC) were obtained through simple magnesium reduction reactions. According to the Nernst equation, the cell voltage based on these pure carbon electrodes without any additives could reach 1.5 V due to the higher di-hydrogen evolution over potential in neutral 3.5 M LiCl electrolytes. In order to improve the electrochemical performance of the electrodes, 3D-CNTs/CC electrodes covered with polyaniline barrier layer (3D-PANI/CNTs/CC) were prepared byin situelectropolymerization using interfacial engineering method. The assembled symmetric supercapacitors display a broadened voltage of 1.8 V, high areal capacitance of 380 mF cm^-2, outstanding areal energy density of 85.5μWh cm^-2and 84% of its initial capacitance after 20 000 charge-discharge cycles. This work demonstrated that the interface engineering strategy provides a promising way to improve the energy density of carbon-based aqueous supercapacitors by widening the voltage and boosting the capacitance simultaneously.

Synchronous Defect and Interface Engineering of NiMoO4 Nanowire Arrays for High-Performance Supercapacitors

Developing high-performance electrode materials is in high demand for the development of supercapacitors. Herein, defect and interface engineering has been simultaneously realized in NiMoO4 nanowire arrays (NWAs) using a simple sucrose coating followed by an annealing process. The resultant hierarchical oxygen-deficient NiMoO4@C NWAs (denoted as "NiMoO4-x@C") are grown directly on conductive ferronickel foam substrates. This composite affords direct electrical contact with the substrates and directional electron transport, as well as short ionic diffusion pathways. Furthermore, the coating of the amorphous carbon shell and the introduction of oxygen vacancies effectively enhance the electrical conductivity of NiMoO4. In addition, the coated carbon layer improves the structural stability of the NiMoO4 in the whole charging and discharging process, significantly enhancing the cycling stability of the electrode. Consequently, the NiMoO4-x@C electrode delivers a high areal capacitance of 2.24 F cm-2 (1720 F g-1) at a current density of 1 mA cm-2 and superior cycling stability of 84.5% retention after 6000 cycles at 20 mA cm-2. Furthermore, an asymmetric super-capacitor device (ASC) has been constructed with NiMoO4-x@C as the positive electrode and activated carbon (AC) as the negative electrode. The as-assembled ASC device shows excellent electrochemical performance with a high energy density of 51.6 W h kg-1 at a power density of 203.95 W kg-1. Moreover, the NiMoO4//AC ASC device manifests remarkable cyclability with 84.5% of capacitance retention over 6000 cycles. The results demonstrate that the NiMoO4-x@C composite is a promising material for electrochemical energy storage. This work can give new insights on the design and development of novel functional electrode materials via defect and interface engineering through simple yet effective chemical routes.

Hierarchically Hybrid Porous Co3O4@NiMoO4/CoMoO4 Heterostructures for High-Performance Electrochemical Energy Storage

Hierarchical, ultrathin, and porous NiMoO₄@CoMoO₄ on Co₃O₄ hollow bones were successfully designed and synthesized by a hydrothermal route from the Co-precursor, followed by a KOH (potassium hydroxide) activation process. The hydrothermally synthesized Co₃O₄ nanowires act as the scaffold for anchoring the NiMoO₄@CoMoO₄ units but also show more compatibility with NiMoO₄, leading to high conductivity in the heterojunction. The intriguing morphological features endow the hierarchical Co₃O₄@NiMoO₄@CoMoO₄ better electrochemical performance where the capacity of the Co₃O₄@NiMoO₄@CoMoO₄ heterojunction being 272 mA·h·g^-1 at 1 A·g^-1 can be achieved with a superior retention of 84.5% over 1000 cycles. The enhanced utilization of single/few NiMoO₄@CoMoO₄ shell layers on the Co₃O₄ core make it easy to accept extra electrons, enhancing the adsorption of OH^- at the shell surface, which contribute to the high capacity. In our work, an asymmetric supercapacitor utilizing the optimized Co₃O₄@NiMoO₄@CoMoO₄ activated carbon (AC) as electrode materials was assembled, namely, Co₃O₄@NiMoO₄@CoMoO₄//AC device, yielding a maximum high energy density of 53.9 W·h·kg^-1 at 1000 W·kg^-1. It can retain 25.92 W·h·kg^-1 even at 8100 W·kg^-1, revealing its potential and viability for applications. The good power densities are ascribed to the porous feature from the robust architecture with recreated abundant mesopores on the composite, which assure improved conductivity and enhanced diffusion of OH^- and also the electron transport. The work demonstrated here holds great promise for synthesizing other heterojunction materials M₃O₄@MMoO₄@MMoO₄ (M = Fe, Ni, Sn, etc).

Two-in-one template-assisted construction of hollow phosphide nanotubes for electrochemical energy storage

In this work, the template-assisted method was used to develop novel Ni2P@PANI hollow nanotubes as a positive electrode material for supercapacitors by using prepared polyaniline (PANI) nanotubes as precursors, and...

Transition metal dichalcogenide (TMDs) electrodes for supercapacitors: a comprehensive review

As globally, the main focus of the researchers is to develop novel electrode materials that exhibit high energy and power density for efficient performance energy storage devices. This review covers the up-to-date progress achieved in transition metal dichalcogenides (TMDs) (e.g. MoS₂, WS₂, MoSe_2,and WSe₂) as electrode material for supercapacitors (SCs). The TMDs have remarkable properties like large surface area, high electrical conductivity with variable oxidation states. These properties enable the TMDs as the most promising candidates to store electrical energy via hybrid charge storage mechanisms. Consequently, this review article provides a detailed study of TMDs structure, properties, and evolution. The characteristics technique and electrochemical performances of all the efficient TMDs are highlighted meticulously. In brief, the present review article shines a light on the structural and electrochemical properties of TMD electrodes. Furthermore, the latest fabricated TMDs based symmetric/asymmetric SCs have also been reported.

High-performance supercapacitor based on highly active P-doped one-dimension/two-dimension hierarchical NiCo2O4/NiMoO4 for efficient energy storage

Multi-dimensional metal oxides have become a promising alternative electrode material for supercapacitors due to their inherent large surface area. Herein, P-doped NiCo₂O₄/NiMoO₄ multi-dimensional nanostructures are synthesized on carbon clothes (CC) with a continuous multistep strategy. Especially, P has the best synergistic effect with transition metals, such as optimal deprotonation energy and OH^- adsorption energy, which can further enhance electrochemical reaction activity. For the above reasons, the P-NiCo₂O₄/NiMoO₄@CC electrode exhibits an ultra-high specific capacitance of 2334.0 F g^-1 at 1 A g^-1. After 1500 cycles at a current density of 10 A g^-1, its specific capacity still maintains 93.7%. Besides, a P-NiCo₂O₄/NiMoO₄@CC//activated carbon device (hybrid supercapacitor or device) was also prepared with a maximum energy density of 45.1 Wh kg^-1 at a power density of 800 W kg^-1. In particular, the capacity retention rate is still 89.97% after 8000 cycles due to its excellent structural stability. Our work demonstrates the vast potential of multi-dimensional metal oxides in energy storage.

A hybrid NiCo2O4@NiMoO4 structure for overall water splitting and excellent hybrid energy storage

In this study, a two-step hydrothermal method is used to prepare NiCo2O4@NiMoO4 nanoscale materials for periodic stability supercapacitors. The synthesized product can be directly used as the electrode material of the supercapacitor, and its specific capacitance is 685.7 C g-1. The composite electrode NiCo2O4@NiMoO4 is used as the positive electrode and the hybrid capacitor is assembled. Meanwhile, at the power density of 4050 W kg-1, the energy density is 96.3 W h kg-1, and the capacitance retention is 100% after 10 000 cycles. At the same time, when the composite is used as a catalyst, it exhibits OER overvoltage (300 mV), HER overvoltage (170 mV) and a low battery voltage of 1.65 V at 10 mA cm-2. After 14 hours of long-term use, NiCo2O4@NiMoO4 maintained good stability, indicating that its structure further improved the electrochemical performance, providing a great advantage for the study of low-cost electrode materials for overall water splitting.

Three-dimensional CoNi alloy nanoparticle and carbon nanotube decorated N-doped carbon nanosheet arrays for use as bifunctional electrocatalysts in wearable and flexible Zn-air batteries

A novel three-dimensional (3D) bifunctional electrocatalyst, CoNi alloy nanoparticle and carbon nanotube decorated N-doped carbon nanosheet arrays on carbon cloth (CoNi alloy/NCNSAs/CC) derived from polymetallic organic frameworks, is firstly prepared. The CoNi alloy/NCNSAs/CC-800 fabricated by pyrolyzing at 800 °C exhibits an oxygen reduction reaction (ORR, limiting current density) of 6.5 mA cm^-2 and a superior oxygen evolution reaction (OER, at 10 mA cm^-2) of 1.51 V, as well as a smaller potential difference of 0.676 V between OER and ORR half-wave potential, outperforming previous self-supporting cathodes. Flexible Zn-air batteries (FZABs) assembled with the CoNi alloy/NCNSAs/CC-800 exhibit higher energy density (98.8 mW cm^-2) and higher capacity (879 mAh g^-1), as well as excellent mechanical cycle ability (lower voltage gap of 0.66 V during the charge/discharge cycles at flat and folded state), significantly outstripping all other FZABs with self-supporting electrodes currently reported. Such a remarkable performance is ascribed to the 3D hierarchical nanostructure which promotes mass transport, the higher graphitization facilitating electronic mobility and the evenly dispersed active sites which accelerate kinetic reactions. So CoNi alloy/NCNSAs/CC-800 is a promising cathode candidate for ideal wearable energy devices and has great potential application in the field of electrochemical energy storage and conversion.

A MoNiO4 flower-like electrode material for enhanced electrochemical properties via a facile chemical bath deposition method for supercapacitor applications

Schematic representation of the synthesis of MoNiO₄ flower-like nanostructures.