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As a cathode in aqueous zinc-ion capacitors (ZICs), nitrogen-doped carbon with a 2D bimetallic chalcogenide (NbMo6S8/NC) was used. The assembled ZIC demonstrated exceptional electrochemical stability and energy efficiency over thousands of charge–discharge cycles.

Porous carbon materials are widely used in capacitive energy storage devices because of their chemical stability, low cost, and controllable textures. Molten salt self-template methods are powerful and sustainable synthesis strategies for preparing porous carbons with tunable pore textures and surface chemistries. Herein, we propose a self-template synthesis strategy for preparing oxygen-rich porous carbons (ORC) by directly carbonizing potassium chloroacetate (ClCH

Multivalent aqueous Zn-ion capacitors (ZICs) are promising next-generation electrochemical energy storage systems (ESSs) owing to distinctive features including good safety characteristics, low costs, and better electrochemical parameters than those of conventional supercapacitors. The key challenge of existing ZICs is their low energy density and limited cycling ability due to carbon cathode materials and conventional electrolyte systems. This paper presents a dual strategy in which the electrode and electrolyte features are engineered to improve the overall electrochemical performance of ZICs. First, the capacitance of the cathode material is improved by engineering reduced graphene oxide (rGO)-incorporating, pseudocapacitive, layered niobium oxyphosphide (NbPO) material; second, the electrochemical stability of the Zn metal anode is improved via an additive to the traditional Zn-electrolyte. The aqueous ZIC with rGO–NbPO cathode and NaClO4 additive electrolyte exhibits the highest capacitance (191.88 F g−1), maximal energy density (56.03 Wh kg−1), and excellent energy efficiency (approximately 50% to 55%). The prepared flexible solid-state rGO–NbPO ZIC has an ultra-long lifespan of over 50,000 cycles with approximately 76.81% capacitance retention (at 4 A g−1) and excellent mechanical tractability. The results provide guidance for improving the design of safe aqueous ESSs with high-level efficiency and long-term stability.

We developed a flexible supercapacitor cell with biocompatible oxidized SWCNTs driven by electrolytes in body fluids through integration with a wireless sensor network for use in implantable electronic medical devices (IEMDs).

The conversion of nitrogen to ammonia offers a sustainable and environmentally friendly approach for producing precursors for fertilizers and efficient energy carriers. Owing to the large energy density and significant gravimetric hydrogen content, NH

The increased demand of energy due to the recent technological advances in diverse fields such as portable electronics and electric vehicles is often hindered by the poor capability of energy-storage systems. Although supercapacitors (SCs) exhibit higher power density than state-of-the art batteries, their insufficient energy density remains a major challenge. An emerging concept of hybrid supercapacitors (HSCs) with the combination of one capacitive and one battery electrode in a single cell holds a great promise to deliver high energy density without sacrificing power density and cycling stability. This Minireview elaborates the recent advances of use of nickel cobaltite (NiCo2 O4 ) as a potential positive electrode (battery-like) for HSCs. A brief introduction on the structural benefits and charge storage mechanisms of NiCo2 O4 was provided. It further shed a light on composites of NiCo2 O4 with different materials like carbon, polymers, metal oxides, and others, which altogether helps in increasing the electrochemical performance of HSCs. Finally, the key scientific challenges and perspectives on building high-performance HSCs for future-generation applications were reviewed.

Herein, a solution-free dry strategy for the growth of self-assembled ordered tricopper phosphide (Cu3P) nanorod arrays is developed and the product is employed as a high-energy, stable positive electrode for a solid-state hybrid supercapacitor (HSC). The ordered Cu3P nanorod arrays grown on the copper foam deliver an excellent specific capacity of 664 mA h/g with an energy efficiency of 88% at 6 A/g and an ultra-long cycling stability over 15,000 continuous charge–discharge cycles. These electrochemical features are attributed to the ordered growth of the Cu3P nanorod arrays, which offers a large number of accessible electroactive sites, a reduced number of ion transfer paths, and reversible redox activity. The potential of the Cu3P nanorod arrays is further explored by engineering solid-state HSCs in which the nanorods are paired with an activated carbon-based negative electrode. The constructed cell is shown to convey a specific energy of 76.85 Wh/kg at a specific power of 1,125 W/kg and an 88% capacitance retention over 15,000 cycles. Moreover, the superior energy storing and delivery capacity of the cell is demonstrated by an energy efficiency of around 65%. The versatile solution-free dry strategies developed here pave the way towards engineering a range of electrode materials for next-generation energy storage systems.

The limited energy storage capacities of carbon-based negative electrodes, which rely on conventional double layer charge storage mechanisms, have limited the electrochemical performances of hybrid supercapacitors (HSCs). The development of nanostructured redox-active materials that serve as alternatives to carbon-based negative electrodes is crucial to overcome the limitations of current HSCs. In this work, a coordination chemistry approach is utilized to tune the nanostructure of zinc ferrite thin films on flexible stainless steel (SS) foil by using several zinc salt precursors, including ZnCl2·6H2O, Zn(NO3)2·6H2O, and ZnSO4·6H2O, while using the same iron precursor (FeCl2·4H2O). Materials prepared with the ZnCl2·6H2O metal salt form porous nanosheets with groundnut-like structures that exhibit maximum specific capacities of 544 mA h/g (454 F/g) at current density of 2.5 A/g. Redox-active solid-state HSCs are assembled by using zinc ferrite as a negative electrode, MnO2 nanoflakes as a positive electrode, and a polymer gel as the electrolyte. The developed solid-state HSC cells show excellent performance as exemplified by a maximum specific capacitance of 123.8 F/g and an energy density of 55.72 Wh/kg, both of which are superior to those of conventional carbon-based symmetric and HSCs.

The present study emulates a one-pot facile synthesis of selenium-enriched CoSe nanotube using a chemical bath deposition (CBD) procedure. Schematic incorporation of 3D Ni foam current collectors as substrates for the growth of CoSe–Se nanotubes helped us achieve a binder-less thin film coating. The controlled synthesis of CoSe–Se nanotube was carried out by optimizing the temperature and time of the deposition. CoSe–Se nanotubes were grown on a porous Ni foam substrate using lithium chloride as a shape directing agent. The study found that the one dimensional structure of the nanotubes with porous nature results in an uninterrupted network of electroactive sites. Due to the superior conductivity, the as-fabricated material exhibited excellent rate capability and a higher degree of electrolyte ion diffusion across the CoSe–Se crystal structure. The CoSe–Se@Ni foam electrodes exhibited a specific capacitance of 1750.81 F g−1 at 1 A g−1. The electrode exhibited excellent cycling stability and showed a capacitance retention of 95% after 4000 charge-discharge cycles. Finally, an asymmetric supercapacitor (ASC) device was fabricated with the as-synthesized CoSe–Se@Ni foam electrode as the cathode, activated carbon@Ni foam electrode as the anode, and a thin filter paper separator soaked in 1 M aqueous KOH electrolyte solution. The ASC device showed a specific capacitance value of 106.73 F g−1 at 0.5 A g−1, and achieved an energy density of 37.94 Wh kg−1 at a power density of 475.30 W kg−1. The ASC device was utilized in an extended potential window of 1.6 V. The fabricated device displayed exceptional cycling stability with a capacitance retention of 93% after 5000 charge-discharge cycles.

There are ongoing efforts to develop novel phosphors with the properties required to make an object look as natural as it does under sunlight. It has been proven that particle morphology influences the luminescent properties of a phosphor. The rare-earth pyrosilicates, such as La2Si2O7 (LSO) are currently regarded as novel promising scintillators and protective pigments because of their good chemical and thermal stabilities. However, to date, there have been no reports available on the definite morphology of the LSO matrix and the precise luminescent properties of the trivalent europium (Eu3+)-doped LSO phosphor. Herein, we report the development of Eu3+-activated dumbbell-shaped LSO nanocrystalline phosphors using a two-step solvothermal and hydrothermal approach. After regrowth, the amorphous natured LSO:Eu3+ precursor was transformed into well-defined LSO:Eu3+ dumbbell-shaped nanocrystalline phosphors (LSO-R:Eu3+) with a pure monoclinic phase. The phase purity was verified by Rietveld refinement analysis. The formation mechanism of the dumbbell-shaped particles was evaluated using surface morphological studies, and the involvement of the crystal splitting mechanism was established. The luminescence spectra revealed robust red emission at 614 nm under ultraviolet (UV) and near-UV excitations. The dipole-dipole interactions between the neighboring Eu3+ ions induced the concentration quenching in LSO host matrix. Chromaticity coordinates (0.645, 0.342) emerged in the reddish-orange region and were comparable to the standard-definition and high-definition digital television coordinates (0.640, 0.330). Therefore, these results indicate that the synthesized LSO-R:Eu3+ dumbbell-shaped nanocrystalline phosphor is a promising auxiliary red component for assembling desired white light-emitting diodes for indoor illuminations.

Polyoxometalates (POMs) represent a class of nanomaterials, which hold enormous promise for a range of energy-related applications. Their promise is owing to their "special"structure that gives POMs a truly unique ability to control redox reactions in energy conversion and storage. One such amazing capability is their large number of redox active sites that arises from the complex three-dimensional cluster of metal-oxide ions linked together by oxygen atoms. Here, a critical review on how POMs emerged from being molecular clusters for fundamental studies, to next-generation materials for energy applications is provided. We highlight how exploiting the versatility and activity of these molecules can lead to improved performance in energy devices such as supercapacitors and batteries, and in energy catalyst applications. The potential of POMs across numerous fields is systematically outlined by investigating structure-property-performance relationships and the determinant factors for energy systems. Finally, the challenges and opportunities for this class of materials with respect to addressing our pressing energy-related concerns are identified. This journal is, D. P. D. acknowledges the Queensland University of Technology (start-up grant: 323000-0424/07) and Australian Research Council (ARC), Australia for the Future Fellowship (FT180100058). D. P. D. would also like to acknowledge the financial support from Centre for Materials Science, QUT, Australia. N. M. acknowledges funding from ARC (DP200102546). Sara Goberna-Ferrón has received funding from the postdoctoral fellowship programme Beatriu de Pinós, funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 programme of research and innovation of the European Union under the Marie Skłodowska-Curie grant agreement No 801370. Partial funding from Ministry of Science, Innovation and Universities (MCIU), the State Research Agency (AEI) and the European Regional Development Fund (FEDER) (grant RTI2018-099826-B-I00) and AGAUR (2017 SGR 00870) are gratefully acknowledged. ICN2 is funded by the CERCA programme/Generalitat de Catalunya, and it is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706).

Potassium-ion battery (KIB) is a promising technology for large-scale energy storage applications due to their low cost, theoretically high energy density and abundant resources. However, the development of KIBs is hindered by the sluggish K+ transport kinetics and the structural instability of the electrode materials during K+ intercalation/de-intercalation. In the present investigation, we have designed a potassium-ion capacitor (KIC) using layered potassium niobate (K4Nb6O17, KNO) nanosheet arrays as anode and orange-peel derived activated carbons (OPAC) as fast capacitive cathode materials. The systematic electrochemical analysis with the ex-situ characterizations demonstrates that KNO-anode exhibits highly stable layered structure with excellent reversibility during K+ insertion/de-insertion. After optimization, the fabricated KNO//OPAC delivers both a high energy density of 116 Wh/kg and high power density of 10,808 W/kg, which is significantly higher than other similar hybrid devices. The cell also displays long term cycling stability over 5000 cycles, with 87 % of capacity retention. This study highlights the utilization of layered nanosheet arrays of niobates to achieve superior K‐storage for KICs, paving the way towards the development of high‐performance anodes for post lithium‐ion batteries.

Human curiosity about the mysteries in outer space has driven humans to organize space explorations. Space missions and polar region solicitations require the use of new energy storage technologies with excellent tolerance to extremely low temperatures and the capability to operate efficiently for an extended time. In this context, it is urgent to explore new approaches and concepts to address the critical challenges via mechanistic understanding of new electrochemical reactions and phenomena in diverse scenarios. This paper presents how electrode and electrolyte materials in supercapacitor (SC) cells operate at extremely low temperatures. The critical challenges related to engineering such SCs and the major breakthroughs that overcome these problems are presented. In addition, the effects of different electrolytes (e.g., aqueous, organic, and ionic liquids (ILs)) on the ion accessibility, interfacial charge transfer, and transport kinetics in SC cells under cold conditions are discussed. This review is expected to contribute to the development of high-performance SC cells that can function at severe temperatures by providing insight into the key challenges and guidelines that facilitate future work.

The structural instability and sluggish kinetics of conventional positive electrodes with the lower capacitance of carbon-based negative electrodes result in an inferior performance for state-of-art supercapacitors (SCs). A general yet sustainable approach is proposed here to overcome this hitch by assembling hybrid SC cells utilising porous and stable 2D-on-2D core–shell and carbon/pseudocapacitive composite electrodes. Porous Co3(PO4)2 transparent stacked micropetals (TSMs) were synthesised and decorated with Co2Mo3O8 nanosheets (NSs) (Co3(PO4)2@Co2Mo3O8) forming a 2D-on-2D core–shell positive electrode, which was combined with a 2D carbon nanotube/MXene (CNT–Ti3C2TX) composite negative electrode. The core–shell electrode achieved a specific capacity of 184.7 mA h g−1 (738 mF cm−2) and cycling stability of 95.6% over 15 000 charge/discharge cycles. The CNT–Ti3C2TX electrode exhibited a remarkable areal capacitance of 187.5 mF cm−2 and cycling stability of 93.1%. Consequently, the assembled unique hybrid solid-state SCs delivered an exceptional volumetric capacitance of 7.9 F cm−3 and a specific energy of 74.06 W h kg−1 (2.47 mW h cm−3) at a specific power and cycling stability of 1.13 kW kg−1 and 93.2%, respectively. Overall, the techniques and electrode materials presented in this study can serve as a reference to produce a range of electrode materials for next-generation energy storage devices.

Due to their unique optical properties like narrow emission bands, the applicability of fluorescent nanomaterials have recently been extended to various fields such as forensic science and urban farming. Herein, we report a novel fluorescent material of Mn4+ ions doped Ba2LaNbO6 (BLN:Mn4+) with nanorod-like morphology for latent fingerprint detection as well as plant growth light-emitting diodes (LEDs) through a facile citric acid-assisted sol-gel route. The crystallization, elemental composition and oxidation states present in the BLN:Mn4+ nanophosphors are confirmed by the X-ray diffraction and X-ray photoelectron spectroscopy analyses. The photoluminescence spectra reveal a promising red emission band at 685 nm wavelength region under both 351 and 510 nm excitations, which is the required far-red emission for phototropism in plants. Furthermore, the optimized BLN:0.25Mn4+ nanophosphors exhibited all the features required for three levels of latent fingerprint detection on various nonporous surfaces under 365 nm illumination. The fluctuation of the red value on pixel profile confirms the good affinity of BLN:0.25Mn4+ nanophosphors with the fingerprint ridges. Because of their excellent luminescent properties and brilliant performance in the latent fingerprint detection process, the synthesized BLN:Mn4+ nanophosphors can be considered as a promising fluorescent material for the fabrication of plant growth LEDs and latent fingerprint applications.

Due to their high capacity, nickel–cobalt-based cathode materials have attracted significant attention as potential components of hybrid solid-state supercapacitors (HSSCs). However, their poor cycling stability and low rate capability have impeded their implementation. In the present study, a single-step, binder-free potentiodynamic polarization approach is presented for the preparation of battery-type phosphorus-containing amorphous trimetal nickel–ruthenium–cobalt hydroxide (P@NRC-OH) nanofibers on Ni foam for use in high-energy, stable HSSCs. The phosphate dopant and the trimetal-rich electrode surface increase the intrinsic electron conductivity and redox activity and generate a large number of active defects. As a consequence, a P@NRC-OH electrode exhibited enhanced energy storage properties in terms of specific capacity (541.66 mA h g−1 at 3 mA cm−2), cycling durability (90.35% over 20 000 cycles), and rate capability (308.64 mA h g−1 at 20 mA cm−2). An assembled full-cell HSSC with P@NRC-OH nanofibers as the cathode material and porous activated carbon as the anode material produced a maximum specific energy of 90.02 W h kg−1 at a specific power of 1363 W kg−1 which remained as high as 37.87 W h kg−1 at a power density of 6818.18 W kg−1, with remarkable cycling stability over 15 000 charge–discharge cycles. The proposed approach thus represents a scalable and efficient strategy for the design of electrodes and devices with superior electrochemical performance.

Ternary metal sulfide based nanostructured materials are promising for commercialization of the electrochemical energy storage devices. Herein, three different NiCo2S4 nanostructures (nanoflakes, nanosheets, and nanoparticles) were fabricated by electrodeposition. Of these, nanosheets consisting of interconnected nanoparticles formed a highly porous network for supercapacitive energy storage. The electrochemical properties of each electrode were studied in detail and it was observed that the self-supported NiCo2S4 nanosheets possess a highest specific capacity of 590 mA h g−1 (2655 F g−1) at 0.25 A g−1 current density and cycling stability of 88.7% after 5000 charge-discharge cycles. This excellent behavior is attributed to several factors of the electrode such as high electrochemical active sites and ability of a nanostructure to withstand under high strain and accommodate large number of electrolyte ions during charge-discharge. The electrochemical storage properties of the NiCo2S4 nanosheets were further explored by fabricating battery-like solid-state asymmetric supercapacitor with activated carbon that delivered an ultra-high specific energy and power of 69.7 Wh kg−1 and 8 kW kg−1, respectively. These outcomes indicate that the novel nanostructured NiCo2S4 network has great potential for the development of energy storage devices.

Developing highly efficient noble-metal-free electrocatalysts with a scalable and environmentally friendly synthesis approach remains a challenge in the field of electrocatalytic water splitting. To overcome this problem, self-supported fluorine-modified 2D ultrathin nickel hydroxide (F-Ni(OH)

A porous nanostructure and high mass loading are crucial for a pseudocapacitor to achieve a good electrochemical performance. Although pseudocapacitive materials, such as MnO2 and MoS2, with record capacitances close to their theoretical values have been realized, the achieved capacitances are possible only when the electrode mass loading is less than 1 mg cm−2. Increasing the mass loading affects the capacitance as electron conduction and ion diffusion become sluggish. Achieving fast ion and electron transport at high mass loadings through all active sites remains a challenge for high-mass-loading electrodes. In this study, 2D MnO2 nanosheets supported on carbon fibers (MnO2@CF) as well as MoS2@CF with high mass loadings (6.6 and 7.2 mg cm−2, respectively) were used in a high-energy pseudocapacitor. These hierarchical 2D nanosheets yielded outstanding areal capacitances of 1187 and 495 mF cm−2 at high current densities with excellent cycling stabilities. A pliable pseudocapacitive solid-state asymmetric supercapacitor was designed using MnO2@CF and MoS2@CF as the positive and negative electrodes, respectively, with a high mass loading of 14.2 mg cm−2. The assembled solid-state asymmetric cell had an energy density of 2.305 mWh cm−3 at a power density of 50 mW cm−3 and a capacitance retention of 92.25 % over 11 000 cycles and a very small diffusion resistance (1.72 Ω s−1/2). Thus, it is superior to most state-of-the-art reported pseudocapacitors. The rationally designed nanostructured electrodes with high mass loading are likely to open up new opportunities for the development of a supercapacitor device capable of supplying higher energy and power.

In present work, we have developed 2.0 V symmetric supercapacitor with rationally prepared iron tungstate (FeWO4) nanoparticles as electrodes and redox-active electrolyte. It is revealed that the electrochemical performances of FeWO4-system were significantly improved due to the addition of potassium iodide (KI) redox additive in conventional KOH electrolyte in terms of the specific capacitance and energy density. Notably, FeWO4-based symmetric cell with KI-additive shown two-fold enhancement in specific energy (113 Wh/kg) compared with the cell with pristine KOH electrolyte (41.62 Wh/kg). Such an excellent enhancement is attributed to the improvement in the stability of existing KOH electrolyte by KI which influences the strength of OH bond in aqueous media and prevents the breakdown of electrolyte without adversely affecting the redox behavior and on contrary supporting the interactions at the higher potential to produce better results.

A new core-shell structured MnO2@Ni2P2O7 (NPO) nanohybrid with unique nano-design is engineered by simple solution process and utilized as promising positive electrode for solid-state hybrid supercapacitors (HSCs). Firstly, two-dimensional (2D) NPO micro-sheets are grown on the Ni foam where the ultrathin MnO2 nanoflakes are decorated on NPO micro-sheets to realise MnO2@NPO core-shell nanohybrid. The as-synthesized MnO2@NPO electrode delivers impressive electrochemical performances with specific capacity of 309 mA h/g with long-term cycling stability over the 12,000 charge-discharge cycles. A solid-state hybrid supercapacitor (HSC) is fabricated using MnO2@NPO and activated carbon (AC) as positive and negative electrodes with polymer-gel electrolyte. The assembled HSC offers an upgraded cell potential of 1.6 V with high specific energy of 66 Wh/kg at specific power of 640 W/kg. More importantly, the HSC delivers excellent cycling stability over the 10,000 cycles (∼93% of capacity retention) with good energy efficiency at all current densities.

Recently, cuprous oxide (Cu2O) based photocathodes have gained research attention for hydrogen (H2) production through photoelectrochemical (PEC) water splitting reactions due to marginally lower synthesis cost and low energy intensity fabrication processes. Unique properties of Cu2O, such as tunable bandgap, appropriate band edge potentials with water redox levels and non-toxic nature makes it beneficial for PEC applications. Cuprite is mainly studied under visible light to facilitate enhanced H2 gas production upon illumination. However, notoriously photocorrosion degrades the PEC performance and restricts the photoactivity of Cu2O. Moreover, because of the redox potentials lies within the band gap of Cu2O; self-photocorrosion or self-oxidation upon illumination is unavoidable. Improvement in the Cu2O photocathodes was achieved by finding elegant solutions such as forming thin heterojunction layers by atomic layer deposition (ALD) as well other methods, co-catalyst deposition, tuning crystal facets and surface modifications with different synthetic methods. In this review, we discuss the improvements in Cu2O photocathodes achieved over the years for enhanced H2 production with recently studied photocathodes.

Summary Pseudocapacitors hold great promise to provide high energy-storing capacity; however, their capacitances are still far below their theoretical values and they deliver much lower power than the traditional electric double-layer capacitors due to poor ionic accessibility. Here, we have engineered MoN nanoparticles as pseudocapacitive material on phosphorus-incorporated carbon fabric with enhanced ionic affinity and thermodynamic stability. This nanocomposite boosts surface redox kinetics, leading to pseudocapacitance of 400 mF/cm2 (2-fold higher than that of molybdenum nitride-based electrodes) with rapid charge-discharge rates. Density functional theory simulations are used to explain the origin of the good performance of MoN@P-CF in proton-based aqueous electrolytes. Finally, an all-pseudocapacitive solid-state asymmetric cell was assembled using MoN@P-CF and RuO2 (RuO2@CF) as negative and positive electrodes, respectively, which delivered good energy density with low relaxation time constant (τ0) of 13 ms (significantly lower than that of carbon-based supercapacitors)., Graphical Abstract, Highlights • MoN nanocrystals coated on P-doped CF are used as high-performance pseudocapacitors • DFT simulations explain the origin of the good performance of MoN@P-CF electrode • MoN@P-CF and RuO2@CF serve as negative and positive electrodes, in asymmetric SC • All-pseudocapacitive ASC delivers high power density with long cycling stability, Chemistry; Inorganic Chemistry; Materials Science; Energy Materials

The rapid oxidation of silicon nanowires (SiNWs) in an aqueous electrolyte imposes boundaries on their real-world applications. To alleviate this drawback, we propose a novel yet simple hybrid material passivation strategy to increase the energy storage capacity and aqueous electrolyte stability of SiNWs for high-energy efficient supercapacitor (SC) applications. Initially, a porous-activated carbon coating was applied to one-dimensional (1-D) metal-assisted chemically-etched (MACE) SiNWs. Later, the redox-active binary nickel cobaltite (NiCo2O4) fine nanoflakes were directly deposited over the carbonized SiNWs via a hydrothermal route. The resultant 1D core–shell architectured hierarchical SiNWs/carbon(C)/NiCo2O4(NCO) (SiNWs/C/NCO) electrode exhibit a peak capacitance of 2166 F/g, with excellent cycling stability over 10,000 charge-discharge cycles in a KOH electrolyte demonstrates its potential practical applications. To prove this claim, the symmetric hybrid SCs was designed. Notably, the symmetric hybrid SCs delivered an excellent energy density of 1.31 mWh/cm3 at a current density of 1 mA/cm2 with an outstanding energy efficiency (∼70–80% over all current densities), which signified a lower energy waste during the discharge process. These results showed that the hybrid material passivation strategy is useful for boosting the energy storage capacity and aqueous electrolyte stability of SiNWs to develop low-cost, high-energy SCs for real-life applications.

The increasing interest in portable and consumable electronics demands efficient and low-cost energy storage devices with excellent energy storing capacity. From this point, a high mass loading of the active electrode material on three-dimensional current collectors is favorable for obtaining a higher energy storing capacity for the corresponding device. The present study demonstrates an ideal example of high-performance aqueous asymmetric supercapacitors (SCs) using α-MnO2 nanowires as the positive electrode and h-WO3 nanorods as the negative electrode, respectively. Initially, one-dimensional (1D) nanostructures composed of α-MnO2 and h-WO3 are prepared on carbon cloth by a conventional hydrothermal method. The prepared α-MnO2 and h-WO3 with a high mass loading of 4.9 mg/cm2 and 5.8 mg/cm2, respectively, show excellent electrochemical features in aqueous Na2SO4 electrolyte in the positive and negative potential regions. A high-performance asymmetric SC is developed with uniquely engineered electrodes, which exhibits the excellent electrochemical performance in an extended potential window of 1.4 V and with excellent cycling stability of ∼135% after 7500 cycles with a volumetric capacitance of 350 mF/cm3 and energy density of 0.095 mWh/cm3. This authentic scheme may offer new opportunities for developing asymmetric arrangements for energy storage devices in various portable electronic systems with a high mass loading.

The integration of two-dimensional (2D) reduced graphene oxide (rGO) and binary metal oxide in a single electrode for asymmetric supercapacitors (ASC) is promising for overcoming the challenges driven by increasing energy-storage demands. In present work, we proposed a novel rGO/FeCo2O4 hybrid electrode as a negative electrode for asymmetric supercapacitors (ASC). Briefly, we engineered 3-dimensional nanocomposite materials by decorating FeCo2O4 nanoparticles on rGO nanosheets using facile strategy. Owing to the strong chemical bonding between the FeCo2O4 nanoparticles and rGO nanosheets, as-prepared rGO/FeCo2O4 hybrid electrode shows an ultrahigh specific capacitance of 1710 F/g on the negative potential side. Later, asymmetric supercapacitor was assembled using MnO2 nanowires as positive electrode and rGO/FeCo2O4 hybrid as negative electrode, respectively. The proposed device achieved a maximum specific capacitance of 260 F/g with a specific energy of 67.5 Wh/kg and exhibited excellent cycling performance (96.02% capacity retention after 5000 cycles). Thus, the proposed design of the high-energy ASC is promising for next-generation energy-storage devices being developed for modern consumer applications.

The demand for battery-type materials having hierarchical architectures, large surface areas, and excellent redox properties, to develop high energy density asymmetric supercapacitors (ASCs), is increasing. Herein, a facile single-step wet chemical method is proposed, which allows an engineered combination of α-NiMoO4 hierarchical heterostructures to be used as advanced battery-type electrodes for ASCs. The as-synthesized architectures consist of versatile nanogeometries including nanowires, nanosheets, and nanoparticles in the form of Rhynchostylis retusa-like heterostructures, which synergistically enhance the energy storage properties; specifically, at a current density of 2 A g−1, heterostructured α-NiMoO4 exhibits a superior specific capacitance of 1061 F g−1 and an outstanding cycling stability of 96%. Moreover, an aqueous ASC is fabricated by combining such a redox-type α-NiMoO4 heterostructure and activated porous carbon as the positive and negative electrodes, respectively, separated with a piece of filter paper. This device shows high energy and power densities (31.8 W h kg−1 and 786.5 W kg−1, respectively), which are useful to operate various portable electronic appliances. Together with the excellent cycling stability and energy storage properties, the synthesized heterostructured metal molybdates exemplify a new approach to develop novel electrode materials for high-performance aqueous ASCs.