CoOx @NiMoN/Ti3 C2 Tx Interface for Stable High-Performance Electrochemical Energy Storage Devices.

Transition metal nitrides (TMNs) are promising electrode materials for use in high-performance electrochemical energy storage devices due to their unique properties, which include a high conductivity, pseudocapacitance, and energy density. However, structural instability during electrochemical reactions has limited their practical deployment for energy storage devices. In this context, the present study fabricated a CoOx @NiMoN/Ti3 C2 Tx electrode via in situ growth on Ni foam using hydrothermal treatment with post-nitrogenization. The effect of atomic layer deposition (ALD) of CoOx on the TMN/Ti3 C2 Tx interface and the consequent electrochemical charge storage mechanisms are investigated in detail. The proposed CoOx @NiMoN/Ti3 C2 Tx electrode delivers an impressive specific capacity in a 2 m potassium hydroxide (KOH) electrolyte and is then employed in both a hybrid solid-state supercapacitor (HSSC) with reduced graphene oxide and a symmetric SC in a 2 m KOH + polyvinyl alcohol (PVA) gel electrolyte. Outstanding charge storage and high capacity retention during cyclic testing are observed for both energy storage devices. The exceptional electrochemical performance of the fabricated electrode is a result of its high conductivity and high number of active sites. Here a feasible new strategy is demonstrated for the fabrication of stable energy storage devices with a high energy density using TMNs and MXenes.

Regulating Electronic Structure of Iron Nitride by Tungsten Nitride Nanosheets for Accelerated Overall Water Splitting.

Two essential characteristics that are required for hybrid electrocatalysts to exhibit higher oxygen and hydrogen evolution reaction (OER and HER, respectively) activity are a favorable electronic configuration and a sufficient density of active sites at the interface between the two materials within the hybrid. In the present study, a hybrid electrocatalyst is introduced with a novel architecture consisting of coral-like iron nitride (Fe2 N) arrays and tungsten nitride (W2 N3 ) nanosheets that satisfies these requirements. The resulting W2 N3 /Fe2 N catalyst achieves high OER activity (268.5 mV at 50 mA cm-2 ) and HER activity (85.2 mV at 10 mA cm-2 ) with excellent long-term durability in an alkaline medium. In addition, density functional theory calculations reveal that the individual band centers experience an upshift in the hybrid W2 N3 /Fe2 N structure, thus improving the OER and HER activity. The strategy adopted here thus provides a valuable guide for the fabrication of cost-effective multi-metallic crystalline hybrids for use as multifunctional electrocatalysts.

Boosting Pseudocapacitive Behavior of Supercapattery Electrodes by Incorporating a Schottky Junction for Ultrahigh Energy Density.

Pseudo-capacitive negative electrodes remain a major bottleneck in the development of supercapacitor devices with high energy density because the electric double-layer capacitance of the negative electrodes does not match the pseudocapacitance of the corresponding positive electrodes. In the present study, a strategically improved Ni-Co-Mo sulfide is demonstrated to be a promising candidate for high energy density supercapattery devices due to its sustained pseudocapacitive charge storage mechanism. The pseudocapacitive behavior is enhanced when operating under a high current through the addition of a classical Schottky junction next to the electrode-electrolyte interface using atomic layer deposition. The Schottky junction accelerates and decelerates the diffusion of OH‒/K+ ions during the charging and discharging processes, respectively, to improve the pseudocapacitive behavior. The resulting pseudocapacitive negative electrodes exhibits a specific capacity of 2,114 C g-1 at 2 A g-1 matches almost that of the positive electrode's 2,795 C g-1 at 3 A g-1. As a result, with the equivalent contribution from the positive and negative electrodes, an energy density of 236.1 Wh kg-1 is achieved at a power density of 921.9 W kg-1 with a total active mass of 15 mg cm-2. This strategy demonstrates the possibility of producing supercapacitors that adapt well to the supercapattery zone of a Ragone plot and that are equal to batteries in terms of energy density, thus, offering a route for further advances in electrochemical energy storage and conversion processes.

Recent Development Strategies for Bismuth-Driven Materials in Sustainable Energy Systems and Environmental Restoration.

Bismuth(Bi)-based materials have gained considerable attention in recent decades for use in a diverse range of sustainable energy and environmental applications due to their low toxicity and eco-friendliness. Bi materials are widely employed in electrochemical energy storage and conversion devices, exhibiting excellent catalytic and non-catalytic performance, as well as CO2 /N2 reduction and water treatment systems. A variety of Bi materials, including its oxides, chalcogenides, oxyhalides, bismuthates, and other composites, have been developed for understanding their physicochemical properties. In this review, a comprehensive overview of the properties of individual Bi material systems and their use in a range of applications is provided. This review highlights the implementation of novel strategies to modify Bi materials based on morphological and facet control, doping/defect inclusion, and composite/heterojunction formation. The factors affecting the development of different classes of Bi materials and how their control differs between individual Bi compounds are also described. In particular, the development process for these material systems, their mass production, and related challenges are considered. Thus, the key components in Bi compounds are compared in terms of their properties, design, and applications. Finally, the future potential and challenges associated with Bi complexes are presented as a pathway for new innovations.

Core-Shell Engineered WO3 Architectures: Recent Advances from Design to Applications.

Ongoing efforts to design novel materials with efficient structure-property-performance relations prove challenging. Core-shell structures have emerged as novel materials with controlled production routes and highly tailorable properties that offer extensive advantages in advanced oxidation processing, particularly in photocatalysis and photoelectrochemical applications. WO3 , which is an optoelectronically active semiconductor material, is a popular material in current studies in the field of photo(electro)catalysis. Considerable progress has been made using core-shell WO3 architectures, which warrants an evaluation in terms of processing and preparedness for their use in versatile catalytic and energy storage applications. This paper presents an in-depth assessment of core-shell WO3 architectures by highlighting the design challenges and protocols in powder and thin-film chemical processing. The development of specific core-shell designs for use in targeted applications, such as H2 production, CO2 reduction, wastewater treatment, batteries, supercapacitors, and sensing, is analyzed. The fundamental role of WO3 in core-shell structures to enhance efficiency is also discussed, along with the limitations and improvement strategies. Further, the prospects of core-shell WO3 architectures in energy conversion and environmental applications are suggested.

Multilayer Strategy for Photoelectrochemical Hydrogen Generation: New Electrode Architecture that Alleviates Multiple Bottlenecks.

Years of research have demonstrated that the use of multiple components is essential to the development of a commercial photoelectrode to address specific bottlenecks, such as low charge separation and injection efficiency, low carrier diffusion length and lifetime, and poor durability. A facile strategy for the synthesis of multilayered photoanodes from atomic-layer-deposited ultrathin films has enabled a new type of electrode architecture with a total multilayer thickness of 15-17 nm. We illustrate the advantages of this electrode architecture by using nanolayers to address different bottlenecks, thus producing a multilayer photoelectrode with improved interface kinetics and shorter electron transport path, as determined by interface analyses. The photocurrent density was twice that of the bare structure and reached a maximum of 33.3 ± 2.1 mA cm-2 at 1.23 VRHE. An integrated overall water-splitting cell consisting of an electrocatalytic NiS cathode and Bi2S3/NiS/NiFeO/TiO2 photoanode was used for precious-metal-free seawater splitting at a cell voltage of 1.23 V without degradation. The results and root analyses suggest that the distinctive advantages of the electrode architecture, which are superior to those of bulk bottom-up core-shell and hierarchical architectures, originate from the high density of active sites and nanometer-scale layer thickness, which enhance the suitability for interface-oriented energy conversion processes.

Surface Roughening Strategy for Highly Efficient Bifunctional Electrocatalyst: Combination of Atomic Layer Deposition and Anion Exchange Reaction.

Electrocatalytic water splitting, which is an interface-dominated process, can be significantly accelerated by increasing the number of front-line surface active sites (NA ) of the electrocatalyst. In this study, a unique method is used for increasing the NA by converting the smooth ultrathin atomic-layer-deposited nanoshells of the electrocatalysts into nano-roughened active shell layers using a controlled anion-exchange reaction (AER). The coarse thin nanoshells present abundant surface active sites, which are generated owing to the inherent unit-cell volume mismatch induced during the AER. Consequently, the nano-roughened electrodes accelerate the sluggish water reaction kinetics and lower the overpotentials required for the hydrogen and oxygen evolution reactions. In addition, the electronic modulation induced by the nanoshell layer at the core-nanoshell interface amplifies the local electron density, as confirmed using electrochemical analysis data and density functional theory calculations. Because of the integrity of the composite electrodes during water-splitting half-cell reactions, their durability for industrial seawater electrolysis is evaluated. The results indicate that their electrochemical activity does not change significantly after 10 days of continuous overall water splitting.

Three-Dimensional Hierarchical Core/shell Electrodes Using Highly Conformal TiO2 and Co3O4 Thin Films for High-Performance Supercapattery Devices.

The rational design and development of novel electrode materials with promising nanostructures is an effective technique to improve their supercapacitive performance. This work presents high-performance core/shell electrodes based on three-dimensional hierarchical nanostructures coated with conformal thin transition-metal oxide layers using atomic layer deposition (ALD). This effective interface engineering creates disorder in the electronic structure and coordination environment at the interface of the heteronanostructure, which provides many more reaction sites and rapid ion diffusion. At 3 A g-1, the positive CuCo2O4/Ni4Mo/MoO2@ALD-Co3O4 electrode introduced here exhibits a specific capacity of 1029.1 C g-1, and the fabricated negative Fe3O4@ALD-TiO2 electrode significantly outperforms conventional carbon-based electrodes, with a maximum specific capacity of 372.6 C g-1. The supercapattery cell assembled from these two interface- and surface-tailored electrodes exhibits a very high energy density of 110.4 W h kg-1 with exceptional capacity retention over 20,000 cycles, demonstrating the immense potential of ALD for the next generation of supercapacitors.

1D/2D constructed Bi2S3/Bi2O2CO3 direct Z-Scheme heterojunction: A versatile photocatalytic material for boosted photodegradation, photoreduction and photoelectrochemical detection of water-based contaminants.

In this work, two-dimensional Bi2O2CO3 disk is synthesized, followed by the growth of Bi2S3 over Bi2O2CO3 via topotactic transformation by controlling the amount of thiourea under hydrothermal conditions. The synthesized composite catalyst is investigated for photocatalytic oxidation and reduction of tetracycline hydrochloride and hexavalent chromium under visible light irradiation. High interfacial contact between the Bi2O2CO3 disk0 and Bi2S3 fiber is confirmed via high-resolution microscopic imaging. Enhanced light absorption and increased charge carrier separation is observed after the formation of the Bi2S3/Bi2O2CO3 composite. The Bi2S3/Bi2O2CO3 composite grown using 1 mmol of thiourea shows approximately 98% degradation of tetracycline hydrochloride after 120 min and 99% Cr(VI) reduction after 90 min of photochemical reaction under visible light irradiation. The charge separation is due to the formed internal electric field at the interface, which upon light irradiation follows a z-scheme charge transfer hindering the recombination at the Bi2S3 and Bi2O2CO3 interface, thereby contributing efficiently to the photochemical process. In addition, the mechanism of the photochemical reaction for the degradation of pollutants is supported using quencher and probe experiments. Furthermore, photoelectrochemical detection of antibiotic in aqueous solution is conducted to understand the sensing feasibility of the synthesized system.

Encapsulation of Co3 O4 Nanocone Arrays via Ultrathin NiO for Superior Performance Asymmetric Supercapacitors.

Designing of multicomponent transition metal oxide system through the employment of advanced atomic layer deposition (ALD) technique over nanostructures obtained from wet chemical process is a novel approach to construct rational supercapacitor electrodes. Following the strategy, core-shell type NiO/Co3 O4 nanocone array structures are architectured over Ni-foam (NF) substrate. The high-aspect-ratio Co3 O4 nanocones are hydrothermally grown over NF following the precision controlled deposition of shell NiO considering Co3 O4 nanocone as host. NiO thickness of 5 nm exhibits the highest specific capacity of 1242 C g-1 (2760 F g-1 ) at current density 2 A g-1 , which is greater than pristine Co3 O4 @NF (1045.8 C g-1 or 2324 F g-1 ). The rate capability with 5 nm NiO/Co3 O4 @NF nanocone structures is about 77% whereas Co3 O4 @NF retains 46 % of capability at 10 A g-1 . The ultrathin ALD 5 nm NiO accelerates both rate capability and 95.5% cyclic stability after 12 000 charge-discharge cycles. An asymmetric device fabricated between 5 nm NiO/Co3 O4 @NF (positive) || activated carbon (negative) achieves an energy density of 81.45 Wh kg-1 (4268 W kg-1 ) with good cycling device stability. Additionally, LEDs can be energized by two ASC device in series. This work opens the path in both advanced electrode material and surface modification of earth-abundant systems for efficient and real-time supercapacitor applications.

Effect of Randomly Grown Morphology of ZnO Nanorods in Inverted Organic Solar Cells.

Here, we analyzed the photovoltaic properties of the inverted organic solar cells (IOSCs) by using randomly oriented medium density ZnO nanorods (ZnO-NR) synthesized hydrothermally at low temperature conditions to avoid morphological defects. The IOSC with ZnO-NR (length < 150 nm) of medium density and random orientation showed an improvement of 83% in power conversion efficiency compared to the cell with (length < 20 nm) hydrothermally grown ZnO-NR. The optimized hydrothermal growth conditions for ZnO-NR enhanced the photovoltaic performance indicators by reducing recombination rate evidenced by the photovoltaic data. The qualitative elemental analysis of the ZnO-NR based interface was performed by the EDX, which confirmed that the as-grown ZnO-NR contain the Zn and O elements.

Insights into the interfacial nanostructuring of NiCo2S4 and their electrochemical activity for ultra-high capacity all-solid-state flexible asymmetric supercapacitors.

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.

Interactive Fe2O3/porous SiO2 nanospheres for photocatalytic degradation of organic pollutants: Kinetic and mechanistic approach.

A uniformly distributed mesoporous silica nanospheres has been successfully synthesized. Silica nanospheres have been loaded with different content of Fe2O3 nanoparticles synthesized by the sol-gel process followed by calcination to form the Fe2O3 supported on silica nanospheres composite. The as-synthesized photocatalyst has been characterized for crystal structure, morphology, stability, surface area and also surface composition was determined. The photocatalytic oxidation ability of the composite photocatalyst was evaluated by degrading aqueous solutions of Methylene Blue and Congo red dyes under visible light having intense absorption in the wavelength range between 550 and 560 nm. The prime significance of silica is to act as catalyst support for uniform distribution of hematite particles for enhanced catalytic reactivity. Highest degradation has been achieved with 20 wt % loading of hematite nanoparticles indicating the less agglomeration and availability of more catalytic sites. Furthermore, colorless organic pollutants 2-chlorophenol and 2, 4-dichlorophenol have been degraded with high efficiency in the presence of H2O2 oxidizer. The scavenger experiments confirmed that hydroxyl radicals are the majorly participating species in this catalytic system. The composite system also shows good recyclability of the materials and advocates the promising nature of the designed system for multiple hazardous environmental contaminants.

Self-Assembled Nickel Pyrophosphate-Decorated Amorphous Bimetal Hydroxides 2D-on-2D Nanostructure for High-Energy Solid-State Asymmetric Supercapacitor.

To obtain a supercapacitor with a remarkable specific capacitance and rate performance, a cogent design and synthesis of the electrode material containing abundant active sites is necessary. In present work, a scalable strategy is developed for preparing 2D-on-2D nanostructures for high-energy solid-state asymmetric supercapacitors (ASCs). The self-assembled vertically aligned microsheet-structured 2D nickel pyrophosphate (Ni2 P2 O7 ) is decorated with amorphous bimetallic nickel cobalt hydroxide (NiCo-OH) to form a 2D-on-2D nanostructure arrays electrode. The resulting Ni2 P2 O7 /NiCo-OH 2D-on-2D array electrode exhibits peak specific capacity of 281 mA hg-1 (4.3 F cm-2 ), excellent rate capacity, and cycling stability over 10 000 charge-discharge cycles in the positive potential range. The excellent electrochemical features can be attributed to the high electrical conductivity and 2D layered structure of Ni2 P2 O7 along with the Faradic capacitance of the amorphous NiCo-OH nanosheets. The constructed Ni2 P2 O7 /NiCo-OH//activated carbon based solid-state ASC cell operates in a high voltage window of 1.8 V with an energy density of 78 Wh kg-1 (1.065 mWh cm-3 ) and extraordinary cyclic stability over 10 000 charge-discharge cycles with excellent energy efficiency (75%-80%) over all current densities. The excellent electrochemical performance of the prepared electrode and solid-state ASC device offers a favorable and scalable pathway for developing advanced electrodes.

Interface-Engineered Nickel Cobaltite Nanowires through NiO Atomic Layer Deposition and Nitrogen Plasma for High-Energy, Long-Cycle-Life Foldable All-Solid-State Supercapacitors.

The large-scale application of supercapacitors (SCs) for portable electronics is restricted by low energy density and cycling stability. To alleviate the limitations, a unique interface engineering strategy is suggested through atomic layer deposition (ALD) and nitrogen plasma. First, commercial carbon cloth (CC) is treated with nitrogen plasma and later inorganic NiCo2 O4 (NCO)/NiO core-shell nanowire arrays are deposited on nitrogen plasma-treated CC (NCC) to fabricate the ultrahigh stable SC. An ultrathin layer of NiO deposited on the NCO nanowire arrays via conformal ALD plays a vital role in stabilizing the NCO nanowires for thousands of electrochemical cycles. The optimized NCC/NCO/NiO core-shell electrode exhibits a high specific capacitance of 2439 F g-1 with a remarkable cycling stability (94.2% over 20 000 cycles). Benefiting from these integrated merits, the foldable solid-state SCs are fabricated with excellent NCC/NCO/NiO core-shell nanowire array electrodes. The fabricated SC device delivers a high energy density of 72.32 Wh kg-1 at a specific capacitance of 578 F g-1 , with ultrasmall capacitance decline rate of 0.0003% per cycle over 10 000 charge-discharge cycles. Overall, this strategy offers a new avenue for developing a new-generation high-energy, ultrahigh stable supercapacitor for real-life applications.

Dendritic Nanostructured Waste Copper Wires for High-Energy Alkaline Battery.

Rechargeable alkaline batteries (RABs) have received remarkable attention in the past decade for their high energy, low cost, safe operation, facile manufacture, and eco-friendly nature. To date, expensive electrode materials and current collectors were predominantly applied for RABs, which have limited their real-world efficacy. In the present work, we propose a scalable process to utilize electronic waste (e-waste) Cu wires as a cost-effective current collector for high-energy wire-type RABs. Initially, the vertically aligned CuO nanowires were prepared over the waste Cu wires via in situ alkaline corrosion. Then, both atomic-layer-deposited NiO and NiCo-hydroxide were applied to the CuO nanowires to form a uniform dendritic-structured NiCo-hydroxide/NiO/CuO/Cu electrode. When the prepared dendritic-structured electrode was applied to the RAB, it showed excellent electrochemical features, namely high-energy-density (82.42 Wh kg-1), excellent specific capacity (219 mAh g-1), and long-term cycling stability (94% capacity retention over 5000 cycles). The presented approach and material meet the requirements of a cost-effective, abundant, and highly efficient electrode for advanced eco-friendly RABs. More importantly, the present method provides an efficient path to recycle e-waste for value-added energy storage applications.

Enhancing Durability and Photoelectrochemical Performance of the Earth Abundant Ni-Mo/TiO2 /CdS/CIGS Photocathode under Various pH Conditions.

Cu(In,Ga)(S,Se)2 (CIGS) is a promising photocathode material owing to its high absorption coefficient, adjustable band gap, and suitable band edge for the hydrogen evolution reaction (HER). However, most CIGS photocathodes have suffered from instability in applications that require a wide range of pH conditions and have utilized noble metal HER catalysts to achieve a high performance. Thus, improving the durability of the CIGS photocathode under various pH conditions and developing a cost-effective non-noble metal catalyst are critical issues in the photoelectrochemical (PEC) application of this promising photocathode material. Here, we catalyze the CIGS photocathode with Ni-Mo as a non-noble metal to enhance the PEC efficiency, and we employ atomically grown TiO2 to passivate the CdS/CIGS surface and improve the stability under a wide range of pH conditions. Our Ni-Mo alloy exhibits the best HER catalytic activity among reported earth-abundant HER catalysts in both acidic and alkaline solutions. The Ni-Mo/CdS/CIGS photocathode yields an onset potential of 0.5 V (vs. RHE) and a short-circuit photocurrent density as high as 15-25 mA cm-2 under various pH conditions ranging from 0.4 to 14, which is highly comparable to that of Pt/CdS/CIGS. Furthermore, the passivation of CdS/CIGS with a thin TiO2 layer, obtained by atomic layer deposition, effectively prevents the photocorrosion of CdS and the dissolution of the Mo back contact, which are the main causes of the degradation of the photocathode. The optimized Ni-Mo/TiO2 /CdS/CIGS photocathode produces a stable photocurrent density at 0 VRHE for 100 minutes except under strong alkaline conditions. The current work presents a very useful method to improve the efficiency and durability of the CIGS photocathodes with an earth-abundant metal catalyst, which completely replaces Pt.

Towards flexible solid-state supercapacitors for smart and wearable electronics.

Flexible solid-state supercapacitors (FSSCs) are frontrunners in energy storage device technology and have attracted extensive attention owing to recent significant breakthroughs in modern wearable electronics. In this study, we review the state-of-the-art advancements in FSSCs to provide new insights on mechanisms, emerging electrode materials, flexible gel electrolytes and novel cell designs. The review begins with a brief introduction on the fundamental understanding of charge storage mechanisms based on the structural properties of electrode materials. The next sections briefly summarise the latest progress in flexible electrodes (i.e., freestanding and substrate-supported, including textile, paper, metal foil/wire and polymer-based substrates) and flexible gel electrolytes (i.e., aqueous, organic, ionic liquids and redox-active gels). Subsequently, a comprehensive summary of FSSC cell designs introduces some emerging electrode materials, including MXenes, metal nitrides, metal-organic frameworks (MOFs), polyoxometalates (POMs) and black phosphorus. Some potential practical applications, such as the development of piezoelectric, photo-, shape-memory, self-healing, electrochromic and integrated sensor-supercapacitors are also discussed. The final section highlights current challenges and future perspectives on research in this thriving field.

Asymmetric Supercapacitors Based on Reduced Graphene Oxide with Different Polyoxometalates as Positive and Negative Electrodes.

Nanofabrication using a "bottom-up" approach of hybrid electrode materials into a well-defined architecture is essential for next-generation miniaturized energy storage devices. This paper describes the design and fabrication of reduced graphene oxide (rGO)/polyoxometalate (POM)-based hybrid electrode materials and their successful exploitation for asymmetric supercapacitors. First, redox active nanoclusters of POMs [phosphomolybdic acid (PMo12 ) and phosphotungstic acid (PW12 )] were uniformly decorated on the surface of rGO nanosheets to take full advantage of both charge-storing mechanisms (faradaic from POMs and electric double layer from rGO). The as-synthesized rGO-PMo12 and rGO-PW12 hybrid electrodes exhibited impressive electrochemical performances with specific capacitances of 299 (269 mF cm-2 ) and 370 F g-1 (369 mF cm-2 ) in 1 m H2 SO4 as electrolyte at 5 mA cm-2 . An asymmetric supercapacitor was then fabricated using rGO-PMo12 as the positive and rGO-PW12 as the negative electrode. This rGO-PMo12 ∥rGO-PW12 asymmetric cell could be successfully cycled in a wide voltage window up to 1.6 V and hence exhibited an excellent energy density of 39 Wh kg-1 (1.3 mWh cm-3 ) at a power density of 658 W kg-1 (23 mW cm-3 ).

Ultrathin Mesoporous RuCo2 O4 Nanoflakes: An Advanced Electrode for High-Performance Asymmetric Supercapacitors.

A new ruthenium cobalt oxide (RuCo2 O4 ) with a unique marigold-like nanostructure and excellent performance as an advanced electrode material has been successfully prepared by a simple electrodeposition (potentiodynamic mode) method. The RuCo2 O4 marigolds consist of numerous clusters of ultrathin mesoporous nanoflakes, leaving a large interspace between them to provide numerous electrochemically active sites. Strikingly, this unique marigold-like nanostructure provided excellent electrochemical performance in terms of high energy-storage capacitance (1469 F g-1 at 6 A g-1 ) with excellent rate proficiency and long-lasting operating cycling stability (ca. 91.3 % capacitance retention after 3000 cycles), confirming that the mesoporous nanoflakes participate in the ultrafast electrochemical reactions. Furthermore, an asymmetric supercapacitor was assembled using RuCo2 O4 (positive electrode) and activated carbon (negative electrode) with aqueous KOH electrolyte. The asymmetric design allowed an upgraded potential range of 1.4 V, which further provided a good energy density of 32.6 Wh kg-1 (1.1 mWh cm-3 ). More importantly, the cell delivered an energy density of 12.4 Wh kg-1 even at a maximum power density of 3.2 kW kg-1 , which is noticeably superior to carbon-based symmetric systems.