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 (Ni2P2O7) is decorated with amorphous bimetallic nickel cobalt hydroxide (NiCo‐OH) to form a 2D‐on‐2D nanostructure arrays electrode. The resulting Ni2P2O7/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 Ni2P2O7 along with the Faradic capacitance of the amorphous NiCo‐OH nanosheets. The constructed Ni2P2O7/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.

traditional battery systems. [10,11] Practically, lower energy density bounds the applicability of supercapacitors over battery systems, leaving more room in developing high energy density supercapacitors without having to compromise the power competence. [12-14] A well-known approach offering such outstanding energy density is via fabrication of asymmetric supercapacitor device that focusses on the positive materials excellency exhibiting high specific capacitance and providing a broad potential window when combined with a double-layer type negative electrode material. [15-17] Co 3 O 4 , a pseudocapacitive metal oxide, belonging to the family of spinel is a promising positive active material in electrochemical energy storage devices owing to its high specific capacitance (3560 F g −1) theoretically with being earthabundant, cost-effective, and also environment friendly. [18-20] Pseudocapacitors follow faradaic redox electrochemical reactions on the material's surface through continuous intercalation/deintercalation of electrons or ions which makes the surface vulnerable to destruction resulting in lower efficiency of the electroactive material affecting the electrochemical cycles. [21-23] Therefore, much effort has been put forward to increase the efficiency and stability of the Co 3 O 4 structures through nanostructured, [18] heterostructured, [24,25] and core-shell type structures [26] to reduce the structural deterioration from Co 3 O 4 and increase the overall specific capacitances. For instance, a 3D hierarchical structure of CoWO 4 /Co 3 O 4 was developed that exhibited significantly high specific capacitance of 1728 F g −1 at a current density of 1 A g −1 retaining about 85.9% specific capacitance after 5000 cycles. [27] Paliwal and Meher design a heterostructure of Co 3 O 4 /NiCo 2 O 4 perforated nanosheets that delivers specific capacitance of 1767 F g −1 at a current density of 0.5 A g −1 maintaining 552 F g −1 capacitance at high current density 16 A g −1. Additionally, the asymmetric device composed of Co 3 O 4 /NiCo 2 O 4 ||N-rGO retains 93.8% areal capacitance after 10 000 operating cycles. [28] An excellent core-shell type CoO@Co 3 O 4 nanocrystals were grown solvothermally which delivered 3377 F g −1 specific capacitance at current density 2 A g −1 and the capacity retention was about 58.6% after 4000 charge-discharge cycles. [29] Lu et al. reported Co 3 O 4 /CoS core-shell nanosheets grown over Ni-foam by room temperature sulfurization process. The structure showed an improved specific capacitance as high as 1658 F g −1 at 1 A g −1 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/Co 3 O 4 nanocone array structures are architectured over Ni-foam (NF) substrate. The high-aspect-ratio Co 3 O 4 nanocones are hydrothermally grown over NF following the p...

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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 NiCo2O4 (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.

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Consequently, many different materials, including carbon, [2] metal oxides, [3] metal sulfides, [4] and conducting polymers, [5] have been assessed for SC applications in order to achieve electrodes with the desired electrochemical properties. Particularly, the redox chemistry of an electrode material strongly affects its electrochemical properties. Considering the importance of redox chemistry in SCs, electrode materials based on redox-rich mixed-transition-metal oxides such as MCo 2 O 4 , MFe 2 O 4 , and MMn 2 O 4 (where M is a metal cation) have been extensively tested in SCs owing to their multiple oxidation states and superior electrical conductivities, specific capacitances, and electrochemical stabilities as compared to those their parent unitary metal oxides. [6] Consequently, several mixed-transitionmetal oxides with different compositions, such as NiCo 2 O 4 , FeCo 2 O 4 , CoFe 2 O 4 , and NiMn 2 O 4 , have already been assessed for application as SC materials. [7][8][9][10] However, among these possible compositions, NiCo 2 O 4 has been the most studied. [11] Cationic substitution of the Co content in MCo 2 O 4 -based electrodes by any new metal cation having a different oxidation state will effectively improve its electrochemical performance. Therefore, it is necessary to test some advanced Co-replacing metal cations. In that respect, RuCo 2 O 4 provides better electrochemical results as both the metal cations have different oxidation states and high electrical conductivity. [12] The problem with the production of Ru/Co-based materials is the high cost of the raw materials. Consequently, researchers are constantly trying to find cheaper alternatives to Ru/Co-based materials. However, there is no doubt that Ru/Co-based metal oxides exhibit superior supercapacitive properties in terms of electrical conductivity, specific capacitance, and cycling stability. More importantly, the different oxidations states of the Ru and Co metal cations improve energy storing capacity, while the higher electrical conductivity supports fast charge-transfer processes. Thus, the aim of the present work was to combine Ru and Co metal cations in a single electrode to take full advantage of both metal cations.In this work, novel thin films composed of RuCo 2 O 4 nanobelts have been grown on low-cost stainless steel mesh The superfast (≈30 min) and template-free electrochemical approach is developed to prepare the unique nanobelts-architectured RuCo 2 O 4 thin films over the stainless steel mesh substrates. The vertically aligned and interconnected RuCo 2 O 4 nanobelts present sufficient interspace to provide more electroactive sites and shorten the diffusion path for electrolyte ions. Owing to their unique nanostructure and higher electrical conductivity, the RuCo 2 O 4 nanobelts exhibit excellent electrochemical features, including a specific capacitance of 1447 F g −1 , and excellent electrochemical stability (82.25% retention over 16 000 cycles). Additional electrochemical kinetic analysis is carried out to confirm whet...

HIGHLIGHTS • Electronic waste Cu wires were successfully used as a cost-effective current collector for high-energy wire-type rechargeable alkaline batteries. • The scalable approach was applied to reduce, reuse, and recycle electronic waste. • A developed wire-type rechargeable alkaline battery exhibited a high-energy-density of 82.42 Wh kg −1 with long-term cycling stability. ABSTRACT Rechargeable alkaline batteries (RABs) have received remarkable attention in the past decade for their high energy, low cost, safe operation, facile manufacture, and ecofriendly 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 atomiclayer-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.

Carbon cloth (CC) is a basic component for various electrochemical applications including supercapacitors, batteries, and catalysts. However, the hydrophobic nature and poor compatibility of CC with electrolyte ions remain an issue. In the present work, we developed a simple yet effective nitrogen plasma approach to induce nanostructuring over the CC, thereby significantly increasing the wettability and surface area of the CC, which both favor robust electrochemical reactions. In addition to this, nitrogen doping on the surface of the CC allowed more electroactive species for electrochemical reactions. Benefiting from these integrated merits, the plasma-treated nitrogen-doped CC (NCC) shows excellent supercapacitive features including an areal capacitance of 741 mF/cm 2 , which is much higher than that of the bare CC. Moreover, the NCC shows excellent cycling stability over 5000 charge-discharge cycles without losing its initial capacitance. The presented approach provides an innovative route to design and develop highly efficient carbon-based electrodes for supercapacitor applications. The irregularity of renewable energy resources induced by environmental pollution and global warming has driven the development of efficient and pollution-free energy-generating and storage devices.1-3 Among the different available technologies, the production of hydrogen via the electrocatalysis of water and storing electricity in electrochemical energy storage devices are promising approaches. 4-9The critical factor for such devices is the design and development of advanced electrode materials and electrolytes using cost-effective techniques. In previous research, various electroactive materials and electrolytes have been utilized to enhance the electrochemical performance of energy-generating and -storing devices. Current collectors are also important in determining the overall electrochemical performance of such devices, but current collectors are rarely explored in existing literature toward enhancing the electrochemical performance of devices.10 Typically, metal-based current collectors like stainless steel (SS), nickel foam, and plates of copper and titanium are used for electrochemical devices because they offer high electrical conductivity and ductility. Despite this advantage, the bulky and heavy nature of metallic current collectors limit their large-scale application. Moreover, the corrosion of metal-based current collectors in liquid electrolytes constrained the working lifetimes of metal-based electrochemical devices. From a practical perspective, high areal and volumetric electrochemical performances (like the areal capacitance) are very important. For metal-based current collectors, achieving the desired area-or volumenormalized electrochemical performance requires larger current collectors, thereby lowering the weight-normalized electrochemical performance in the final product.Carbon-based current collectors such as carbon cloth (CC) and graphite paper have numerous advantages over metal-based current collectors,...