Co3O4 Supraparticle-Based Bubble Nanofiber and Bubble Nanosheet with Remarkable Electrochemical Performance

Oxygen vacancies refilling and potassium ions intercalation of δ-manganese dioxide with high structural stability toward 2.3 V high voltage asymmetric supercapacitors

Oxygen vacancies occupation and coordination environment modulation of the transition-metal based electrodes are effective strategies to improve the structural stability and electrochemical performance. In this work, the 2-methylimidazole (2-MI) doped manganese dioxide (MnO2) anchored on carbon cloth (CC) is fabricated via a simple method (MI-MnO2-x/CC), where the oxygen defects on/inside the K+ doped δ-MnO2 nanosheets are in-situ created by reductive ethanol/Mn2+ and occupied by 2-MI ligands. With the pre-embedded K+ ions and abundant ligand-refilled defects, the electronic coordination structure, structural stability and electron/ion diffusion efficiency can be effectively enhanced. Therefore, the MI-MnO2-x/CC reveals a remarkable specific capacitance of 721.2 mF cm-2 with excellent cycle durability (capacitance retention of 93.4% after 10,000 cycles) under 1.3 V operation potential window. In addition, an asymmetric supercapacitor assembled by MI-MnO2-x/CC and activated mechanical exfoliated graphene oxide yields a maximum energy density of 57.0 Wh kg-1 and a highest power density of 23.0 kW kg-1 under 2.3 V. This effective oxygen defect stabilization strategy by ligands refilling can be extended to various metal oxide-based electrodes for energy storage and conversion.

Pd Doped Co3O4 Loaded on Carbon Nanofibers as Highly Efficient Free-Standing Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions

Self-supporting electrodes usually show excellent electrocatalytic performance which does not require coating steps, additional polymer binders, and conductive additives. Rapid in situ growth of highly active ingredient on self-supporting electric conductors is identified as a straight forward path to prepare binder-free and integrated electrodes. Here, Pd-doped Co₃O₄ loaded on carbon nanofiber materials through electrospinning and heat treatment was efficiently synthesized, and used as a free-standing electrode. Benefiting from its abundant active sites, high surface area and effective ionic conduction capability from three-dimensional (3D) nanofiber framework, Pd-Co₃O₄@CNF works as bifunctional oxygen electrode and exhibits superior activity and stability superior to commercial catalysts.

Flexible electrodes with high areal capacity based on electrospun fiber mats

The ever-growing portable, flexible, and wearable devices impose new requirements from power sources. In contrast to gravitational metrics, areal metrics are more reliable performance indicators of energy storage systems for portable and wearable devices. For energy storage devices with high areal metrics, a high mass loading of the active species is generally required, which imposes formidable challenges on the current electrode fabrication technology. In this regard, integrated electrodes made by electrospinning technology have attracted increasing attention due to their high controllability, excellent mechanical strength, and flexibility. In addition, electrospun electrodes avoid the use of current collectors, conductive additives, and polymer binders, which can essentially increase the content of the active species in the electrodes as well as reduce the unnecessary physically contacted interfaces. In this review, the electrospinning technology for fabricating flexible and high areal capacity electrodes is first highlighted by comparing with the typical methods for this purpose. Then, the principles of electrospinning technology and the recent progress of electrospun electrodes with high areal capacity and flexibility are elaborately discussed. Finally, we address the future perspectives for the construction of high areal capacity electrodes using electrospinning technology to meet the increasing demands of flexible energy storage systems.

All Si3 N4 Nanowires Membrane Based High-Performance Flexible Solid-State Asymmetric Supercapacitor

Recently, much attention has been drawn in the development of flexible energy storage devices due to the increasing demands for flexible/portable electronic devices with high energy density, low weight, and good flexibility. Herein, vertically oriented graphene nanosheets (VGNs) are in situ fabricated on the surface of free-standing and flexible Si₃ N₄ nanowires (NWs) membrane by plasma-enhanced chemical vapor deposition (PECVD), which are directly used as flexible nanoscale conductive substrates. NiCo₂ O₄ hollow nanospheres (HSs) and FeOOH amorphous nanorods (NRs) are finally prepared on Si₃ N_4NWs @VGNs, which are served as the positive and negative electrodes, respectively. Profiting from the structural merits, the synthesized Si₃ N_4NWs @VGNs@NiCo₂ O_4HSs and Si₃ N_4NWs @VGNs@FeOOH_NRs membrane electrodes exhibit remarkable electrochemical performance. Using Si₃ N_4NWs membrane as the separator, the assembled all Si₃ N_4NWs membrane-based flexible solid-state asymmetric supercapacitor (ASC) with a wide operating potential window of 1.8 V yields the outstanding energy density of 96.3 Wh kg^-1 , excellent cycling performance (91.7% after 6000 cycles), and good mechanical flexibility. More importantly, this work provides a rational design strategy for the preparation of flexible electrode materials and broadens the applications of Si₃ N_4NWs in the field of energy storage.

Metal-Organic Framework (MOF)-Derived Electron-Transfer Enhanced Homogeneous PdO-Rich Co3 O4 as a Highly Efficient Bifunctional Catalyst for Sodium Borohydride Hydrolysis and 4-Nitrophenol Reduction

Developing a bifunctional catalyst with low cost and high catalytic performance in NaBH₄ hydrolysis for H₂ generation and selective reduction of nitroaromatics will make a significant impact in the field of sustainable energy and water purification. Herein, a low-loading homogeneously dispersed Pd oxide-rich Co₃ O₄ polyhedral catalyst (PdO-Co₃ O₄ ) with concave structure is reported by using a metal-organic framework (MOF)-templated synthesis method. The results show that the PdO-Co₃ O₄ catalyst has an exceptional turnover frequency (3325.6 mol_H2  min^-1  mol_Pd ^-1 ), low activation energy (43.2 kJ mol^-1 ), and reasonable reusability in catalytic H₂ generation from NaBH₄ hydrolysis. Moreover, the optimized catalyst also shows excellent catalytic performance in the NaBH₄ selective reduction of 4-nitrophenol to 4-aminiphenol with a high first-order reaction rate of approximately 1.31 min^-1 . These excellent catalytic properties are mainly ascribed to the porous concave structure, monodispersed Pd oxide, as well as the unique synergy between PdO and Co₃ O₄ species, which result in a large specific surface area, high conductivity, and fast solute transport and gas emissions.

A General Electrodeposition Strategy for Fabricating Ultrathin Nickel Cobalt Phosphate Nanosheets with Ultrahigh Capacity and Rate Performance

Transition-metal phosphates/phosphides possess promising theoretical electrochemical characteristics and exhibit great potential in advanced supercapacitors. Unfortunately, limited by the processing techniques and overall structure, their specific capacity and rate performance are still unsatisfactory. Herein, we report the fabrication of transition-metal phosphate electrodes with an ultrathin sheetlike array structure by one-step electrodeposition at room temperature. As a proof-of-concept, a transition-metal phosphate member of NiCo(HPO₄)₂·3H₂O with an ultrathin nanosheet structure (thickness ∼2.3 nm) was synthesized and investigated. The as-prepared NiCo(HPO₄)₂·3H₂O electrode showcases an ultrahigh specific capacity of 1768.5 C g^-1 at 2 A g^-1 (the highest value for transition-metal phosphates/phosphides reported to date), superb rate performance of 1144.8 C g^-1 at 100 A g^-1, and excellent electrochemical stability. Moreover, the transition-metal phosphate nanosheet array can be uniformly deposited on various conductive substrates, demonstrating the generality of our strategy. Therefore, this simple electrodeposition strategy provides an opportunity to fabricate ultrathin transition-metal phosphate nanosheet materials that can be used for energy storage/conversion, electrocatalysis, and other electrochemical energy-related devices.

Efficient antimony removal by self-assembled core-shell nanocomposite of Co3O4@rGO and the analysis of its adsorption mechanism

Co₃O₄@rGO were facilely prepared by template free self-assemble in this study. The morphology of Co₃O₄@rGO was actiniaria-like core-shell structural nanocomposites. The formation mechanism of Co₃O₄@rGO core-shell nanocomposite was discussed according to its significant time-dependent morphology evolution course. To evaluate the application potential of Co₃O₄@rGO, its adsorption performance toward highly toxic antimony ions were studied. The Co₃O₄@rGO nanocomposite exhibit high anti-interference ability and high adsorption ability. The maximum adsorption capacities towards Sb(III) and Sb(V) are 151.04 and 165.51 mg/g, respectively. River water samples containing antimony violating the limit were used to evaluate the practical application of Co₃O₄@rGO, and high performance was achieved. The EU and China limits for antimony in drinking water can be met by using mesoporous Co₃O₄@rGO treating the actual river water samples with original antimony concentration lower than 50 μg/L. Adsorption isotherm, adsorption kinetics, pH and co-existing ions effects were also studied in details. The results indicate that mesoporous Co₃O₄@rGO is an excellent adsorbent for antimony removal. Mesoporous Co₃O₄@rGO nanocomposite is a potential candidate for antimony removal from waste water.

High performance flexible hybrid supercapacitors based on nickel hydroxide deposited on copper oxide supported by copper foam for a sunlight-powered rechargeable energy storage system

Herein, an integrated system combining solar cells with a hybrid supercapacitor for operating a homemade windmill device was assembled, achieving energy conversion, storage and utilization. As a candidate for positive electrode of hybrid supercapacitor devices, battery-like Ni(OH)₂@CuO@Cu binder-free electrode was fabricated by a two-step process at ambient temperature. CuO@Cu was prepared by chemical oxidation method to act as the supporting electrode for electrochemical deposition of Ni(OH)₂. Various deposition times (30, 50, 90, 150 and 200 s) were investigated to optimize the energy storage characteristics of the resulting Ni(OH)₂@CuO@Cu electrode materials. Among all the samples, Ni(OH)₂@CuO@Cu-150 exhibited the largest areal capacity of 7063 mC cm^-2 at 20 mA cm^-2, and was therefore chosen as the positive electrode in a hybrid supercapacitor device. Using N-doped reduced graphene oxide on nickel foam (N-rGO/NF) as the negative electrode, a hybrid supercapacitor was assembled. It displayed good flexibility, cycling stability and high areal energy density of 130.4 μWh cm^-2 at a power density of 1.6 mW cm^-2. Two hybrid supercapacitor devices were connected in series to successfully lighten up a red LED for 12 min 39 s, while three devices assembled in series were able to successfully power a three-digit digital display for 1 min 28 s. Interestingly, the hybrid supercapacitor device, charged by solar cells, further operated a homemade windmill device for 59 s, achieving sunlight-powered integration system. All of the findings suggested the practical application potential of the hybrid supercapacitor based on Ni(OH)₂@CuO@Cu composite as energy storage device.

Hierarchical Porous Molybdenum Carbide Based Nanomaterials for Electrocatalytic Hydrogen Production

The electrocatalytic hydrogen evolution reaction (HER) for the preparation of hydrogen fuel is a very promising technology to solve the shortage of hydrogen storage. However, in practical applications, HER catalysts with excellent performance and moderate price are very rare. Molybdenum carbide (Mo_xC) has attracted extensive attention due to its electronic structure and natural abundance. Here, a comprehensive review of the preparation and performance control of hierarchical porous molybdenum carbide (HP-Mo_xC) based catalysts is summarized. The methods for preparing hierarchical porous materials and the regulation of their HER performance are mainly described. Briefly, the HP-Mo_xC based catalysts were prepared by template method, morphology-conserved transformations method, and secondary conversion method of an organic-inorganic hybrid material. The intrinsic HER kinetics are enhanced by the introduction of a carbon-based support, heteroatom doping, and the construction of a heterostructure. Finally, the future development of HP-Mo_xC based catalysts is prospected in this review.

Hierarchically hollow structured NiCo2S4@NiS for high-performance flexible hybrid supercapacitors

Hierarchical nanostructures with outstanding electrochemical properties and mechanical stability are ideal for constructing flexible hybrid supercapacitors. Herein, hierarchically hollow NiCo2S4@NiS nanostructures were designed and synthesized by sulfurizing the hierarchical NiCo double hydroxides (DHs) coated with nickel hydroxide nanostructures on carbon fabrics (NiCo-DHs@Ni(OH)2/CF), which trigger excellent electrochemical performances. The NiCo2S4@NiS/CF exhibits a high specific capacity of 1314.0 C g-1 at a current density of 1 A g-1, and maintains the rate performance at about 79.2% of the initial capacity at 30 A g-1. The hybrid supercapacitors of NiCo2S4@NiS//AC display a high energy density of 62.4 W h kg-1 at a power density of 800 W kg-1 with a remarkable cycling stability (96.2% of initial capacitance after 5000 cycles) and robust mechanical flexibility (no obvious decay of specific capacitance during various deformations). Consequently, NiCo2S4@NiS electrodes are expected to be a promising candidate for new smart energy storage devices with high security, stability and flexibility.