Bendable quasi-solid-state aqueous sodium-ion batteries operated at -30 °C

Aqueous sodium-ion batteries (ASIBs) have garnered considerable attention for large-scale energy storage because of inherent safety and the Na abundance. Nonetheless, the solidification of aqueous electrolytes under sub-zero conditions results in diminished ionic conductivity and increased viscosity, hindering the electrochemical performance and versatility of ASIBs. Herein, we introduce a novel freeze-tolerant ASIB using antifreezing ethylene glycol-polyacrylamide-sodium perchlorate hydrogel electrolyte, paired with new couple of Na3MnTi(PO4)3 cathode and Fe-based anode. The addition of ethylene glycol in the electrolyte enhances ionic conductivity at cold temperatures and optimizes electrode capacity by reduced hydrogen bonding within the water molecules and a decline in free water activity. The pronounced interaction between ethylene glycol and water, combined with the cooperative effect of the crosslinked polyacrylamide network, enables the hydrogel electrolyte to effectively suppress water solidification and maintain better water-retaining capability, achieving remarkable mechanical extensibility and good ionic conductivity (2.5 mS cm-1) at - 40 °C. Consequently, the ASIB equipped with hydrogel electrolyte delivers high energy density of 43.6 Wh kg-1 and retains 64 % at - 30 °C. Furthermore, the flexible ASIB demonstrates robust mechanical durability when bent or compressed, efficiently powering electronic devices even at - 30 °C. Our findings will pave the way for advancing low-temperature ASIBs with hydrogel-based electrolytes.

Polypyrrole-Assisted Ag Doping Strategy to Boost Co(OH)2 Nanosheets on Ni Foam as a Novel Electrode for High-Performance Hybrid Supercapacitors

Battery-type electrode materials have attracted much attention as efficient and unique types of materials for hybrid battery supercapacitors due to their multiple redox states and excellent electrical conductivity. Designing composites with high chemical and electrochemical stabilities is beneficial for improving the energy storage capability of battery-type electrode materials. We report on an interfacial engineering strategy to improve the energy storage performance of a Co(OH)₂-based battery-type material by constructing polypyrrole-assisted and Ag-doped (Ag-doped@Co(OH)₂@polypyrrole) nanosheets (NSs) on a Ni foam using a hydrothermal process that provides richer electroactive sites, efficient charge transportation, and an excellent mechanical stability. Physical characterization results revealed that the subsequent decoration of Ag nanoparticles on Co(OH)₂ nanoparticles offered an efficient electrical conductivity as well as a reduced interface adsorption energy of OH^- in Co(OH)₂ nanoparticles as compared to Co(OH)₂@polypyrrole-assisted nanoparticles without Ag particles. The heterogeneous interface of the Ag-doped@Co(OH)₂@polypyrrole composite exhibited a high specific capacity of 291.2 mAh g^-1 at a current density of 2 A g^-1, and showed a good cycling stability after 5000 cycles at 5 A g^-1. The specific capacity of the doped electrode was enhanced approximately two-fold compared to that of the pure electrode. Thus, the fabricated Ag-doped@Co(OH)₂@polypyrrole nanostructured electrodes can be a potential candidate for fabricating low-cost and high-performance energy storage supercapacitor devices.

Surface and Interface Engineering of Nanoarrays toward Advanced Electrodes and Electrochemical Energy Storage Devices

The overall performance of electrochemical energy storage devices (EESDs) is intrinsically correlated with surfaces and interfaces. As a promising electrode architecture, 3D nanoarrays (3D-NAs) possess relatively ordered, continuous, and fully exposed active surfaces of individual nanostructures, facilitating mass and electron transport within the electrode and charge transfer across interfaces and providing an ideal platform for engineering. Herein, a critical overview of the surface and interface engineering of 3D-NAs, from electrode and interface designs to device integration, is presented. The general merits of 3D-NAs and surface/interface engineering principles of 3D-NA hybrid electrodes are highlighted. The focus is on the use of 3D-NAs as a superior platform to regulate the interface nature and unveiling new mechanism/materials without the interference of binders. The engineering and utilization of the surface of 3D-NAs to develop flexible/solid-state EESDs with 3D integrated electrode/electrolyte interfaces, or 3D triphase interfaces involving other active species, which are characteristic of (quasi-)solid-state electrolyte infiltration into the entire device, are also considered. Finally, the challenges and future directions of surface/interface engineering of 3D-NAs are outlined. In particular, potential strategies to obtain electrode charge balance, optimize the multiphase solid-state interface, and attain 3D solid electrolyte infiltration are proposed.

Sensitive electrochemical sensing platform for selective determination of dopamine based on amorphous cobalt hydroxide/polyaniline nanofibers composites

In this study, amorphous cobalt hydroxide/polyaniline nanofibers (Co(OH)₂/PANINF) composites were successfully prepared. The formation of amorphous Co(OH)₂ with irregular surface structure was confirmed by x-ray diffraction, scanning electron microscopy, and selected-area electron diffraction. The non-enzymatic electrochemical sensor for the selective and sensitive determination of dopamine (DA) has been constructed by using Co(OH)₂/PANINF composites modified glassy carbon electrode (Co(OH)₂/PANINF/GCE), which exhibited excellent electrocatalytic activity toward DA, in a large part owing to the advantages of large surface area of amorphous Co(OH)₂ and the synergetic effect between Co(OH)₂ and PANINF. The electrochemical kinetics reveal that the DA oxidation involves two electrons and two protons in a quasi-reversible electrode reaction. Differential pulse voltammetry (DPV) studies show remarkable sensing performance for the determination of DA, with a low detection limit of 0.03 μM, and a wide linear range from 0.1 to 200 μM. From a broader perspective, the present study demonstrates that Co(OH)₂/PANINF composites would be promising supporting materials for novel sensing platforms.

Cobalt/Nickel Ions-Assisted Synthesis of Laminated CuO Nanospheres Based on Cu(OH)2 Nanorod Arrays for High-Performance Supercapacitors

The development for environmentally friendly energy conversion and storage equipment has given rise to tremendous research efforts as a result of the growing requirements for environmental friendly resources and the rapid consumption of traditional fossil fuel. Herein, a novel hierarchical CoO/NiO-Cu@CuO heterostructure is successfully devised and synthesized. Cobalt/nickel ions are used to generate novel CoO/NiO-doped laminated CuO nanospheres through the facile in situ wet oxidation combined with cation exchange and calcination strategies. As a result, the electrochemical supercapacitance of the as-prepared CoO/NiO-Cu@CuO electrode can reach 875 C cm^-2 (2035 mF cm^-2), which exhibits much better electrochemical performance compared to other precursor electrodes at a same current density of 2 mA cm^-2. Moreover, an excellent rate capacity of 1395 mF cm^-2 (50 mA cm^-2) can be achieved when measured at a relative high current density; 90.3% of the initial supercapacitance remains even after 5000 cycles. Furthermore, the as-prepared hierarchical hybrid of laminated CoO/NiO-CuO nanospheres in situ generated on three-dimensional (3D) porous Cu foam is applied to prepare a solid-state asymmetric supercapacitor equipment unit. The fabricated equipment unit shows an energy density of 69.3 W h kg^-1 at a power density of 1080 W kg^-1. Additionally, the commercially applied 2.5 V light-emitting-diode indicator with blue light can be energized for 4 min when two as-fabricated supercapacitor devices are in series connection. The unique hierarchical heterostructure of the novel laminated nanospheres combined with the 3D grid structure brings about the outstanding electrochemical capacitor performances. This strategy for the fabrication of hierarchical heterostructure electrodes could have an enormous potential for high-performance electrochemical equipment.

A facile fabrication of 1D/2D nanohybrids composed of NiCo-hydroxide nanowires and reduced graphene oxide for high-performance asymmetric supercapacitors

1D/2D nanohybrids composed of NiCo-hydroxide nanowires and graphene have been successfully fabricated by a simple method.

Graphitic carbon nitride decorated with FeNi3 nanoparticles for flexible planar micro-supercapacitor with ultrahigh energy density and quantum storage capacity

Schematic description of graphitic-C₃N₄@FeNi₃ (pseudocapacitive FeNi₃ and electrochemical double layer g-C₃N₄) heterostructure having energy density and quantum storage capacity for in-plane micro-supercapacitor application.