Ni(OH)₂ Nanoflowers/Graphene Hydrogels: A New Assembly for Supercapacitors

A novel structure of graphene-based hybrid hydrogels was constructed, in which α-Ni­(OH)₂ nanoflowers with nanopetals thicknesses of approximately 20 nm were uniformly anchored on a three-dimensional graphene framework. Benefiting from the unique morphological nickel hydroxide nanoflowers and hydrogels, the nickel hydroxide nanoflowers/graphene hydrogels exhibited great specific capacitances (1 A·g^–1; 1632 F·g^–1), great rate capabilities, and longer cycle life (after 1000 cycles, 95.2% capacitance retention) when used as electrodes in supercapacitors

Solvothermal-Induced 3D Macroscopic SnO₂/Nitrogen-Doped Graphene Aerogels for High Capacity and Long-Life Lithium Storage

3D macroscopic tin oxide/nitrogen-doped graphene frameworks (SnO₂/GN) were constructed by a novel solvothermal-induced self-assembly process, using SnO₂ colloid as precursor (crystal size of 3–7 nm). Solvothermal treatment played a key role as N,N-dimethylmethanamide (DMF) acted both as reducing reagent and nitrogen source, requiring no additional nitrogen-containing precursors or post-treatment. The SnO₂/GN exhibited a 3D hierarchical porous architecture with a large surface area (336 m²g^‑1), which not only effectively prevented the agglomeration of SnO₂ but also facilitated fast ion and electron transport through 3D pathways. As a result, the optimized electrode with GN content of 44.23% exhibited superior rate capability (1126, 855, and 614 mAh g^‑1 at 1000, 3000, and 6000 mA g^‑1, respectively) and extraordinary prolonged cycling stability at high current densities (905 mAh g^‑1 after 1000 cycles at 2000 mA g^‑1). Electrochemical impedance spectroscopy (EIS) and morphological study demonstrated the enhanced electrochemical reactivity and good structural stability of the electrode

Development of Cobalt Hydroxide as a Bifunctional Catalyst for Oxygen Electrocatalysis in Alkaline Solution

Co­(OH)₂ in the form of hexagonal nanoplates synthesized by a simple hydrothermal reaction has shown even greater activity than cobalt oxides (CoO and Co₃O₄) in oxygen reduction and oxygen evolution reactions (ORR and OER) under alkaline conditions. The bifunctionality for oxygen electrocatalysis as shown by the OER–ORR potential difference (Δ<i>E</i>) could be reduced to as low as 0.87 V, comparable to the state-of-the-art non-noble bifunctional catalysts, when the Co­(OH)₂ nanoplates were compounded with nitrogen-doped reduced graphene oxide (N-rGO). The good performance was attributed to the nanosizing of Co­(OH)₂ and the synergistic interaction between Co­(OH)₂ and N-rGO. A zinc–air cell assembled with a Co­(OH)₂–air electrode also showed a performance comparable to that of the state-of-the-art zinc–air cells. The combination of bifunctional activity and operational stability establishes Co­(OH)₂ as an effective low-cost alternative to the platinum group metal catalysts

High-Performance Aqueous Zinc-Ion Batteries Enabled by Binder-Free and Ultrathin V₂O_5–<i>x</i>@Graphene Aerogels with Intercalation Pseudocapacitance

As a result of the absence of solid-state diffusion limitation, intercalation pseudocapacitance behavior is emerging as an attractive charge-storage mechanism that can greatly facilitate the ion kinetics to boost the rate capability and cycle stability of batteries; however, related research in the field of zinc-ion batteries (ZIBs) is still in the initial stage and only found in limited cathode materials. In this study, a novel V2O5–x@rGO hybrid aerogel consisting of ultrathin V2O5 nanosheets (∼1.26 nm) with abundant oxygen vacancies (Vö) and a three-dimensional (3D) graphene conductive network was specifically designed and used as a freestanding and binder-free electrode for ZIBs. As expected, the ideal microstructure of both the material and the electrode enable fast electron/ion diffusion kinetics of the electrode, which realize a typical intercalation pseudocapacitance behavior as demonstrated by the simulation calculation of cyclic voltammetry (CV), ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and first-principles density functional theory (DFT) calculation. Thanks to the elimination of solid-state diffusion limitation, the V2O5–x@rGO electrode delivers a high reversible rate capacity of 153.9 mAh g–1 at 15 A g–1 and 90.6% initial capacity retention at 0.5 A g–1 after 1050 cycles in ZIBs. The intercalation pseudocapacitance behavior is also realized in the assembled soft-pack battery, showing promising practical application prospects

Fabricating 3D Macroscopic Graphene-Based Architectures with Outstanding Flexibility by the Novel Liquid Drop/Colloid Flocculation Approach for Energy Storage Applications

Inspired by “water ripples” in nature and the flocculation phenomenon in colloid chemistry, a novel liquid drop/colloid flocculation approach is developed to fabricate an extremely flexible and compressible 3D macroscopic graphene-based architecture (hydrogels or aerogels), via a new coagulation-induced self-assembly mechanism. This facile and universal technique can be achieved in a neutral, acidic, or basic coagulation bath, producing microsized hydrogels with various structures, such as mushroom, circle, disc shapes, etc. The method also allows us to introduce various guest materials in the graphene matrix using transition metal salts as the coagulating bath. A mushroom-shaped NiCo oxide/GS hybrid aerogel (diameter: 3 mm) is prepared as an example, with ultrathin NiCo oxide nanosheets in situ grown onto the surface of graphene. By employing as binder-free electrodes, these hybrid aerogels exhibit a specific capacitance of 858.3 F g^–1 at 2 A g^–1, as well as a good rate capability and cyclic stability. The asymmetric supercapacitor, assembling with the hybrid aerogels as cathode and graphene hydrogels as anode materials, could deliver an energy density of 21 Wh kg^–1 at power density of 4500 W kg^–1. The ease of synthesis and the feasibility of obtaining highly flexible aerogels with varied morphologies and compositions make this method a promising one for use in the field of biotechnology, electrochemistry, flexible electronics, and environment applications