NiCo₂O₄ Nanosheets on Hollow Carbon Nanofibers for Flexible Solid-State Supercapacitors

The carbon nanofiber-based all-solid-state supercapacitors hold great promise in powering portable electronics, while the low specific capacitance and intrinsic fragility have hindered their practical application. Here, flexible N-doped hollow carbon nanofibers (HCNFs) were prepared using poly(acrylonitrile-co-acrylamide) as a precursor by the coaxial electrospinning method. The leaf-like NiCo2O4 nanosheets are located on the inner and outer walls of the carbon layer via a simple solvothermal method to construct 3D freestanding NiCo2O4/HCNFs electrodes for a flexible all-solid-state supercapacitor. The hollow structure of HCNFs provides both inner and outer surfaces for NiCo2O4 nanosheets and shortens the distance of ion transportation. NiCo2O4/HCNFs possesses an enhanced specific capacitance of 1864.0 F g–1 at 1 A g–1 and a good capacitance retention capability of 91.7% after 5000 times cycling, which is one of the best reported cycling stabilities to date. The symmetrical all-solid-state supercapacitors (ASSCs) were directly prepared with NiCo2O4/HCNFs as an electrode without adding any conductive agents and binders, which have good flexibility and a maximum energy density of 44.3 W h kg–1 at a specific power of 814.8 W kg–1. Five series-connected ASSCs assembled by NiCo2O4/HCNFs can lighten a “DHU” logo composed of 36 light-emitting diodes, indicating their potential application prospect in wearable and portable devices

Spatial Isolation of Carbon and Silica in a Single Janus Mesoporous Nanoparticle with Tunable Amphiphilicity

Like surfactants with tunable hydrocarbon chain length, Janus nanoparticles also possess the ability to stabilize emulsions. The volume ratio between the hydrophilic and hydrophobic domains in a single Janus nanoparticle is very important for the stabilization of emulsions, which is still a great challenge. Herein, dual-mesoporous Fe₃O₄@mC&mSiO₂ Janus nanoparticles with spatial isolation of hydrophobic carbon and hydrophilic silica at the single-particle level have successfully been synthesized for the first time by using a novel surface-charge-mediated selective encapsulation approach. The obtained dual-mesoporous Fe₃O₄@mC&mSiO₂ Janus nanoparticles are made up of a pure one-dimensional mesoporous SiO₂ nanorod with tunable length (50–400 nm), ∼100 nm wide and ∼2.7 nm mesopores and a closely connected mesoporous Fe₃O₄@mC magnetic nanosphere (∼150 nm diameter, ∼10 nm mesopores). As a magnetic “solid amphiphilic surfactant”, the hydrophilic/hydrophobic ratio can be precisely adjusted by varying the volume ratio between silica and carbon domains, endowing the Janus nanoparticles surfactant-like emulsion stabilization ability and recyclability under a magnetic field. Owing to the total spatial separation of carbon and silica, the Janus nanoparticles with an optimized hydrophilic/hydrophobic ratio show spectacular emulsion stabilizing ability, which is crucial for improving the biphasic catalysis efficiency. By selectively anchoring catalytic active sites into different domains, the fabricated Janus nanoparticles show outstanding performances in biphasic reduction of 4-nitroanisole with 100% conversion efficiency and 700 h^–1 high turnover frequency for biphasic cascade synthesis of cinnamic acid