Two-dimensional graphene film exhibits sluggish ion diffusivity while three-dimensional (3D) graphene aerogel has low packing density and poor mechanical flexibility. Consequently, there is an urgent need for graphene-based film with both mechanical robustness and high specific capacitance. Here, we present an easy and scalable strategy for fabricating a free-standing flexible graphene-based aerogel film electrode with a two-layered structure, in which the top layer is an interconnected macroporous reduced graphene oxide/carbon nanotube (RGO/CNT) aerogel, and the bottom layer is a flexible electrospun polyacrylonitrile (PAN) nanofiber membrane. The porous 3D structure of the aerogel provides fast transport of electrolyte ions and electrons, while the nanofiber membrane provides both strong support for the aerogel and mechanical flexibility. Polypyrrole (PPy) can be uniformly loaded on RGO/CNT/PAN (RCP) composite aerogel film to provide pseudocapacitance, and nitrogen-doped RGO/CNT/carbon nanofiber (NRCC) aerogel film can be obtained by further pyrolysis. The resultant RCP@PPy-0.05//NRCC based asymmetric supercapacitor can have a maximum voltage of 1.7 V and a maximum energy density of 60.6 W h kg⁻¹ at 850.2 W kg⁻¹. This indicates that free-standing graphene-based aerogel film can be used in flexible supercapacitors.

The development of highly active and cost-effective hydrogen evolution reaction (HER) catalysts is of vital importance to addressing global energy issues. Here, a three-dimensional interconnected porous carbon nanofiber (PCNF) membrane has been developed and utilized as a support for active cobalt phosphide (CoP) nanoparticles. This rationally designed self-supported HER catalyst has a lotus root-like multichannel structure, which provides several intrinsic advantages over conventional CNFs. The longitudinal channels can store the electrolyte and ensure fast ion and mass transport within the catalysts. Additionally, mesopores on the outer and inner carbon walls enhance ion and mass migration of the electrolyte to HER active CoP nanoparticles, thus shortening the ion transport distance and increasing the contact area between the electrolyte and the CoP nanoparticles. Moreover, the conductive carbon substrate provides fast electron transfer pathways by forming an integrated conductive network, which further ensures fast HER kinetics. As a result, the CoP/PCNF composites exhibit low onset-potentials (?20, ?91, and?84 mV in 0.5 M H₂SO₄, 1 M PBS, and 1 M KOH, respectively). These findings show that CoP/PCNF composites are promising self-supporting and high-performance all-pH range HER catalysts.

NiS nanoparticles (NPs) with excellent electrochemical capacitance have attracted considerable attention as cost-effective energy-storage materials for supercapacitors in recent years. Preventing the aggregation and increasing the conductivity of NiS NPs are key to fully realizing their excellent electrochemical properties. In this work, NiS/N-doped carbon fiber aerogel (N-CFA) nanocomposites were obtained easily through the combination of polymerization, carbonization, and a one-step solvothermal reaction. N-CFA derived from polydopamine (PDA)-coated cotton wool was used as a template for the construction of hierarchical NiS/N-CFA nanocomposites, in which NiS NPs are uniformly immobilized on the surface of N-CFA. In this nanostructured system, N-CFA containing abundant nanofibers not only provides active regions for the growth of NiS NPs to prevent their aggregation, but also offers short pathways for the transport of electrons and ions. The electrochemical properties of the obtained NiS/N-CFA nanocomposites were investigated by cyclic voltammetry, galvanostatic charge–discharge, and alternating current impedance measurements. The optimized NiS/N-CFA nanocomposite exhibits a high specific capacitance of 1, 612.5 F·g^-1 at a charge/discharge current density of 1 A·g^-1 and excellent rate capacitance retention of 66.7% at 20 A·g^-1. The excellent electrochemical properties of NiS/N-CFA nanocomposites make these materials promising electrode materials for supercapacitors.