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Carbonaceous materials are considered strong candidates as anode materials for sodium‐ion batteries (SIBs), which are expected to play an indispensable role in the carbon‐neutral era. Herein, novel braided porous carbon fibres (BPCFs) are prepared using the chemical vapour deposition (CVD) method. The BPCFs possess interwoven porous structures and abundant vacancies. The growth mechanism of the BPCFs can be attributed to the polycrystalline transformation of the nanoporous copper catalyst in the early stage of CVD process. Density functional theory calculations suggest that the Na+ adsorption energies of the mono‐vacancy edges of the BPCFs (−1.22 and −1.09 eV) are lower than that of an ideal graphene layer (−0.68 eV), clarifying in detail the adsorption‐dominated sodium storage mechanism. Hence, the BPCFs as an anode material present an outstanding discharge capacity of 401 mAh g−1 at 0.1 A g−1 after 500 cycles. Remarkably, this BPCFs anode, under high‐mass‐loading of 5 mg cm−2, shows excellent long‐term cycling ability with a reversible capacity of 201 mAh g−1 at 10 A g−1 over 1000 cycles. This study provided a novel strategy for the development of high‐performance carbonaceous materials for SIBs. [ABSTRACT FROM AUTHOR]

This study developed a freestanding nanoporous high-entropy alloy foil as a dual-functional electrocatalyst. The ultrahigh HER activity of the catalyst originates from the synergetic effect of optimized hydrogen adsorption in the segregation area and enhanced H 2 O adsorption in the un-segregation area produced by spinodal decomposition. [Display omitted] • A nanoporous NiCoFeMoMn HEA with ultrahigh catalytic activity is synthesized. • Hierarchical porous structure greatly increases the number of active sites. • The synergistic effect of element segregation area and un-segregation area promotes HER. • The electrode can stably deliver 1000 mA cm−2 at only 150 mV for HER. • Overall water splitting runs stably for 375 h at 10 mA cm−2. The development of low-cost non-noble-metal-based electrocatalysts that can work stably at high current densities is crucial to apply a hydrogen evolution reaction (HER) and an oxygen evolution reaction (OER) in electrolyzed water. This study developed a freestanding nanoporous high-entropy alloy foil as a dual-functional electrocatalyst. The proposed electrocatalyst combines dealloying and polarization and shows excellent electrocatalytic activity in an alkaline electrolyte. It has an extremely small overpotential of 150 mV at 1,000 mA cm−2 for the HER and a low Tafel slope of 29 mV dec−1. At the same current density, the overpotential of the OER is only 350 mV. The alkaline electrolyzer using the electrocatalyst as both anode and cathode requires a cell voltage of only 1.47 V to output a stable current density of 10 mA cm−2. This enables it to be an efficient bifunctional electrocatalyst for alkaline overall water splitting and better stability for more than 375 h of continuous hydrogen production while providing substantial material cost savings relative to platinum. Density functional theory calculations indicate that the ultrahigh HER activity of the catalyst originates from the synergetic effect of optimized hydrogen adsorption in the segregation area and enhanced H 2 O adsorption in the un-segregation area produced by spinodal decomposition. [ABSTRACT FROM AUTHOR]