The synthesis of ceramic materials combining high porosity and permeability with good mechanical stability is challenging, as optimising the latter requires compromises regarding the first two properties. Nonetheless, significant progress can be made in this direction by taking advantage of the structural design principles evolved by nature. Natural cellular solids achieve good mechanical stability via a defined hierarchical organisation of the building blocks they are composed of. Here, we report the first synthetic, ceramic-based scaffold whose architecture closely mimics that of cuttlebone –a structural biomaterial whose porosity exceeds that of most other natural cellular solids, whilst preserving an excellent mechanical strength. The nanostructured, single-component scaffold, obtained by ice-templated assembly of V2O5 nanofibres, features a highly sophisticated and elaborate architecture of equally spaced lamellas, which are regularly connected by pillars as lamella support. It displays an unprecedented porosity of 99.8 %, complemented by an enhanced mechanical stability. This novel bioinspired, functional material not only displays mechanical characteristics similar to natural cuttlebone, but the multifunctionality of the V2O5 nanofibres also renders possible applications, including catalysts, sensors and electrodes for energy storage.

Multifunctional paper-like materials containing metal oxide nanofibers are important for flexible electronics and other redox-based applications, but are often prone to mechanical failure. This work presents the coassembly of V 2 O 5 nanofibers (VNFs) in a dual-fiber approach together with cellulose nanofibers to produce tough (0.26 MJ m −3 ), but strong (250 MPa) flexible hybrid materials. Indeed, nanotensile tests reveal a significant increase in toughness (200%) and strength (85%) of the hybrid films as compared to pristine VNF films. The microstructure of the films shows a transition from an anisotropic texture for the single-component films to an isotropic, entangled network in case of the hybrid films, which facilitates effective fracture resistance mechanisms. The flexible hybrid films display high electrical conductivity (0.2 S cm −1 ) and elastic properties originating from V 2 O 5 nanofibers with excellent toughness and transparency endowed by the cellulose nanofibers. The self-supported hybrid films show reversible electrochromic behavior without the need for common substrates such as conducting indium tin oxide glass. It is conceivable that these self-supported films can be exploited in the future in smart, flexible optoelectronic devices.

The demand to outperform current technologies pushes scientists to develop novel strategies, which enable the fabrication of materials with exceptional properties. Along this line, lightweight structural materials are of great interest due to their versatile applicability as sensors, catalysts, battery electrodes, and acoustic or mechanical dampers. Here, we report a strategy to design ultralight (ρ = 3 mg/cm) and hierarchically structured ceramic scaffolds of macroscopic size. Such scaffolds exhibit mechanical reversibility comparable to that of microscopic metamaterials, leading to a macroscopically remarkable dynamic mechanical performance. Upon mechanical loading, these scaffolds show a deformation mechanism similar to polyurethane foams, and this resilience yields ultrahigh damping capacities, tan δ, of up to 0.47.

Owing to their unique layer structure, high aspect ratio and intercalation capability, vanadium pentoxide (V2O5) nanofibers are close-to-ideal building blocks for high performance electrodes for metal-ion batteries. However, thus far investigated electrodes composed of V2O5 nanofibers mostly contain binders and conductive agents, which reduce the electrodes' gravimetric capacity. Here we demonstrate self-supporting V2O5 nanofiber-based films that combine high mechanical flexibility and stability with good electrical conductivity. This has been achieved by suitable adjustment of the nanofiber length, in combination with a suitable humidity controlled post-treatment, to ensure an effective nanofiber interconnection and aging of the films. The optimization of these two parameters allows for an impressive 81%, 184%, and 281% enhancement in Young's modulus, tensile strength and toughness respectively, along with an increase of electrical conductivity by up to 165%. Such films can reach storage capacities of up to 150 mA h g-1 without the support of conductive agents and binders. Our findings provide fundamental design guidelines for advanced binder-free electrode materials, which unite high specific storage capacity, excellent mechanical stability and good intrinsic electrical conductivity - the key to technologically advanced battery performance and lifetime.

Nature has evolved hierarchical structures of hybrid materials with excellent mechanical properties. Inspired by nacre’s architecture, a ternary nanostructured composite has been developed, wherein stacked lamellas of 1D vanadium pentoxide nanofibres, intercalated with water molecules, are complemented by 2D graphene oxide (GO) nanosheets. The components self-assemble at low temperature into hierarchically arranged, highly flexible ceramic-based papers. The papers’ mechanical properties are found to be strongly influenced by the amount of the integrated GO phase. Nanoindentation tests reveal an out-of-plane decrease in Young’s modulus with increasing GO content. Furthermore, nanotensile tests reveal that the ceramic-based papers with 0.5 wt% GO show superior in-plane mechanical performance, compared to papers with higher GO contents as well as to pristine V2O5 and GO papers. Remarkably, the performance is preserved even after stretching the composite material for 100 nanotensile test cycles. The good mechanical stability and unique combination of stiffness and flexibility enable this material to memorize its micro- and macroscopic shape after repeated mechanical deformations. These findings provide useful guidelines for the development of bioinspired, multifunctional systems whose hierarchical structure imparts tailored mechanical properties and cycling stability, which is essential for applications such as actuators or flexible electrodes for advanced energy storage.