Fabrication of Macroscopically Flexible and Highly Porous 3D Semiconductor Networks from Interpenetrating Nanostructures by a Simple Flame Transport Approach

The remarkable characteristics of nanostructures are typically the result of their nanoscopic dimensions. Forming 3D nanoand microstructured network materials is a way to transfer these special properties to the macroscopic world. [ 1-4 ] Classical semiconductors or ceramics [ 5 ] exhibit important fundamental properties including high chemical inertness and high-temperature stability. State-of-the-art applications include sensory properties or high Li storage capability. [ 6,7 ] However, their rigidity hinders applications as fl exible, high-temperature materials in advanced battery electrodes that cope with large quantities of Li without breaking or as ceramic stents, which would require elastic properties on a macroscopic scale. [ 8 ] Here, we introduce a novel but simple method, called fl ame transport synthesis (FTS), to assemble macroscopic quantities of fl exible 3D interconnected nanostructures from brittle oxide semiconductors or ceramic materials. [ 9 ] A rubber-like effective elastic modulus (tunable from 0 to 40 MPa) enables the manufacturing of fl exible elastic networks while preserving typical ceramic properties such as their high temperature stability. The semiconducting properties of these networks allow multifunctional utilization, e.g., as sensors, photocatalysts, solar cell front contacts, or thermoelectrics. Furthermore, it is the basis material for antiviral fi lters, [ 10-13 ] advanced nanoscale interlockers, [ 14 ] self-reporting materials, [ 15 ] and for aerographite, [ 16 ] which is currently one of the least dense materials. This article mainly discusses the fabrication of highly porous (up to 98%), 3D, interconnected networks via the FTS approach and the