Engineering of Microcage Carbon Nanotube Architectures with Decoupled Multimodal Porosity and Amplified Catalytic Performance

Abstract

New approaches for the engineering of the 3D microstructure, pore modality, and chemical functionality of hierarchically porous nanocarbon assemblies are key to develop the next generation of functional aerogel and membrane materials. Here, interfacially driven assembly of carbon nanotubes (CNT) is exploited to fabricate structurally directed aerogels with highly controlled internal architectures, composed of pseudo‐monolayer, CNT microcages. CNT Pickering emulsions enable engineering at fundamentally different length scales, whereby the microporosity, mesoporosity, and macroporosity are decoupled and individually controlled through CNT type, CNT number density, and process energy, respectively. In addition, metal nanocatalysts (Cu, Pd, and Ru) are embedded within the architectures through an elegant sublimation and shock‐decomposition approach; introducing the first approach that enables through‐volume functionalization of intricate, pre‐designed aerogels without microstructural degradation. Catalytic structure–function relationships are explored in a pharma‐important amidation reaction; providing insights on how the engineered frameworks enhance catalyst activity. A sophisticated array of advanced tomographic, spectroscopic, and microscopic techniques reveal an intricate 3D assembly of CNT building‐blocks and their influence on the functional properties of the enhanced nanocatalysts. These advances set a basis to modulate structure and chemistry of functional aerogel materials independently in a controlled fashion for a variety of applications, including energy conversion and storage, smart electronics, and (electro)catalysis.

Electrothermal Transformations within Graphene-Based Aerogels through High-Temperature Flash Joule Heating

“…Even though the employed Joule-heating durations are relatively short, the level of aerogel graphitization achieved is comparable to a much longer, conventional graphitization treatment carried out in a tube furnace (1000 °C, 2 h) . The furnace-graphitized aerogel sample shows similar structural and chemical material characteristics as the aerogel sample treated via high-current Joule annealing for 30 s (Table ).…”

Density-Induced Joule-Heating Characteristics of Nanocarbon Aerogels: Implications for Tunable Electrothermal Behaviors

“…The electrical conductivity of the nanocarbon aerogels is recovered through high-temperature thermal annealing. 57,58 This excellent conductive feature, combined with the structural integrity (Figure 1b), makes the assynthesized rGO aerogels well-suited for Joule-heating studies.…”

“…Detailed procedures for synthesizing the integral cylindrical rGO aerogel are outlined in Figure a. The electrical conductivity of the nanocarbon aerogels is recovered through high-temperature thermal annealing. , This excellent conductive feature, combined with the structural integrity (Figure b), makes the as-synthesized rGO aerogels well-suited for Joule-heating studies. To distinguish the different aerogels, the low-density rGO aerogels (14.9 mg·cm –3 ) and high-density rGO aerogels (22.6 mg·cm –3 ; Table ) were designated as rGO aerogel-LD and rGO aerogel-HD, respectively.…”

Atomic Aerogel Materials (or Single‐Atom Aerogels): An Interesting New Paradigm in Materials Science and Catalysis Science

“…[41,42] The micrometer-level pores of AAMs can demonstrate at least two structural functions and advantages for the AAMs: 1) providing sufficient space to build compressible and nonrigid self-supporting macroblock materials; 2) providing abundant capillary channels to adsorb solution, shorten transfer path, and accelerate migration. The controllable preparation methods (such as the directional freeze casting, [16] interface driven assembly, [43] 3D printing technology [44] ) for engineering 3D microstructures, pore modes, and chemical functions of aerogel materials with highly controlled micrometer-level pores are the key to developing the next-generation high-performance AAMs. For example, the directional freeze casting has a new porous shape (hollow columnar macroporous structure) than traditional irregular ice templates; [16] the interface driven assembly has a more regular spherical mesoscopic structure than the traditional hydrothermal assembly.…”

“…For example, the directional freeze casting has a new porous shape (hollow columnar macroporous structure) than traditional irregular ice templates; [16] the interface driven assembly has a more regular spherical mesoscopic structure than the traditional hydrothermal assembly. [43] In particular, the multilayer skeleton (woodpile) aerogel based on 3D printing technology has the advantage of precise micrometer-level porosity and controllable dimension, providing a new and efficient "scaffold engineering" strategy for the design of macroscopical AAMs. [45]…”