Scalable Template-Directed Hydrothermal Carbonization Synthesis Of CNFs Aerogels And Their Functionality

During the past decades, with the rapid development of technology of chemical syntheses, many kinds of nanomaterials with different compositions and sizes have been successfully achieved via various physical and chemical strategies. Hydrothermal car-bonization (HTC) process which were a traditional method to fabricate carbonaceous nanomaterials displayed marvelous advantages. On the one hand, HTC synthesis were easy fabricated, economical costed, large-scalable produced, diameter controlled and various composed. On the other hand, HTC process could synthesize macroscopic ma-terials (three-diameter (3D) monolith hydrogels/aerogels).The present dissertation would concentrate on template-directed scalable HTC syn-thesis of 3D carbonaceous nanofibers aerogels materials. By fabricating of different kinds of aerogels consist of a series of one-diameter (1D) carbonaceous nanofibers, re-spectively, which showed a unique superiority and broad applicability of the template-directed HTC process. The as-prepared carbonaceous nanofibers aerogels were further demonstrated as a versatile scaffold for constructing carbon-based composite nanoma-terials. In addition, these carbonaceous nanofibers and carbon-based materials all ex-hibited outstanding potential application in electrocatalyssis and energy storage. The main results can be summarized as follows:1. The large-scale synthesis of monolithic nitrogen-doped carbonaceous aerogel is very challenging. Here, we report a simple strategy for the mass production of a new class of nitrogen-doped carbonaceous nanofibrous (N-CNFs) hydrogels/aerogels. The great versatility of the present synthesis allows us to directly scale up the synthesis from 50 mL to 1600 mL just by using large autoclave and without changing reactant concentrations and reaction time. This is a major breakthrough in gel and nanomaterial synthesis. Taking the advantages of the nanostructured feature of 3D N-CNFs aerogels, we take CO2 as a kind of efficient activated reactant to create more micro-pores and enhance the BET surface area and porosity of N-CNFs aerogels. The as-prepared N-CNF-CO2 aerogels possessed desired density of N-containing active sites (N content, 2%) and very high BET surface area (1324 m2/g). Importantly, the 3D nanofibrous network structure was highly favorable for the rapid transport of ORR species. Such reasonable combination of high reactive surface area and fast transport path resulted in a superior ORR performance which exceeded that of most reported metal-free catalysts and was highly comparable with that of the state-of-the art Pt/C catalyst. On the other hand, the N-CNF-CO2 aerogels presented great potential in energy storage application as supercapacitor electrode material.2. Via changing the HTC precursors, we devolop a novel method to synthesize Fe, N co-doped carbon nanofibers (Fe/N-CNFs) aerogels as efficient NPMs catalysts via a mild template-directed HTC process, where cost-effective D(+)-glucosamine hy-drochloride and ferrous gluconate are used as precursors. The prepared Fe/N-CNFs non-precious metal (NPMs) catalysts display outstanding ORR activity, i.e. onset po-tential of 0.88 V vs RHE and half-wave potential of 0.78 V vs RHE, which is high-ly comparable to that of commercial Pt/C (20% wt Pt) catalyst in alkaline electrolyte. Futhermore, the Fe/N-CNFs catalysts exhibitsuperior long-term stability and better tol-erance to the methanol crossover effect than the Pt/C catalysts in both alkaline and acidic electrolytes. Movever, the HTC technique would be enlarged by and broaded to fabricate other metal-containing NPMs or metal-free catalysts, such as Co, S etc. by changing the precursors of cobalt gluconate or cobalt acetate and cysteine, respectively. Therefore, the HTC method will efficiently enlarge the kinds of electrocatalysts mate-rials and stimulate the potential application of NPMs or metal-free catalysts in clean energy devices.3. The as-prepared nitrogen-doped carbonaceous nanofibers aerogels were next described as a versatile scaffold for constructing carbon-based composite nanomate-rials. For example, we constructed a new kind of TiN/N-CNFs composite aerogels. The composite aerogels inherited the properties of N-CNFs aerogels, such as, macro-scopical 3D structures, high-porosity and unique dimensional (high aspect ratio). The prepared TiN/N-CNFs aerogels displayed acceptable ORR activity, which indicated the traditional ceramic materials might apply in the energy conversion field.