Synthesis of advanced carbon nanomaterials from renewable and waste carbon sources

• Main Author: Chen, Wenqian
• Other Authors: Grzegorz Lisak
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Environmental engineering
• Online Access: https://hdl.handle.net/10356/156982
• Institution: Nanyang Technological University

Graphene-like carbon nanosheets (CNSs) and carbon nanotubes (CNTs) are playing crucial roles in multidisciplinary areas such as energy storage, electronics, and biotechnology. Recently, developments of CNSs or CNTs have attracted great attention in energy storage applications owing to the superior electrical conductivity, tunable porosity as well as large specific surface area. In order to commercialize the carbon-based applications, it is critical to lower the fabrication cost, improve the yield and customize the carbon products with desirable properties. Therefore, the thesis investigated the influences of catalysts and carbon precursors on the properties of CNSs and CNTs synthesized via catalytic chemical vapor deposition (CCVD). Importantly, renewable carbon source, i.e. ethanol and waste plastics were adopted to meet the sustainable targets. The thesis starts with brief introduction of the CNSs and CNTs, their applications as well as existing challenges. After the introduction, a detailed literature review on the structures and properties of CNSs and CNTs, procedure and advantage of catalytic chemical vapor deposition. A summary of state-of-the-art research on the synthesis of CNSs and CNTs via CCVD with various catalyst and carbon sources was presented. Supercapacitor and electrochemical CO2 reduction (CO2RR) were selected as my primary applications of CNSs and CNTs to provide prospective solutions to energy crisis. Based on the literature, we finally identify the research gaps and determine the objectives of my research. The objectives can be summarized in two aspects: (1) Optimize the CCVD catalysts by investigating the relationship between properties of catalysts and as-obtained GCNs from renewable source (i.e. ethanol) for supercapacitors; (2) Accomplish the synthesis of GCNs and CNTs from different waste plastics for excellent performance in CO2RR. In case of objective 1, the physiochemical properties including morphology, crystallinity, specific surface area and porosity of alkali earth metal oxides (MgO, CaO, SrO) as catalysts were studied and found greatly influence the quality and yield of CNSs. By placing iron after SrO, a noticeable improvement of yield and quality of CNSs could be observed which contributed to fabrication of supercapacitor electrodes with excellent performances after KOH activation. For objective 2, real-world plastics (mixture of PE, PP, PS, PET and PVC) were utilized for one-step synthesis of Cu/CNS composites which are highly efficient for CO2RR into CO. Besides, less-studied shoe plastics including PU and EVA were successfully converted to CNTs. Importantly, PU was found to yield few-walled CNTs which promoted CO2RR into CO with high current density after hybridization with zeolitic imidazolate framework. It could be concluded that by selecting appropriate catalysts, the properties of CNSs or CNTs could be customized and can be further applied in the design of electrocatalysts for energy-related applications such as supercapacitor or CO2RR. The feasibility of recycling renewable source or waste plastics into value-added carbon-based electrocatalysts improved the sustainability and promotes the circular economy.