Synthesis protocols to porous carbons for energy storage applications

Abstract

In the context of limited availability of fossil fuel and the impact of fossil-based energy utilization to the environment, novel porous materials have been extensively investigated for applications in environmentally friendly energy storage. This Thesis describes work wherein porous carbons have been systematically studied to include development of existing methods, new synthesis strategies, and material characterization. Two main themes of this thesis are, firstly, to investigate how porosity affects the utilization of activated carbons in energy storage and gas adsorption, and secondly, to develop the synthesis protocols in order to ensure their sustainability. Chapter 1 discusses activated carbon structures, classifications of pores, the fundamental properties of porous materials, and preparation and important applications of the materials. Chapter 2 gives the basics of techniques used for characterization of the porous materials fabricated in this work. Gas sorption techniques applied for methane storage and carbon dioxide uptake are introduced. Chapter 3 examines the effect of varying activation conditions (temperature and degree of activation) on the preparation of activated carbons derived from polypyrrole in terms of application to CO2 uptake and methane storage. A compactivation approach, which incorporates a mechanical compression step before thermochemical activation, is explored. Series of samples were synthesised using the less toxic activating agent ‘potassium oxalate’. Surface area of up to 3000 m2/g and pores of size range 6-12 Å were achieved. The resulting carbons showed excellent CO2 uptake and methane storage at moderate to high pressure and ambient temperature. In Chapter 4, carbon nano-cages with hierarchical 3D structure were prepared via a template-assisted carbonisation method. Magnesium carbonate pentahydrates acted as a template and benzene as a carbon precursor. Carbons with pore volume of 1.5-4.6 cm3/g and surface area of between 750- 1711 m2/g were achieved. The effect of chemical activation for hCNCs in order to develop their SA and textural properties were studied. Chapter 5 reports the synthesis of biomass-derived activated carbons with high microporosity and packing density that is suitable for CO2 and methane storage at high pressure. Prickly pear peels were used as carbon precursor, and a range of carbonisation temperature (350- 600˚C) were employed. Our findings present important insights on synthesis of activated carbons and represent a significant step in the development of cheap porous carbons for gas storage applications. Chapter 6, the efficient storage of energy combined with a minimum carbon footprint is one of the major challenges facing the global pursuit of a transition toward progressive, sustainable, eco-friendly societies. For this reason, a sustainable and scalable method is presented in this study for the preparation of an ultra-microporous (average pore size ca. 0.6 nm) activated carbon cloth (ACC) with a large specific area (> 2000 m2/g) and pore volume (~ 1.5 cm3/g) by combining activation with chemical impregnation of low-cost cellulose-based polymeric fabric. The resultant ACC can store 2.0 mmol/g at 1 bar, 7.7 mmol/ g at 20 bar of CH4 at 25°C, which is much higher than any value reported to date for activated carbon cloths. In addition, it can also store high amounts of CO2 at 25°C; 2.0 mmol/g, 4.2 mmol/g and 13.4 mmol/g at 0.25 bar, 1 bar and 40 bar, respectively. Finally, the conclusions for the Thesis including suggestions for future work are proposed in Chapter 7.