Design and synthesis of porous carbon for energy and environmental applications [electronic resource]
Keywords: Chemical Engineering.

With growing concerns over increasing concentration of carbon dioxide and its effect on global warming, the development of high functional, low cost materials are important for applications in carbon capture, energy storage and electrochemical catalysis. During my PhD study, I developed a general approach of making high-performing, low-cost functional carbon-based materials. Porous carbon is an interesting class of materials with desirable properties including thermal conductivity, high surface area, tunability over pore geometries, as well as flexibility for heteroatom doping. An ideal porous material should possess a hierarchical structure, in which micropores provide high capacity and activity while the mesopores allow fast diffusion of molecules and reactants; however, development of such hierarchical structures remains to be challenging in rationally design and synthesis of carbon-based sorbents. The first part of my research details a scalable method towards low-cost and low-temperature synthesis of 3D porous graphitic carbon networks with ultra-high surface area and hierarchically interconnected pore architecture that is ideal for use as supercapacitor: high conductivity for electron transport, high surface area for effective ion adsorption/desorption and suitable pore architecture for rapid access of ions from electrolyte solution to the carbon surface. Our strategy is to use a 3D crosslinked conjugated polymeric molecular framework that can be readily converted into porous carbon simply by thermal annealing. The resulting 3D hierarchically porous graphitic carbon showed unprecedented energy storage capacity and rate capability compared with previously reported porous carbons, enabling high mass-loading supercapacitors and highly stable lithium-sulfur batteries. To expand the general synthetic approach of the "designer carbon", we further extended the synthetic approach to nitrogen-doped mesoporous carbon. Our porous carbon was prepared using low temperature carbonization (≤500 oC) of a rigid conjugated polymer organic framework synthesized through co-assembly and polymerization of a rationally designed pyrrole monomer and a soft-template. The molecular design of the modified monomer and a low temperature process allow controllability over the ultramicropore volume and nitrogen functional groups, which are essential for CO2 adsorption under post-combustion conditions. This leads to a record-high Henry's law CO2/N2 selectivity (~200:1 at 323 K) among physisorptive carbon materials while possessing high adsorption capacity. In the final part, I further tune the material for application in electrocatalysis via a NH3 activation treatment of the as-synthesized porous carbon. The resulting material exhibits excellent performance for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) as demonstrated by means of fundamental electrochemical studies as well as integration into the oxygen electrode of a regenerative fuel cell. The activities observed for both the ORR and the OER are comparable to that achieved by state-of-the-art Pt and Ir in an alkaline environment, but at a much lower cost. These results are of paramount significance for the deployment of energy storage systems that utilize O2-H2O chemistries such as regenerative fuel cells and metal-air batteries.