Cross-linked polymers of phenylacetylene and 1,3-diethynylbenzene: new polymer precursors for nanoporous carbon materials for supercapacitors and gas storage

Abstract

The increasing threats of global warming, rapid depletion of fossil fuels, and increasing energy demands are driving an enormous amount of research into clean renewable sources of energy, flue gas capture technologies, and environmentally friendly energy storage devices, to name a few. Activated carbons present a multipurpose material commonly used in many of these increasingly popular green technologies. A wide range of cross-linked acetylenic polymers of phenylacetylene and 1,3- diethynylbenzene were synthesized and investigated in this thesis to generate materials for electrochemical double layer capacitors, CO2 capture, and hydrogen storage. Chemical activation of the copolymers in the presence of KOH was shown to produce highly microporous carbons with various textural properties. The specific cross-linking densities of the polymer precursors prior to carbonization were shown to greatly affect the carbon yield, surface area, pore volumes and pore sizes of the carbons produced. Electrochemical measurements of the activated carbons showed their impressive performances as capacitor materials, with high specific capacitances (up to 446 F g−1 at 0.5 A g−1 in 3-electrode cell) and long cycle life. Gas sorption studies also demonstrated impressive H2 and CO2 adsorption capacities (up to 2.66 wt% or 13.3 mmol g−1 for H2 adsorption at 77 K and 1 atm, and up to 30.6 wt% or 6.95 mmol g−1 for CO2 adsorption at 273 K and 1 atm). Owing to the high content of pendent alkyne groups in these polymers, complexation reactions with metallic carbonyl ligands are able to provide an effective iv way of dispersing metallic and metal oxide nanoparticles within the synthesized copolymers, which could provide additional pseudocapacitive properties. An appropriate copolymer with high alkyne content was subjected to complexation with Co2(CO)8, and subsequently carbonized and oxidized to yield carbon-supported CoxOy/Co nanoparticles (CoxOy@C-CPD76%). In addition to pseudocapacitive contributions, the cobalt species also effectively catalyzed the production of graphitic networks within the carbon support, improving their conductive properties. Electrochemical measurements demonstrated impressive specific capacitance (310 F g−1 at 0.1 A g−1) compared with non-activated carbons (160 – 177 F g−1 at 0.1 A g−1) synthesized at identical conditions, and provided a large stable potential window (1.4 V) in an aqueous KOH solution. The combined electrochemical double layer capacitance and pseudocapactiance behaviour of the carbon and CoxOy/Co also provided improved energy densities (21 W h kg−1), and uncompromised power densities (2017 W kg−1) compared with the pristine carbons (~2034 W kg−1).