Abstract
This study presents a direct application for freestanding and monolithic carbon spherogels, which are highly porous carbon aerogels solely composed of hollow nanospheres, as binder-free electrode materials for supercapacitors. By applying polystyrene nanospheres as templating agents in the size range of 277–907 nm and concentrations from 1.5 to 12 wt % in the sol–gel polymerization process of resorcinol–formaldehyde, we can distinctly tailor the hollow spheres’ pore arrangement and thickness of the microporous carbon walls. Furthermore, the required synthesis conditions for mechanically processable (sliceable) carbon spherogels are explored. Following physical activation with carbon dioxide, only 277 nm templated samples, featuring one thin-walled (<20 nm) and one thick-walled (>60 nm) variant, retain a freestanding bulk constitution and hence are suitable for the application as binder-free electrodes. The electrochemical evaluation demonstrates the advantage of hollow carbon sphere aerogels in comparison to conventional carbon aerogels with respect to capacitance, particularly at high scan rates. The analysis of the electrolyte diffusion kinetics and the network morphology after 10,000 charge/discharge cycles reveals the necessity of wall thickness optimization. Thick-walled variants are favored due to a much higher rate capability of 30 kW kg–1 compared to 10 kW kg–1). Additionally, a post-mortem TEM analysis reveals the loss of a central cavity and sphere degradation in thin-walled samples.
Highlights
Carbon aerogels are a fascinating and unique class of synthetic open porous materials
The sol−gel process is depicted in Figure 1 and can be described by three main steps: (1) gelation of a sol, containing resorcinol (R) and formaldehyde (F) with polystyrene (PS) nanospheres as a templating agent in deionized water (W); (2) solvent exchange to acetone and supercritical drying with CO2 to minimize shrinkage effects and retain mechanically flexible bulk material behavior; (3) carbonization of the RF gel and decomposition of PS under an argon atmosphere to convert the cross-linked resin into an electrically conductive carbon spherogel, followed by physical activation with carbon dioxide
This proof-of-concept study investigated the synthesis parameters for the preparation of freestanding and monolithic carbon spherogels which were directly applied as electrode materials in electrochemical investigations of supercapacitor setups
Summary
Carbon aerogels are a fascinating and unique class of synthetic open porous materials. Our group templated single-shell hollow carbon aerogels structures, carbon spherogels, by introducing polystyrene (PS) nanospheres into the sol−gel process of resorcinol−formaldehyde (RF) with the result of monolithic and reversibly compressible samples.[19] PS was discovered to be a perfect polymer in the templated sol−gel process of RF due to its molecular similarity to resorcinol. This chemical resemblance results in attractive molecular interactions, such as π−π stacking, between the aromatic rings and facilitates the coating of resorcinol onto PS. Physical activation by carbon dioxide suitable candidates for electrode slicing were selected
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
