Boosting the thermal stability of emulsion-templated polymers via sulfonation: an efficient synthetic route to hierarchically porous carbon foams

Abstract

Hierarchically porous carbon foams with specific surface areas exceeding 600 m 2 g À1 can be derived from polystyrene foams that are synthesized via water-in-oil emulsion templating. However, most styrene-based polymers lack strong crosslinks and are degraded to volatile products when heated above 400 o C. A common strategy employed to avert depolymerization is to introduce potential crosslinking sites such as sulfonic acids by sulfonating the polymers. This article unravels the thermal and chemical processes leading up to the conversion of sulfonated high internal phase emulsion polystyrenes (polyHIPEs) to sulfur containing carbon foams. During pyrolysis, the sulfonic acid groups (-SO 3 H) are transformed to sulfone (-C-SO 2 -C-) and then to thioether (-CÀS-C-) crosslinks. These chemical transformations have been monitored using spectroscopic techniques: in situ IR, Raman, X-ray photoelectron and X-ray absorption near edge structure spectroscopy. Based on thermal analyses, the formation of thioether links is associated with increased thermal stability and thus a substantial decrease in volatilization of the polymers.

Tailoring the Microstructure and Electrochemical Performance of 3D Microbattery Electrodes Based on Carbon Foams

“…The experimental details regarding the synthesis of the carbon foams were published previously . In a typical preparation, a HIPE was prepared by mixing an organic oil phase with an aqueous phase using a rotor–stator homogenizer (Heidolph RZR2020) operated at angular speeds of 500, 1000, and 2000 rpm, respectively.…”

“…The emulsion was polymerized at 65 °C for 48 h. After a series of washing steps using water and ethanol, pieces of the polymer were sulfonated with concentrated H 2 SO 4 (Merck, 95–97%) at 100 °C during 24 h. After rinsing off excess acid with water and drying, the sulfonated polymers were carbonized at 1000 °C in a tube furnace (Heraeus) in an Ar atmosphere. A detailed description of the procedure can be found in the previous study . The as‐prepared carbon foams were further heated up to 1500 and 2200 °C for 1 h in a graphite furnace (Thermal Technology) under a constant flow of N 2 gas.…”

“…A similar trend was manifested in the pore volume, which decreased from 0.1 to 0.05 cm 3 g −1 . After carbonization at 1000 °C, both the BET specific surface areas and pore volumes increased considerably, as can be observed in Table S2, Supporting Information, due to the introduction of micropores as a result of the oxidation caused by the sulfonation step . The carbon foams derived from the polyHIPE synthesized at 2000 rpm possessed specific surface areas of around 620 m 2 g −1 and a pore volume of roughly 0.3 cm 3 g −1 .…”

“…This study focuses on the synthesis of carbon foams with optimum pore sizes and high graphitic contents as well as their potential use in 3D‐structured Li‐ion batteries. The carbon foams were derived from high internal phase emulsion (HIPE)‐templated polymers as this approach has been found attractive when preparing monoliths of porous polymers that ultimately can be converted to carbon foams . Varying the synthesis conditions of the polymerizations and the pyrolysis temperature enables the optimization of the porosity, surface area, and degree of graphitization of the carbon foams.…”

High-Surface-Area, Emulsion-Templated Carbon Foams by Activation of polyHIPEs Derived from Pickering Emulsions

“…When a charable polyHIPE is produced, it can be used as a precursor to porous carbon foams, or carboHIPEs, which retain the emulsion-templated macroporosity of the polyHIPE while developing micro- and mesopores upon carbonization, creating hierarchical porosity. The production of carboHIPEs has been described in the literature from a wide variety of starting materials, some of which include sulfonated poly(styrene- co -divinylbenzene) [ 18 , 19 ], Kraft black liquor [ 20 ], lignin [ 21 ], tannins [ 22 ], and polyacrylonitrile [ 23 ]. Recently, we described the production of carboHIPEs from poly(divinylbenzene)HIPEs synthesized from simple Pickering water-in-divinylbenzene (DVB) HIPE templates [ 24 ].…”