Sulphur-linked graphitic and graphene oxide platelet-based electrodes for electrochemical double layer capacitors

This study presents novel investigations of sulphur-graphitic nanoplatelet (S-GNP) and sulphur-microwave expanded graphene oxide (S-MWGO) composite electrodes for structural electrochemical double layer capacitors (EDLCs) with liquid organic electrolyte 1 M TEABF(4) (tetraethylammonium tetrafluoroborate) in propylene carbonate (PC). Elucidating the chemical structure of these electrodes, XPS (X-ray photoelectron spectroscopy) and Raman spectroscopy indicated the presence of C-S-S-C links while mixed EDX (energy dispersive X-ray spectroscopy) elemental maps displayed elemental S outlining the edges of nanoplatelets, concluding the presence of S-links between nanoplatelets. While S-linking improved the mechanical properties and ensured structural integrity of the produced monoliths without the need of any binder, it also decreased the specific surface area of the resulting materials. Furthermore, additional sulphur might have been trapped in other forms, amounting to up to 26 wt% sulphur in the composite graphitic and graphene oxide-based electrodes. Three-point bend testing yielded that an S-GNP-MWCNT monolith with 20 wt% S and 0.24 wt% MWCNT exhibited similar mechanical properties to those of a rigid polyurethane foam. The same S-GNP-MWCNT monolith exhibited an average electrode capacitance of 12.2 F g(-1) during discharge at 2.2 mA/cm(2). An S-MWGO-MWCNT monolith electrode with 9.6 wt% S, 16.4 wt% carbon black and 0.24 wt% MWCNT exhibited an average electrode capacitance of 64.9 F g(-1) during discharge at 2.2 mA/cm(2) but higher resistance than the S-GNP electrodes. (C) 2019 Elsevier B.V. All rights reserved.