Effect of graphene oxide/carbon nanotube ratio on electrochemical behaviors of spongy bone-like reduced graphene oxide/carbon nanotube foam prepared by simple and green approach

Modifying nano/micro structure of materials based on graphene has been studied extensively. However, the existing methods are complex and involve multi-step procedures. In this study, we successfully prepared graphene oxide (GO)/carbon nanotube (CNT) foams with different GO/CNT ratios by integrating GO nanosheets and CNTs in aqueous media of water and ethanol without using any other materials and further treatments. The GO sheets acted as a dispersing agent for CNTs in water by p-p interactions and the CNTs located at sp(2) carbon plane of GO which is non-oxidized carbon region provide conductive electron pathway and connect GO sheets. Ethanol molecules added to water inhibit the decrease of mobility of water as the temperature gets lower and prevent the growth of ice crystals. By exploiting the characteristics of the materials and media, it was possible to fabricate macroscopic, stereoscopic, and continuous spongy bone-like GO/CNT hybrid foams in an eco-friendly and straightforward manner. Furthermore, the GO/CNT foam could be reduced by thermal treatment without deformation, resulting in a graphene-based foam capable of energy storage. A supercapacitor consisting of the reduced foam as electrode and GO membrane as separator was fabricated. The resultant supercapacitor was stably operated in different electrolytes and showed distinctive electrochemical behaviors. The inserted CNTs between reduced GO layers and spongy bone-like structure increased the accessible areas of the electrolytes and led to rapid electrolyte ion diffusion, indicating that energy and power characteristics were improved by nano/micro structure mediation.