Sandwiched graphene with nitrogen, sulphur co-doped CQDs: an efficient metal-free material for energy storage and conversion applications

Here, a hybrid material composed of sandwiched reduced graphene oxide (rGO) and N,S co-doped carbon quantum dots (N,S-CQDs) was prepared following a facile synthetic route. This metal-free composite has demonstrated their dual performance as an electrode material for supercapacitors and fuel cell catalysts. It shows robust cyclic stability with high energy and power density without any binders. The enhanced activity of the composite can be ascribed to the CQDs present within the interlayer of the rGO which enhance the accessibility of the charged ions and increase the capacitance of the composite. In addition, the electrocatalytic activity of the composite has been assessed as a metal-free cathode catalyst towards the oxygen reduction reaction (ORR) for fuel cell applications. It shows better performance in terms of high reduction potential and high reduction current as compared to rGO. This can be ascribed to the significant contribution of electron rich heteroatom doped CQDs as well as the synergistic effect of both the CQDs and rGO for the electrocatalytic reduction of oxygen. The interesting dual performance of heteroatom doped CQDs and graphene hybrid composites hold potential for the development of energy storage and conversion devices.