Thermal Evolution of the Structure and Activity of Non-Doped Graphene as Metal-Free Oxygen Reduction Electrocatalysts

Herein, graphene oxide (GO) is directly heat-treated in N2 atmosphere at different temperatures to investigate thermal evolution of the structure and activity as a non-doped metal-free oxygen reduction reaction (ORR) electrocatalyst. Heat-treatment temperature plays a crucial effect on improving the ORR electrocatalytic performance in alkaline electrolyte: the higher the heat-treatment temperature the better the electrocatalytic performance. Generation of defects arising from the removal of oxygen-containing group as a consequence of heat-treatment plays an essential role. Both XRD and Raman indicate that the higher heat-treatment temperature the greater defective nature of graphene, indicating the significant contribution of carbon intrinsic defects to its ORR activity. XPS of GO-800 distinctly shows the only presences of C1s and O1s without any other element, especially metal signal, namely the dopant-free graphene. This work confirms graphene without interruption by any other dopants can be applied as an efficient ORR electrocatalyst.