Biotemplate derived three dimensional nitrogen doped graphene@MnO2 as bifunctional material for supercapacitor and oxygen reduction reaction catalyst.

Natural diatomite with abundant pores was used as a biotemplate for the massive production of three-dimensional (3D) porous graphene by chemical vapor deposition method. Subsequent template removal and nitrogen doping treatment yield nitrogen doped 3D graphene with preserved shape and complex internal features of the diatomite. After further deposition with MnO2 nanosheets, the N-doped 3D graphene@MnO2 (N-G@MnO2) hybrid exhibited excellent supercapacitor and good oxygen reduction reaction (ORR) performance. Accordingly, the porous N-G@MnO2 electrode exhibited a high specific capacitance (411.5 F g-1) and a good cycling performance (88.3% capacitance retention after 4000 charge/discharge cycling test). When tested in a two-electrode configuration, N-G@MnO2 achieved a wide potential window up to 1.8 V with a high energy density of 46.1 Wh kg-1. Furthermore, the as-prepared N-G@MnO2 showed good performance in oxygen reduction reaction, which is comparable to those of commercially available Pt/C electrode. The enhanced capacitive and electrocatalytic properties and stability is due to the synergistic interactions between the porous 3D graphene and MnO2 nanosheets. The results indicate that the 3D N-G@MnO2 could be useful for supercapacitor and ORR catalyst.