There has been a great deal of interest recently in three-dimensional (3D) graphene based materials, as they exhibit large surface areas, unique electronic properties, and other attractive features. Particularly, 3D graphene doped with heteroatoms catalysts show high electrocatalytic activity toward oxygen reduction reaction (ORR), which can be used as metal-free catalysts. Most of the existing synthesis strategies of 3D graphene invariably involve multiple steps and procedures are often energy intensive and time-consuming. In this paper, we reported a one-pot and green method to synthesize boron-doped 3D reduced graphene oxide (B-3DrGO) using the supercritical carbon dioxide (ScCO2) technique. The resulting products exhibit hierarchical porous structures, leading to a high specific surface area of 541 m2 g−1. A high content of B (2.9 at%) was detected in the product, suggesting that B-doping was efficient using this technique. The B-3DrGO displays electrocatalytic activity toward ORR, which is comparable to the commercially available Pt/C (20 wt%) catalyst, in addition to their superior durability and resistance to the crossover effect. Moreover, the supercritical fluid technique, which uses non-flammable, essentially nontoxic, inexpensive, and environmentally benign CO2, is a new and green approach for the synthesis of heteroatom doped 3D graphene.