Facile Synthesis of Three-Dimensional Graphene Nanomaterials via Supercritical Fluid for Oxygen Reduction Reaction

The considerable interest in polymer electrolyte membrane fuel cells (PEMFCs) has sparked a sustained research effort on more active and reliable oxygen reduction reaction (ORR) electrocatalyst. Although great progress has been made on ORR catalysts in recent decades, the further development of PEMFCs is severely restrained by high-priced Pt in the cathode catalysts and the slow kinetics of the ORR. Control of nanostructures at the atomic level can precisely and effectively tune catalytic properties of materials, optimizing the structural and compositional effect and further enabling enhancement in both activity and durability. Besides, most electrochemical systems consist of porous electrode materials. These 3D porous architectures are able to provide higher specific surface areas and larger pore volumes, not only maximizing the availability of electron transfer within nanosized electrocatalyst surface area but also providing better mass transport of reactants to the electrocatalyst. Fabricating interconnected mesoporous arrays/superstructures is critical to achieve both high surface area and fast mass transfer. Under the circumstances, constructing novel 3D porous nanostructures with non- and low Pt group metal (PGM) nanocatalysts have received significant attention to further enhance ORR electrocatalytic performance.

Supercritical CO₂ (sc-CO₂) process offers an elegant and efficient route for the synthesis and processing of novel nanocomposite materials, consisting of active nanocarbon and nanocrystals. Herein, we developed the sc-CO₂ technique to synthesize boron-doped 3D graphene and low PGM-based graphene/PtFe with 3D porous nanostructures. Significantly, these 3D nanocomposites show excellent electrocatalytic activity and high stability toward the ORR, holding great promise for the development of PEMFCs.