Synergistic Effects of Mo₂C-NC@Co_xFe_y Core–Shell Nanoparticles in Electrocatalytic Overall Water Splitting Reaction

Transition metals (TMs) are highly investigated as nonprecious electrocatalysts for hydrogen evolution (HER) and oxygen evolution (OER) reactions. There is a strong demand for highly efficient and inexpensive catalysts for overall water splitting. Herein, the bimetallic Co_xFe_y alloy nanoparticles encapsulated in a N-doped graphene shell containing molybdenum carbide (Mo₂C) nanoparticles are synthesized by the pyrolysis of cobalt ferrite (Co_xFe_3−xO₄) nanoparticles coated by melamine-formaldehyde resin cross-linked with molybdic acid. Molybdic acid not only serves as precursor for the formation of highly dispersed Mo₂C nanoparticles in the N-doped graphene shell but also enhances the thermal stability of the organic shell, resulting in the formation of smaller Co_xFe_y cores. The formation of Mo₂C nanoparticles in the graphene shell is promoted by the Co_xFe_3−xO₄ core. Interestingly, the synergistic presence of Mo₂C nanoparticles not only enhances the HER activity of the material but also renders a partial breakage of the graphene shell, which increases the surface concentration of OER-active Co and therefore enhances the OER activity. The as-prepared TM-based materials serve as bifunctional catalysts for the overall water splitting and exhibit improved electrocatalytic performances compared to standard cells based on precious metals, with the potentials of 1.53 and 1.60 V at 10 and 20 mA cm⁻² in alkaline media, respectively.