Biomass-Derived CoFe@N-Doped Graphitic Carbon Core–Shell Electrocatalysts for Low-Energy Hydrogen Production via Methanol-Assisted Water Electrolysis

Bimetallic CoFe nanoparticles encapsulated in nitrogen-doped graphitic carbon (CoFe@NGC) are synthesized via hydrochar polymerization of furfural followed by pyrolysis. The resulting core–shell heterostructures are obtained at pyrolysis temperatures of 500, 600, and 700 °C. Among them, CoFe@NGC-700 exhibits optimal bifunctional electrocatalytic activity, delivering overpotentials of 1.47 V for the oxygen evolution reaction (OER), 1.37 V for the methanol oxidation reaction (MOR), and 0.151 V for the hydrogen evolution reaction (HER) at a current density of 10 mA cm⁻². In a two-electrode configuration, CoFe@NGC-700 achieved a low cell voltage of 1.66 V for overall water electrolysis (HER||OER) in 1.0 m KOH. Under methanol-assisted electrolysis conditions (HER||MOR) in 1.0 m KOH + 1.0 m MeOH, the cell voltage further decreased to 1.45 V, with a Faradaic efficiency of 97%. These results highlight the potential of CoFe@NGC-700 as a sustainable, high-performance bifunctional electrocatalyst for energy-efficient hydrogen production.