Prussian Blue Analogues-Derived Transition-Metal Nitrogen-Doped Carbon (Transition Metal = Fe, Co, Ni) Nanomaterials as Cathodic ORR Electrocatalysts for Mg–Air Batteries

Magnesium (Mg)–air batteries are regarded as promising large-scale energy-storage devices because of their high theoretical energy density, low material cost, intrinsic safety, and environmental benignity. Nevertheless, their practical deployment is severely hindered by sluggish oxygen reduction reaction (ORR) kinetics at the cathode. Herein, nanoscale transition-metal–nitrogen-doped carbon (M-N-C, M = Fe, Co, Ni) electrocatalysts─denoted FNC, CNC, and NNC─are prepared by argon-pyrolysis of Prussian blue analogues (PBAs). The cationic and anionic ligands are systematically varied to tailor the crystal phase, pore architecture, and nanoscale M-Nx coordination environment. Comprehensive characterization shows that CNC possesses the highest density of well-dispersed Co-Nx active nanosites embedded in a graphitic matrix. This ensures rapid electron transfer and abundant accessible active centers. Electrochemical tests in alkaline (0.1 M KOH) and neutral (3.5 wt % NaCl) electrolytes demonstrate that CNC delivers the most robust ORR activity and stability (CNC > FNC > NNC) via a near-ideal 4 e pathway. Meanwhile, CNC exhibits better stability than commercial Pt/C in both alkaline and neutral electrolytes. As the cathode nanocatalyst in Mg-air batteries, CNC is found to yield a peak power density of 19.14 mW/cm2─only 0.66 mW/cm2 below that of commercial Pt/C. The decisive role of nanoscale M-Nx coordination environments in boosting ORR kinetics is thus elucidated. This work provides a nanomaterials-driven strategy for developing high-performance, cost-effective electrocatalysts for Mg-air batteries.