High-Loading and Stable Co-N₄ Single-Atom Catalytic Sites for Long-Cycle Dendrite-Free Potassium Metal Batteries

Single-atom (SA) engineering coupled with three-dimensional porous conductive carbon effectively boosts substrate potassiophilicity, optimizes potassium (K) nucleation kinetics, and eliminates dendrites. However, poor coordination stability under high SA loading and unclear regulatory mechanisms limit its use. Larger, more reactive K⁺ induces drastic volume expansion, recurrent solid-electrolyte interphase (SEI) breakdown, and continuous corrosion. SA-Fe/Ni carbons suffer irreversible C─C/C─N bond distortion, skeleton pulverization and atomic loss after repeated K cycling. Herein, we synthesized SA-Co doped porous carbon nanofibers (SA-Co-PCNF) with a Co loading of 1.53 wt% as hosts for potassium metal anodes (PMAs). Studies reveal that SA-Co doping affords higher K adsorption energy (-2.34 eV), which reduces the nucleation overpotential to a mere 36 mV. Furthermore, the in situ formed Co─N─C coordination structure strengthens the stability of C─N and C─C bonds, significantly mitigating the structural degradation of the host during repeated K deposition/stripping processes. The K@SA-Co-PCNF electrode exhibits exceptional cycling stability in symmetric cells, maintaining stable operation for 1000 h at 0.5 mA cm^-2/0.5 mAh cm^-2, 2600 h at 0.2 mA cm^-2/0.2 mAh cm^-2. Paired with 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), the K@SA-Co-PCNF//PTCDA full cell achieves long cycling stability (1000 cycles, 500 mA g^-1) and outstanding rate capability (127.11 mAh g^-1, 2000 mA g^-1).