Porous carbon nanosheets supported Co single-atom catalysts via dual-molten-salt synergy for advanced zinc–air batteries

Abstract

Enhancing electrocatalyst performance relies heavily on recognizing the importance of structural design and micro-morphology control in non-precious metal carbon-based materials. Herein, this work reports a dual-molten-salt-assisted gradient pyrolysis strategy to construct a single-atom Co catalyst (Co-DNC-2) featuring a three-dimensionally interconnected nanosheet architecture. The KCl–NH₄Cl eutectic system enables dynamic structural evolution during pyrolysis. The decomposition of NH₄Cl generates gas-etching-induced defects and hierarchical porosity, while molten KCl drives shear-assisted exfoliation and ordered stacking of ultrathin carbon nanosheets via intercalation and spatial confinement. Concurrently, ionic exchange and confinement effects stabilize cobalt at the atomic scale, yielding abundant and uniformly distributed Co–N_x sites. The resulting Co-DNC-2 possesses mesoporous channels penetrating stacked carbon layers and a high specific surface area, which together enhance electrolyte infiltration, oxygen diffusion, and charge transport. Consequently, Co-DNC-2 demonstrates an ORR half-wave potential of 0.87 V, leading to a peak power density of 240.5 mW cm⁻² in the liquid zinc–air battery, which exceeds the performance of commercial Pt/C catalysts. This work provides a rational strategy for designing efficient non-precious metal catalysts with optimized mass transfer pathways.