Iron phthalocyanine catalyst accelerates polysulfide conversion in practical magnesium-sulfur batteries

Magnesium-sulfur batteries promise high energy density with abundant and safe elements but suffer from sluggish polysulfide conversion, severe polarization, and unstable cycling. Here, we introduce an iron phthalocyanine (FePc) molecular catalyst to address these challenges. Guided by the Sabatier principle, the well-defined Fe-N 4 sites modulate polysulfide adsorption energetics, regulating the precipitation of solid products. This mechanism promotes uniform three-dimensional growth of MgS 2 /MgS and accelerates interfacial charge transfer, mitigating concentration polarization. Cells with FePc achieve capacities of ∼1,400 mAh/g (based on sulfur mass) and deliver up to 840 Wh/kg (based on cathode mass). Notably, we also assembled a prototype pouch cell that delivers 58.4 Wh/kg. These results validate molecular catalysis as an effective approach for overcoming kinetic bottlenecks in multivalent sulfur systems and underscore the broader potential of structurally precise catalysts as both functional materials and model platforms for advancing sustainable energy storage technologies.