Spin-orbital regulation of Iron-nitrogen sites in phthalocyanine catalysts for ultrahigh energy efficiency Zn–Air/Iodide hybrid batteries

Abstract

As a promising energy storage technology, zinc-air/iodide hybrid batteries (ZAIHBs) require efficient bifunctional catalysts capable of simultaneously mediating both oxygen reduction reaction (ORR) and iodide oxidation reaction (IOR). Herein, we demonstrate a spin-orbital and hybridized energy level strategy by constructing heteroatom-doped carbon nanotube-supported iron phthalocyanine polymers (S/N-CNT@PFePc). Zero-field cooling (ZFC) measurements reveal that both S and N-doping on the axial position induces a spin-state transition from low-spin to intermediate-spin in the Fe centers, stemming from the broken symmetry of crystal field. Moreover, density functional theory (DFT) calculations justify that axial S coordination causing a closer energy level between the intermediates (*OH and *I) and Fe 3dz2 orbital, enabling promoted electron transfer compared to N-doping. As a result, the spin-orbital regulation in S-CNT@PFePc achieved a record-low charge–discharge voltage gap ORR-IOR potential gap of 0.34 V (ΔE = Ej=10IOR- E1/2ORR). Impressively, when implemented in ZAIHBs, the S-CNT@PFePc-based cathode delivers an exceptional energy efficiency of 70% with remarkable stability, retaining 66% efficiency after 500 hours - among the best performances reported for hybrid battery systems. Furthermore, the flexible solid-state ZAIHBs incorporating this catalyst demonstrate excellent mechanical robustness and cycling stability, underscoring their practical applicability.