d-Orbital Induced Electronic Structure Reconfiguration toward Manipulating Electron Transfer Pathways of Metallo-Porphyrin for Enhanced AlCl₂⁺ Storage

The positive electrodes of non-aqueous aluminum ion batteries (AIBs) frequently encounter significant issues, for instance, low capacity in graphite (mechanism: anion de/intercalation and large electrode deformation induced) and poor stability in inorganic positive electrodes (mechanism: multi-electron redox reaction and dissolution of active materials induced). Here, metallo-porphyrin compounds (employed Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ as the ion centers) are introduced to effectively enhance both the cycling stability and reversible capacity due to the formation of stable conjugated metal-organic coordination and presence of axially coordinated active sites, respectively. With the regulation of electronic energy levels, the d-orbitals in the redox reactions and electron transfer pathways can be rearranged. The 5,10,15,20-tetraphenyl-21H,23H-porphine nickle(II) (NiTPP) presents the highest specific capacity (177.1 mAh g⁻¹), with an increment of 32.1% and 77.1% in comparison with the capacities of H₂TPP and graphite, respectively, which offers a new route for developing high-capacity positive electrodes for stable AIBs.