Hafnium Diboride Spherical Superstructure Born of 5d-Metal Hf-MOF-Induced p Orbital Activity of B Atom and Enhanced Kinetics of Sulfur Cathode Reaction

Improving the intrinsic catalytic activity of electrocatalysts is considered to be the "gold standard" to inhibit the shuttle effect in Li-S batteries. The question of how to expose active sites for anchoring and catalytic conversion of the polysulfides represents the direction of this research. The assembly of 0D nanoparticles or 2D nanosheets into 3D spherical superstructure is one of the problems of materials synthesis. Here, a spherical superstructure hafnium diboride derived from metal-organic framework (MOF) nanoparticles is synthesized by one-step borification. Benefiting from its unique superstructure, the obtained HfB2 exhibits excellent catalytic activity for the conversion of polysulfide. Theoretical calculations indicate that the strong spin-orbital coupling property of electron configuration of 5d Hf induces p orbitals of nonmetallic atoms closer to the Fermi level, thus endowing the anions with redox activity and unconventional superconductivity. These merits enable the HfB2-based sulfur cathode to deliver a high initial discharge capacity of 1433 mAh g(-1) at 0.2 C and 580 mAh g(-1) at 5 C. With sulfur loading of 12.8 mg cm(-2) and electrolyte dosage of 4 mu L mg(-1), the areal capacity can reach 15.5 mAh cm(-2). This work provides a new understanding for designing superstructure borides involving 5d metals in Li-S batteries.