A Chiral MOF Coupling Structural Order with Spin-Selective Catalysis for Oxygen Evolution Reaction

The efficiency of Electrochemical Water Splitting (EWS) can be improved exploiting spin-polarized currents produced by chiral materials through the Chiral-Induced Spin Selectivity (CISS) effect. During EWS, electron spin polarization (SP) favours the formation of O 2 in its triplet ground state lowering the overpotential required to drive the Oxygen Evolution Reaction (OER). However, most systems studied so far lack of well-defined structural properties. In this work, a family of nickel(II)-based coordination polymers exhibiting low (Ni-L1), intermediate (Ni-L2), and high (Ni-L3) crystallinity were prepared by solvothermal synthesis using 1,4-benzenedicarboxylic acid ligands (H 2 L) functionalized with both achiral (L=A) and chiral (L=C) alkoxy side chains. Ni-L3 are 2D Metal-Organic Frameworks (MOFs) composed by sheets of hexanickel(II) metallacrown subunits. The Ni-C materials show asymmetric SP accompanied by enhanced catalytic activity during OER as compared with their Ni-A counterparts. Moreover, the largest values of SP (~50%) and OER enhancement are observed in the most crystalline samples Ni-C2 and Ni-C3, although these materials and their achiral analogues retain ~40% and ~25% of intact alkoxy groups, respectively. Our work demonstrates that long-range order has a determining role in SP, indicating that chiral MOFs are ideal system to investigate CISS effect through structureproperties correlation studies.