Nickel-based Single-Molecule Catalysts with Synergistic Geometric Transition and Magnetic Field-assisted Spin Selection Outperforms RuO2 for Oxygen Evolution

Abstract

Overcoming slow kinetics and high overpotential in electrocatalytic oxygen evolution reaction (OER) requires innovative catalysts and approaches that transcend the scaling relationship between binding energies for intermediates and catalyst surfaces. Inorganic complexes provide unique catalyst designs with customizable geometries, which can help enhance their efficiencies. However, they are unstable and susceptible to oxidation under extreme pH conditions. Immobilizing complexes on substrates creates single-molecule catalysts (SMCs) with functional similarities to single-atom catalysts (SACs). Here, an efficient SMC, composed of dichloro(1,3-bis(diphenylphosphino)propane) nickel [NiCl2dppp] anchored to a graphene acid (GA), is presented. This SMC surpasses ruthenium-based OER benchmarks, exhibiting an ultra-low onset and overpotential at 10 mAcm-2 when exposed to a static magnetic field. Comprehensive experimental and theoretical analyses imply that an interfacial charge transfer from the Ni center in NiCl2dppp to GA enhances the OER activity. Spectroscopic investigations reveal an in-situ geometrical transformation of the complex and the formation of a paramagnetic Ni center, which under a magnetic field, enables spin-selective electron transfer, resulting in enhanced OER performance. The results highlight the significance of in-situ geometric transformations in SMCs and underline the potential of an external magnetic field to enhance OER performance at a single-molecule level, pushing the boundaries of volcano limits.