Optimally Designed Bimetallic Ni-Based Layered Double Hydroxide with Chirality-Induced Spin Selectivity Effect for Advanced Zinc–Air Batteries

Zinc–air batteries (ZABs) have received considerable attention as one of the promising next-generation energy storage systems owing to their high theoretical energy density (≈ 1086 W h kg^–1), stable safety, and low cost of Zn metals. However, the further development of ZAB has been hindered by the sluggish kinetics of oxygen evolution reaction (OER), which occurs at the air cathode during the charging process of ZAB. To ameliorate this technical issue, various OER electrocatalysts have been extensively studied. Especially, bimetallic Ni-based layered double hydroxides (LDHs) (i.e. NiFe, NiCo, and NiAl LDH) have stood out as promising OER electrocatalysts owing to their decent OER activity comparable to noble-metal-based electrocatalysts. Moreover, the flexible tunability of the chemical composition of Ni-based LDH facilitates the electronic regulation and exposure of active sites, which are beneficial for the improvement of OER kinetics. However, considering that the OER involves spin-dependent electrochemical reactions, fine control of the spin orientation of electrons is imperative to improve the OER performance to the theoretical level. Specifically, by inducing the spin alignment of intermediate radicals (●OH), chemically stable triplet O₂ can be readily generated, whereas the formation of energetically unfavorable byproducts including singlet O₂ and H₂O₂ is suppressed, which can further accelerate the OER kinetics. In this study, we successfully prepared chiral bimetallic Ni-based LDHs with helical structures for the OER electrocatalyst of ZAB. The chiral LDH samples notably exhibited chirality-induced spin selectivity (CISS) effect, in which electrons acquired spin polarization via transport through the helical structure of LDH. In particular, chiral NiFe LDH exhibited efficient CISS effect with a superior spin selectivity compared to NiCo and NiAl LDH-based samples owing to the considerable lattice distortion within the helical structure induced by the large size difference between Ni and Fe ions. In addition, optimal electronic spin configuration of Fe active sites not only improved adsorption of O intermediates but also promoted electron transfer with the decreased spin electron-dependent scattering. As a result, the chiral NiFe LDH afforded superior OER performance with an overpotential of 260 mV at a current density of 10 mA cm^–2, which was significantly lower than those of achiral counterpart and NiCo and NiAl LDH-based samples. Furthermore, by integrating the chiral NiFe LDH into the air cathode, the ZAB delivered a high open-circuit voltage of 1.62 V, which was close to the theoretical limit (1.66 V). The ZAB also exhibited stable long-term cycling performance over 300 h with a minimum charge-discharge potential gap of 0.75 V. Impressively, the chiral NiFe LDH-based ZAB also maintained high stability even in neutral media, further highlighting the effective OER performance of the optimally designed NiFe LDH with efficient CISS effect.