Atomic Ruthenium-Riveted Metal–Organic Framework with Tunable d-Band Modulates Oxygen Redox for Lithium–Oxygen Batteries

Abstract

Non-aqueous Li−O 2 batteries have aroused considerable attention because of their ultrahigh theoretical energy density, but they are severely hindered by slow cathode reaction kinetics and large overvoltages, which are closely associated with the discharge product of Li 2 O 2 . Herein, hexagonal conductive metal−organic framework nanowire arrays of nickel-hexaiminotriphenylene (Ni-HTP) with quadrilateral Ni-N 4 units are synthesized to incorporate Ru atoms into its skeleton for NiRu-HTP. The atomically dispersed Ru-N 4 sites manifest strong adsorption for the LiO 2 intermediate owing to its tunable d-band center, leading to its high local concentration around NiRu-HTP. This favors the formation of film-like Li 2 O 2 on NiRu-HTP with promoted electron transfer and ion diffusion across the cathodeelectrolyte interface, facilitating its reversible decomposition during charge. These allow the Li−O 2 battery with NiRu-HTP to deliver a remarkably reduced charge/ discharge polarization of 0.76 V and excellent cyclability. This work will enrich the design philosophy of electrocatalysts for regulation of kinetic behaviors of oxygen redox.

Morphology-Dictated Mechanism of Efficient Reaction Sites for Li2O2 Decomposition

“…For the film-like deposit, the two high-potential charging platforms in Figure f are obviously lower than those of the disk-like deposit, which indicates a more facile decomposition of the former . The corresponding in situ AFM images (Figure g–i) further show that the morphology evolution of the film-like Li 2 O 2 deposit during OER appears to be an inverse process of the ORR.…”

Recent strategies for improving the performances of rechargeable lithium batteries with sulfur- and oxygen-based conversion cathodes

“…Reproduced with permission from Ref. [77] (Copyright 2021, Wiley-VCH GmbH). (D) preparation of the flexible hybrid free-standing film using a layer-by-layer approach.…”

“…Lv et al obtained a conductive nickel catecholate framework (Ni III -NCF) as a bifunctional catalyst by adjusting the spin state of the Ni 2+ site of Ni II -NCF. The regulation of the spin state enhances the covalence of nickel-oxygen in Ni III -NCF [77] , promotes the electron exchange between the Ni site and the oxygen adsorbent, and accelerates the redox kinetics of oxygen. The high affinity of the Ni 3+ site with the intermediate LiO 2 promotes the formation of Li 2 O 2 nanosheets in the void space of Ni III -NCF nanowires after discharge [Figure 9C].…”

“…(C) Ni III -NCF and Ni II -NCF cathode discharge mechanisms. Reproduced with permission from Ref [77]. (Copyright 2021, Wiley-VCH GmbH).…”

In situ potential-regulated architecture of an ultrafine Ru-based electrocatalyst for ultralow overpotential lithium–oxygen batteries

“…2 On the other hand, the carbon-based cathode is unstable at a high potential (>3.5 V) due to the presence of Li 2 O 2 . 3 This causes large polarization and poor cycle life of LOBs. Although metal oxides are stable at high potential, their poor conductivity and catalytic activity lead to a high overpotential for oxygen reduction/evolution reactions (ORR/OER), which would inevitably cause large energy loss and serious side reactions in LOBs.…”