Rechargeable Li-O₂ batteries have been considered as the most promising chemical power owing to their ultrahigh specific energy density. However, the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) result in high overpotential (∼1.5 V), poor rate capability, and even a short cycle life, which critically hinder their practical applications. Herein, we propose a synergistic strategy to boost the electrocatalytic activity of Co₃O₄ nanosheets for Li-O₂ batteries by tuning the inner oxygen vacancies and the exterior Co³⁺/Co²⁺ ratios, which have been identified by Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption near edge structure spectroscopy. Operando X-ray diffraction and ex situ scanning electron microscopy are used to probe the evolution of the discharge product. In comparison with bulk Co₃O₄, the cells catalyzed by Co₃O₄ nanosheets show a much higher initial capacity (∼24051.2 mAh g^–1), better rate capability (8683.3 mAh g^–1@400 mA g^–1) and cycling stability (150 cycles@400 mA g^–1), and lower overpotential. The large enhancement in the electrochemical performances can be mainly attributed to the synergistic effect of the architectured 2D nanosheets, the oxygen vacancies, and Co³⁺/Co²⁺ difference between the surface and the interior. Moreover, the addition of LiI to the electrolyte can further reduce the overpotential, making the battery more practical. This study offers some insights into designing high-performance electrocatalysts for Li-O₂ batteries through a combination of the 2D nanosheet architecture, oxygen vacancies, and surface electronic structure regulation.

中文翻译：

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通过调节内部氧空位和外部Co ³⁺ / Co ²⁺比率来提高Co ₃ O ₄纳米片对Li-O ₂电池的电催化活性

可充电的Li-O ₂电池因其超高的比能量密度而被认为是最有前途的化学动力。然而，缓慢的氧气还原反应（ORR）和氧气释放反应（OER）导致高电势（〜1.5 V），较差的倍率能力甚至较短的循环寿命，严重地阻碍了它们的实际应用。本文中，我们提出了一种协同策略，通过调节内部氧空位和外部Co ³⁺ / Co ²⁺来提高Co ₃ O ₄纳米片对Li-O ₂电池的电催化活性。可以通过拉曼光谱，X射线光电子能谱和X射线吸收近边缘结构光谱来确定比率。Operando X射线衍射和异位扫描电子显微镜用于探测放电产物的演变。与块状Co ₃ O _4相比，被Co ₃ O ₄纳米片催化的细胞显示出更高的初始容量（〜24051.2 mAh g ^–1），更好的速率容量（8683.3 mAh g ^–1 @ 400 mA g ^–1）和循环稳定性（150循环@ 400 mA g ^–1），并降低过电势。电化学性能的大幅提高主要归因于结构化2D纳米片的协同效应，氧空位以及表面和内部之间的Co ³⁺ / Co ²⁺差异。此外，在电解液中添加LiI可以进一步降低过电势，从而使电池更加实用。这项研究通过结合2D纳米片结构，氧空位和表面电子结构调节，为设计用于Li-O ₂电池的高性能电催化剂提供了一些见识。