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首页> 外文期刊>The Journal of Chemical Physics >O_2 reduction by lithium on Au(111) and Pt(111)
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O_2 reduction by lithium on Au(111) and Pt(111)

机译：锂在Au（111）和Pt（111）上还原O_2

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Lithium-oxygen has one of the highest specific energies among known electrochemical couples and holds the promise of substantially boosting the specific energy of portable batteries. Mechanistic information of the oxygen reduction reaction by Li (Li-ORR) is scarce, and the factors limiting the discharge and charge efficiencies of the Li-oxygen cathode are not understood. To shed light on the fundamental surface chemistry of Li-ORR, we have performed periodic density functional theory calculations in conjunction with thermodynamic modeling for two metal surfaces, Au(111) and Pt(111). On clean Au(111) initial O_2 reduction via superoxide (LiO_2) formation has a low reversible potential of 1.51 V. On clean Pt(111), the dissociative adsorption of O_2 is facile and the reduction of atomic O has a reversible potential of 1.97 V, whereas the associative channel involving LiO_2 is limited by product stability versus O to 2.04 V. On both surfaces O_2 lithiation significantly weakens the O-O bond, so the product selectivity of the Li-ORR is monoxide (Li_x O), not peroxide (Li_x O_2). Furthermore, on both surfaces Li_x O species are energetically driven to form (Li_x O) _n aggregates, and the interface between (Li_x O) _n and the metal surfaces are active sites for forming and dissociating LiO_2. Given that bulk Li_2 O (s) is found to be globally the most stable phase up to 2.59 V, the presence of available metal sites may allow the cathode to access the bulk Li_2 O phase across a wide range of potentials. During cycling, the discharge process (oxygen reduction) is expected to begin with the reduction of chemisorbed atomic O instead of gas-phase O_2. On Au(111) this occurs at 2.42 V, whereas the greater stability of O on Pt(111) limits the reversible potential to 1.97 V. Therefore, the intrinsic reactivity of Pt(111) renders it less effective for Li-ORR than Au(111).
机译：锂-氧具有已知电化学对中最高的比能之一，并有望大大提高便携式电池的比能。 Li（Li-ORR）进行的氧还原反应的机理信息很少，并且不了解限制Li-氧阴极的放电和充电效率的因素。为了阐明Li-ORR的基本表面化学性质，我们结合两个金属表面Au（111）和Pt（111）的热力学模型进行了周期性密度泛函理论计算。在纯净Au（111）上，通过超氧化物（LiO_2）形成的初始O_2还原具有1.51 V的低可逆电位。在纯净Pt（111）上，O_2的解离吸附很容易，原子O的还原具有1.97的可逆电位。 V，而涉及LiO_2的缔合通道受产物稳定性（相对于O到2.04 V）的限制。在两个表面上，O_2的锂化显着削弱了OO键，因此Li-ORR的产物选择性是一氧化碳（Li_x O），而不是过氧化物（Li_x O_2）。此外，在两个表面上大力驱动Li_x O物种形成（Li_x O）_n聚集体，并且（Li_x O）_n与金属表面之间的界面是用于形成和离解LiO_2的活性位点。假定发现整体上Li_2 O是高达2.59 V的最稳定相，可用金属位点的存在可使阴极在很宽的电位范围内进入整体Li_2O相。在循环过程中，预计放电过程（氧还原）将从化学吸附原子O的还原而不是气相O_2的还原开始。在Au（111）上，这发生在2.42 V，而O在Pt（111）上的更大稳定性将可逆电位限制在1.97V。因此，Pt（111）的固有反应性使其对Li-ORR的作用不如Au （111）。

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