ABSTRACT
Li-S battery technology, with high theoretical capacity and energy density, has drawn much attention in recent years as a possible replacement for current Li-ion battery technologies. A major drawback of Li-S batteries is a severe capacity fading effect which, to a large extent, stems from the dissolution and diffusion of lithium polysulfides (LiPS) that are formed during both charge and discharge cycles. The self-discharge caused by the LiPS migration during the charge process (the so-called "shuttle effect") often leads to the capacity decay of Li-S batteries. Herein, hollow structured metal oxide (Co3O4, Mn2O3, and NiO) submicro-spheres are prepared by a novel method and employed as efficient LiPS immobilizers. These Li-S batteries, based on the developed metal oxide spheres, possess outstanding rate capability and cycling stability. The best performing S/C/Co3O4 electrode delivers excellent cycling stability with only a 0.066% capacity decay per cycle during 550 cycles. Moreover, its discharge capacity is as high as 428 mA h g-1 at a 3C rate which is far superior to that of bare S/C (115 mA h g-1) at 3C. The fast kinetics of the electrocatalytic conversion of LiPS on the developed Co3O4 electrode and its unique hollow structure are the key factors that lead to its outstanding performance as a Li-S battery cathode material.
ABSTRACT
Deactivation of an anode catalyst resulting from the poisoning of COad-like intermediates is one of the major problems for methanol and ethanol electro-oxidation reactions (MOR & EOR), and remains a grand challenge towards achieving high performance for direct alcohol fuel cells (DAFCs). Herein, we report a new approach for the preparation of ultrafine cobalt-doped CeO2 dots (Co-CeO2, d = 3.6 nm), which can be an effective anti-poisoning promoter for Pd catalysts towards MOR and EOR in alkaline media. Compared to Pd/CeO2 and pure Pd, the hybrid Pd/Co-CeO2 nanocomposite catalyst exhibited a much enhanced activity and remarkable anti-poisoning ability for both MOR and EOR. The nanocomposite catalyst showed much higher mass activity (4×) than a state-of-the-art PtRu catalyst. The promotional mechanism was elucidated using extensive characterization and density-functional theory (DFT). A bifunctional effect of the Co-CeO2 dots was discovered to be due to (i) an enhanced electronic interaction between Co-CeO2 and Pd dots and (ii) the increased oxygen storage capacity of Co-CeO2 dots to facilitate the oxidation of COad. Therefore, the Pd/Co-CeO2 nanocomposite appears to be a promising catalyst for advanced DAFCs with low cost and high performance.