An effective way to optimize the functionality of inorganic 2D nanosheets can be developed by tailoring their interfacial electronic coupling and crystal defect in the hybrid structure. The heterolayer hybridization between exfoliated Co−Fe-layered double hydroxide (LDH) and RuO2 nanosheets can provide an efficient way of optimizing the interfacial coupling and oxygen vacancy of restacked nanosheets. The obtained Co−Fe-LDH−RuO2 nanohybrid shows outstanding electrode performance for Li−O2 batteries with excellent bifunctional oxygen electrocatalytic activity, which is much superior to those of the precursor materials. In-situ X-ray absorption spectroscopic and electrochemical characterizations highlight the remarkable improvement of electrocatalysis kinetics and electrochemical stability upon hybridization, which is attributable to the intimate interfacial interaction and oxygen vacancy formation of restacked 2D inorganic nanosheets. This study underscores that a fine-control of electronic coupling and defect structure via heterolayer hybridization is quite effective in exploring high-performance bifunctional electrocatalysts applicable as Li−O2 cathode.
Bibliographical noteFunding Information:
This work was supported by the National Research Foundation of Korea grant funded by the Korea government (MSIP) (No. NRF-2017R1A2A1A17069463 ) and by the Korea government (MSIT) (No. NRF-2017R1A5A1015365 ). The experiments at PAL were supported in part by MOST and POSTECH .
According to CV analysis (Fig. 4e), the ORR activities of CFR and Co−Fe-LDH are confirmed by the observation of a cathodic peak at an onset potential ~2.7 V. For the OER process, the CRF0.5 nanohybrid displays a much higher activity with a broader anodic peak at an onset potential of ~3.25 V than the other materials, indicating the promoted decomposition of discharge products. As probed by XANES/EXAFS analyses (Fig. 1f−k), a strong interfacial coupling between RuO2 and Co−Fe-LDH induces net RuO2 to LDH charge redistribution with creation of oxygen defects, thus facilitating the adsorption of the oxide species (LiO2 or Li2O2) with a moderate bond strength for enhanced OER activities [37,38]. The beneficial effect of hybridization on charge transfer kinetics is evidenced by the EIS analysis conducted after the 1st discharging without the capacity limitation demonstrating a significant decrease of Rct upon hybridization (Fig. 4f and Fig. S11 of Supporting information). Also, the discharge products on CFR0.5, RuO2, and Co−Fe-LDH are analyzed with FE-SEM, see Fig. S12 of Supporting information. The CFR0.5 cathode after the discharge process displays a homogenous deposition of sheet-like discharge products with 2D structure over the entire electrode, which must be beneficial for mass transfer and electron transport for improved ORR and OER activities. Conversely, the unhybridized RuO2 and Co−Fe-LDH cathodes demonstrate the formation of a film-like and typical toroidal discharge products, respectively, leading to the significant impeding of the following OER process. The homogenous charge redistribution of electrocatalytically-active LDH NS caused by the effective electronic coupling with highly-conductive RuO2 NS is responsible for the optimization of the microstructure of discharge products in the CFR nanohybrid and the following efficient facilitation of its decomposition during OER.This work was supported by the National Research Foundation of Korea grant funded by the Korea government (MSIP) (No. NRF-2017R1A2A1A17069463) and by the Korea government (MSIT) (No. NRF-2017R1A5A1015365). The experiments at PAL were supported in part by MOST and POSTECH.
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All Science Journal Classification (ASJC) codes
- Renewable Energy, Sustainability and the Environment
- Materials Science(all)
- Electrical and Electronic Engineering