Chang Wu,Yuyang Hou,Jicheng Jiang,Haipeng Guo,Hua-Kun Liu,Jun Chen,Jiazhao Wang
Li–O 2 batteries has been widely investigated for its ultra-high capacity as next generation batteries. Nevertheless, some problems like sluggish kinetic reaction and instability hugely impede the practical use of Li–O 2 batteries. In this work, Mo 2 C/MoO 2 @RGO heterostructures was fabricated by in-situ growth of Mo 2 C between MoO 2 and RGO during calcination and being employed as cathode to explore the synergistic effect in Li–O 2 batteries. As a result, Mo 2 C/MoO 2 @RGO exhibits good specific capacity with 2365 mAh g −1 , high round-trip efficiency (89% at first cycle) and improved cycling performance. Density functional theory calculations indicated that the Mo 2 C/MoO 2 @RGO heterostructures have better capability of oxygen adsorption than sole constituent (Mo 2 C@RGO or MoO 2 @RGO), which triggers the formation of film-like amorphous discharge products, leading to lower overpotential and stable performance. Our study reveals the important role of heterostructures in Li–O 2 batteries system and demonstrates a promising design strategy for heterostructured catalyst.
The electrocatalytic nitrogen reduction reaction (NRR) has been regarded as a promising strategy for producing ammonia (NH3) at ambient conditions. However, the development of the NRR is severely hindered by the difficult adsorption and activation of N2 on the catalyst surface and the competitive hydrogen evolution reaction (HER) due to the lack of efficient NRR electrocatalysts. Herein, Mo2C-MoO2 heterostructure quantum dots embedded in reduced graphene oxide (RGO) are proposed as efficient catalysts for the electrocatalytic NRR. The ultrasmall size of the quantum dot is beneficial for exposing the active sites for the NRR, and the synergetic effect of Mo2C and MoO2 can promote N2 adsorption and activation and suppress the competitive HER simultaneously. As a result, a well-balanced NRR performance is achieved with a high NH3 yield rate of 13.94 ± 0.39 μg h–1 mg–1 at −0.15 V vs RHE and a high Faradaic efficiency of 12.72 ± 0.58% at −0.1 V vs RHE. Density functional theory (DFT) calculations reveal that the Mo2C (001) surface has a strong N2 adsorption energy of −1.47 eV with the side-on configuration, and the N≡N bond length is elongated to 1.254 Å, indicating the enhanced N2 adsorption and activation on the Mo2C surface. On the other hand, the low ΔGH* for HER over the MoO2 (−111) surface demonstrates the impeded HER process for MoO2. This work may provide effective catalyst-design strategies for enhancing the electrocatalytic NRR performance of Mo-based materials.
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