Bifunctional Catalytic Activity Guided by Rich Crystal Defects in Ti_3C_2 Mxene Quantum Dot Clusters for Li–O_2 Batteries

摘要

Ameliorating round-trip efficiency and mitigating parasitic reaction play a key role in enhancing the activity and durability of lithium-oxygen batteries. Herein, it is first reported that Ti3C2 MXene quantum dot clusters full of rich crystal defects anchored on N-doped carbon nanosheets (Ti3C2 QDC/N-C) can operate well as bifunctional catalyst for Li-O-2 batteries. The well-defined grain boundary and edge defects make crucial contributions in modulating the local unsaturated coordination state of active titanium atoms and thus the electronic structure of Ti3C2 QDC/N-C, greatly enhancing the catalytic capability. Furthermore, density functional theory calculations disclose that the fruitful crystal defects governed catalytic centers endow substantial benefits for inducing charge density delocalization, regulating the LixOy intermediate adsorption and reducing the oxidation-reduction energy barriers. The geometric morphology and distribution of final Li2O2 accommodations are distinctly altered with optimized decomposition reversibility, which strengthens electro-catalytic kinetics and lowers redox voltage gaps. As expected, Li-O-2 cells based on Ti3C2 QDC/N-C show favorable long-period stability (240 cycles at 200 mA g(-1)) with minimal side reactions and distinguished discharge/charge overpotential (0.62 V). Critically, this crystal defect strategy paves a new way for expanding the active sites in MXenes for catalytic applications.