1. College of Physics and Center of Quantum Materials and Devices, Chongqing University, Chongqing 401331, P. R. China
2. State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, P. R. China