1. Environmental Science and New Energy Technology Engineering Laboratory, Tsinghua–Berkeley Shenzhen Institute, Tsinghua Univ., Shenzhen, P.R. China.
2. Environmental Science and New Energy Technology Engineering Laboratory, Tsinghua–Berkeley Shenzhen Institute, Dept. of Automation, Tsinghua National Laboratory for Information Science and Technology, Graduate School at Shenzhen, Tsinghua Univ., Shenzhen, P.R. China.