Electronic Supplementary Information (ESI) The main factor to improve the performance of CoSe 2 for photocatalytic CO 2 reduction: element doping or phase transformation Yong Xu, ab Jiang Mo, a Guanqun Xie, a Xiaoxia Wang,* a and Shujiang Ding* b a School of Materials Science and Engineering, Dongguan University of Technology, Dongguan 523808, China. b Department of Applied Chemistry, School of Science, Xi´an Jiaotong University, Xi´an, 710049, P.R. China *Corresponding Author E-mail: wangxx@dgut.edu.cn; dingsj@mail.xjtu.edu.cn Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is © The Royal Society of Chemistry 2020