S1 Supplementary Information Highly Durable Photoelectrochemical H 2 O 2 Production via Dual Photoanode and Cathode Processes under Solar Simulating and External Bias-free Condition Tae Hwa Jeon, a Hyejin Kim, a Hyoung-il Kim,* b,c and Wonyong Choi* a,d a Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea. b Department of Civil and Environmental Engineering, Yonsei University, Seoul 03722, Korea. c Future City Open Innovation Center, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea. d Institute for Convergence Research and Education in Advanced Technology, Yonsei University, Seoul 03722, Korea. *To whom correspondence should be addressed: (W.C.) E-mail: wchoi@postech.edu; Tel: +82-54-279-2283 (H. K.) E-mail: hi.kim@yonsei.ac.kr; Tel:+82-2-2123-2798 Total number of pages: 15 Number of Tables: 2 (S1-S2) Number of Figures: 10 (S1-S10) Electronic Supplementary Material (ESI) for Energy & Environmental Science. This journal is © The Royal Society of Chemistry 2020