Zwitterionic covalent organic framework triggering enhanced H2O2 photoproduction via controllable built-in electric field design

• The zwitterionic COFs (SO 3 H-EB-COF) exhibited the outstanding H 2 O 2 photosynthesis under pure water. • SO 3 H-EB-COF improved the charge separation/migration properties by the design of built-in electric field. • Experimental and theoretical investigations proved that SO 3 H-EB-COF realized H 2 O 2 photogeneration via 2e - ORR pathway. Ionic covalent organic framework (COF) with anionic or cationic units has been widely used as the high performance photocatalyst. However, the integration of anionic and cationic units into the same COF as a zwitterionic material is not been widely explored in photocatalysis field. Herein, the zwitterionic COF (SO 3 H-EB-COF) was synthesized by incorporating anionic and cationic units for efficient photoproduction of hydrogen peroxide (H 2 O 2 ) without sacrificial agents. The alternating positive and negative charge units in zwitterionic COF established a well-oriented built-in electric field, facilitating efficient electron separation/migration through substantial electron orbital rearrangement. As expected, the zwitterionic COF exhibited remarkable photocatalytic activity with a H 2 O 2 generation rate of 1730 μmol g -1 h −1 in O 2 -saturated water, which was higher than that of EB-COF (476 μmol g -1 h −1 ) and SO 3 H-COF (998 μmol g -1 h −1 ). Moreover, the relevant experimental results combined with theoretical calculations showed that the introduced anionic unit (SO 3 H) served as the 2e - oxygen reduction reaction centers with lower binding strength of the key intermediates (·OOH) in H 2 O 2 photosynthesis. This work highlights the potential of designing the zwitterionic COF for the advanced photocatalyst development.