Hydrophilic phthalocyanine covalent organic frameworks for enhanced electrocatalytic H2O2 production

•CoPc-2SO3H-COF displays superior 2e− ORR activity in alkaline solutions as well as good stability.•More importantly, when employed as the cathodic active materials of flow cell, CoPc-2SO3H-COF shows a tremendous electrocatalytic H2O2 production.•The introduction of −SO3H into the skeleton of phthalocyanine covalent organic frameworks improves their hydrophilic properties, thus leading to the enhanced electrocatalytic performance towards O2-to-H2O2 conversion. The electrocatalytic 2e− oxygen reduction reaction (ORR) is considered as a promising pathway to replace conditional anthraquinone process for hydrogen peroxide (H2O2) manufacture. However, the efficient electrocatalysts towards 2e− ORR remain urgently desired. Herein, hydrophilic two-dimensional cobalt phthalocyanine (CoPc) covalent organic frameworks (COFs), denoted as CoPc-2SO3H-COF and CoPc-SO3H-COF, were afforded via the imidization reaction of 2,3,9,10,16,17,23,24-octacarboxyphthalocyaninato cobalt(II) with hydrophilic building blocks 2,5-diaminobenzenesulfonic acid and 1,4-benzenedisulfonic acid, respectively. Powder X-ray diffraction, transmission electron microscope, and N2 sorption experiment results reveal the crystalline and porous structure of these two COFs. Moreover, the water contact angle and proton conduction measurements demonstrate the hydrophilic properties of these two COFs owing to the introduction of −SO3H into their skeleton. This, in combination with the high-efficiency active Co-N4 sites towards 2e− ORR, endows these two COFs with enhanced 2e− ORR activity in the aqueous electrolyte. In particular, CoPc-2SO3H-COF exhibits outstanding electrocatalytic H2O2 production performance with a stable H2O2 selectivity of 88.3 % under a high current density of 125 mA cm−2 for 20 h in a flow cell.