Liquid–liquid micromixing strategy enables low KOH-amount synthesis of ultrahighly porous carbon for zinc-ion storage

Ultrahigh specific surface area and low KOH amount are normally mutually exclusive and hard to attain simultaneously when using the traditional KOH activation. In this work, we report a facile approach to synthesize a series of porous carbons with ultrahigh specific surface area about 3000 m 2 g −1 by using a very low mass ratio of KOH to carbon precursor, e.g. , 0.42. The key to this preparation strategy is development of a liquid–liquid micromixing strategy for mixing KOH with biomass-based carbon precursors that can be well dispersed in KOH aqueous solution. Compared with solid–solid mixing strategy normally used in traditional KOH activation methods, the liquid–liquid micromixing strategy enables to form a homogeneous solution with highly mixing between macromolecular-scale carbon precursor and ion-scale KOH at the microscopic level, which significantly increases the activation reaction efficiency. The typical porous carbon obtained based on the liquid–liquid micromixing strategy exhibits a specific surface area as high as 3009 m 2 g −1 , which is much higher than that of porous carbon prepared through a solid–solid mixing strategy, i.e. , 2228 m 2 g −1 . Benefiting from the ultrahigh specific surface area, the resultant carbon materials show very attractive electrochemical performances when used as the cathode material in zinc-ion hybrid supercapacitor, such as an intriguing average specific capacity of 344 mAh g −1 and a remarkable cycling stability of 98.5% capacity retention after 10,000 cycles.