Electric Field Guided Fast and Oriented Assembly of MXene into Scalable Pristine Hydrogels for Customized Energy Storage and Water Evaporation Applications

Abstract The assembly of MXene nanosheets into a hydrogel framework is key to their grand success in practical applications. However, the scalable realization of such stable structures is challenging and requires critically high dispersion concentration for gelation. Herein, a simple yet highly controllable approach for the development of 2D and 3D monolithic hydrogels of MXene via electro‐tunable ordered assembly is reported. Directional electrophoretic drag of MXene and their gelation by voltage‐controlled in situ released ions at the electrode interface gives rise to stable hydrogels with tunable sheet orientations. Nanosheets can be arranged in‐plane or out‐of‐plane depending on the parallel or radial field created by customized electrode assembly. Further, the gelation rate can be easily regulated by the applied potential to achieve self‐standing hydrogel films in a few tens of seconds. The 2D hydrogels display excellent supercapacitive performance of 395 F g −1 at 2 mV s −1 with high retention of 42% at 5000 mV s −1 . In another customized application, the 3D‐monolithic MXene hydrogel displays outstanding performance as a solar‐thermal evaporator on behalf of its vertical sheet orientations, showing an excellent evaporation rate of 1.91 kg m −2 g −1 . This simple, fast, scalable, and sheet orientation‐controlled assembly can pave the way for future development of MXene hydrogels and beyond.