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

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.