Hydroiodic Acid Initiated Dense yet Porous Ti 3 C 2 T x MXene Monoliths towards Superhigh Areal Energy Storage.

The assembly of three-dimensional (3D) structured materials from two-dimensional (2D) units paves up a royal road for building thick and dense electrodes, which is the long pursuit for a practical energy storage device. 2D transitional metal carbides (MXene) make promises for this due to their capabilities of solution-based assembly and intrinsic high density, yet facing huge challenges in yielding high areal capacitance electrodes owing to the absence of porous ion transport paths. Here, a gelation-densification process initiated by hydroiodide acids (HI) is proposed, where the protons break the electrostatic balance of MXene nanosheets to trigger the gelation, while HI serves as the spacers to prevent nanosheets from restacking during the capillary shrinkage. More promising, the controlled evaporation of reductive HI leaves superiorly shrinking yet porous network for ion transport, and the produced monoliths exhibit a high density of 2.74 g cm -3 and an unprecedented areal capacitance of 18.6 F cm -2 . This article is protected by copyright. All rights reserved.