Tunable ordered assembly of MXene and related nanomaterials for scalable energy applications

Abstract

quotDevelopment of functional macrostructures form two-dimensional materials while addressing the key fundamental challenges in supercapacitive energy storage systems remains a monumental task in the field of energy storage. Meanwhile MXene, a new family of two-dimensional materials has emerged as a highly attractive material in supercapacitive applications due to their high conductivity, hydrophilicity and pseudocapacitive nature. This thesis aims towards development of functional macrostructures from MXene and related nanomaterials in the form of hydrogels while ensuring scalability and low-cost of synthesis. MXene hydrogels are an interconnected network of these two-dimensional materials which offers highly restacking controlled porous structure that enables facile accessibility of the bulk of the electrodes to the electrolyte ions. Such restacking controlled assembly enables high utilization of active mass ensuring high specific capacity and rate performance. This thesis introduces a room-temperature self-assembling strategy with the help of a small amount of graphene to induce gelation in a system of MXene and graphene for hybrid hydrogel development. It is shown that such room temperature induced assembly not only protects the intrinsic properties of MXene by preventing synthesis induced oxidation, but also enables state-of the-art performance even in commercial scale mass loading electrodes. Furthermore, development of hydrogels of pristine MXene has been a great challenge due to the relative small sheet size and intrinsic stiffness of MXene. Here, in this thesis, for the first time a critical-density induced gelation strategy is introduced which enables the development of self-supporting pristine MXene hydrogels. It is established that liquid crystallinity induced ordering in MXene dispersion can lead to higher crosslinking of MXenes into the hydrogels which leads to better stability in such systems. The as developed hydrogels were used as supercapacitive electrodes having mass loading as high as ~ 15 mg cm-