Recently, a new family of two-dimensional (2D) early transition metal carbides and carbonitrides, called MXenes, was discovered. Unlike graphene, whose chemistry is restricted to carbon, MXenes allow a variety of chemical compositions and are establishing themselves as a new class of two-dimensional materials. MXenes combine the metallic conductivity of transition metal carbides with the hydrophilic nature of their mostly hydroxyl or oxygen terminated surfaces. They behave as “conductive clays” and demonstrate much promise for electrochemical energy storage systems, thanks to transition metal atoms in the structure that are capable of reversible redox reactions. We explored the potential of MXenes in electrochemical capacitors. It was established that variety of single- and multiply charged cations (such as Li+, Na+, K+, NH4+, Mg2+) can intercalate MXenes (chemically or electrochemically) and participate in energy storage. In most cases, the cations intercalated spontaneously. We show high capacitance (pseudocapacitance) more than 1000 Farads per cubic centimeter (much higher than that of porous carbons or graphene) of flexible Ti3C2Tx paper electrodes in aqueous electrolytes. We found that tuning of material surface chemistry can improve MXenes’ capacitive performance. We also delved into mechanism of charge storage in MXenes and addressed how different electrode architectures can lead to maximizing the electrochemical performance.

Two-dimensional transition metal carbides – New materials for electrochemical capacitors

253rd National Meeting (2017)

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