Mapping (Pseudo)Capacitive Charge Storage Dynamics in Titanium Carbide MXene Electrodes in Aqueous Electrolytes Using 3D Bode Analysis

Pseudocapacitive materials offer high charge storage capacities at high rates with charging time scales of tens of seconds to a few minutes. Voltammetry methods are extensively employed in understanding complex charge storage processes in pseudocapacitive materials. In this study, three-dimensional (3D) Bode analysis is employed in investigating charge storage dynamics of two-dimensional (2D) titanium carbides, Ti 3 C 2 T x and Ti 2 CT x MXenes. Ti 3 C 2 T x is used as a model system due to its high metallic conductivity and electrolyte-dependent capacitive/redox charge storage properties to better understand the charge storage dynamics in acidic and neutral electrolytes. In electrochemical impedance measurements, Ti 3 C 2 T x /acidic electrolyte interface shows a high real capacitance accompanied by a low phase angle at specific potentials in the capacitive domain of frequencies (10 mHz to 1 Hz), demonstrating pseudocapacitive behavior. On the other hand, Ti 3 C 2 T x /neutral electrolyte interface exhibits invariant low real capacitance with high phase angle values in the low frequency regime, indicating a double-layer charge storage mechanism. The charge storage dynamics of MXene electrodes determined using 3D Bode analysis corroborates well with the kinetic analyses using voltammetry methods.