Size Scaling of the Electrochemical Performance of Ti ₃ C ₂ T _x MXene Microelectrode Arrays for Electrophysiological Recording and Stimulation

ABSTRACT Miniaturized neural interfaces for research, diagnostics, and neuromodulation therapies require electrode materials that maintain low impedance and high charge injection capacity as device dimensions shrink to ensure high‐quality recordings and safe stimulation. Conventional interfaces rely on metals like platinum (Pt), which are limited by intrinsically high impedance and low charge transfer capacity, reducing their performance in sub‐100 µm applications. Ti ₃ C ₂ T _x MXene has emerged as a promising alternative for high‐density recording and stimulation interfaces, though the fundamental charge transfer mechanisms governing its performance remain poorly understood. This study evaluates Ti ₃ C ₂ T _x MXene microelectrodes across a range of diameters (25–500 µm) and systematically elucidates the mechanisms governing their recording and stimulation capabilities. Electrochemical impedance spectroscopy, cyclic voltammetry, and voltage transient measurements—supported by equivalent‐circuit modeling—revealed enhanced recording and stimulation capabilities of the MXene microelectrodes over size‐matched Pt microelectrodes, attributed to reduced charge‐transfer resistance and increased double‐layer capacitance. Finally, varying the volume and concentration of the spray‐coated Ti ₃ C ₂ T _x films showed that increased MXene concentration and volume enhanced performance by creating thicker, rougher interfaces. Together, these results establish Ti ₃ C ₂ T _x MXene as a promising electrode material with exceptionally low impedance, high capacitance, and high charge‐injection capacity across the microscale.