Ti₃C₂T_<i>x</i> and Mo₂TiC₂T_<i>x</i> MXene-based biocompatible supercapacitors for implantable medical devices

Implantable medical devices (IMDs) use batteries with toxic electrolytes that can be harmful when leaked and have a limited lifespan, necessitating frequent replacements through painful surgeries. A practical solution is to utilize biocompatible supercapacitors that function with biocompatible electrolytes, making any potential leakages non-toxic and safe while also prolonging device lifespan by incorporating self-powered nanogenerators as their energy source. However, the current biocompatible material-based supercapacitors perform unsatisfactorily with biocompatible electrolytes. In this work, we developed biocompatible MXenes that can work with a biocompatible electrolyte. Two MXenes, with single (Ti₃C₂T_<i>x</i>) and double (Mo₂TiC₂T_<i>x</i>) transition metals, are synthesized, and both exhibit biocompatibility with human dermal fibroblast cells. The supercapacitor performance of both MXenes is evaluated in conventional and biocompatible phosphate buffer saline (PBS) electrolyte using cyclic voltammetry, charge-discharge, and electrochemical impedance spectroscopy. Our results reveal that in a three-electrode configuration, Ti₃C₂T_<i>x</i> outperforms Mo₂TiC₂T_<i>x</i> due to its high electrochemically active surface area. Furthermore, the device comprising Ti₃C₂T_<i>x</i> MXene exhibits a high specific capacitance of 87.54 ± 2.88 mF cm^-2 and high energy and power densities of 2.97 μW h cm^-2 and 500.00 μW cm^-2, respectively, which is sufficient to drive IMDs such as pacemakers and neurostimulators. Hence, using MXene supercapacitors in IMDs is proven to be plausible.