Physiological fluid based flexible NbN TiN supercapacitor for biocompatible energy storage applications.

For medical electronic devices, batteries and capacitors are crucial power sources. However, several challenges are associated with these power sources, such as their inflexibility, poor performance, and non-biocompatibility. In this work, a flexible and biocompatible supercapacitor device was fabricated with niobium nitride (NbN) and titanium nitride (TiN) electrodes. Magnetron sputtering was used to deposit NbN and TiN directly on stainless steel-304 (SS). The fabricated asymmetric supercapacitor device (NbN@SS TiN@SS) demonstrated efficient electrochemical stability, with excellent electrode material adhesion on the substrate, high capacitive performance, and excellent cyclic stability (87.11% capacitive retention after 10,000 cycles at 0.2 mAcm-2 current density) in physiological fluid (phosphate buffer saline). The device delivered a voltage window of 1.2 V, with superb electrochemical performance (areal energy and power density of 1.86 µWhcm-2 and 239.14 mWcm-2 respectively). Cell viability studies were performed to establish the in-vitro biocompatibility of the electrodes. There was significant cell growth (93% for TiN@SS and 94% for NbN@SS) and excellent protein adsorption after 72 hours incubation of L929 fibroblasts. These astounding outcomes and the ideal bending electrochemical performance make it a potential candidate for powering medical and implantable electronic devices by directly utilizing physiological fluid.