Low mass loading of graphene quantum dots on titanium nitride nanotube arrays for boosting capacity and operating voltage of symmetric supercapacitor in an aqueous electrolyte

Compared to other supercapacitors, aqueous supercapacitors offer reliability, a long lifecycle, and affordability. However, the significant challenge in advancing aqueous supercapacitors lies in their limited operating voltage window. This limitation has resulted in a notable reduction in energy density. Therefore, contemporary electrode materials exhibiting high electrochemical activity and wide operating potential windows are imperative. This study introduces a technique that not only boosts energy density but also signifies a significant breakthrough for metal nitride-based aqueous supercapacitors. This method broadens the operating voltage range and necessitates optimization of the heterostructure design. A distinctive titanium nitride/graphene quantum dot (TiN/GQD) heterostructure was synthesized through electrophoretic deposition of GQDs onto plasma-nitrided TiO2 nanotubes. This novel heterostructure demonstrates the capability to function across an extended voltage range of 2 V. It is noteworthy that the TiN/GQD nanocomposite has excellent bonding at the interface of TiOC and a large surface area, resulting in an exceptional areal capacitance of 190 mF cm−2 at a current density of 0.2 mA cm−2 in 0.5 M Na2SO4 aqueous solution. It also displays excellent cycle stability (91.5 % after 6000 galvanostatic charge-discharge cycles). Moreover, the optimum GQDs deposition time (15 min) was determined to achieve the most efficient electrochemical performance. Furthermore, a symmetric TiN/GQD-15 supercapacitor device was assembled, reaching a high energy density of 8.2 Wh kg−1 at a power density of 77 W kg−1.