Scalable and bendable organized mesoporous TiN films templated by using a dual-functional amphiphilic graft copolymer for solid supercapacitors

Organized mesoporous titanium nitride (om-TiN) films with a large surface area, high porosity, and good interconnectivity were prepared on Ti substrates by nitration of TiO₂ templated by using an amphiphilic graft copolymer, poly(vinyl chloride)-graft-poly(oxyethylene methacrylate) (PVC-g-POEM). This resulted in a much higher specific capacitance compared with randomly organized TiN (ran-TiN) films. Upon addition of a small amount (2 wt%) of carboxylic-acid-functionalized carbon nanotubes (COOH-CNTs) to the om-TiN, the surface area, conductivity, and pore size further increased, leading to an improved specific capacitance of up to 213.6 F g^-1 for solid supercapacitors with poly(vinyl alcohol) (PVA)/H₃PO₄ electrolyte. Large electrodes (15 cm × 15 cm) were successfully fabricated and their electrochemical performance did not change when bent. The PVC-g-POEM graft copolymer used for om-TiN formation was also applied as the matrix of a mechanically strong solid electrolyte, which further increased the capacitance up to 266.8 F g^-1 and widened the potential window, demonstrating the dual functionality of the graft copolymer. This capacitance is the highest value observed for TiN-based solid symmetric supercapacitors.