The making of a high performance supercapacitor active at negative potential using sulphonic acid activated starch-gelatin-TiO₂ nano-hybrids

This work reports the design of nano-level starch-gelatin biopolymeric blends incorporated with nano-TiO₂ for energy storage applications in areas which need to utilise negative voltages. Six different activated nanoarchitectures were designed, push coated on nickel foam substrates and characterized with FTIR, a Zeta sizer, XRD, TEM, CV, EIS, and GCD techniques for structural, functional and electrochemical properties respectively. The C[sbnd]O[sbnd]C glucosidic linkage, amide A bond, Ti[sbnd]O bond were seen at 1068, 2783, 602 cm⁻¹ to confirm the succesful synthesis of starch-gelatin-TiO₂ nanohybrids, while TEM confirmed well dispersed TiO₂ NPs dispersed within the crystalline starch nanoparticles and oval shaped nano-gelatin NPs. XRD analysis revealed crystallite sizes to be in the range of 21–98 nm for all nano-architectures, and confirmed the prescence of highly ordered phases suitable for energy storage, after activation. The zeta sizer investigations determined that the samples were nanoparticulates with sizes below 100 nm. The highest specific capacitances obtained at 5 mVs⁻¹ were 237, 246, 349, 686, 691, 808F/g in the three electrodes configuration and 194, 204, 287, 541, 570, 617F/g in the two electrodes configurations for AS-NPs, AG-NPs, ASG-NHs, AS-TiO₂ NHs, AG-TiO₂-NHs and ASG-TiO₂-NHs respectively. When the samples were tested using a three-electrode and two-electrode configuration, the activated starch-gelatin-TiO₂ nanohybrid showed the lowest R_ct of 0.28 Ω and 0.51 Ω, energy densities of 208.3 and 176.4 Wh/Kg, and power densities of 6213 and 5406 W/Kg. All samples had retention capacities of 86–95%, with the activated starch-gelatin-TiO₂ nanohybrid having values of 95% and 92% for the GCD experiments run using three and two electrode configurations. This work demonstrates that biopolymer nanohybrids can be effective electrodes for supercapacitors devices in energy storage applications.