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The growing demand for sustainable energy storage solutions has accelerated research into sodium-ion systems, such as sodium-ion batteries (SIBs) and sodium-ion capacitors (NICs), as promising alternatives to lithium-ion energy storage. However, SIBs face challenges such as low energy density, sluggish kinetics, and limited cycle life, necessitating the development of advanced pseudocapacitor electrode materials. This study reports the fabrication of nanostructured TiO2 and TiO2-graphene multilayered electrodes using ultrashort laser pulses for in situ nanostructure generation (ULPING) for aqueous sodium-ion pseudocapacitors. The TiO2 layer was directly grown on titanium substrates via pulsed laser ablation using a ytterbium picosecond fiber laser, achieving a highly porous floret-like morphology conducive to ion diffusion. An additional graphene layer, applied with a carboxymethyl cellulose (CMC) binder, improved conductivity and surface area. Structural characterization revealed a mixed anatase/rutile TiO2 phase with predominant rutile, which is advantageous for high-power performance. Electrochemical characterization in a 1 M Na2SO4 electrolyte using a three-electrode testing system demonstrated that the TiO2-graphene electrodes exhibited a significantly higher areal capacitance of 46.9 mF/cm2 and an energy density of 22.3 μWh/cm2, approximately 3.5× higher than pristine TiO2. Cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) confirmed a pseudocapacitive behavior with a stable capacitance retention of over 85% after 200 cycles. Moreover, the TiO2-graphene electrode showed a reduced charge transfer resistance and a higher sodium-ion diffusion coefficient (2.124 × 10–14 cm2/s) compared to pristine TiO2, indicating enhanced electrochemical kinetics. This study highlights the potential of ULPING as a scalable and cost-effective technique for engineering high-performance electrode materials, positioning TiO2-graphene hybrids as viable candidates for next-generation aqueous sodium-ion pseudocapacitors.
Muttumthala et al. (Wed,) studied this question.