Photoinduced supercapacitance and photocatalytic performance of TiO2 enhanced by electronic band structure modification using Cu-doping

We demonstrate that doping a modest quantity of Cu impurity into anatase TiO₂ enhances its photoinduced electrocatalytic supercapacitance by about 84% and its photocatalytic activity by more than two-fold. X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy analyses validate that the Cu dopant is fully incorporated into the tetragonal crystal structure of the host material and creates Ti³⁺ and oxygen vacancies. Furthermore, UV-vis spectroscopy and photoluminescence (PL) studies demonstrate that the smallest optical band gap energy (E_b) of 2.85 eV and minimal recombination of photoinduced charge carrier pairs occur at a 3% Cu doping amount. Transmission electron microscopy (TEM) images reveal that pristine TiO₂ and Cu-doped TiO₂ exhibit nearly identical pebble-like nanoparticle morphologies. This 3% Cu-doped TiO₂ demonstrates more than double photodegradation (95.7%; 150 min) of a toxic Rhodamine B dye molecule and a nearly 84% improved supercapacitance (347 F g⁻¹; 0.5 M aq. Na₂SO₄; pH = 7) compared to that of pristine anatase TiO₂. Under suitable testing conditions of other electrolytes, molecular dyes, light intensity, etc., Cu-doped TiO₂ with different particle shapes may demonstrate even greater supercapacitive behavior and photodissociation properties, leading to more advantageous applications for photoactive Cu-doped TiO₂ materials.