DEVELOPMENT AND CHARACTERIZATION OF NANOMATERIALS FOR ENERGY STORAGE AND CONVERSION

Abstract

The rising global energy demand, combined with the intermittent nature of renewable sources such as solar and wind, has created an urgent need for efficient and affordable energy storage and conversion technologies. This study aimed to develop and characterize advanced nanomaterials with tailored structures for enhanced energy performance. Rare-earth-doped zinc oxide nanostructures were synthesized using a wet-chemical sol–gel and hydrothermal route, and their structural, morphological, optical, and electrochemical properties were systematically investigated. X-ray diffraction confirmed a phase-pure hexagonal wurtzite structure with crystallite size reduced from 21.25 nm in the undoped sample to 10.23 nm for 2% Nd-doped and 12.23 nm for 5% Er-doped materials. Microscopy revealed a hexagonal rod-like morphology with particle sizes of 9–30 nm and reduced aggregation upon doping, while Brunauer–Emmett–Teller analysis showed an increase in specific surface area from 38.23 to 73.22 m² g⁻¹. Fourier-transform infrared, X-ray photoelectron, and energy-dispersive X-ray analyses confirmed successful dopant incorporation and abundant surface hydroxyl groups. Importantly, doping narrowed the optical band gap from 3.3 eV to 2.74 eV and 2.66 eV, extending light absorption into the visible region, and photoluminescence measurements indicated suppressed electron–hole recombination. Electrochemical evaluation demonstrated specific capacitances of 320–525 F g⁻¹, volumetric capacitances up to 350 F cm⁻³, and approximately 90% capacitance retention after 5000 cycles, attributed to shortened ion-diffusion pathways and efficient interfacial charge transfer. The doped photocatalysts also exhibited enhanced degradation of methylene blue (30.7%) and reactive red (19.4%) within 10 minutes under visible light, following pseudo-first-order kinetics, along with notable hydrogen evolution of 0.53 µmol cm⁻². These findings establish that nanostructuring combined with rare-earth doping simultaneously improves surface area, visible-light harvesting, charge separation, and ionic transport, making these nanomaterials promising candidates for supercapacitors, photocatalytic wastewater treatment, and solar hydrogen production.