Sustainable Carbon Quantum Dots from Biomass for Fluorescence and Acidic Hydrogen Evolution

Carbon quantum dots (CQDs) were synthesized from orange peel (OP) waste via a hydrothermal process and subsequently modified by nitrogen doping and tungsten oxide (WO₃) incorporation to enhance electrocatalytic performance. The resulting OP-CQDs exhibit abundant active sites, improved electronic properties, and blue luminescent behavior. Comprehensive characterization using TEM, EDX, FTIR, Raman, XRD, XPS, UV−Vis, and photoluminescence (PL) confirmed successful material formation and modification. The electrochemical investigations demonstrated effective hydrogen evolution reaction (HER) activity for the modified 20% WO₃/N-doped OP-CQDs and unmodified 20% WO₃/OP-CQDs nanocomposites in an acidic medium. The 20% WO₃/N-doped OP-CQDs exhibited high activity with an overpotential of 72.8 mV and a Tafel slope of 22.5 mV.dec⁻¹. This improvement is attributed to new active defect sites and electronic modulation, as reflected by the enhanced ECSA (104 cm²), the high TOF (0.95 s⁻¹), and the low R_ct (0.81 Ω.cm²). Furthermore, it retained 96.7% of its electrocatalytic efficiency after 10 hours, demonstrating good stability. The 20% WO₃/N-doped OP-CQD nanocomposite enhanced conductivity and increased the number of active sites, thereby enabling greater mass transfer and, consequently, higher HER activity. Hence, this study introduces a cost-efficient and environmentally friendly approach to fabricating these nanocomposites as an effective electrocatalyst for hydrogen generation.