Multiphase nickel-based carbon nanofibers for enhanced electrooxidation of urea and glycerol

In this study, nickel-based carbon nanofibers embedded with a combination of NiO (dominant phase), metallic Ni, and NiS nanoparticles were successfully synthesized via electrospinning of a poly(vinyl alcohol)-nickel acetate-ammonium sulfite sol-gel, followed by controlled calcination at 750 °C in a closed atmosphere. The resulting composite nanofibers were thoroughly characterized using XRD, SEM, mapping and TEM, confirming the formation of a hybrid fibrous structure with uniformly distributed crystalline nanoparticles and an amorphous graphitic carbon matrix. The nanofibers were evaluated as electrocatalysts for the electrooxidation of urea and glycerol in alkaline media. Cyclic voltammetry revealed excellent redox activity, with significant current density enhancements observed at 1.0 M urea and 0.5 M glycerol, and with maximum activity recorded at 50 °C for urea and 60 °C for glycerol. Chronoamperometry measurements showed sustained performance over long durations (up to 7000 s), even when using the same electrode consecutively, indicating outstanding durability and surface stability. These results establish the synthesized NiO/Ni/NiS-carbon nanofibers as efficient, low-cost, and stable electrocatalysts for use in direct urea and glycerol fuel cells and electrochemical treatment of organic wastewater.