Electrochemical and computational study of novel 5-fluoro-2-(methylamino) benzenesulfonamide as an organic catalyst for hydrazine electrooxidation

This study presents the synthesis, characterization, and electrochemical assessment of a new fluorinated sulfonamide-based organic catalyst, FBS⁻, which is immobilized on a glassy carbon electrode (GCE) using Nafion for the electrocatalytic oxidation of hydrazine (N₂H₄) in an alkaline environment. Structural analysis through ¹H and ¹³C NMR, including 2D COSY, confirms the anticipated substitution pattern on the aromatic ring, which includes a fluorine atom that enhances electronic stability and oxidative resistance. Density Functional Theory (DFT) calculations- including HOMO–LUMO analysis, Electron Localization Function (ELF), Localization of Orbitals (LOL), Average Local Ionization Energy (ALIE), and Molecular Electrostatic Potential (MEP) maps- demonstrate a weak HOMO–LUMO gap (2.122 eV), substantial electron density concentration on the sulfonamide part, and significant redox activity of the anionic form. Electrochemical tests reveal that FBS⁻ serves as a bifunctional catalyst, facilitating electron transfer and local deprotonation of hydrazine. Cyclic voltammetry demonstrates a significant increase in current density (up to 33.33 mA/cm²) in the presence of hydrazine, while chronoamperometry and electrochemical impedance spectroscopy (EIS) corroborate its outstanding stability and low charge transfer resistance. The analysis of the scan rate-dependent CV reveals a linear relationship between peak current and the square root of the scan rate (R² = 0.993), suggesting a diffusion-controlled mechanism. Relative to other organic and noble-metal-based systems, FBS⁻ exhibits superior performance, merging high catalytic activity, chemical durability, and straightforward synthetic accessibility. These results position FBS⁻ as a promising, metal-free electrocatalyst for hydrazine oxidation and related energy and environmental, analytical, and electroanalytical applications.