An experimental and theoretical approach to electrochemical sensing of hydrazine at silver and copper hexacyanoferrates electrodes

This work evaluates the electrocatalytic oxidation of hydrazine (HDZ) by silver (AgHCF) and copper (CuHCF) hexacyanoferrates-modified glassy carbon electrodes kinetically and analytically through experimental electrochemistry and theoretical approaches. The materials were prepared by a two-step cyclic voltammetry (CV) routes and had their structural and morphological attributes attested by microscopic and spectroscopic characterization techniques. The AgHCF and CuHCF-modified electrodes showed quasi-reversible characteristics driven by K+ diffusion and adsorption processes, respectively. The kinetic properties of the materials towards HDZ electrooxidation were evaluated through CV and chronoamperometry techniques. The analyte exhibited irreversible electron transfer controlled by semi-infinite diffusion process for both Prussian blue analogs. The CuHCFmodified electrode showed superior diffusion coefficient (D = 2.17x10-5 cm2 s- 1) and catalytic rate constant (kcat = 1.75x103 L mol-1 s- 1) comparing to the silver analog (D = 2.31x10-6 cm2 s- 1 and kcat = 8.06x102 L mol-1 s- 1). The copper-based material also exhibited higher sensitivity (S) obtained through CV (S = 42 nA L mu mol L-1) and batch injection analysis-coupled amperometry (BIA/amp) (S = 66.8 nA L mu mol L-1) measurements, in comparison to AgHCF-modified electrode (S = 25 nA L mu mol L-1 - CV; S = 22.3 nA L mu mol L-1 - BIA/ amp). Theoretical approaches showed that CuHCF material required lower energy (Delta Egap = 0.0397 eV) to promote an electron to the lowest unoccupied molecular orbital due to its cubic structural arrangement, justifying the better electrocatalytic results comparing to the hexagonal structure of the AgHCF material (Delta Egap = 0.0840 eV).