Unraveling the Effect of the Chemical and Structural Composition of ZnxNi1-xFe2O4 on the Electron Transfer at the Electrochemical Interface

In order to deepen the understanding of the role of transition metal oxides in electron transfer at the electrochemical interface, the performance of ZnxNi1-xFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) nanomaterials in electrochemical sensing is studied. Nanomaterials are synthesized by simple autocombustion synthesis procedure. Field-emission scanning electron microscopy characterization shows that the particles have a size between 30 and 70 nm with an average crystallite size between 24 and 35 nm. The bandgap energies of the nanomaterials, as estimated by UV-vis experiments, are in the 2.32-2.56 eV range. The valence band maximum is evaluated using X-ray photoelectron spectroscopy and the position of the conduction band minimum is estimated. The ZnFe2O4 sensor has the best performances: highest rate constant (13.1 & PLUSMN; 2.8 ms(-1)), lowest peak-to-peak separation (386 & PLUSMN; 2 mV), and highest sensitivity (37.75 & PLUSMN; 0.17 & mu;A mM(-1)). Its limit of detection (7.94 & PLUSMN; 0.04 & mu;M) is second best, and its sensitivity is more than twice the sensitivity of the bare sensor (16.7 & PLUSMN; 0.9 & mu;A mM(-1)). Nanomaterials energy bands mapping with the experimental redox potentials is performed to predict the electron transfer at the electrochemical interface, and the importance of surface states/defects is highlighted in the electron transfer mechanism.