Unraveling the Effect of the Chemical and Structural Composition of Zn_xNi_1−xFe₂O₄ on the Electron Transfer at the Electrochemical Interface

Abstract

In order to deepen the understanding of the role of transition metal oxides in electron transfer at the electrochemical interface, the performance of Zn x Ni1−x Fe2O4 (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 ± 2.8 ms−1), lowest peak‐to‐peak separation (386 ± 2 mV), and highest sensitivity (37.75 ± 0.17 μA mM−1). Its limit of detection (7.94 ± 0.04 μM) is second best, and its sensitivity is more than twice the sensitivity of the bare sensor (16.7 ± 0.9 μA 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.

Unraveling the Electrocatalytic Response of Zn-Substituted Nickel Ferrite for Overall Water Splitting

“…The “small polaron hopping” model explains that conduction in spinel ferrite is due to charge transfer among cations in Octahedral (Oh) sites (B sites) of various valency electrons, i.e., hole hopping of Ni­(III)/Ni­(II) ions (for p-type) and electron hopping between Fe­(II)/Fe­(III) ions (for n-type) at B-sites. As discussed earlier in Figure S1, the increase in electrical conductivity of Zn 0.5 Ni 0.5 Fe 2 O 4 is dictated by the higher occupancy of Fe­(III) on the octahedral sites due to Ni­(II) replacement . However, a decline in conductivity was noticed beyond Zn = 0.5 due to the proportional reduction of Ni­(II) ions in Oh sites of the ferrites, as required for the reaction Ni­(II) + Fe­(III) ↔ Ni­(III) + Fe­(II) in this site …”