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 Ni_1−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.

The development of new and high-performing electrode materials for sensing applications is one of the most intriguing and challenging research fields. There are several ways to approach this matter, but the use of nanostructured surfaces is among the most promising and highest performing. Graphene and graphene-related materials have contributed to spreading nanoscience across several fields in which the combination of morphological and electronic properties exploit their outstanding electrochemical properties. In this review, we discuss the use of graphene and graphene-like materials to produce gas sensors, highlighting the most relevant and new advancements in the field, with a particular focus on the interaction between the gases and the materials.

This work presents the application of ZnO and ZnFe₂O₄ for electrochemical pH sensing. ZnO and ZnFe₂O₄ are synthesized by auto combustion synthesis method. FESEM images revealed that ZnO particles have pyramid and spherical shaped morphology with micrometer dimensions while ZnFe₂O₄ particles have spherical shape at the nanoscale. The surface modified screen-printed electrodes with ZnO and ZnFe₂O₄ particles are initially characterized by the ferri/ferrocyanide redox couple. Significant improvement in sensitivity (bare carbon: 6.3 ± 0.4 μA/mM, ZnO: 8.5 ± 0.3 μA/mM, ZnFe₂O₄: 8.9 ± 0.5 μA/mM) and rate constant (bare carbon: 10 ± 1 ms^-1, ZnO: 46 ± 4 ms^-1, ZnFe₂O₄: 42 ± 3 ms^-1) is observed with the surface modified sensors. Chronopotentiometric pH response of the sensors showed hysteresis behavior with pH loop. No interference effects are observed, and the pH sensitivity of the bare carbon sensor (23.9 ± 1.4 mV/pH) is increased by the introduction of ZnO (38.1 ± 1.3 mV/pH) and ZnFe₂O₄ (37.2 ± 1.1 mV/pH) particles. Stability of the pH response is discussed and ways for its improvement are proposed.