The pH Response and Sensing Mechanism of n-Type ZnO/Electrolyte Interfaces

Abstract

Ever since the discovery of the pH-sensing properties of ZnO crystals, researchers have been exploring their potential in electrochemical applications. The recent expansion and availability of chemical modification methods has made it possible to generate a new class of electrochemically active ZnO nanorods. This reduction in size of ZnO (to a nanocrystalline form) using new growth techniques is essentially an example of the nanotechnology fabrication principle. The availability of these ZnO nanorods opens up an entire new and exciting research direction in the field of electrochemical sensing. This review covers the latest advances and mechanism of pH-sensing using ZnO nanorods, with an emphasis on the nano-interface mechanism. We discuss methods for calculating the effect of surface states on pH-sensing at a ZnO/electrolyte interface. All of these current research topics aim to explain the mechanism of pH-sensing using a ZnO bulk- or nano-scale single crystal. An important goal of these investigations is the translation of these nanotechnology-modified nanorods into potential novel applications.

Development and characterization of miniaturized LTCC pH sensors with RuO 2 based sensing electrodes

“…Due to adsorption or diffusion of ions from the solution to the metal oxide surface either protonation or deprotonation (depending on pH value of solution) occurrs on the oxide surface and it becomes hydroxylated [27][28][29]. Hence, while varying the pH value of the solution the electrical properties of the sensitive layer are changing.…”

Effects of surface modification of MoS2:TiO2:Pt counter electrodes by argon plasma treatment on photovoltaic performance of dye-sensitized solar cells

“…The Fermi level is higher than the redox potential of the electrolyte, and hence electrons will be transferred from the CE into the solution. The Fermi level is lower than the redox potential, and hence electrons must transfer from the solution to the CE to attain equilibrium [26][27][28]. However, the redox peak for the MoS 2 :TiO 2 :Pt(IV) CE is shifted towards a negative potential compared to that for the MoS 2 :TiO 2 CE and the current density of the redox peak for MoS 2 :TiO 2 :Pt(IV) CEs is lower than that of the redox peak for MoS 2 :TiO 2 CEs, suggesting that there are higher overpotential losses in the MoS 2 :TiO 2 :Pt(IV) CE.…”

“…Another source of degradation in photovoltaic performance of DSSCs with the MoS 2 : TiO 2 :Pt(IV) CE is associated with a significant density of surface states. The Fermi level becomes pinned to these states, so that the flat-band potential will depend on the redox potential and the equilibrium band bending will be independent of the redox potential [26][27][28]. To achieve the high value for g of DSSCs, the overpotential loss and overpotential should be modified.…”

CuO nanoflowers as an electrochemical pH sensor and the effect of pH on the growth

“…A Helmholtz layer is developed by the adsorption of the ions or the molecules on the CuO surface, by oriented dipoles, or by the formation of surface bonds between the solid surface and species in the solution [30,31].…”