A Comparative Study of Fabricating IrOx Electrodes by High Temperature Carbonate Oxidation and Cyclic Thermal Oxidation and Quenching Process

Abstract

IrOx electrodes were fabricated by cyclic thermal heating and water quenching (CHQ) process and high temperature carbonate oxidation (HCO), respectively. By examining the E-pH relationship, response rate, potential drift behavior of the fabricated electrodes, the electrodes prepared by CHQ process seemed to show better comprehensive performance. Characterization tests such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electrochemical impedance spectroscopy (EIS) were used to characterize the fabricated IrOx electrodes and find out the reason for the better performance of the electrodes prepared by CHQ process. Morphology tests indicate that the CHQ electrode shows a multi-layer structure with more ion channels, which could provide larger surface area for the H+ response process. Furthermore, combining the XPS, Raman and EIS tests etc., more effective response composition, better crystal quality, and smaller response reaction resistance of surface IrOx film could account for the better performance of the CHQ-fabricated IrOx electrode. The film formation process, H+ response mechanism, as well as the response behavior difference between the two kinds of the electrodes are further elaborated.

Understanding the stabilization effect of the hydrous IrOx layer formed on the iridium oxide surface during the oxygen evolution reaction in acid

“…The XPS O 1s spectra of pristine BaIrO 3 and SrIrO 3 can be deconvoluted into three peaks centering at 529.3, 530.7 and 532.3 eV, which are normally assigned to the oxygen species from the M-O lattice, hydroxide and the adsorbed water molecules, respectively. 35,36 After the OER, the signatures from the lattice O disappeared, while a broad absorption peak appeared at ∼535.3 eV, originating from the adventitious species from the Nafion binder. A new peak centering at 531.8 eV was suggested as a proof for the presence of BaSO 4 on the catalyst surface.…”

Insight into Factors Influencing Thermal Oxidation of Iridium Oxide Electrode: Thermostatic Post-Treatment Temperature

“…8 Among its application, pH sensitive material is one of the most important one. Methods used for fabricating the pH sensitive film include electrodeposition, electrochemical cyclic voltammetry (CV), 9,10 radio frequency (RF) magnetron sputtering deposition, 11,12 high temperature carbonate oxidation [13][14][15][16][17] and thermal oxidation etc. [17][18][19][20][21] Cyclic heat treatment and quenching (CHQ) process is proved to be a promising method for fabricating the IrO x pH electrode by evaluating the Nernst sensitivity, E-pH response range, potential (E) intercept, response rate, and also the long-term stability, 20,22 etc.…”

“…IrO x electrodes went through thermostatic heating process at 700 and 750 °C demonstrated inadequate oxidation phenomenon in spite of the heating time constrained within 0.5, 1.0, 1.5, and 2.0 h. The surface oxide films produced from the above conditions were thinner, showing smaller surface roughnesses, and more cracks in the surfaces, and therefore the reaction resistance of which was high, the response rate was slow, and also lack in rigidity. 17 The influence of thermostatic heat treatment temperature (750, 800, and 870 °C) and CHQ times (1 ∼ 3) on the performance of the IrO x pH electrodes were also investigated. The IrO x film prepared through CHQ 3 at 800 °C illustrated larger surface roughness, and showed a two-layer structure: i.e., dense homogeneous inner layer and porous loose outer layer indicating more active site for the H + response process, and therefore exhibited the most excellent comprehensive properties including near Nernst E-pH relationship, relatively faster response rate and the minimum potential drift in long-term stability test.…”