Relationship Between Electronic Structures and Capacitive Performance of the Electrode Material IrO2-ZrO2

First-principles calculations were employed to study the effects of the addition of ZrO2 on the electrochemical activity and structure of Ir-Zr binary oxide. In the computation model employed, Zr atoms replaced Ir atoms in IrO2 supercells, so as to form a rutile-type solid solution of Ir1-xZrxO2 (0 <= x <= 1). IrO2-ZrO2 oxide coatings were prepared on Ti substrates by thermal decomposition. X-ray diffraction (XRD) analyses, cyclic voltammetry, and galvanostatic charge/discharge tests were performed to investigate the effects of the Zr content on the structure and capacitive performance of the synthesized Ti/IrO2-ZrO2 electrodes. As the Zr content was increased, the density of state of Ir1-xZrxO2 moved to a higher energy level, and a forbidden band was formed, which reduced its electronic conductivity. The XRD analyses showed that ZrO2 restrained the crystallization of IrO2. Thus, the extent of the amorphous phase increased with the increase in the ZrO2 content, indicating that the proton conductivity of the binary oxide coating increased with the ZrO2 content. When the ZrO2 content was higher than 50 mol%, the IrO2-ZrO2 coating exhibited a relatively narrow energy band gap (0.42eV) and a amorphous/crystalline structure, as well as the highest charge capability, indicating that its electronic and protonic conductivities had reached an equilibrium. This was in accordance with the sudden variation in the length of the M-O bond and the change in the bulk modulus.