A comparative study on Ti/IrO2–Ta2O5 anodes prepared by microwave plasma-assisted sintering and conventional thermal decomposition methods

Abstract

This work presents the comprehensive and comparative study on microstructures and properties (including morphology, composition, phase structure, electrochemical performance, etc.) of the iridium oxide-tantalum oxide (IrO2–Ta2O5) coated titanium (Ti) anodes prepared by novel microwave plasma-assisted sintering (MPAS) and conventional thermal decomposition (CTD) methods. To characterize and evaluate these anodes, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), X-ray photoelectron spectrometer (XPS), and electrochemical tests are employed. The results demonstrate that the surfaces of the anodes prepared by CTD and MPAS at 500 °C have “mud cracks” with the latter having more, but the anode prepared by MPAS at 600 °C does not present any crack, and the surface is spongy and porous. Compared with the anode by CTD method, the total pore area of the coating prepared by MPAS at 600 °C decreases obviously, from 2.124% to 0.908%. Meanwhile, the coating prepared by CTD has more high valence species and oxygen vacancy defects. Metallic iridium, amorphous iridium oxide or fine crystallites of rutile IrO2, and low-valent Ta oxides will be formed on the electrode surface treated by MPAS. In addition, the onset potentials of oxygen evolution reaction (OER) of the anodes by MPAS methods (1.15–1.16 V) are much lower than that of the anode by CTD process (1.21 V). The voltammetric charge of the anode prepared by MPAS at 500 °C is nearly four times that of the anode by CTD method. The oxide anodes fabricated by MPAS method demonstrate very large electrochemically active surface area and excellent electrocatalytic activity of OER, but show inferior stability that should be further improved.