Perovskite BiFeO3 nanocatalysts for electrochemical water oxidation

Abstract

Perovskite BiFeO3 nanocatalyst electrodes for electrochemical water oxidation were fabricated using mineralizing agents, such as potassium hydroxide (KOH) and sodium hydroxide (NaOH) to produce two different kinds of morphologies, such as BiFeO3 nanocubes and nanorods by hydrothermal method. Pure-phase, good-quality rhombohedral BiFeO3 produced by NaOH was revealed by X-ray powder diffraction (XRD). Five intrinsic phonon vibration modes [Eg(1)+Ag(1)+Ag(2)+Ag(3)+Ag(4)] of rhombohedral BiFeO3 nanostructures were confirmed by Raman spectra. The optical properties of both nanocubes and nanorods were investigated by photoluminescence (PL) and UV-vis diffuse reflection spectra (UV-vis DRS). The optical bandgap of nanocubes and nanorods estimated by Tauc plot was 2.88 and 2.94 eV. The role of a mineralizing agent that strongly influenced the morphology of BiFeO3 was revealed by scanning electron microscope (SEM) images of nanocubes synthesized by KOH and nanorods by NaOH. Electrochemical water oxidation by the cyclic voltammogram (CV) study for nanorods exhibited a higher specific capacitance of 156 F/g at 10 mV/s scan rate and possessed higher water oxidation catalytic activity observed by the current density of 1.77 mA/g at 10 mV/s from the linear sweep voltammogram (LSV) study and higher ionic mobility and conductivity with a smaller Tafel slope value of 229 mV/dec. The stability was reported for 4 h for both the electrodes with 99% activity.