Electrocatalytic OER behavior of the Bi-Fe-O system: an understanding from the perspective of the presence of oxygen vacancies.

This study aims to understand and correlate the role of the nature and relative concentration of oxygen vacancies with the trend observed in the OER with the Bi-Fe-O system. To understand this, we first investigated the system of oxides using X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR), which revealed the presence of oxygen vacancies in the system. Density functional theory (DFT) was employed to investigate the relative concentration of these vacancies by calculating their formation energies. Positron annihilation lifetime spectroscopy (PALS) was carried out to understand the nature of these oxygen vacancies. We observed that the presence of a higher concentration of monovacancies created due to the absence of oxygen from the structure of Bi 2 Fe 4 O 9 was mainly responsible for the high performance of the oxide towards the OER compared to that of the other oxides viz -BiFeO 3 and Bi 25 FeO 40 of the Bi-Fe-O system.