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

Abstract

This study aims to understand and correlate the role of the nature and relative concentration of the oxygen vacancies with the trend observed in 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 by the absence of oxygen from the structure of Bi2Fe4O9 was majorly responsible for the high performance of the oxide towards OER compared to the other oxides viz—BiFeO3 and Bi25FeO40 of the Bi-Fe-O system