Bandgap and electrochemical engineering for disordered LaFeO3

Abstract

Being a charge transfer Mott insulator with low metal-insulator temperature, disordered LaFeO3 (as an air electrode) is a potential material for electrochemical engineering. High electronic conductivity and inexpensive catalytic activity are the prime requisites for electrode materials. Here, we systematically substituted hole (Sr) at La-site and electron (Ti) at Fe-site. Our objective is here twofold, first to get material with improved catalytic behavior and to understand the role of bandgap engineering. All the investigated samples are oxygen-rich and show orthorhombic(Pbnm) phase at 300 K. The prominent cation vacancies are closely associated with the self-trapping of carriers. These trapping centers may be detrimental if they shift toward conduction band minima. However, this energy shift can be controlled with proper selection of substitution but require intricate understanding. At 300 K, we observe higher conductivity with band shrinkage for hole substitution, i.e., La0.5Sr0.5FeO3 (LSF). A field dependent electrical study reveals trap free conduction for the hole substituted sample while undoped and compensated show ohmic conduction. Our results suggest that there is a correlation between band tuning and corrosion resistance. Dynamic numerical simulation, where interfacial electrochemical behavior up to 4000 s is studied, suggests that LSF has the least surface charge degradation. Experimentally, LSF proves to be a robust and efficient electrode due to chronopotentiometry stability with a potential of 2 V (vs Ag/AgCl) at a higher current of 150 mA/cm2 in neutral media. Further, this study provides concomitant charge dynamics for these samples and the foster mechanism to get better air electrodes.