Enhancement of Photocatalytic Oxygen Evolution Reaction of BiFeO3 using IrO2 Nanoparticles

W. Ramadan, D. Bahnemann
Leibniz Universität Hannover,
Germany

Keywords: BiFeO3, multiferriocs, oxygen evolution reaction, IrO2 Co-catalyst, transient absorption spectroscopy

Summary:

BiFeO3 (BFO) is a multiferriocs that combines antiferromagnetic and ferroelectric order well above room temperature also it is narrow band gap semiconductor ( 2.2-2.7 eV) hence, it can harvest significant amount of visible light. Combining such desired properties on simple ternary compound makes it easier to utilize in many different folds. However, the performance of BFO is still poor due to the fast recombination of the photogenerated charges which will negatively affect their performance in the field of photocatlysis. Here we report on the photocatalytic oxygen evolution reaction, OER, of BiFeO3 nanoparticles synthesized by sol gel. To enhance BFO photocatalytic OER, IrO2 nanoparticles were loaded on the surface using impregnation method. OER showed two folds enhancement upon loading with 2wt% IrO2. IrO2 is one of the best catalyst for OER, unfortunately it is also one of the most expensive rare elements hence and their applicability is limited by the high cost. Reducing IrO2 content onto the system should be an option to make its application feasible and cost effective and loading on IrO2 nanoparticles on the surface could be feasible solution. Scanning the loaded IrO2 content from 0.5 wt% to 4 wt% showed a maximum of OER at 2wt % followed by a decrease in activity. XPS showed the formation of Ir (IV) and TEM indicated non uniform distribution of it on the surface. Charge carrier life time and dynamics for pure BFO and IrO2 loaded BFO have been studied by means of diffuse reflectance laser flash photolysis spectroscopy. Transient absorption of the charge carriers indicated a significant increase in the charge life time in the case of 2wt% IrO2 loading compared to the other IrO2 contents. Band positions between BFO and IrO2 favors the formation of heterojunction at the interface between IrO2 and BiFeO3 that enhances the separation of the photogenerated charges and the photocatalytic OER performance.