Nitrogen Incorporated Photoactive Brownmillerite Ca2Fe2O5 for Energy and Environmental Applications

Durga Sankar Vavilapalli,Masato Murakami,Raja Gopal Peri,Klimkowicz Alicja,Muralidhar Miryala,Ramachandra Rao M S,Soma Banik,Muthuraaman B,Asokan K,Shubra Singh

doi:10.1038/s41598-020-59454-w

Abstract

Ca2Fe2O5 (CFO) is a potentially viable material for alternate energy applications. Incorporation of nitrogen in Ca2Fe2O5 (CFO-N) lattice modifies the optical and electronic properties to its advantage. Here, the electronic band structures of CFO and CFO-N were probed using Ultraviolet photoelectron spectroscopy (UPS) and UV-Visible spectroscopy. The optical bandgap of CFO reduces from 2.21 eV to 2.07 eV on post N incorporation along with a clear shift in the valence band of CFO indicating the occupation of N 2p levels over O 2p in the valence band. Similar effect is also observed in the bandgap of CFO, which is tailored upto 1.43 eV by N+ ion implantation. The theoretical bandgaps of CFO and CFO-N were also determined by using the Density functional theory (DFT) calculations. The photoactivity of these CFO and CFO-N was explored by organic effluent degradation under sunlight. The feasibility of utilizing CFO and CFO-N samples for energy storage applications were also investigated through specific capacitance measurements. The specific capacitance of CFO is found to increase to 224.67 Fg−1 upon N incorporation. CFO-N is thus found to exhibit superior optical, catalytic as well as supercapacitor properties over CFO expanding the scope of brownmillerites in energy and environmental applications.

Highlights

Multifunctional brownmillerite Ca2Fe2O5 is a promising material for energy and environmental applications such as fuel cells, supercapacitors, batteries, H2 production and CO2 capture, attributed mostly to its multifaceted property like those in catalysis and mixed ionic electronic conduction (MIEC)[1,2,3,4,5]
To explore the use of CFO and CFO-N in environmental remediation applications, we have investigated sunlight driven photocatalytic degradation of organic effluent Mythylene blue (MB)
Ca2Fe2O5, by virtue of its unique properties as mentioned above, could be used for energy harvesting applications such a supercapacitors, batteries and fuel cells etc. In this regard,we have explored the feasibility of CFO and CFO-N for supercapacitor applications

Summary

Introduction

Multifunctional brownmillerite Ca2Fe2O5 is a promising material for energy and environmental applications such as fuel cells, supercapacitors, batteries, H2 production and CO2 capture, attributed mostly to its multifaceted property like those in catalysis and mixed ionic electronic conduction (MIEC)[1,2,3,4,5]. Detailed investigation on the feasibility of using nitrogen incorporated CFO (CFO-N) for solar energy utilization as well supercapacitor applications is the focus of this work. XPS spectra corresponding to Ca 2p of CFO and CFO-N (Fig. 4(a)) reveal a split into doublet due to spin-orbit coupling of Ca 2p3/2 and Ca 2p1/2 with binding energy difference ~3.42 eV and ~3.41 eV respectively.

Results

Conclusion