title: Nitrogen Doping in Oxygen-Deficient Ca2Fe2O5: A Strategy for Efficient Oxygen Reduction Oxide Catalysts.
abstract: Oxygen reduction reaction (ORR) is increasingly being studied in oxide systems due to advantages ranging from cost effectiveness to desirable kinetics. Oxygen-deficient oxides like brownmillerites are known to enhance ORR activity by providing oxygen adsorption sites. In parallel, nitrogen and iron doping in carbon materials, and consequent presence of catalytically active complex species like C-Fe-N, is also suggested to be good strategies for designing ORR-active catalysts. A combination of these features in N-doped Fe containing brownmillerite can be envisaged to present synergistic effects to improve the activity. This is conceptualized in this report through enhanced activity of N-doped Ca2Fe2O5brownmillerite when compared to its oxide parents. N doping is demonstrated by neutron diffraction, UV-vis spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Electrical conductivity is also found to be enhanced by N doping, which influences the activity. Electrochemical characterization by cyclic voltammetry, rotating disc electrode, and rotating ring disk electrode (RRDE) indicates an improved oxygen reduction activity in N-doped brownmillerite, with a 10 mV positive shift in the onset potential. RRDE measurements show that the compound exhibits 4-electron reduction pathways with lower H2O2production in the N-doped system; also, the N-doped sample exhibited better stability. The observations will enable better design of ORR catalysts that are stable and cost-effective.
authors.affiliation: Academy of Scientific and Innovative Research, New Delhi, India.
authors.forename: Chamundi P
authors.initials: CP
authors.lastname: Jijil
authors.affiliation: SRM Research Institute, SRM University , Chennai 603203, India.
authors.forename: Moorthi
authors.initials: M
authors.lastname: Lokanathan
authors.affiliation: Academy of Scientific and Innovative Research, New Delhi, India.
authors.forename: Sundaresan
authors.initials: S
authors.lastname: Chithiravel
authors.forename: Chandrani
authors.initials: C
authors.lastname: Nayak
authors.forename: Dibyendu
authors.initials: D
authors.lastname: Bhattacharyya
authors.forename: Shambhu Nath
authors.initials: SN
authors.lastname: Jha
authors.forename: P D
authors.initials: PD
authors.lastname: Babu
authors.affiliation: SRM Research Institute, SRM University , Chennai 603203, India.
authors.forename: Bhalchandra
authors.initials: B
authors.lastname: Kakade
authors.affiliation: Academy of Scientific and Innovative Research, New Delhi, India.
authors.forename: R Nandini
authors.identifier: http://orcid.org/0000-0002-6219-8089
authors.initials: RN
authors.lastname: Devi
keywords: EXAFS; N-doping; Rietveld refinement; brownmillerite; fuel cell; neutron diffraction; oxygen reduction reaction