Abstract
One of the practical efforts in the development of oxygen reduction reaction (ORR) catalysts applicable to fuel cells and metal-air batteries is focused on reducing the cost of the catalysts production. Herein, we have examined the ORR performance of cheap, non-noble metal based catalysts comprised of nanosized mixed Fe-Co spinels deposited on N,S-doped mesoporous carbon support (N,S-MPC). The effect of the chemical and phase composition of the active phase on the selectivity of catalysts in the ORR process in alkaline media was elucidated by changing the iron content. The synthesized materials were thoroughly characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy (RS). Detailed S/TEM/EDX and Raman analysis of the phase composition of the synthesized ORR catalysts revealed that the dominant mixed iron-cobalt spinel is accompanied by minor fractions of bare cobalt and highly dispersed spurious iron oxides (Fe2O3 and Fe3O4). The contribution of individual phases and their degree of agglomeration on the carbon support directly influence the selectivity of the obtained catalysts. It was found that the mixed iron-cobalt spinel single phase gives rise to significant improvement of the catalyst selectivity towards the desired 4e− reaction pathway, in comparison to the reference bare cobalt spinel, whereas spurious iron oxides play a negative role for the catalyst selectivity.
Highlights
Design and fabrication of new electrocatalysts for oxygen reduction reaction (ORR) with high activity, selectivity, and durability is one of the most important challenges in the context of practical use of the rechargeable metal-air batteries as well as the anion-exchange membrane (AEMFCs) and microbial fuel cells [1,2,3,4,5,6,7]
We examined the selectivity of electrocatalysts obtained by partial substitution of Co cations in a cobalt spinel active phase by the cheap and ecofriendly element, such as iron, with simultaneous use of carbon support promoted with nitrogen and sulfur
The obtained results indicate that bare carbon support doped with N and S show relatively high activity in the ORR in the alkaline environment
Summary
Design and fabrication of new electrocatalysts for oxygen reduction reaction (ORR) with high activity, selectivity, and durability is one of the most important challenges in the context of practical use of the rechargeable metal-air batteries as well as the anion-exchange membrane (AEMFCs) and microbial fuel cells [1,2,3,4,5,6,7] Development of those green and sustainable technologies is motivated by the growing demand for alternative energy sources with low environmental impact [8,9,10]. Transition metal oxides of the spinel structure due to their unique redox properties and facile control of their composition and morphology are considered as an interesting group of catalytic materials for many photo/electro/catalytic reactions, including the ORR in the alkaline conditions [13,14,15,16] Owing to their good activity, low cost, simple preparation, and high stability they are extensively investigated as electrocatalysts [17]. Doping of carbon materials by various heteroatoms, such as sulfur, nitrogen, phosphorus, and boron have been reported as promising approaches to increase the surface polarity, regulate the acid-base properties, and create active adsorption and/or catalytic reaction centers [26,37,38,39]
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