Electrospun High-Entropy Spinel Oxides as Catalysts for as Electrocatalysts for Oxygen Evolution in Alkaline Environment

The generation of H₂ via the electrochemical splitting of water is a promising and sustainable technology. Nonetheless, the oxygen evolution reaction (OER) still represents the bottleneck of the process. Spinel-structured transition metal (TM) oxides have shown great potential as an alternative to platinum group metal-based electrocatalysts as they are Earth-abundant, inexpensive and stable. Among them, those based on the high-entropy concept, benefiting from the synergy among their multiple-metallic components, are in focus due to their interesting performance in various energy applications [1,2], including the OER in alkaline environment.<br/>This contribution focuses on the case of electrospun spinel-type high-entropy oxide (HEO) nanofibers (NFs), which thanks to their granular architecture are suitable to the preparation of ink-jet printable OER electrocatalysts [3]. It presents the results of the evaluation of a large set of HEO NFs with oxygen-deficient surface as electrocatalysts in alkaline medium. HEO NFs based on different equimolar TM combinations, are prepared under different calcination conditions and characterized by a combination of benchtop analytical techniques to investigate the complex and interdependent changes in the morphology of the fibers, crystallinity and inversion degree of the spinel oxide, concentration of the oxygen-vacancies, cation distribution in the lattice produced by the variation of HEO composition and calcination temperature (400-900 °C) and to identify the relationships with the different electrochemical properties of the fibers. The electrocatalytic performance of HEO NFs are discussed in terms of the most common descriptors, namely outer 3<i>d</i>-electron number, <i>e</i>_g filling and occupation of 16<i>d</i> sites.<br/><br/><br/>[1] C. Triolo, W. Xu, B. Petrovičovà, N. Pinna, S. Santangelo, Adv. Funct. Mater. <b>2022</b>, 32, 2202892.<br/>[2] C. Triolo, S. Santangelo, B. Petrovičovà, M.G. Musolino, I. Rincón, A. Atxirika, S. Gil, Y. Belaustegui, Appl. Sci. <b>2023</b>, 13, 721<br/>[3] C. Triolo, S. Schweidler, L. Lin, G. Pagot, V. Di Noto, B. Breitung, S. Santangelo, Energy Adv. <b>2023</b>, 2, 667.