Vol.:(0123456789) htps:doi.org10.1007s10853023090671 J Mater Sci Ceramics High‑entropy oxide nanofbers as catalysts to oxygen evolution reaction Vinícius D. Silva 1 , Rafael A. Raimundo 2 , Thayse R. Silva 1 , Thiago A. Simões 1,3 , Daniel A. Macedo 1, *, and Eliton S. Medeiros 1, * 1 Materials Science and Engineering Postgraduate Program (PPCEM), Materials and Biosystems Laboratory (LAMAB/DEMAT), UFPB, João Pessoa 58051‑900, Brazil 2 Department of Theoretical and Experimental Physics, UFRN, Natal 59078‑970, Brazil 3 Engineering Campus, UACSA, Federal Rural University of Pernambuco (UFRPE), Cabo de Santo Agostinho 54518‑430, Brazil ABSTRACT The need to replace electrodes based on noble metals is a necessity for the popu larization of strategic energy technologies. In the catalysis of the oxygen evolu tion reaction (OER), where iridium (Ir) and ruthenium (Ru) are the main refer ences, transition metals have gained prominence for aligning good efciency and low cost, in addition to the possibility of obtaining them in the most varied forms (oxide, hydroxide, alloys, and composites). In this work, the synthesis of highentropy oxide (HEO) nanofbers of composition (Co 0.2 Cu 0.2 Mg 0.2 Ni 0.2 Zn 0.2 ) O obtained by solution blow spinning (SBS) is reported for the frst time. It was found that the time of heat treatment has a signifcant infuence on obtaining impurityfree HEO. In practice, a residence time varying between 2 and 5 h at the calcination threshold temperature leads to the formation of CuO as a secondary phase. The obtained nanofbers had an average diameter of 185 nm and are made up of cohesive nanoparticles of diferent sizes and have a highly rough surface texture. The electrocatalytic performance of the OER was mainly infuenced by the presence of the secondary phase, which tends to delay the catalytic activity and increase the electrode impedance. For the purest phase sample treated for 9 h at 900 °C (HEO9), the electrocatalyst reveals a low overpotential of 310 mV vs. RHE at J = 10 mA cm −2 and a Tafel slope of 54 mV dec −1 . These results are superior to other HEO with diferent morphologies reported in the literature. Furthermore, it was verifed that the surface roughness of these nanofbers con tributes to the excellent operational stability of the electrocatalyst. Hence, the advantages of nanofbrous structures over other HEO morphologies were sug gested and discussed. Received: 25 July 2023 Accepted: 19 October 2023 The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature, 2023 Handling Editor: Christopher Blanford. Address correspondence to Email: daniel.macedoacademico.ufpb.br; esmacademico.ufpb.br