High-entropy oxide nanofibers as catalysts to oxygen evolution reaction

• Published in: Journal of materials science 2023-12, Vol.58 (45), p.17141-17153
• Main Authors: Silva, Vinícius D., Raimundo, Rafael A., Silva, Thayse R., Simões, Thiago A., Macedo, Daniel A., Medeiros, Eliton S.
• Format: Article
• Language: English
• Subjects: Alloys; Catalysis; Catalysts; Catalytic activity; Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crystallography and Scattering Methods; Electrocatalysts; Electrodes; Energy; Energy technology; Entropy; Heat treatment; Hydroxides; Iridium; Materials Science; Metals; Morphology; Nanofibers; Nanomaterials; Nanoparticles; Nitrates; Noble metals; Oxygen evolution reactions; Polymer Sciences; Ruthenium; Solid Mechanics; Spinning (metals); Surface layers; Surface roughness; Transition metals
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-023-09067-1

The need to replace electrodes based on noble metals is a necessity for the popularization of strategic energy technologies. In the catalysis of the oxygen evolution reaction (OER), where iridium (Ir) and ruthenium (Ru) are the main references, transition metals have gained prominence for aligning good efficiency 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 high-entropy oxide (HEO) nanofibers 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 first time. It was found that the time of heat treatment has a significant influence on obtaining impurity-free 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 nanofibers had an average diameter of 185 nm and are made up of cohesive nanoparticles of different sizes and have a highly rough surface texture. The electrocatalytic performance of the OER was mainly influenced 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 (HEO-9), 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 different morphologies reported in the literature. Furthermore, it was verified that the surface roughness of these nanofibers contributes to the excellent operational stability of the electrocatalyst. Hence, the advantages of nanofibrous structures over other HEO morphologies were suggested and discussed. Graphical Abstract