Electrospun spinel-structured high-entropy oxide nanofibers as electrocatalysts for oxygen evolution in alkaline medium.

Water electrolysis powered by renewable sources is the greenest way to produce $H_2$, a promising energy vector that could help bring the World to net zero emissions in the coming decades. However, the slow kinetics of the oxygen evolution reaction (OER) represents a limitation for its broad market penetration. Spinel transition metal oxides have shown great potential as a sustainable alternative to precious metal-based electrocatalysts. In this communication, electrospun spinel high-entropy (Cr, Mn, Fe, Co, Ni), (Cr, Mn, Fe, Co, Zn) and (Cr, Mn, Fe, Ni, Zn) oxide nanofibers (NFs) are evaluated as OER electrocatalysts in 1 M KOH solution.($Cr_{0.2}Mn_{0.2}Fe_{0.2}Co_{0.2}Ni_{0.2})_{3}O_{4}$ NFs outperform not only $(Cr_{0.2}Mn_{0.2}Fe_{0.2}Co_{0.2}Zn_{0.2})_{3}O_{4}$ and $(Cr_{0.2}Mn_{0.2}Fe_{0.2}Ni_{0.2}Zn_{0.2})_{3}O_{4}$ NFs, but also $IrO_{2}$ reference electrocatalyst (Tafel slopes: 49.1, 62.5, 59.6 and 52.9 mV/dec, respectively). The higher concentration of oxygen vacancies on their surface and the higher occupation of octahedral sites by redox-active $Co^{2+}$ and $Ni^{2+}$ centres are responsible for their behaviour.