High-entropy spinel oxide (Mn_0.5Co_0.9Cr_0.9Rh_0.5Fe_0.2)O₄ nanotubes: Cr-driven disorder engineering for enhanced oxygen evolution reaction

Spinel-structured high-entropy oxides (HESOs) have emerged as remarkable electrocatalysts for oxygen evolution reactions (OER) due to their intrinsic compositional tunability and structural complexity. In this study, spinel-type high-entropy oxide (Mn_0.5Co_0.9Cr_0.9Rh_0.5Fe_0.2)O₄ nanotubes (MCCRF-HEO) were synthesized via simple electrospinning and following calcination process to serve as a superior alkaline OER catalysts. The incorporation of Cr critically promoted the development of a unique nanostructure, where crystalline HESO nanoparticles are uniformly embedded within an amorphous nanotube matrix. The MCCRF-HEO demonstrated excellent electrocatalytic activity for OER in 1.0 M KOH, including lower overpotential (303.8 mV at 10 mA cm⁻²) and smaller Tafel slope (69.6 mV dec⁻¹) than commercial Ir-based catalysts. In addition, it exhibited outstanding long-term stability under 24-h continuous operation under alkaline conditions. The results highlight that the synergistic effects arising from strategic incorporation of heterogenous metal cations facilitate structural disorder and entropy stabilization, thereby optimizing catalytic performance in high-entropy spinel systems.