Tube-in-tube hollow RuCrMn oxide nanofibers for noble-metal-efficient oxygen evolution via Cr/Mn-regulated Ru active sites

Abstract

Reducing the Ru content while maintaining high oxygen evolution reaction (OER) activity remains a major challenge. In this study, single phase Ru0.30Cr0.31Mn0.39O2 nanofibers were prepared through electrospinning process followed by temperature-regulated heat treatment. The temperature regulation process induces a unique formation of a hollow tube-in-tube structure while simultaneously influencing crystallinity and defect distribution. Among the prepared samples, the material treated at 400 degrees C shows the most favorable performance for OER. This behavior is associated with improved transport properties and increased accessibility of catalytically active sites. The catalyst reaches an overpotential of only 211 mV at 10 mA cm- 2 and maintains stable operation in alkaline electrolyte. The mass-normalized activity and turnover frequency (TOFmetal) are significantly 293- and 104-fold higher than those of commercial RuO2, respectively, highlighting its superior catalytic efficiency with reduced Ru content. Theoretical calculations based on density functional theory suggest that the incorporation of Cr and Mn modulates the electronic structure of RuO2, particularly near the Fermi level, and adjusts the d-band center position. These changes lower the energy barrier associated with the O* to OOH* step. The results thus demonstrate that simultaneous control of composition and morphology can improve OER performance in alkaline media.