Defect and interface engineering in Sn–Eu2O3/α-MnO2 nanocomposites for oxygen evolution reaction

A Sn-doped Eu 2 O 3 /α-MnO 2 nanocomposite was synthesized via a one-pot chemical co-precipitation method and evaluated as a noble-metal-free electrocatalyst for the oxygen evolution reaction (OER) in alkaline media. X-ray diffraction (XRD) confirmed the formation of tetragonal α-MnO 2 with well-dispersed cubic Eu 2 O 3 nanodomains. At the same time, the absence of distinct Sn-based secondary phases suggested effective lattice incorporation or high dispersion of Sn species. Halder–Wagner analysis revealed a reduction in crystallite size and changes in microstrain following Eu₂O₃ incorporation and Sn modification. High-resolution transmission electron microscopy (HRTEM) demonstrated well-defined lattice fringes with clear interplanar spacings, confirming high crystallinity and heterointerface formation. In contrast, selected-area electron diffraction patterns revealed the polycrystalline nature of the nanocomposite. X-ray photoelectron spectroscopy (XPS) confirmed stable Eu³⁺ and Sn⁴⁺ oxidation states, mixed Mn 3 + /Mn 4+ redox chemistry, and an enhanced concentration of oxygen vacancies. Electrochemical investigations showed that the Sn–Eu 2 O 3 /α-MnO 2 electrode exhibits improved charge-transfer characteristics and moderate enhancement of OER activity, delivering a low overpotential of 350 mV at 10 mA cm −2 , a reduced Tafel slope, improved charge-transfer characteristics, and increased interfacial capacitive behaviour. The enhanced electrocatalytic performance is attributed to the synergistic effects of Sn-induced defect engineering, Eu 2 O 3 -mediated interfacial charge modulation, and optimized Mn redox chemistry, highlighting the potential of this nanocomposite for efficient alkaline OER applications. This study shows that using both rare-earth oxide promotion and heteroatom doping can change the electronic structure, defect chemistry, and interfacial charge transfer in MnO 2 -based catalysts. This combined approach offers a promising way to develop affordable and scalable noble-metal-free electrocatalysts for sustainable water-splitting technologies.