GeAl _2‐2x Fe _2x O ₃ (OH) ₄ Nanotubes: New Electrocatalyst for Oxygen Evolution Reaction

Abstract Ge‐imogolite nanotubes (Ge‐INT) are analogs of natural clay nanotubes formed in volcanic soils that attract growing interest. Despite their amazing structural properties, their use in water oxidation has not been reported yet. In this work, the potential of Fe‐doped double‐walled germanium imogolite nanotubes as low‐cost and noble metal‐free electrocatalysts for oxygen evolution reaction (OER) is demonstrated for the first time. Nanotube samples are synthesized via a one‐step hydrothermal method, with Fe substitution ratios x up to 0.075. Fe‐doped nanotubes retain their tubular structure, and investigation indicated homogeneous Fe distribution all over the nanotubes. Comprehensive structural, spectroscopic, and electrochemical analyses confirm successful Fe incorporation and enhanced electrochemical performance. The sample with x = 0.05 Fe content shows the best OER performance, achieving a low overpotential of 285 mV at 10 mA cm ⁻² , a Tafel slope of 175 mV dec ⁻¹ , and excellent charge transfer properties. Fe‐doped INT demonstrates strong electrochemical stability over prolonged operation. These results highlight the promising use of geo‐inspired Fe‐doped imogolite as a sustainable and credible nobel‐free electrocatalyst for efficient OER, expanding the potential of imogolite‐based nanomaterials in water oxidation.