Scalable, Bottom‐Up Synthesis of Transition Metal–Doped Quantum Confined, 1D Titanate‐Based Lepidocrocite Nanofilaments, Their Electronic Structures and Oxygen Evolution Reactivity

ABSTRACT This work presents a scalable, bottom‐up approach for doping quantum confined, 1D lepidocrocite (1DL) titanate nanofilaments (NFs) with transition metal (TM) cations Mn 2 ⁺, Fe 2 ⁺, Co 2 ⁺, Ni 2 ⁺, and Cu 2 ⁺ to enhance their photo‐ and electrocatalytic properties. Here we react titanium oxysulfate with tetramethylammonium hydroxide at 80°C for 12 h at one atmosphere. By incorporating metal salts during synthesis, uniform doping within the 1DL backbone is achieved. The resulting TM‐doped 1DL NFs all exhibit lower bandgap energies, E g , than the undoped samples (3.89 eV); some by as much as 0.8 eV for Mn 2 ⁺ at 1 mol% doping, extending optical absorption into the visible region. X‐ray diffraction, scanning electron microscopy, UV–Vis spectroscopy, inductively coupled plasma analysis, and X‐ray photoelectron spectroscopy confirm the successful doping and structural integrity of our materials. The photocatalytic performance of the 1 mol% doped NFs is significantly enhanced, with a 95% degradation of rhodamine 6G dye under visible light in just 30 min, compared to only 65% degradation for the undoped 1DL NFs. In electrocatalysis, the Ni‐doped 1DL NFs show superior oxygen evolution reaction (OER) activity, with an overpotential of 319 mV at 10 mA cm −2 , which is lower than the 383 mV for undoped 1DL NFs. The Ni‐doped 1DL also has the lowest Tafel slope of 145 mV/dec at 1 mol% doping and 143 mV/dec at 5 mol%, compared to 204 mV/dec for the undoped 1DLs, indicating faster reaction kinetics. The Ni‐doped NFs also exhibit excellent stability, maintaining a constant potential at 10 mA cm −2 for > 50 h. Adding methanol to all colloidal suspensions results in their gelation within seconds. These findings highlight the potential of TM doping as an effective strategy to optimize 1DL's electronic and photochemical catalytic properties.