Banca de DEFESA: NATANE MARTINIANO DOS SANTOS

Obtaining an iron-doped molybdenum carbide electrocatalyst via a gas-solid reaction for oxygen evolution.

Electrocatalysts, Mo2C, iron, gas-solid reaction, OER.

The increased environmental impacts due to the use of fossil fuels in recent decades have driven global interest in the development and application of clean, sustainable, and renewable energy sources. One alternative that has been gaining prominence is the use of hydrogen (H₂), widely recognized as one of the most promising renewable energy sources to meet growing global demand. One method of obtaining hydrogen that has received considerable attention is water electrolysis, which occurs through two half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). However, the water electrolysis process still has limitations, as it occurs slowly due to the multiple steps involved, which compromises the energy efficiency of the system.Thus, the development of efficient, stable, and low-cost electrocatalysts is a central challenge to make this technology viable on a large scale. Molybdenum carbide (Mo₂C) has emerged as an attractive catalytic material due to its electronic properties similar to those of noble metals and its high chemical stability. However, its activity for OER can still be improved through structural engineering and electronic modulation strategies. In this context, the present study aims to synthesize and investigate iron-doped Mo₂C electrocatalysts (1%, 3%, and 5% by mass), obtained by gas-solid reaction from ammonium heptamolybdate and iron nitrate, under a reducing/carburizing atmosphere (H₂/CH₄) at 700 °C for 2 hours, in order to understand how the incorporation of Fe influences the structural and electronic properties and the electrocatalytic performance in the oxygen evolution reaction (OER). °C for 2 hours, aiming to understand how the incorporation of Fe influences the structural and electronic properties and the electrocatalytic performance in the oxygen evolution reaction (OER). X-ray diffraction analysis revealed a single Mo₂C phase in samples containing 0, 1, and 3% Fe, while the sample with 5% Fe contained mainly Mo₂C and a small amount of metallic iron (α-Fe), as confirmed by Mössbauer spectroscopy. Micrographs obtained by high-resolution scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) revealed agglomerated nanoscale particles with a heterogeneous size distribution and coexistence of crystalline and amorphous regions. XPS analysis confirmed the presence of Mo, Fe, C, and O, with different oxidation states. Raman spectra revealed the presence of the β-Mo₂C phase. In electrocatalytic tests in alkaline medium, with increasing Fe concentration, the overpotential decreased from 346 mV to 268 mV at 20 mA cm⁻² and significantly reduced the charge transfer resistance from 21.0 to 1.9 Ω cm⁻². The catalysts also showed stability for 24 hours. These results indicate that incorporating Fe into Mo₂C improves activity and makes the material promising for the oxygen evolution reaction (OER).