Banca de QUALIFICAÇÃO: ALPHIA VITORIA LIMA SOARES

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : ALPHIA VITORIA LIMA SOARES
DATE: 28/08/2026
TIME: 14:00
LOCAL: Auditorio do LIME
TITLE:

Pressurized hydrothermal synthesis of α-MoO₃ catalysts for the oxygen evolution reaction for green hydrogen production

KEY WORDS:

α-MoO₃; hydrothermal synthesis; electrocatalysis.

PAGES: 80
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Materiais Não-Metálicos
SPECIALTY: Cerâmicos
SUMMARY:

Green hydrogen has emerged as a strategic energy carrier for decarbonization and can be produced by water electrolysis powered using renewable energy sources. However, the high cost of noble-metal-based electrocatalysts limits the widespread use of this technology, motivating the investigation of alternative materials such as transition metal oxides. Among these materials, molybdenum trioxide (MoO₃) shows potential for electrocatalytic applications because of its layered structure, the different oxidation states of molybdenum, and the possibility of tailoring its structural and morphological properties. In this process, MoO₃ acts as an electrocatalyst, promoting the reactions that occur at the electrode surface and reducing the additional energy required for water electrolysis. This study aims to synthesize MoO₃ by the hydrothermal method and evaluate the influence of synthesis pressure on its structural, morphological, and electrochemical properties. The MoO₃ used as the precursor was obtained by calcining ammonium heptamolybdate tetrahydrate at 500 °C for 4 h and was subsequently subjected to hydrothermal treatment at 160 °C. To evaluate the effect of reaction time, syntheses were performed for 3, 6, 12, and 24 h under autogenous pressure. The influence of pressure was investigated for the 24 h syntheses conducted under autogenous pressure and at 45 and 90 bar, established by argon injection. The materials were calcined at 400 °C for 2 h and characterized by X-ray diffraction, field-emission scanning electron microscopy coupled with energydispersive X-ray spectroscopy, and electrochemical analyses. The X-ray diffraction patterns showed the formation of orthorhombic α-MoO₃ under all conditions investigated, with no secondary phases, indicating that reaction time and pressure did not change the crystalline phase. Pressure, however, modified the particle morphology from elongated and flattened rods under autogenous pressure to shorter and thicker structures at 45 and 90 bar, with more pronounced self-organization at the highest pressure. Electrochemical analyses demonstrated the activity of α-MoO₃ toward the oxygen evolution reaction, while the Tafel and double-layer capacitance results were used to evaluate the reaction kinetics and estimate the electrochemically active surface area, respectively. The results demonstrate that external pressure modifies the morphology of α-MoO₃ without changing its crystalline phase, highlighting the influence of hydrothermal conditions on particle growth and organization.

COMMITTEE MEMBERS:
Presidente - 1298936 - ANTONIO EDUARDO MARTINELLI
Interno - 1300987 - CARLOS ALBERTO PASKOCIMAS
Externo à Instituição - ARMANDO MONTE MENDES - UFRN
Externa à Instituição - THERESA BEATRIZ OLIVEIRA NUNES