Banca de QUALIFICAÇÃO: KÍVIA FABIANA GALVÃO DE ARAÚJO

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : KÍVIA FABIANA GALVÃO DE ARAÚJO
DATE: 27/02/2026
TIME: 15:00
LOCAL: Virtual
TITLE:

Synthesis and structural, morphological, vibrational, and magnetic characterizations of transition metal niobates for application in oxygen evolution reactions.

KEY WORDS:

Niobate, ceramics, OER

PAGES: 111
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Materiais Não-Metálicos
SPECIALTY: Cerâmicos
SUMMARY:

The search for efficient and low-cost catalysts for water electrolysis has intensified due to the rising demand for clean energy. However, the water electrolysis process faces significant challenges, particularly regarding the water oxidation half-reaction, also known as the Oxygen Evolution Reaction (OER), due to the high overpotential that compromises the overall energy efficiency. Currently, electrocatalysts based on noble metals, such as Ir, RuO2, and PtO2, are predominantly used. Nevertheless, these materials are scarce, costly, and toxic, which hinders their large-scale application. In this context, research on electrocatalysts based on niobium compounds and first-row transition metals (3d) has grown, demonstrating significant catalytic efficiency for the OER. Columbite niobates (ANb2O6) have emerged as strong candidates due to their structural versatility, which allows for the tuning of their properties through structural adjustments. Therefore, to understand the OER catalytic performance of these materials, this study synthesized ANb2O6 (where A = Cu, Mn, Zn, Co, and Ni) via solid-state and liquid-state reactions, followed by thermal treatments optimized for each system. A comparative evaluation of the synthesis routes classified all methods as efficient for producing these niobates, however liquid-state routes (sol-gel and solvothermal) yielded smaller particle sizes. The CuNb2O6 exhibits two phases, the monoclinic and orthorhombic. This study evaluated the influence of the crystalline phase on electrochemical OER performance, observing superior results for the orthorhombic phase, which exhibits antiferromagnetic (AFM) behavior. The remaining compounds were configured solely in the orthorhombic phase, consistent with the P b c n space group, as confirmed by XRD characterization and Rietveld refinement. FTIR analysis identified no inconsistent vibrational modes, revealing only those corresponding to the M-O (M = transition metal) and Nb-O octahedral bonds. The particles presented similar morphologies, characterized by irregular and agglomerated spheres, with solvothermally synthesized ZnNb2O6 producing the smallest particles (ranging from 100 to 200 nm). The predominant magnetic behavior among the niobates was paraferromagnetic, evaluated in relation to ꭕ vs. T, and regarding hysteresis, the M vs. H curves at low temperature indicated aspects of AFM, with only the cobalt and nickel niobates showing weak ferromagnetic behavior, with the exception of ZnNb2O6 which is not magnetic. Electrochemical measurements indicated satisfactory
overpotential values for all samples. The lowest values were attributed to orthorhombic CuNb2O6 323 mV with a Tafel slope of 58.1 mV dec-1 and MnNb2O6 324 mV and 41.8 mV dec-1, whereas monoclinic CuNb2O6 exhibited the highest overpotential 363 mV and 60.5 mV dec-1. Finally, CDL and ECSA values ranged from 1.3 to 4.54 mF and 30 to 113 cm2, respectively. Thus, these results expand current knowledge and underscore the potential of columbite niobates for electrochemical catalysis applications.

 

COMMITTEE MEMBERS:
Presidente - 1674707 - MARCO ANTONIO MORALES TORRES
Interno - ***.121.804-** - UILAME UMBELINO GOMES - UFRN
Externa à Instituição - MARIA JOSE SANTOS LIMA
Externo à Instituição - RAFAEL ALEXANDRE RAIMUNDO - UFPB
Externo à Instituição - ROMUALDO RODRIGUES MENEZES - UFCG