Banca de DEFESA: VICTOR DOS SANTOS PINHEIRO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE : VICTOR DOS SANTOS PINHEIRO
DATA : 25/02/2022
HORA: 14:00
LOCAL: https://meet.google.com/nja-fdon-vcb
TÍTULO:

Hybrid Electrocatalysts Based on Pd, Pt and Sn Nanoparticles, and on Ceria Nanorods for Application in Fuel Cells

PÁGINAS: 272
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Química
SUBÁREA: Físico-Química
ESPECIALIDADE: Eletroquímica
RESUMO:

Fuel cells are important energy conversion devices as alternatives to fossil fuels and are increasingly being studied. Fuel cells using hydrogen gas show excellent results, however, due to the dangers of direct use of hydrogen gas, Alkaline Direct Ethanol Fuel Cells (ADEFCs) have gained importance as ethanol is a renewable fuel and non-toxic to humans, such as methanol. However, there are still challenges ahead, such as the low efficiency of electrocatalysts for the oxygen reduction reaction (ORR), which occurs slowly at its cathode and also the difficulty in breaking the C-C bond of the ethanol molecule in the ethanol oxidation reaction (EOR) that occurs at the ADEFCs anode, in addition to the high-cost of the electrocatalysts based only on palladium (Pd) or platinum (Pt). In this sense, this work aims the synthesis, characterization and application of different hybrid electrocatalysts containing reduced amounts of Pd and/or Pt nanoparticles combined with tin nanoparticles (Sn) and/or ceria nanorods (CeO₂ NR), used as metals and metal oxides auxiliaries in ORR and EOR, increasing their efficiencies and also reducing the total cost of the electrocatalyst, which were supported on Vulcan XC-72 carbon (Vn), aiming to increase the surface area of the material and further reduce the final cost of the electrocatalyst. The different hybrid electrocatalysts synthesized were physicochemically characterized by X-ray diffraction (XRD), X-ray photoelectronic spectroscopy (XPS), energy dispersive spectroscopy (EDS), inductively coupled plasma mass spectroscopy (ICP-MS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), contact angle, Raman spectroscopy and Fourier transform infrared spectroscopy (FT-IR). Among the electrocatalysts evaluated in the ORR at the fuel cells, there was a great importance of the CeO₂ NR addiction due to the increase in the number of defects, oxygenated species and vacancies in the electrocatalysts, which were proven by different techniques and by the best results presented by these materials compared to the results obtained by the commercial electrocatalysts, Pt/C Alfa Aesar (cathode) and Pd/C Alfa Aesar (anode), in unitary ADEFC experiments. Among the binary and ternary hybrid electrocatalysts evaluated in the ORR (Pt_x(CeO₂ NR)_y(Vn)_z, Pd_x(CeO₂ NR)_y(Vn)_z e Pd_xPt_y/Vn e (Pd₃Pt₁)_x(CeO₂ NR)_y(Vn)_z), the ternary hybrid electrocatalyst (Pd₃Pt₁)₁₅(CeO₂ NR)₁₀(Vn)₇₅ stands out when used as a cathode in unitary ADEFC experiments with the commercial Pd/C Alfa Aesar electrocatalyst as anode, as it presented open circuit potential (OCP), maximum current density and maximum power density of 1130 mV, 219 mA cm^-2 e 61 mW cm^-2, respectively, these being the best results replacing only the ADEFC cathode, and using the commercial electrocatalysts were achieved only 969 mV, 123 mA cm^-2 and 23 mW cm^-2, respectively. Among the binary and ternary hybrid electrocatalysts evaluated in EOR (Pd_x(CeO₂ NR)_y(Vn)_z, e Pd_xSn_y/Vn e (Pd₁Sn₃)_x(CeO₂ NR)_y(Vn)_z), the ternary hybrid electrocatalyst (Pd₁Sn₃)₁₀(CeO₂ NR)₂₀(Vn)₇₀ stands out when used as anode in single ADEFC experiments with the commercial Pt/C Alfa Aesar electrocatalyst as cathode, as it presented OCP, maximum current and power densities of 1100 mV, 113 mA cm^-2 e 30 mW cm^-2, respectively, and its Pd load was about eight times lower than that used in the evaluation of commercial electrocatalysts (0.13 mg _Pd cm^-2 versus 1 mg _Pd cm^-2). Thus, these maximum current and power densities results for this electrocatalyst normalized per Pd milligram were 869 mA cm^-2 mg _Pd^-1 and 231 mW cm^-2 mg _Pd^-1, while using the commercial electrocatalyst at the anode, were obtained only 123 mA cm^-2 mg _Pd^-1 and 23 mW cm^-2 mg _Pd^-1, respectively. Therefore, the ternary hybrid electrocatalyst (Pd₁Sn₃)₁₀(CeO₂ NR)₂₀(Vn)₇₀ presented the best results as an ADEFC anode. The binary hybrid electrocatalysts Pd_x(CeO₂ NR)_y(Vn)_z proved to be versatile, and these electrocatalysts showed good results in both ORR and EOR, using the electrocatalyst Pd₁₅(CeO₂ NR)₁₀(Vn)₇₅ as cathode and Pd₁₀(CeO₂ NR)₂₀(Vn)₇₀ as anode in single ADEFC experiments were obtained OCP, maximum current and power densities of 1270 mV, 190 mA cm^-2 and 65 mW cm^-2, respectively. These results in both applications may have occurred due to the high number of defects, oxygenated species and vacancies in these electrocatalysts and also due to the synergistic effect between CeO₂ NR and Pd nanoparticles. However, the ternary hybrid electrocatalyst (Pd₃Pt₁)₁₅(CeO₂ NR)₁₀(Vn)₇₅ showed the best results when used in the cathode in unitary ADEFC experiments and the ternary hybrid electrocatalyst (Pd₁Sn₃)₁₀(CeO₂ NR)₂₀(Vn)₇₀ presented the best results when used on the anode in single ADEFC experiments. In this sense, these ternary hybrid electrocatalysts are promising to be applied in ADEFCs due to the increase in efficiency in the ORR and EOR and the decrease in the noble metal charge, resulting in a decrease in the cost of these electrocatalysts.

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1544381 - MAURO COELHO DOS SANTOS
Membro Titular - Examinador(a) Interno ao Programa - 1844792 - AMEDEA BAROZZI SEABRA
Membro Titular - Examinador(a) Interno ao Programa - 1814655 - LUCIA HELENA GOMES COELHO
Membro Titular - Examinador(a) Externo à Instituição - ROBERTO MANUEL TORRESI - USP
Membro Titular - Examinador(a) Externo à Instituição - ARTUR DE JESUS MOTHEO - USP
Membro Suplente - Examinador(a) Interno ao Programa - 1864481 - HUEDER PAULO MOISES DE OLIVEIRA
Membro Suplente - Examinador(a) Externo ao Programa - 1671688 - ANDRE SARTO POLO
Membro Suplente - Examinador(a) Externo à Instituição - LÚCIA CODOGNOTO DE OLIVEIRA - UNIFESP