Banca de DEFESA: LUIZA MARIA CERQUEIRA SILVA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : LUIZA MARIA CERQUEIRA SILVA
DATE: 28/06/2023
TIME: 14:00
LOCAL: Sala de seminários do IQ
TITLE:

Pseudocapacitor materials for application in charge storage devices

KEY WORDS:

MnO₂; charge storage; pseudocapacitors; EQCM

PAGES: 95
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Inorgânica
SPECIALTY: Físico Química Inorgânica
SUMMARY:

The development of new materials applicable to energy storage and conversion has been of great relevance in the last four decades. There is significant emphasis on research with transition metal oxides due to the chemical, electronic, optical, and magnetic properties inherent in this class of materials. Manganese oxide (MnO₂), because it's a low-cost oxide, easy to obtain, and has several synthesis methods, presents itself as a promising oxide for application in energy storage devices, especially in batteries and electrochemical capacitors. From a practical standpoint, the electrochemical properties of MnO₂ can be improved as the variables of oxide preparation are studied. This work proposes to verify how it is possible to improve these properties, investigating the use of metallic titanium (Ti), stainless steel (SS), platinized titanium (Ti/Pt), and platinum (Pt) substrates, as well as the use of Na₂SO₄ 1 mol L^-1 as supporting electrolyte in the MnSO₄ 0.4 mol L^-1 solution used in the electrodeposition process. Furthermore, the mechanism of charge storage and electronic transfer of the oxide through mechanical oscillation frequencies during the electrochemical synthesis of materials was investigated using the Electrochemical Quartz Crystal Microbalance (EQCM) technique as a function of different temperature conditions. In these processes, an initial potential of the peak oxidation was observed, in the anodic scan, varied according to the substrate used. There was a shift towards more positive potentials as Ti, SS, Ti/Pt, and Pt substrates were used, respectively. However, using the MnSO₄ solution in Na₂SO₄, the oxidation process started at less positive potentials, which favors the system in terms of energy. Furthermore, regardless of the electrolyte used, the electrodeposition curve was preserved in the voltammetric profile. The electrochemical characterization of the deposited MnO₂ thin films shows a significant difference in the current densities of the anodic and cathodic processes. Furthermore, the anodic peak associated with the Mn^IV-Mn^VI transition appeared well-defined and at the less anodic potential for the MnO₂ films deposited on the SS, Ti/Pt, and Pt electrodes. Analyzed the electrochemical characterizations, a significant increase in current density is observed in comparison with the solution without this electrolyte. The electrodeposits on Ti substrates showed a more rectangular voltammetric profile, which is characteristic of pseudocapacitive materials, however, Ti/Pt/MnO₂ electrodes showed the highest values of specific capacitance. The presence of Na₂SO₄ in the deposition solution resulted effectively in an increase in the storage capacity of the deposited oxide. With the MnSO₄+Na₂SO₄+H₂O solution, the specific capacitance was 450 F g^-1, against 216 F g^-1 (for the film deposited on MnSO₄+H₂O), at a speed of 2 mV s^-1. In morphological terms, all electrodes showed cracks, which is a characteristic morphology of MnO₂ oxides, however, the islands were smaller in the materials synthesized in the presence of the Na₂SO₄ electrolyte, thus resulting in a greater number of cracks and this condition directly reflects on the increase of the pseudocapacitive properties of the electrode.

COMMITTEE MEMBERS:
Presidente - 1488945 - ADRIANE VIANA DO ROSARIO
Interno - 2356272 - ARTUR JOSE SANTOS MASCARENHAS
Externo à Instituição - ERNESTO CHAVES PEREIRA DE SOUZA - UFSCAR
Externo ao Programa - 1194490 - IURI MUNIZ PEPE - UFBAInterno - 2362069 - RAILDO ALVES FIUZA JUNIOR
Interna - 1861434 - VALERIA CRISTINA FERNANDES