2024 - SERNA, M.M.; GALEGO, E.; FARIA, R.N.; SAKATA, S.K.

In the search for clean energy generation, solar energy has so far occupied the leading role; among the various factors that favor it are the possibility of generating energy on the surface of the planet and in outer space, in addition to the small environmental impact of generation plants and the possibilities of generation in urban environments. Within the different types of solar cells, dye-sensitized solar cells (DSSC) promise to revolutionize energy generation through their application as the external coating of large buildings. In the manufacture of this type of cell, non-toxic and low-cost materials are used; however the maximum conversion efficiency is still low when compared to silicon cells. One of the factors that contribute to the decrease in efficiency is the process of recombination of the photogenerated electron with the electrolyte. In the most common type of DSSC that uses a glass substrate coated with SnO2:F (FTO) to manufacture the photoanode, this surface acts as a recombination site. The objective of this work was to study the addition of a graphene layer between the FTO and the semiconductor oxide film in order to minimize recombination processes through the insertion of a new energy level. The deposition of reduced graphene oxide (rGO) was carried out by dip coating with different numbers of deposition cycles (0, 2, 5, 10 cycles). A ZnO paste was deposited on this film using the doctor blade technique with a green thickness of 50 µm. The assembly was heat treated at 450 °C for 1 h, aiming to reduce rGO to graphene and aggregate ZnO into a porous structure. The set was sensitized with the dye N719 and the solar cells were assembled with an FTO/Pt counter electrode and an electrolyte with the iodide/triodide redox couple. The electrical parameters were obtained from the survey of IV curves in a solar simulator with a power of 100 mW cm-2 and air mass 1.5. The morphology of the photoanode was studied by scanning electron microscopy (SEM). The micrographs obtained by SEM show that a porous ZnO film was formed with an average thickness of 25 µm. The cell efficiency increased with the increase in the number of dip coating cycles from 0.39% without rGO to 0.72% with 10 cycles of rGO deposition. The variation in the fill factor was less than 10%. The series resistance values are of the same order of magnitude, indicating that the rGO did not act to increase the conductivity at the rGO/FTO interface, whereas the series resistance values will increase with the increase in the number of cycles, which allows us to conclude that the rGO acts as a blocking layer preventing the regeneration of the electrolyte with the photogenerated electron.

2024 - GOMES, D.

In the 1960s, the space nuclear program started reactor propulsion designs, sparking interest in uranium mononitride (UN) as a fuel. Since then, UN has become attractive due to its higher thermal conductivity and elevated uranium density compared with standard UO2. Reactors using sodium and lead as liquid coolants show a long experience with UN fuel. Recently, uranium UN mixed with uranium silicide (U3Si2) has been an option as a more tolerant fuel for power units. However, a few silicide compounds exist, such as USi, USi2, USi3, U3Si, U3Si2, and U3Si5. Thus, nitride-silicide composites like UN-U3Si5 took the place of UN-U3Si2 in order to reduce the energetic interaction with steam and shield the nitride phase from water reactions. Ther is increasing interest in UN-U3Si5 fuel, which has a secondary fissile phase with an elevated uranium density. This way, we compare UN-U3Si2 and UN-U3Si5 using Kanthal APMT as cladding.

2024 - GALEGO, E.; SAKATA, S.K.; SERNA, M.M.; FARIA, R.N.

The conversion of solar energy into electricity is considered one of the best sustainable technologies for the future replacement of traditional methods of generating electrical energy, such as thermoelectric and nuclear plants. Photovoltaic conversion is the generation system with the greatest potential for growth to meet growing demand, which includes dye-sensitized solar cells (DSSC). DSSC is notorious for mimicking photosynthesis, which mainly focuses on generating electricity under any light intensity. The DSSC is composed by: a semiconductor oxide layer (SO), that functions as a support for the adsorption of a dye; this set is encapsulated between two translucent electrodes and; the space between them is filled with a specific electrolyte. The DSSC, being translucent, acquires the color of the adsorbed dye, which gives it a colorful appearance, a desirable characteristic for applications such as: decorative and architectural objects, among others. The dye is the active element in DSSC and, to have the best possible performance, the dye must be exposed to lighting over the largest area possible. To achieve this, the OS film must have a nanometric porous structure that will guarantee a greater apparent exposure area. This structure is obtained using a mixture of semiconductor oxide with organic products which, after heat treatment, are eliminated. This work aimed to study the influence of organic compounds: polyethylene glycol, ethyl cellulose and glycerin, on the paste viscosity for application by the doctor blade (DB) technique and on the efficiency of DSSC. The pastes were prepared using nanoparticulate ZnO (< 100 nm) in the following compositions: (a) ZnO + ethyl cellulose + terpineol (0.2 g + 0.1 g + 0.5 mL); (b) ZnO + PEG 400 G (0.3 g + 0.3 m?) and; (c) ZnO + liquid glycerin (0.3 g + 0.3 mL). All mixtures were homogenized in an agate mortar and rested for 24 h. Afterwards, they were applied to a glass electrode (FTO) by DB, with a defined area of 8 x 8 mm and subjected to heat treatment: from room temperature to 450 °C with a heating rate of 5 °C min-1 maintained for 1h. Then, the samples were sensitized in the dye N719 for 16h. Next, sealed DSSCs were assembled using an FTO+Pt counter-electrode and filled with electrolyte (I-/I3-). The electrical parameters were obtained from the IV curve obtained under lighting of 100 mW cm-2, air mass: 1.5 G. From the point of view, the applicability by DB, paste (a) presented best result evaluated by ease of application and homogeneity in green. However, electrical parameters revealed that using paste (c) presented the highest short-circuit current value (Isc) however, lowest conversion efficiency n= 0.49%; pastes (a) and (b) showed similar efficiency: n = 0.58% and n = 0.56%. The paste (a) was chosen for future application and studies.

2024 - ARAUJO, S.G.; LANDINI, L.; SALVADOR, V.L.; GARCIA, R.H.; GALEGO, E.; SERNA, M.M.; LINHARES, H.M.

As excelentes propriedades do grafeno proporcionam um enorme potencial para aplicações estruturais e funcionais de compósitos grafeno-cerâmicos, como material de enchimento em cerâmicas monolíticas, eletrodos renováveis de superfície, células de combustível de baixa temperatura, materiais de armazenamento de energia, próteses de quadril e dispositivos eletrônicos. O grafeno é um material cristalino leve, composto de átomos de carbono interligados, formando uma estrutura hexagonal, espessura de um só átomo, grande elasticidade e dureza, alta condutividade elétrica e térmica, além de suas propriedades mecânicas, é 200 vezes mais forte do que o aço, mas também o mais fino (um milhão de vezes mais fino do que um fio de cabelo). Produtos a base de grafeno têm infinitas possibilidades em diferentes setores. Os desafios para a sua disseminação no mercado prendem-se, em muito, com os métodos de produção, o seu custo e limitações. O grafite tem sido usado como matéria-prima para a produção de grafeno desde sua descoberta, porém recentemente, alternativas verdes para a sua produção têm sido exploradas. A utilização da agro-resíduos como fonte de carbono é benéfica para o meio ambiente porque reduz os resíduos. Estes materiais podem ser de resíduos de colheitas, indústrias de papel etc., com potencial na produção de grafeno, pois são abundantes. O anual global de agro-resíduos é 1 x 10 a 10 T/A, e continuará a aumentar com base no incremento global, projetado da área de cultivo até 2050. O método químico para produção do grafeno, geralmente emprega como fonte de carbono o grafite, sendo que uma das principais sínteses de produção, utiliza-se o Método de Hummer, que é caro, sofisticado, libera gases tóxicos, nocivo ao meio ambiente, além de demorado. Agro-resíduo tem uma estrutura rica em carbono, muito promissor para síntese de grafeno e seus derivados. Neste trabalho, o óxido de grafeno reduzido (OGr) foi obtido a partir de agro-resíduos, como bagaço de cana-deaçúcar e resíduos de jaca, em unidade reacional de batelada, assistida por micro-ondas do IPEN-CNEN/SP, o processamento foi com micro-ondas (MO), frequência de 2,45GHz; potência de 1000W; proporção em massa de agroresíduo/agente redutor (5:1); tempo de reação de 20min; agitação das amostras: 600rpm; temperatura da reação: 300ºC a 800ºC. Após o processamento, as amostras foram caracterizadas por DRX e FRX. A tecnologia de MO é considerada favorável para síntese de OGr, a partir de agro-resíduos, com baixo consumo de energia, taxa de reação mais rápida, facilidade no controle de aquecimento e economia de tempo, por vezes sem necessidade do uso de outros reagentes, com possibilidade de aumentar produção e reduzir custos.