Materiais usados na constituição dos principais componentes de células a combustível de óxido sólido

Abstract

ResumoAs células a combustível de óxido sólido (SOFC) são dispositivos capazes de gerar energia elétrica com alta eficiência e baixa emissão de poluentes. As altas temperaturas de operação dessas células (600 a 1000 ºC) são benéficas no sentido de possibilitar a reforma in situ do combustível utilizado, bem como sua aplicação em sistemas de co-geração de energia, aumentando sua eficiência teórica total que pode chegar entre 80 e 85%. Entretanto, essas altas temperaturas, o contato direto entre materiais de constituições químicas diferentes e a utilização de gases redutores e oxidantes, são alguns dos fatores que impõem severas restrições aos materiais usados na preparação de seus principais componentes. O presente artigo tem como objetivo revisar o desenvolvimento do estado da arte, com relação aos materiais de ânodo, cátodo, eletrólito, interconectores e selantes, usados em SOFCs. Os requisitos necessários para o bom funcionamento de cada componente e os materiais que melhor se adequam aos mesmos são descritos. As vantagens e desvantagens dos principais materiais encontrados na literatura são também comentadas e comparadas. Palavras-chave: células a combustível de óxido sólido, ânodo, cátodo, eletrólito. Abstract Solid oxide fuel cells (SOFC

Chemical synthesis of materials based on calcium zirconate for solid oxide fuel cells (SOFC)

“…It is necessary that they have a well‐adjusted thermal expansion behavior, chemical compatibility and stability on reducing and oxidizing atmosphere . The electrolyte must be dense, in direct contact with two porous electrodes, called anode and cathode . The electrolyte, due to its high density, is impermeable to the gases that are diffused in these electrodes, preventing them from mixing .…”

“…Regarding the anode, it has the function of providing the sites where the electrochemical reactions of catalytic oxidation of the combustible gas with O 2 ions from the cathode occur. The researchers indicate that the most commonly used is nickel oxide, this NiO is reduced to metallic Ni and may also be metallic platinum, among others .…”

“…There are some requirements that must be met in order to ensure the stability of anode during cell operation. Among them can be mentioned: electrical conductivity, high electrocatalytic activity, being stable on reducing atmosphere, having a coefficient of thermal expansion compatible with other components, being porous, etc . To maintain porosity, some researchers deposit a thin layer of nickel oxide particles, while others use a mixture of nickel particles (metal phase) with particles of the electrolyte.…”

One-step synthesis and microstructure of CuO-SDC composites

“…In these cermets, Ni metal offers good electronic conductivity and catalytic activity for fuel oxidation, while the ceramic phase provides ionic conductivity, structural support, and reduces the Ni agglomeration during fuel cell operation at 800 to 1000 °C [1][2][3]. It is well known that the cermet performance depends on content, distribution and grain size of both metallic and ceramic phases, which together with the gaseous phase make up the triple phase boundaries, electrochemical sites where the fuel oxidation reactions take place [4][5][6]. Although widely used, Ni-based anodes have some disadvantages, especially the carbon deposition on the nickel surface, a poisoning phenomenon commonly observed when hydrogen fuel is replaced by hydrocarbons.…”

“…Although widely used, Ni-based anodes have some disadvantages, especially the carbon deposition on the nickel surface, a poisoning phenomenon commonly observed when hydrogen fuel is replaced by hydrocarbons. This problem causes the decrease of Ni electrocatalytic activity for the electrochemical oxidation of fuels such as methane or natural gas [2][3][4]. Poisoning due to carbon can be avoided or reduced by replacing Ni with another electrical conductor having lower potential to catalyze the carbon formation.…”