Interações metal-suporte em eletrocatálise: influência de suportes contendo carbetos na redução de oxigênio em nanopartículas de Pd
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2021-04-28
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Universidade Estadual Paulista (Unesp)
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As interações metal-suporte podem modificar as propriedades eletrônicas do metal que, por sua vez, podem alterar consideravelmente a velocidade de etapas dos mecanismos de reação onde participam espécies adsorvidas. Esta tese apresenta um estudo comparativo e sistemático dos efeitos de suportes alternativos na eletrocatálise da reação de redução de oxigênio sobre nanopartículas de Pd em meio ácido e alcalino, que foi estudada sobre nanopartículas de Pd suportadas em híbridos contendo carbono e carbeto (C-SiC, C-TiC, C-WC) e em carbetos puros (SiC, TiC e WC) com a finalidade de elucidar a influência dos suportes na atividade catalítica do Pd. Estes estudos foram realizados comparando-se as respostas catalíticas para a reação de redução de oxigênio de catalisadores preparados com nanopartículas de Pd idênticas e analisando o efeito de carbetos distintos com igual tamanho de partícula (TiC – 50 nm vs. SiC – 50 nm; e TiC – 200 nm vs. WC – 200 nm), bem como avaliando-se os efeitos do tamanho de partícula do carbeto (TiC – 50 nm vs. TiC – 200 nm). Além de caracterizar os catalisadores por difração de raios X (DRX) e microscopia eletrônica de transmissão (TEM), os efeitos das interações metal-suporte na ocupação eletrônica da banda 4d do Pd foram investigados por espectroscopia de absorção de raios X (XAS) in situ. A atividade catalítica para a redução de oxigênio e a estabilidade dos materiais foram avaliadas por técnicas eletroquímicas (eletrodo de disco anel rotatório e varreduras de potencial). O trabalho desenvolvido demonstrou os efeitos dos suportes contendo carbetos nas propriedades eletrônicas do Pd e a sua relação com a atividade catalítica para a reação de redução de oxigênio, e visou contribuir à compreensão dos fatores que influenciam a atividade catalítica de catalisadores de Pd e ao desenvolvimento de catalisadores sem Pt para catodos de células a combustível.
Metal-support interactions can modify the electronic properties of the metal, which can considerably modify the speed of steps of the reaction mechanism where adsorbed species participate. This thesis presents a comparative and systematic study of the effects of alternative supports on the electrocatalysis of the oxygen reduction reaction on Pd nanoparticles in acidic and alkaline media, that was studied on Pd nanoparticles supported on hybrids carbon-carbide (C-SiC, C-TiC and C-WC) and on pure carbides (SiC, TiC and WC) aiming to elucidate the influence of the supports on the catalytic activity of Pd. These studies were performed comparing the catalytic responses for the oxygen reduction reaction of catalysts prepared with identical Pd nanoparticles and analyzing the effect of different carbides with the same particle size (TiC – 50nm vs. SiC – 50nm; TiC – 200 nm vs. WC – 200nm), as well as by evaluating the effects of particle size of the carbide (TiC – 50nm vs. TiC – 200nm). Besides characterizing the catalysts by X-ray diffraction (XRD) and transmission electron microscopy (TEM), the effects of metal-support interactions on the electronic occupancy of the Pd 4d band were investigated by in situ X-ray absorption spectroscopy (XAS). The catalytic activity for the oxygen reduction reaction and the stability of the materials were evaluated by electrochemical techniques (rotating ring disc electrode and cyclic voltammetry). This work demonstrated the effects of supports containing carbides on the Pd electronic properties and their relation with the catalytic activity for the oxygen reduction reaction and aimed to contribute to the understanding of the factors that influence the catalytic activity of Pd catalysts and to the development of Pt-free catalysts for fuel cell cathodes.
Metal-support interactions can modify the electronic properties of the metal, which can considerably modify the speed of steps of the reaction mechanism where adsorbed species participate. This thesis presents a comparative and systematic study of the effects of alternative supports on the electrocatalysis of the oxygen reduction reaction on Pd nanoparticles in acidic and alkaline media, that was studied on Pd nanoparticles supported on hybrids carbon-carbide (C-SiC, C-TiC and C-WC) and on pure carbides (SiC, TiC and WC) aiming to elucidate the influence of the supports on the catalytic activity of Pd. These studies were performed comparing the catalytic responses for the oxygen reduction reaction of catalysts prepared with identical Pd nanoparticles and analyzing the effect of different carbides with the same particle size (TiC – 50nm vs. SiC – 50nm; TiC – 200 nm vs. WC – 200nm), as well as by evaluating the effects of particle size of the carbide (TiC – 50nm vs. TiC – 200nm). Besides characterizing the catalysts by X-ray diffraction (XRD) and transmission electron microscopy (TEM), the effects of metal-support interactions on the electronic occupancy of the Pd 4d band were investigated by in situ X-ray absorption spectroscopy (XAS). The catalytic activity for the oxygen reduction reaction and the stability of the materials were evaluated by electrochemical techniques (rotating ring disc electrode and cyclic voltammetry). This work demonstrated the effects of supports containing carbides on the Pd electronic properties and their relation with the catalytic activity for the oxygen reduction reaction and aimed to contribute to the understanding of the factors that influence the catalytic activity of Pd catalysts and to the development of Pt-free catalysts for fuel cell cathodes.
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Oxigênio, Catalisadores, Células a combustível, Paládio, Nanopartículas