Melhora da performance da reação de oxidação da água pelo design de vacancias formadas eletroquimicamente em catalisadores a base de análogos do azul da Prússia

Author(s)

Rafael Lavagnolli Germscheidt

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2023-09-11

Examining board members

Juliano Alves Bonacin; Raphael Nagao de Sousa; Paulo Cesar de Sousa Filho; Caterina Gruenwaldt Cunha Marques Netto

• Advisor: Juliano Alves Bonacin; Tulio Costa Rizuti da Rocha

Abstract

The search for clean, renewable, and environmentally friendly hydrogen sources has made water an excellent feedstock candidate to produce hydrogen. The production of green H2 from water occurs by a system known as Water Splitting (WS), which is limited by the anodic process, called Oxygen Evolution Reaction (OER), thus, it requires a catalyst to be effective. Prussian Blue (PB) is an inorganic material of mixed valence in a tridimensional framework formed by Fe(II) bound to Fe(III) through a cyanide bridge. Moreover, the iron can be substituted by some other transition metals and an analogue structure known as Prussian blue analogues (PBA) can be obtained. PBAs are represented by M1(x)[M2(CN)6](y), where M2 is an hexacyanometalate that plays a structural role and it can modulate the donor-acceptor effect to the other metal and M1 a first-row transition metal and it is coordinated to the N atoms forming a 3D network. Due to their outstanding electrochemical properties, it represents a great alternative as an Earth-abundant catalyst for OER, presenting great performance, activity, and stability under mild conditions. Nonetheless, despite their high stability and activity, the main shortcoming is their low concentration of active sites, thus, engineering the structure and defects is essential to lead to a high concentration of active sites. In this thesis, the electrochemical mechanisms of water oxidation using catalysts based on Prussian Blue analogues is investigated, moreover, strategies to enhance their activity are proposed. Thus, I report a photochemical pre-treatment for the quantification of the total iron from heterogeneous thin films composed of iron-based materials. The photochemical approach is used to ensure a full dissociation of iron ions before the quantification. Furthermore, an alternative methodology to synthesize the Prussian blue was proposed, by applying a high and constant potential to the electrode in a solution containing [Fe(CN)6]4- that is oxidized along with some cyanide groups, obtaining a catalyst with electrochemically formed vacancies and have its performance towards WOR studied, presenting an outstanding activity. Furthermore, the same methodology was applied to create these cyanide vacancies on a CoFe Prussian blue analogue catalyst, allowing the understanding of the role of these vacancies on the enhancement of these catalysts’ performance towards OER. Finally, synchrotron-based soft X-ray spectroscopy was used to probe the composition and the nature of these defects (AU)

• FAPESP's process: 18/25092-9 - Study of the mechanism of oxidation of water by catalysts with structure analogous to Prussian blue
• Grantee: Rafael Lavagnolli Germscheidt
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)