Modificação da superfície de fotoeletrodos de óxidos metálicos na melhora da eficiência da quebra da molécula de água

Author(s)

Saulo do Amaral Carminati

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2020-12-09

Examining board members

Ana Flávia Nogueira; Lucia Helena Mascaro; Luiz Henrique Dall'Antonia; Juliano Alves Bonacin; Pablo Sebastián Fernández

• Advisor: Ana Flávia Nogueira

Abstract

Among many semiconductors studied for photoelectrochemical (PEC) water splitting, hematite (alfa-Fe2O3) has emerged as a promising candidate as photoanode due to its advantageous properties such as abundance, visible light absorption, stability in alkaline media and non-toxicity. Despite these many advantages, alfa-Fe2O3 presents several drawbacks such as short diffusion length of minority carriers, sluggish water oxidation kinetics and low minority carriers mobility, leading to fast charge carrier recombination. In the first part, to overcome these shortcomings, alfa-Fe2O3 photoanodes were modified with single layer graphene (SLG) and a detailed investigation on improved photoelectrochemical (PEC) properties has been addressed. The role of the SLG as overlayer on enhanced PEC performance of alfa-Fe2O3/SLG photoanodes was investigated. Herein, the charge carrier dynamics were investigated combining transient absorption spectroscopy (TAS) and surface photovoltage spectroscopy (SPS). In the second part, it is discussed the incorporation of cobalt hexacyanoferrate (Co-NC-Fe) with different iron oxidation states (FeII and FeIII) on alfa-Fe2O3 nanorods photoanodes. Co-NC-Fe which has an analogous structure to Prussian Blue (PB), has shown good electrocatalytic activity owing to its both fundamental and practical perspectives. A detailed investigation using in-situ techniques (UV-Vis and FTIR) was carried out to understand the fundamental aspects of chemical reactions during PEC characterization under neutral pH. The alfa-Fe2O3/Co-NC-Fe photoanodes showed higher photoelectrochemical performance as well as photocurrent density, compared to the individual materials which was found to be dependent of the oxidation states of the materials at different applied potentials. In the third part, bismuth vanadate (BiVO4) was the semiconductor for oxygen evolution reaction (OER). BiVO4 has attracted substantial attention for photocatalytic applications owing to its many advantages as semiconductor for OER. Despite promising characteristics, the fast electron-hole pairs recombination is still one of its biggest drawbacks. The use of conformal layers in order to minimize such limitation and to improve charge separation was the aim of this work. Herein, the incorporation of SnO2 as a conformal coating layer over the BiVO4 surface for O2 evolution was carried out. The BiVO4@SnO2 photocatalyst showed the beneficial effect in O2 evolution compared to the pristine material, resulting in 490 µmol after 6h of irradiation. TAS and SPS measurements indicate enhanced charge carrier separation and transport by passivating BiVO4 with SnO2 thin layer, showing promising results for further studies (AU)

• FAPESP's process: 15/23775-3 - Metal oxides nanocomposites with reduced graphene oxide for water splitting reactions and photocatalytic reduction of CO2
• Grantee: Saulo do Amaral Carminati
• Support Opportunities: Scholarships in Brazil - Doctorate