Application of oxide supports is considered as a viable approach to decrease iridium loading in oxygen evolution reaction catalysis in acid electrolyte. While the most of the promising oxides are poor conductors, the need for doping is typically taken as granted, and a representative example is tin dioxide. There are still, however, serious concerns on the feasibility of this approach as we lack consensus on any activity gain by using such oxides, while doubts on stability are numerous. In this work, a set of catalyst/support combinations including two catalysts, viz. hydrous (IrO x ) and rutile (IrO 2 ) iridium oxides, and four supports, viz. SnO 2 and Sb-(ATO), F-(FTO), and In-doped (ITO) SnO 2 , are synthesized and character-ized by a selection of complementary experimental techniques including rotating disk electrode and on-line inductively coupled plasma mass spectrometry. It is found that the electrochemical activity in acid media of supported Ir catalysts is essentially the same, independent on presence or absence of dopants. Sb and In dopants are shown to be unstable and cause an increased dissolution of Sn. Besides, the degradation of the doped supports results in destabilization of iridium oxides. These results raise doubts on the real need for the use of dopants in SnO 2 -based catalyst supports for electrochemical water splitting.

Pt/CeO2/C electrocatalysts in different compositions were prepared and their structural characteristics and activities for ethanol oxidation in alkaline media were evaluated. In the presence of CeO2, an increase in the platinum particle size was observed. XANES measurements indicated that the Pt d-band vacancies increased with increasing CeO2 amounts. For the first time, the decrease in electro activity was described to an electronic effect for high CeO2 contents. The dependence of the activity for ethanol oxidation on CeO2 content went to a maximum, due to the counteracting bifunctional and electronic effects of the metal oxide.

A deep understanding of the ammonia oxidation reaction (AOR) over platinum surfaces may facilitate the use of ammonia as a carbon-free source for energy storage and conversion. Herein, using an unprecedented experimental approach of combining online electrochemical mass spectrometry (OLEMS) and ion chromatography (IC) with high-area Pt/C surfaces, many AOR products were simultaneously detected and the variation in AOR selectivity depending on the surface conditions was demonstrated. In the low-potential region of 0.40−0.82 V, the adsorbed OH − was the dominant oxygenated surface species. The AOR onset potential was 0.40 V, and the surface intermediates were NH x,ads and N 2 H y,ads , which were the main precursors of N 2 , considered a major product. N 2 H 4 , NO, and NH 2 OH were considered minor products in this potential region. In the high-potential region, from 0.82 V, adsorbed O 2− was the main oxygenated surface species, owing to the strong interactions between OH − and oxidized Pt. We found that NO and N 2 O play a key role as reaction intermediates. Another remarkable result is the detection of HN 3 as a gaseous product. NO 2 , N 2 H 4 , and NH 2 OH were considered the minor products. The nitrite and nitrate detected by IC were solution-phase products of the AOR at high potentials. The real-time identification of seven gaseous products, viz., N 2 , NO, N 2 H 4 , NH 2 OH, HN 3 , N 2 O, and NO 2 , and two solution-phase products, NO 2 − and NO 3 − , enabled us to propose AOR mechanistic pathways, opening more possibilities for the electrochemical generation of high-value-added nitrogenated products depending on Pt surface conditions.

Paulo como parte dos requisitos para a obtenção do título de mestre em ciências. Área de concentração: Físico-Química Orientador: Prof a. Dr a. Joelma Perez São Carlos 2019 ii DEDICATÓRIA Dedico essa dissertação aos meus pais, Waldemar Gastoni Venturini Filho e Célia Inoue Venturini, aos meus irmãos, Yuri Inoue Venturini e Ralf Inoue Venturini, e à Larissa Almeida, pelo grande apoio e pela sua companhia. Gostaria de dedicar também à professora Joelma, pela paciência na orientação е incentivo qυе tornaram possível а conclusão desta dissertação, e a todos os envolvidos. iii AGRADECIMENTOS À Universidade de São Paulo (USP), por propiciar condições para o meu crescimento intelectual e profissional. Às agências financiadoras FAPESP, CNPq pelos reagentes químicos e verbas de pesquisa. Agradeço ao auxílio financeiro por meio da bolsa CAPES. Ao Instituto de Química de São Carlos pelo espaço físico, auxílios e demais serviços fornecidos. À Biblioteca Prof. Johannes Rudiger Lechat pelo suporte. A minha família por todo o apoio. À orientadora Joelma pela paciência, ânimo e entusiasmo e sempre disponível para orientar. À Larissa Almeida, pela grande ajuda em todos os momentos, pela sincera amizade, e pelos grandes momentos que passamos juntos.