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Mechanistic studies in water oxidation catalysis promoted by ruthenium complexes bearing imidazole units

Grant number: 18/03576-4
Support type:Scholarships abroad - Research
Effective date (Start): August 01, 2018
Effective date (End): July 31, 2019
Field of knowledge:Physical Sciences and Mathematics - Chemistry - Inorganic Chemistry
Principal researcher:André Luiz Barboza Formiga
Grantee:André Luiz Barboza Formiga
Host: Javier Concepcion
Home Institution: Instituto de Química (IQ). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
Research place: Brookhaven National Laboratory, United States  
Associated research grant:13/22127-2 - Development of novel materials strategic for integrated analytical devices, AP.TEM

Abstract

World's energetic demands are currently supplied in majority by fossil fuels. Climate change is associated with combustion of these fuels due to CO2 and methane emissions. The cleanest alternative energy source is sunlight that can be used in two ways, either directly producing electric current or promoting a chemical transformation. In this last case, a very promising, clean and sustainable alternative is water splitting into dihydrogen (H2) and dioxygen (O2). These two gases could be further recombined with only one by-product, water. Several challenges persist and one of them is the production of catalysts for the most difficult reaction in the process, the oxidation of water to produce O2. The most studied homogeneous catalysts for this reaction are ruthenium complexes but many aspects of the field still need to be investigated. The understanding of reaction mechanisms would help in the planning of more efficient and robust catalysts. Our proposal aims at answering two fundamental questions: 1) is it possible to achieve a two protons-two electrons RuII/RuIV oxidation with a lower potential than previously observed? If this is achieved, we would expect a much lower O2-evolving potential and this class of ruthenium complexes could be very competitive with the best catalysts known; 2) is it possible to promote ligand-based water oxidation (not on the metal center)? This is a completely new approach to the problem and, if successful, this mechanism could be extended to first row transition metals. To achieve our goal, we will investigate the pH-dependent electrochemistry of five new complexes bearing at least one imidazole unit. Moreover, the mechanism of water oxidation will also be determined by kinetic studies using CeIV as the sacrificial oxidant with O2 monitoring. Besides the spectroscopic methods, theoretical calculations will be used to support experimental data. For that, transition state activation energies will be calculated using DFT with standard methods. With this approach, different pathways will be compared to the experiment. Moreover, the structures of key intermediates will also be studied. Using DFT, theoretical estimates of pKa values and redox potentials will be obtained in order to get insight into the electronic structures of the catalyst in different oxidation/protonation states.

Scientific publications
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
PIRES, BRUNO M.; DOS SANTOS, PAMYLA L.; KATIC, VERA; STROHAUER, STEFAN; LANDERS, RICHARD; FORMIGA, ANDRE L. B.; BONACIN, JULIANO A. Electrochemical water oxidation by cobalt-Prussian blue coordination polymer and theoretical studies of the electronic structure of the active species. DALTON TRANSACTIONS, v. 48, n. 15, p. 4811-4822, APR 21 2019. Web of Science Citations: 2.
MATIAS, TIAGO A.; REIN, FRANCISCA N.; ROCHA, REGINALDO C.; BARBOZA FORMIGA, ANDRE LUIZ; TOMA, HENRIQUE E.; ARAKI, KOITI. Effects of a strong pi-accepting ancillary ligand on the water oxidation activity of weakly coupled binuclear ruthenium catalysts. DALTON TRANSACTIONS, v. 48, n. 9, p. 3009-3017, MAR 7 2019. Web of Science Citations: 0.

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