Efficient catalysts for water oxidation: synthesis, characterization and computational study

Identifier:  TDX:4315

Handle: https://hdl.handle.net/20.500.11797/TDX4315

Authors:  Azmani Oualite, Khalid

Abstract:
Storage energy into chemical bonds has become nowadays the primary key to make possible the transition from carbon dependency to renewable (i.e., solar or wind) energy solving the intermittency of this. Water splitting involves storing of the energy in H2 and O2. However, the oxidation reaction of water to O2 is a bottleneck in this process. This Thesis cover the international challenge of deeply understanding of water oxidation and search for an efficient, robust, and inexpensive heterogeneous catalysts. We have focused on the use of already described polyoxometalates (POMs) as water oxidation catalysts at different pH. We have synthesized, characterized, and evaluate their catalytical activity. We have confirmed the stability and integrity of the catalysts by performing a pre and post catalytic characterization. First, we have deeply studied the Co-containing polyoxometalate in acidic media by exploring structure, composition and nuclearity through a series of Cobalt-POM incorporated into carbon paste electrodes as insoluble salts of Cs+ and Ba2+. Then we have moved to evaluate POM based on the most abundant and cheapest transition metal (Iron). We have focused on the tetrairon Weakley sandwich [(FeIIIOH2)2FeIII2(PW9O34)2]6- (Fe4P2W18) as is isostructural of tetracobalt Weakley sandwich one of the most extensively studied Co-POMs. We have started evaluating the catalytic activity in the neutral media confirming true catalyst and faradaic efficiency. Then we have investigated the reaction mechanism employing computational methods to understand the different catalytic performance of Co-POM. Finally, we want to test the robust character of POM in acidic media in the carbon paste environment, we have evaluated Fe4P2W18 as water oxidation catalyst in acidic media to determine the pH effect. Effectively, we could confirm the stability of the Fe-POM. Surprisingly, our results show a low faradaic efficiency which we could relate to a competitive reaction to water oxidation based on carbon oxidation.