Over the last four decades, the field of molecular water oxidation catalysis has witnessed a tremendous progress improving the catalytic performance up to six orders of magnitude higher than the first reported molecular catalyst. Despite the success, there are still several challenges that need to be addressed in order to transfer the high catalytic activity into efficient water splitting devices.

The present doctoral thesis focuses on some of these challenges, such as lowering the working potential of the water oxidation process. For this purpose, a series of homogeneous Ruthenium based catalysts have been prepared with different ligand scaffolds containing one or two anionic carboxylates group that are able to reduce the overpotential for water oxidation all the way to 500 mV. In addition, the factors that rule their performance and mechanistic pathways for the reaction have been studied in detail.

Another challenge is to transfer the high catalytic activity of homogeneous catalysts into solid supports with the ultimate goal of building powerful devices in the field of artificial photosynthesis. The second half of the thesis focuses on the design of highly active catalysts that are suitable for attachment to conductive supports. In this line, a large family of Ruthenium based mononuclear, oligomeric and coordination polymers with different arrays have been prepared. All these molecules and materials have been used to prepare molecular electroanode for the water oxidation reaction obtaining current densities up to 0.3 A/cm² at E = 1.45 V at pH 7, which are in the range of commercial electrolyzers but working in a much milder conditions. These results open a new avenue of opportunities in the design of new and efficient water splitting devices.