Synthesis, characterization, and photo-catalytic activity of homogeneous molybdenum sulfide complexes serving as hydrogen evolution catalysts
Description
In Chapter 1 an overview of the field of water reduction catalysis is given, with an introduction to the concept of photo-catalytic water splitting. A background of the current research on molecular catalysts is also described. An introduction to the project is made detailing the approach to studying the molybdenum sulfide catalysts that were synthesized, characterized, and analyzed for this work. Chapter 2 describes in detail the synthesis and characterization of all the molybdenum sulfide complexes that were made. Initially looking at [Mo3S13]2- and later synthesizing derivatives of the type [Mo3S7(S2CNR2)3]+, [Mo3S4(S2CNR2)3]+, and [Mo3S4(S2CNR2)4]0 were successful. These complexes were characterized using 1H NMR, MALDI-TOF-MS, electronic absorption, and elemental analysis. A new ligand (S2CNiBu2) was also prepared for the synthesis of [Mo3S7(S2CNiBu2)3]+ complex. Chapter 3 lists all the crystal structures that were obtained for the ligands and metal complexes in this work. Metal complexes were purified using various crystallization techniques and identified and characterized. Starting from [Mo3S7(S2CNR2)3]+ complex type, the series included R = Et, Me, iBu, and 3,5-tBu(C6H3). A unique double cluster crystal structure was obtained after photolysis of [Mo3S7(S2CNiBu2)3]+ in the photosystem. The last set of four structures was found for the complex [Mo3S4(S2CNEt2)4]. Chapter 4 describes all the electro-chemical experiments and characterizations for all the metal complexes that were studied. Using cyclic voltammetry provided a starting point for understanding the behavior of these catalysts in catalytic experiments. Spectro-electrochemistry observes changes to the complexes during reductive processes and was used to test stability of the catalysts following reduction. Lastly, bulk electrolysis was used to test the electro-catalytic capability of the [Mo3S7(S2CNR2)3]+ catalysts. It was found that electrolysis at the second reduction potential yielded the highest faradaic yield for hydrogen. Chapter 5 introduces and describes the various types of photo-systems used in the field of photo-catalysis. Initial photo-catalytic experiments showed moderate activity of the [Mo3S13]2- and improvement was observed after preparing complexes of the type [Mo3S7(S2CNR2)3]+. Combining photolysis and MALDI-TOF-MS analysis revealed a transformation from the [Mo3S7(S2CNR2)3]+ cluster to [Mo3S4(S2CNR2)3]+ cationic complexes. After synthesizing and testing [Mo3S4(S2CNR2)3]+ and [Mo3S4(S2CNR2)4]0 species, they were not as efficient at generating hydrogen.