Design of Catalyst Interfaces for Heterogeneous Dihydrogen Production Manifolds and Incorporation into Photocathode Systems.

Abstract

Engineering solar-powered catalyst systems for fuel production is of critical importance to the advancement of the global energy economy. Heterogeneous catalyst manifolds most promising for photocatalysis are those that boast versatile and cheap, stable components. Huisgen’s 1,3-dipolar cycloaddition (‘click’ chemistry) and π-stacking graphene adsorption systems provide a range of facile methods for electrode-surface modification and catalyst binding to build stable photocathode systems. Prior to this work, CoIII bis(benzenedithiolate) catalysts had been reported as active proton reduction catalysts in homogeneous phase. Due to the novelty of these complexes for use as proton reduction catalysts, no work prior to that reported in this thesis has attempted to heterogenize cobalt bis(dithiolene) catalysts and attach them to semiconductor surfaces. While several hydrogen production catalyst systems had been reported electrostatically adsorbed to graphitic supports, these studies lacked in-depth analysis of the ligand and graphitic support’s effects on catalyst adsorption, activity and retention on the surface. Previous studies have succeeded in functionalizing several semiconductor surfaces (such as silicon) with alkyne or azide groups; however, such modification of gallium-based 3,5-semiconductor systems containing an inherently strong driving force for proton reduction was previously unreported. Finally, previous literature examples of hydrogen production catalysts electrostatically adsorbed on graphene-coated semiconductors were relatively scarce, and were severely outweighed by work on covalent catalyst tethered systems. This work has for the first time heterogenized cobalt bis(dithiolene) complexes, a new class of H2 production catalysts, on graphitic supports and further attached the catalysts to the surface of GaP by means of the graphitic interface. These studies have provided insight into how the catalyst ligand structure and even the type of carbon in the interface can affect catalyst loading, activity and retention on the surface of the support. Initial studies of graphene- and Click-catalyst interfaces on gallium phosphide surfaces reported here represent some of the first examples of such interface development on these materials. These results push the edge of knowledge in solar-to-fuel conversion by expanding possibilities in the design of inexpensive, robust and easily modifiable photocathode systems with interchangeable catalyst and semiconductor components.