Design, Synthesis, and Analysis of Molecular Photoelectrochemical Ligand Design (2015)

Undergraduates: Rebecca McCoy, Kate Pitman

Faculty Advisor: Alexander Miller
Department: Chemistry

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Production of hydrogen from light-driven water splitting is an attractive method to store solar energy for later use. One method for hydrogen evolution is photoelectrochemical water-splitting. Typically, photoelectrocatalytic systems require an expensive high purity semiconductor light absorber (e.g. silicon) and a hydrogen producing catalyst (e.g. platinum). When the light hits the semiconductor, an electron is promoted to the conduction band. The electron is then transferred to the platinum, which catalyzes the formation of the H-H bond and reproduces the catalyst. The Miller group recently discovered a semiconductor-free approach to photoelectrochemical hydrogen evolution with a single homogeneous photoelectrocatalyst, [Cp*Ir(2,2¿¿¿-bipyridine)(H)]+ (Cp* = pentamethylcyclopendienyl). To better understand this approach to hydrogen production, the limits of this system have been explored by seeing how structural changes to the catalyst affect reactivity. Replacing bpy changes the characteristics of the catalyst and understanding the behavior of structurally different ligands will inform future catalyst design. Complexes containing bis(pyridine), di(2-pyridyl)ketone, and various alpha-diimine ligands have been synthesized and studied using electrochemical techniques such as cyclic voltammetry and cyclic amperometry under irradiation. A new catalyst, [Cp*Ir(pyridine)2(Cl)][OTf], was discovered for molecular photoelectrochemical hydrogen evolution.