In the pursuit of alternative fuel sources, many researchers are investigating the storage and conversion of solar energy. Hydrogen gas is one forerunner as a storage medium due to its high energy density and its ability to be produced by splitting water molecules, a process requiring 1.23 eV, or a wavelength of ~1000 nm. Most of the sunlight reaching earth contains enough energy to drive this thermodynamically uphill process. Typically, photocatalytic water splitting systems consist of multiple components, namely a light absorbing molecule working in conjunction with the catalyst. Dirhodium complexes of the type [Rh2(μ-form)2(L)2]2+ (form = formamidinate; L = chelating diimine dpq, dppz, or dppn) proposed herein are able to absorb visible light, giving rise to a triplet metal-centered state in which electron density is on the axial σ* orbital on a rhodium center. This reactive excited state is believed to be involved in the formation of an axial hydride from protons in solution, and the resulting species represents an intermediate in the catalytic cycle to leads to hydrogen evolution. Therefore, catalysis in this system in accomplished by a single component. To study potential complexes for photocatalytic water splitting, electrochemical techniques such as cyclic voltammetry (CV) may be used to help uncover details of the catalytic mechanism and intrinsic properties of the catalyst. By increasing the concentration of acetic acid and analyzing the catalytic response in the CV, it was determined that the reaction is second order with respect to proton concentration at low equivalents of acetic acid, and independent of proton concentration at high equivalents. In the acid independent regime, turnover frequencies (TOF) of ­­­3.5 – 4.0 x 104 s-1 were calculated, establishing the reactive nature of this Rh2II,II architecture. This work has been generously funded by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences (contract no. DE-SC0010542).

Formamidinate bridged dirhodium complexes as a single component photocatalytic hydrogen evolution system

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.