Interplay between Light Flux, Quantum Efficiency, and Turnover Frequency in Molecular-Modified Photoelectrosynthetic Assemblies

We report on the interplay between light absorption, charge transfer, and catalytic activity at molecular-catalyst-modified semiconductor liquid junctions. Factors limiting the overall photoelectrosynthetic transformations are presented in terms of distinct regions of experimental polarization curves, where each region is related to the fraction of surface-immobilized catalysts present in their activated form under varying intensities of simulated solar illumination. The kinetics associated with these regions are described using steady-state or pre-equilibrium approximations yielding rate laws similar in form to those applied in studies involving classic enzymatic reactions and Michaelis-Menten-type kinetic analysis. However, in the case of photoelectrosynthetic constructs, both photons and electrons serve as reagents for producing activated catalysts. This work forges a link between kinetic models describing biological assemblies and emerging molecular-based technologies for solar energy conversion, providing a conceptual framework for extracting kinetic benchmarking parameters currently not possible to establish.