Photocatalytic Hydrogen Generation by Vesicle‐Embedded [FeFe]Hydrogenase Mimics: A Mechanistic Study

Abstract

Artificial photosynthesis—the direct photochemical generation of hydrogen from water—is a promising but scientifically challenging future technology. Because nature employs membranes for photodriven reactions, the aim of this work is to elucidate the effect of membranes on artificial photocatalysis. To do so, a combination of electrochemistry, photocatalysis, and time‐resolved spectroscopy on vesicle‐embedded [FeFe]hydrogenase mimics, driven by a ruthenium tris‐2,2′‐bipyridine photosensitizer, is reported. The membrane effects encountered can be summarized as follows: the presence of vesicles steers the reactivity of the [FeFe]‐benzodithiolate catalyst towards disproportionation, instead of protonation, due to membrane characteristics, such as providing a constant local effective pH, and concentrating and organizing species inside the membrane. The maximum turnover number is limited by photodegradation of the resting state in the catalytic cycle. Understanding these fundamental productive and destructive pathways in complex photochemical systems allows progress towards the development of efficient artificial leaves.

Supramolecular strategies in artificial photosynthesis

“…These effects were further investigated in the group of Woutersen and Reek. 119 In their system the hydrophobic hydrogenase mimic as HEC was fully embedded within the membrane layer ( Fig. 28 ).…”

Mechanistic Insights into the Charge Transfer Dynamics of Photocatalytic Water Oxidation at the Lipid Bilayer–Water Interface

“…Important efforts have been dedicated to achieving artificial photosynthesis by mimicking natural photosynthesis using supramolecular systems, such as micelles, , liposomes, − polymers, − and metal–organic frameworks. , In liposomes, amphiphilic lipid molecules constituting the bilayer are oriented with their polar head groups toward the inner and outer aqueous solutions, while the hydrophobic chains form a nonpolar region between the two interfaces (see Scheme ). In such systems, the bulk solution, the interface, and the membrane core are characterized by distinct dielectric constants, which offers opportunities to prearrange redox-active sites and modify chemical reaction rates and mechanisms, compared to homogeneous conditions. ,− After pioneering but rare reports in the 1980s, several reports about photocatalytic water oxidation in liposomes have recently appeared.…”

Interfacial Characterization of Ruthenium-Based Amphiphilic Photosensitizers

“…Surfactants represent an incredibly rich class of molecules, some of which include a metal center in the polar head. , Recently, new molecules of that type have been introduced where the metal head provides a catalytic or light-harvesting function. For example, amphiphiles with light-absorbing or catalytic properties have been prepared to realize photocatalytic water oxidation or CO 2 reduction at soft interfaces, with a perspective to produce solar fuels. , Initially, these molecules have been designed to support the different components of a photocatalytic system onto liposomes. − More recently, they have also been considered for the building of photocatalytic soap films and monolayers, because the escape of O 2 , H 2 , or CO 2 -reduction products such as CO or CH 4 is easier at a water–gas interface than inside a liquid …”