Unraveling Activity and Decomposition Pathways of [FeFe] Hydrogenase Mimics Covalently Bonded to Silicon Photoelectrodes

Abstract The presence of molecular monolayers on semiconductor surfaces can improve the stability of semiconductor interfaces by inhibiting the growth of native oxides and defects which affect the materials’ electronic properties. The development of catalytically active passivated interfaces on semiconductor materials presents a useful material design for value‐added product conversion. Herein, an iron‐based catalyst covalently attached to silicon (Si) is reported for the investigation of activity and electrochemical decomposition pathways of diiron hydrogenase enzyme mimics. The employed catalyst, Fe₂(CO)₆(µ‐S‐C₆H₄‐p‐OH)₂ ([FeFe]), mimics the active sites of these enzymes. Surface modification using this catalyst passivates the interface, hindering the formation of native SiO₂ for more than 300 h. [FeFe] modification improves the overpotential required to produce 10 mA cm^–2 by 100 mV, with a hydrogen evolution rate of 2.31 × 10^–5 mol h^–1 cm^–2 (−0.78 V versus RHE). However, structural rearrangement transpires within 1 h of electrolysis, where Fe‐S bond dissociates at the catalytic center, resulting in an aromatic linkage modified Si interface. While semiconductor−catalyst interfaces have often been reported in the literature, their decomposition pathways have received limited discussion. Herein, this Si−[FeFe] interface is used as a tool for understanding the activity and decomposition mechanisms of the attached molecular catalyst.