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

• Published in: Advanced materials interfaces Vol. 8; no. 10
• Main Authors: Williams, Nicholas B., Nash, Aaron, Yamamoto, Nobuyuki, Patrick, Margaret, Tran, Ich C., Gu, Jing
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01.05.2021
• Subjects: Catalysts; Decomposition; decomposition mechanism; Electrolysis; Hydrogen evolution; hydrogen evolution reaction; Hydrogenase; Interface stability; Interfaces; Iron; molecular monolayer catalysts; photoelectrochemical conversion; Semiconductor materials; semiconductor surface modification; Silicon dioxide; Surface stability
• DOI: 10.1002/admi.202001961
• ISSN: 2196-7350

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. A derivative of the diiron hydrogenase active center, Fe2(CO)6(µ‐S‐C6H4‐p‐OH)2 ([FeFe]), is covalently bound to a silicon interface for photoelectrochemical hydrogen evolution. Using surface sensitive techniques, the organometallic catalyst is found to degrade via Fe−S bond dissociation with the aromatic linkage still intact on the silicon interface.