Conjugated Linkers Improve the Photoelectrocatalytic H₂‐Evolution Activity of Cobaloxime‐Modified Silicon Photocathodes by Largely Suppressing Charge Recombination

Abstract

For molecular catalyst‐modified semiconductor hybrid photoelectrodes, the linker that tethers a molecular catalyst to an electrode surface is one of the important structural factors to influence the photoelectrocatalytic (PEC) H2‐evolution activity of the photoelectrode. A better understanding about the impact of different linkers on charge transfer kinetics of hybrid photoelectrodes will shed light on the design of more efficient photoelectrodes for the selected molecular catalyst and semiconductor. In this work, a series of cobaloxime catalysts, CoPy‐4‐L‐HA (CoPy = cobaloxime; HA = hydroxamate anchor; L = none, CH2, CHCH, and (CHCH)2), are immobilized to the surface of p‐Si|TiO2 with different linkers. Comparative studies on PEC performance of these hybrid photocathodes reveal that the p‐Si|TiO2|CoPy‐4‐(CHCH)2‐HA) electrode exhibits the highest PEC activity among the tested photocathodes, despite the longer linker of (CHCH)2 compared to other ones. The j(0 V) of −0.68 mA cm−2 for p‐Si|TiO2|CoPy‐4‐(CHCH)2‐HA is higher than those reported for planar Si‐based photocathodes decorated with molecular catalysts. The impacts of the length and conjugation property of linkers on the kinetics of surface charge transfer and recombination are probed by transient absorption spectroscopy, and the results well clarify the origin for the disparity in the PEC activities of p‐Si|TiO2|CoPy‐4‐L‐HA photocathodes with different linkers.

Synthesis and Surface Attachment of Molecular Re(I) Complexes Supported by Functionalized Bipyridyl Ligands

“…In particular, covalent attachment via the modification of the ancillary ligand(s) of the complex often leads to robust attachment of the catalyst to the solid support, but this strategy requires synthetic modification of the ligand to facilitate immobilization, which can be challenging . Additionally, rigorous studies exploring how the nature of the attachment group affects catalyst performance or stability are uncommon, which means that it is difficult to rationally choose a functional group for catalyst immobilization . The development of simple synthetic routes to common ancillary ligands that contain different functional groups for covalent surface attachment would be valuable, as these ligands could then be bound to a variety of different complexes and the catalytic performance and stability of immobilized systems could be evaluated across many reactions.…”