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.