Unexpected Boosted Solar Water Oxidation by Nonconjugated Polymer-Mediated Tandem Charge Transfer

Conjugated polymers are deemed as conductive carrier mediators for engendering the π electrons along the molecular framework, while the role of nonconjugated insulated polymers has been generally overlooked without the capability to participate in the solar-powered oxidation-reduction kinetics and charge-transfer process. Alternatively, considering the ultrashort charge lifetime and significant deficiency of metal nanocluster (NC)-based photosystems, the fine tuning of charge migration over atomically precise ultrasmall metal NCs as novel light-harvesting antennas has so far not yet been unleashed. Here, we unlock the charge-transfer capability of a nonconjugated polymer to modulate the charge flow over metal NCs (Au and Au₂₅) by such a solid-state nonconductive polymer via a conceptually new chemistry strategy by which l-glutathione (GSH)-capped gold (Au@GSH) NCs and poly(diallyl-dimethylammonium chloride) (PDDA) were alternately self-assembled on the metal oxide (MO: WO₃, Fe₂O₃, and TiO₂) substrates. The ultrathin nonconjugated PDDA interim layer periodically intercalated in-between Au (Au₂₅) NC layers concurrently serves as an unexpected charge-transfer mediator to foster the unidirectional electron flow from Au(Au₂₅) NCs to MOs by forming a tandem charge-transfer chain, hence endowing the multilayered MO/(PDDA-Au) heterostructures with significantly boosted photoelectrochemical water oxidation performance under light irradiation. The unanticipated role of PDDA as a cascade charge mediator is demonstrated to be universal. Our work would unlock the potential charge-transport capability of nonconjugated polymers as a novel charge mediator for solar-to-chemical conversion.