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

Abstract

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 x and Au25) by such a solid-state nonconductive polymer via a conceptually new chemistry strategy by which l-glutathione (GSH)-capped gold (Au x @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 x (Au25) NC layers concurrently serves as an unexpected charge-transfer mediator to foster the unidirectional electron flow from Au x (Au25) NCs to MOs by forming a tandem charge-transfer chain, hence endowing the multilayered MO/(PDDA-Au x ) n 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.

Tuning atomically precise metal nanocluster mediated photoelectrocatalysis via a non-conjugated polymer

“…Our previous work on solid-state non-conjugated polymers has indicated that the solar-to-current conversion efficiency of semiconductors can be significantly improved by judiciously harnessing PEs as the intermediate charge mediator to craft unidirectional vectorial charge transport pathways in photoelectrochemical (PEC) cells. 33 In this case, the PEs not only act as a molecular binder to enable LbL assembly, but also facilitate enhanced charge transfer without causing detrimental defects. 34–37 This inspired us to rationally design tunable charge transport pathways between atomically precise metal NCs and semiconductors in heterostructured photoelectrodes for PEC water splitting with the assistance of PEs.…”

Unleashing non-conjugated polymers as charge relay mediators

“…Polyelectrolytes (PEs), which are dened as polymers with positively or negatively charged properties in repeating monomeric units, 22,23 have been extensively utilized as surface charge modiers to fabricate spatially multilayered multi-dimensional nano-architectures in a precise, controllable and exquisite manner at the nanoscale level. [24][25][26][27] In these ways, PEs mainly play a crucial role as self-assembly initiators, by which oppositely charged building blocks are well organized into well-dened heterostructures. However, utilizing PEs that are mainly composed of non-conjugated polymers as the carrier mediator to regulate the vectorial charge transport pathways has so far not yet been reported in terms of their intrinsic insulating properties in the solid state.…”

Solar-Powered Photocatalysis and Photoelectrocatalysis over Atomically Precise Metal Nanoclusters

“…This is heavily dependent on the elaborate interface engineering and constructing metal NCs-involved composite photocatalysts or photoelectrodes to achieve regulated charge transfer of metal NCs. As demonstrated in our recent work, 52 tailor-made atomically precise metal NCs, [e.g., Au x @GSH NCs, Au 25 (GSH) 18 NCs] were alternately integrated with the ultrathin polyelectrolyte (PDDA) interim layer on the metal oxides (MOs: TiO 2 , WO 4a). In this well-defined multilayered heterostructure, the intermediate PDDA layer functions as an unexpected interfacial charge mediator to regulate the carriers transport over metal NCs from the LUMO level to the CB of MOs substrates in a tandem charge transfer fashion (Figure 4, parts b and c).…”

“…(a) Schematic illustration of the PEC water oxidation mechanism of MOs–[PDDA–Au x (Au 25 )@GSH] n multilayered heterostructure. LSV (scan rate: 5 mV s –1 ) curves of WO 3 –(PDDA–Au x ) 2 , WO 3 –(Au x ) 2 , WO 3 –(PDDA) 2 , and WO 3 NPAs under (b) simulated solar light (AM 1.5G) and (c) visible light (λ > 420 nm) irradiation using Na 2 SO 4 (0.5 M, pH = 6.69) aqueous solution as the electrolyte . Reprinted with permission from ref .…”