Surfactant Effects on Hydrogen Evolution by Small-Molecule Nonfullerene Acceptor Nanoparticles

Organic donor:acceptor semiconductor nanoparticles (NPs) formed through the miniemulsion method have been shown to be active photocatalysts. Here, we report photocatalytic hydrogen (H₂) evolution under sacrificial conditions with Pt as a cocatalyst by NPs comprising only the nonfullerene acceptor Y6, stabilized by either sodium dodecyl sulfate (SDS) or the thiophene-containing surfactant 2-(3-thienyl)ethyloxybutylsulfonate sodium salt (TEBS). Typically, changes in the photocatalytic activity of donor:acceptor NPs are associated with differences in morphology due to the use of surfactants. However, as these NPs are single component, their photocatalytic activity has a significantly lower dependence on morphology than two-component donor:acceptor NPs. Results from ultrafast transient absorption spectroscopy show a minor difference between the photophysics of the TEBS- and SDS-stabilized Y6 NPs, with free charges present with either surfactant. The similar photophysics suggest that both TEBS- and SDS-stabilized Y6 NPs would be expected to have similar rates of H₂evolution. However, the results from photocatalysis show that Y6 NPs stabilized by TEBS have a H₂evolution rate 21 times higher than that of the SDS-stabilized NPs under broadband solar-like illumination (400-900 nm). Transmission electron microscopy images of the Y6 NPs show effective photodeposition of Pt on the surface of the TEBS-stabilized NPs. In contrast, photodeposition of Pt is inhibited when SDS is used. Furthermore, the ζ potential of the NPs is higher in magnitude when SDS is present. Hence, we hypothesize that SDS forms a dense, insulating layer on the NP surface which hinders the photodeposition of Pt and reduces the rate of H₂evolution. This insulating effect is absent for TEBS-stabilized Y6 NPs, allowing a high rate of H₂evolution. The TEBS-stabilized Y6 NPs have a H₂evolution rate higher than most single-component organic photocatalysts, signaling the potential use of the Y-series acceptors for H₂evolution in Z-scheme photocatalysis.