Surfactant Effects on Hydrogen Evolution by Small Molecule Non-Fullerene Acceptor Nanoparticles

Abstract

Organic donor:acceptor semiconductor nanoparticles (NPs) formed through the miniemul- sion method have been shown to be active photocatalysts. Here we report photocatalytic hydrogen (H2) evolution under sacrificial conditions with Pt as a co-catalyst by NPs comprising only the non-fullerene 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 H2 evolution. However, the results from photocatalysis show that Y6 NPs stabilized by TEBS have a H2 evolution 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 zeta 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 H2 evolution. This insulating effect is absent for TEBS-stabilized Y6 NPs, allowing a high rate of H2 evolution. The TEBS-stabilized Y6 NPs have a H2 evolution rate higher than most single-component organic photocatalysts, signaling the potential use of the Y-series acceptors for H2 evolution in Z-scheme photocatalysis.