Inhibition of Photocatalyst-Assisted Electron Transfer at ITIES Under Simulated Solar Irradiation-the Role of Supporting Electrolyte

Photocatalyst-assisted charge transfer at the interface between two immiscible electrolyte solutions (ITIES) has been previously proven. However, its practical application requires information on its performance under solar irradiation. We investigated photocatalyst-assisted oxidation of water at ITIES under solar irradiation using TCNQ 7,7,8,8-Tetracyanoquinodimethane (TCNQ) as electron scavenger and bis(triphenylphosphoranylidene) ammonium tetrakis(4-chlorophenyl)borate (BTPPA-TPBCl) as organic phase electrolyte. No enhancement of water oxidation after assembling photocatalyst nanoparticles at the ITIES was observed. Photocurrents with photocatalyst were similar to those without but in the presence of TCNQ. Photocurrents observed both with and without photocatalyst are shown to be due to photogeneration of TCNQ⋅⁻, either by reaction with the organic electrolyte or by interfacial oxidation of water. The former dominates at positive potentials and results in a positive photocurrent due to transfer of TCNQ⋅⁻ across the ITIES. The latter dominates at negative potentials and results in a negative photocurrent. Electron paramagnetic resonance (EPR) detected TCNQ⋅⁻ and revealed its stabilisation by formation of an adduct with BTPPA⁺, which must contribute to making the photoactivity of TCNQ the dominant process even with photocatalyst. These findings highlight the necessity of research on alternative suitable electron scavenger-supporting electrolyte combinations for implementing ITIES in the photoelectrocatalytic conversion of solar energy.