Constructing an Electron Highway: Steering Charge Flow in Organic/Inorganic S-Scheme Heterojunctions for Efficient Solar-Driven Photocatalytic Hydrogen Production

Abstract

Developing low-cost and highly efficient S-scheme heterojunction photocatalysts is still a significant challenge towards enhancing the activity of photocatalytic hydrogen evolution (PHE). This study created an S-scheme heterojunction by in situ growing inorganic Al-doped SrTiO₃ (ASTO), which possesses superior oxidation capability, on a substrate of the covalent organic framework (TpPa-1-COF), which has great reduction capacity, using a solvothermal method. With the advantages of stronger redox capacity, quicker electron transport, and more potent carrier separation, the optimal 5% ASTO/TpPa-1 S-scheme heterojunction achieved remarkable photocatalytic performance in ascorbic acid (AsA) solution when exposed to simulated solar light, with a hydrogen production rate of 4.12 mmol g^-1 h^-1, which is 14.2 and 11.4 times higher than that of pure TpPa-1 and ASTO, respectively. This performance outperforms most recently reported SrTiO₃-based and TpPa-1-COF-based heterojunctions under similar conditions. Notably, an intense interfacial internal electric field (IEF) in ASTO/TpPa-1 heterojunction was formed resulting from the free electron consumption in TpPa-1 and accumulation in ASTO, which could speed up the transfer dynamics of photoinduced electrons from the conduction band (CB) of ASTO to the valence band (VB) of TpPa-1 via an interfacial electron-transfer channel that follows the directed S-scheme migration process. Moreover, the direction of the IEF is from TpPa-1 to ASTO, which could accelerate charge separation and migration, thereby prolonging the lifetimes of charge carriers. The dynamic behavior of photoinduced carriers was confirmed by femtosecond transient absorption spectroscopy (fs-TAS). Overall, this study provides valuable guidance for the rational design of an innovative organic/inorganic hybrid S-scheme heterojunction.

Keywords

Al-doped SrTiO₃ / covalent organic framework / photocatalytic hydrogen production / S-scheme heterojunction

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