| Summary: | The well-defined heterostructure of the photocathode is desirable for photoelectrochemically producing hydrogen from aqueous solutions. Herein, enhanced heterostructures were fabricated based on typical stable covalent organic framework (TpPa-1) films and TiO<sub>2</sub> nanotube arrays (NTAs) as a proof-of-concept model to tune the photoelectrochemical (PEC) hydrogen generation by tailoring the photoelectrode microstructure and interfacial charge transport. Ultrathin TpPa-1 films were uniformly grown on the surface of TiO<sub>2</sub> NTAs via a solvothermal condensation of building blocks by tuning the monomer concentration. The Pt<sub>1</sub>@TpPa-1/TiO<sub>2</sub>-NTAs photoelectrode with single-atom Pt<sub>1</sub> as a co-catalyst demonstrated improved visible-light response, enhanced photoconductance, lower onset potential, and decreased Tafel slope value for hydrogen evolution. The hydrogen evolution rate of the Pt<sub>1</sub>@TpPa-1/TiO<sub>2</sub>-NTAs photoelectrode was five times that of Pt<sub>1</sub>@TpPa-1 under AM 1.5 simulated sunlight irradiation and the bias voltage of 0 V. A lower overpotential was recorded as 77 mV@10 mA cm<sup>−2</sup> and a higher photocurrent density as 1.63 mA cm<sup>−2</sup>. The hydrogen evolution performance of Pt<sub>1</sub>@TpPa-1/TiO<sub>2</sub>-NTAs photoelectrodes may benefit from the well-matched band structures, effective charge separation, lower interfacial resistance, abundant interfacial microstructural sites, and surficial hydrophilicity. This work may raise a promising way to design an efficient PEC system for hydrogen evolution by tuning well-defined heterojunctions and interfacial microstructures.
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