A Heterostructure Photoelectrode Based on Two-Dimensional Covalent Organic Framework Film Decorated TiO 2 Nanotube Arrays for Enhanced Photoelectrochemical Hydrogen Generation.

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 2 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 2 NTAs via a solvothermal condensation of building blocks by tuning the monomer concentration. The Pt 1 @TpPa-1/TiO 2 -NTAs photoelectrode with single-atom Pt 1 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 1 @TpPa-1/TiO 2 -NTAs photoelectrode was five times that of Pt 1 @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 -2 and a higher photocurrent density as 1.63 mA cm -2 . The hydrogen evolution performance of Pt 1 @TpPa-1/TiO 2 -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.