Molecular Ir-Based Coordination Compound Grafted onto Covalent Organic Framework for Efficient Photocatalytic H2 Evolution

The urgency of reducing pollution and developing clean energy storage requires efficient photocatalytic hydrogen evolution (PHE) tactics. To improve solar conversion efficiency, it is highly imperative to accelerate the photocarriers separation and transport through materials design. A stable hydrogen evolution photocatalyst based on TpPa-COFs (triformylphloroglucinol phenylenediamine covalent organic frameworks) was developed by a molecular-level design strategy. The study successfully introduced a molecular-scale Ir active site onto the surface of TpPa-COFs via coordination bonds. It verified the structural integrity of TpPa-COFs and the existence of Ir through the basic structural characterizations, such as Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). After the Ir-based coordination compound joining, the absorption edge of TpPa-COF-M1 and TpPa-COF-M2 was extended to 750 nm. The TpPa-COF + M1 exhibited the highest photocatalytic H₂ evolution rate of 662 µmol/h (10 mg catalyst) under visible-light (λ ≥ 420 nm) irradiation. The apparent quantum yield (AQY) of TpPa-COF-M1 is calculated to be 1.9%, 3.8%, 4.8%, 2.8%, 1.8%, and 0.3% at monochromatic wavelengths of 420, 450, 470, 500, 550, and 600 nm, respectively. Our findings confirm that the molecular-level design of photocatalysts can effectively boost performance and reduce cost in photocatalytic reactions and provide an important strategy for designing efficient photocatalysts.