Evaluation of Iridium Complex-Based Photocatalytic Hydrogen Generation System for Artificial Photosynthesis Studies

Importance of the Topic

Artificial photosynthesis is a promising route to produce green hydrogen using solar energy and photocatalysts, contributing to carbon neutrality by avoiding CO2 emissions in both fuel use and production.

Objectives and Study Overview

This study evaluates a visible light–responsive photocatalytic hydrogen generation system based on an iridium complex photosensitizer with coumarin ligands and a cobalt catalyst. The performance is assessed in terms of photoreaction quantum yield and photosensitizer stability using Shimadzu instrumentation.

Methodology and Instrumentation

• Sample Composition:
  • Iridium photosensitizer (8 µM)
  • Cobalt reduction catalyst (335 µM)
  • Sodium ascorbate sacrificial reagent (0.1 M)
  • CH₃CN-pH 4.5 acetic acid buffer
• Photon Measurement:
  • Instrument: Lightway Photoreaction Evaluation System
  • Irradiation wavelength: 460 nm
  • Photon flux: 9.0 × 10⁻⁸ einstein/s
  • Measurement intervals: 5 s; durations: 5, 10, 20 min
• Hydrogen Quantitation:
  • Instrument: Nexis GC-2030 gas chromatograph with TCD
  • Carrier gas: Argon (constant linear velocity 30 cm/s)
  • Column: Micropacked ST 2 m × 1 mm I.D.
  • Injection: 200 µL headspace gas, split 1:2, port 150 °C
  • Oven: 35 °C; detector: 260 °C

Used Instrumentation

• Lightway Photoreaction Evaluation System for photon flux measurement
• Nexis GC-2030 with TCD-2030 detector and SPL-2030 injection port
• Micropacked ST column (2 m × 1 mm I.D., df = 10 µm)
• Argon as carrier and make-up gas

Main Results and Discussion

• Absorbed photons and H₂ production show linear correlation, confirming measurement reliability.
• Quantum yield calculations:
  • Φ1 (H₂ molecules per photon): 1.44 %
  • Φ2 (electrons per photon, two electrons per H₂): 2.88 %
• Compared to a literature system (Φ2 = 0.13 % at 446 nm), this system achieves roughly 22-fold higher quantum yield.
• Absorbance at 477 nm decreased by ~5 % over 20 min, indicating moderate photostability of the iridium photosensitizer.

Benefits and Practical Applications

• Accurate assessment of photoreaction quantum yield for artificial photosynthesis research.
• Sensitive H₂ detection using GC-TCD with inert carrier gas.
• Scalable evaluation method supports development of efficient photocatalytic systems for green hydrogen production.

Future Trends and Opportunities

• Design of long-wavelength-absorbing photosensitizers to better utilize solar spectrum.
• Engineering more stable photosensitizer–catalyst assemblies to extend operational lifetimes.
• Integration with solar concentrators or flow reactors for pilot-scale green hydrogen generation.

Conclusion

The combination of the Lightway system and Nexis GC-2030 provides a robust platform for evaluating visible light–driven hydrogen evolution. The iridium–cobalt system demonstrates significantly enhanced quantum yield and acceptable photostability, underscoring its potential in artificial photosynthesis applications.

Reference

1. S. Takizawa et al., Inorg. Chem. 2016, 55, 8723–8735.
2. S. De Kreijger et al., Inorg. Chem. 2022, 61, 5245–5254.