Unbiased Photoelectrochemical Solar Fuel Generation Enabled by Antimony Trisulfide Photoanode Based on Iodide Oxidation Reaction

The traditional photoelectrochemical (PEC) tandem configuration of hydrogen evolution reaction and oxygen evolution reaction (OER) is limited by thermodynamic and kinetic barriers. Iodide oxidation reaction (IOR) is a promising alternative to OER due to its low thermodynamic energy and two-electron-involved fast reaction kinetics. Herein, we report a high-performance catalyst-modified Sb₂S₃ photoanode to drive IOR. A compact thin-film-type Sb₂S₃ absorber is fabricated via solution processing based on a thorough understanding of the molecular interaction in the precursor ink state. Moreover, the deposition of multilayered catalyst RuO₂ nanosheet and polydiallyldimethylammonium chloride not only efficiently enhances the charge transfer kinetics but also passivates the surface defects of the Sb₂S₃ absorber. The resulting photoanode exhibits a remarkable photocurrent density of 10 mA cm^-2 at 0.6 V compared to the reversible hydrogen electrode in hydroiodic acid. In conclusion, we demonstrate a bias-free PEC tandem device based on a RuO₂-modified Sb₂S₃ photoanode paired with a silicon photocathode, yielding a record-high operation current density of 4 mA cm^-2, which is equivalent to 5% solar-to-hydrogen conversion efficiency in a water splitting device.