Tungsten Sulfide Decorated One-Dimensional Sb₂S₃ Photoanode Combined with Iodide Oxidation Reaction for Bias-Free Solar Fuel Generation

The unassisted solar fuel photosynthesis using photoelectrochemical (PEC) configuration composed of photocathode and photoanode has emerged as a promising technology to solve both of energy crisis and environmental contamination. However, the lack of competitive photoanodes, which is ascribed to inferior light harvesting and suboptimal charge separation/injection characteristics of photoabsorbers constituting photoanodes, has been paramount barrier for efficient unbiased solar fuel production system. The one-dimensional (1D) nanostructured photoabsorber can be rational methodology to improve light absorption <i>via</i> complex morphological property that allow light scattering as well as superior electron-hole separation ability by employing the favorable crystallographic direction. Along with these beneficial optoelectronic capabilities, the mesoporous 1D nanostructure promotes charge carrier injection to electrolyte <i>via</i> large surface area, and the passivation strategy that alleviate surface trap states further elevates the extraction of photo-induced holes from photoelectrode to electrolyte by repressing charge carrier recombination.<br/><br/>Herein, we demonstrate solution-processed 1D Sb₂S₃ nanorod arrays deposited on substrate modified by Au seed layer. This Au seed layer modulate the interaction between molecules in precursor solution and substrate, resulting in self-orientated crystalline structure. Moreover, the (NH₄)₂WS₄ treatment was performed on the surface of Sb₂S₃ nanorod-based absorber, resulting in formation of WS_x layer which passivates surface states distributed on surface of photoabsorber. The resulting photoanode (denoted as WS-1D Sb₂S₃) was used to enable an iodide oxidation reaction (IOR), a prominent alternative to sluggish oxygen evolution reaction, revealing a photocurrent density of nearly 10 mA cm^–2 at 0.6 V versus the reversible hydrogen electrode. Afterwards, by coupling WS-1D Sb₂S₃ photoanode with perovskite-based photocathode in a parallel illumination configuration, the unbiased solar-to-hydrogen conversion device was afforded, exhibiting a solar to hydrogen conversion efficiency of 2.95% without external bias along with the stability of 2 h. Our study demonstrates the feasibility of unbiased solar fuel generation device using IOR on Sb₂S₃-based photoanode with facile morphology control and a surface passivation process.