Enhanced Water Splitting Using a Densely Structured Dendritic Bismuthinite Photoanode with FeOOH Cocatalyst

Solar water splitting is a promising method for sustainable hydrogen production, but current systems suffer from efficiency limitations. Bismuth sulfide (Bi₂S₃), a semiconductor with desirable optical properties and a suitable band gap for water oxidation, has drawn considerable interest for its potential. Despite various approaches, including organic- and inorganic-based heterostructures and plasmonic enhancement, the efficiency of Bi₂S₃-based photoelectrodes remains below the theoretical maximum, primarily due to severe charge recombination and sluggish surface reactions. This study addresses these issues through morphology engineering and surface functionalization. A densely packed dendritic Bi₂S₃ photoanode, obtained from an electrochemically deposited bismuth metal sacrificial structure, exhibited enhanced light absorption, while decoration with an ultrathin layer of an oxyhydroxide cocatalyst further contributed to efficiency by improving surface reaction kinetics. After these modifications, the photocurrent of the Bi₂S₃/FeOOH photoanode increased 1.7 times from 2.2 mA·cm^-2 (1.23 V vs RHE) to 3.7 mA·cm^-2 compared to the pristine Bi₂S₃. The solar energy conversion efficiency showed a 3-fold increase at low bias potentials, and its photon-to-current conversion efficiency improved 1.5-fold (32-48% @ 600 nm). This work underscores the importance of the morphology and surface modifications in advancing the efficiency of photoanodes for solar water splitting.