Oxysulfide semiconductor, Y2Ti2O5S2, has recently discovered its exciting potential for visible-light-induced overall water splitting, and therefore, imperatively requires the probing of unknown fundamental charge loss pathways to engineer the photoactivity enhancement. Herein, transient diffuse reflectance spectroscopy measurements are coupled with theoretical calculations to unveil the nanosecond to microsecond time range dynamics of the photogenerated charge carriers. In early nanosecond range, the pump-fluence-dependent decay dynamics of the absorption signal is originated from the bimolecular recombination of mobile charge carriers, in contrast, the power-law decay kinetics in late microsecond range is dominated by hole detrapping from exponential tail trap states of valence band. A well-calibrated theoretical model estimates various efficiency limiting material parameters like recombination rate constant, n-type doping density and tail-states parameters. Compared to metal oxides, longer effective carrier lifetime ~6 ns is demonstrated. Different design routes are proposed to realize efficiency beyond 10% for commercial solar-to-hydrogen production from oxysulfide photocatalysts.

A semitransparent Ta3N5 photoanode is designed for efficient and durable solar water splitting. The Ta3N5-CuInSe2 tandem device exhibits an initial and stabilized solar-to-hydrogen efficiency of ∼9% (highest for metal oxides/nitrides) and 4%, respectively.

High-performance solar-water-splitting technologies are of paramount interest for the cost-effective generation of hydrogen fuel; however, their realization is majorly limited by the poor solar light absorption and charge separation inside photoanode semiconductors. Herein, we develop photoanodes made from polycrystalline tantalum nitride nanorods (Ta 3 N 5 NRs) to overcome the above-mentioned challenges. The morphology and crystalline properties of Ta 3 N 5 NRs are optimized by tuning essential parameters of glancing angle deposition and nitridation techniques, respectively. Under a simulated AM1.5G solar spectrum, the photoanodes demonstrate a tremendous gain in photocurrent from 1.54 mA cm −2 to 10.96 mA cm −2 at 1.23 V versus reversible hydrogen electrode for water oxidation activity. Photoluminescence, transient diffuse reflectance spectroscopy, and theoretical analyses identify prominent factors (like charge carrier lifetime, diffusion length, etc.) responsible for the enhanced performance. Our work presents the significance of designing the narrow-energy band-gap photoanodes with broad implications toward efficient solar-water-splitting devices for green hydrogen production.

Y2Ti2O5S2, a stable oxysulfide photocatalyst with a bandgap energy of 1.9 eV, has been studied for the purpose of H2 production via sunlight-driven water splitting. Although this material absorbs a...

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