Z-scheme overall water splitting on photocatalyst sheet mediated by carbon nanotubes using oxysulfide photocatalyst responsive to long wavelengths

Abstract

Narrow-bandgap photocatalysts enable broad visible-light absorption and, theoretically, should provide high solar-to-hydrogen (STH) energy conversion efficiencies. However, the actual performance of such materials is highly dependent on the design and fabrication of the water-splitting system. In this study, photocatalyst sheets were constructed using the Ga-doped La5Ti2Cu0.9Ag0.1O7S5 (Ga-LTCA, with absorption at λ < 700 nm) as the hydrogen evolution photocatalyst together with BiVO₄ (BVO) as the oxygen evolution photocatalyst, and carbon nanotubes (CNTs) as the electron mediator, employing a cost-effective filtration process. The three components were tightly integrated on a filter paper substrates, allowing the resulting sheets to drive Z-scheme overall water splitting (OWS). Using a two-step Cr2O3 deposition to coat Ga-LTCA/CNTs/BVO sheets was found to prolong the stability of the system at elevated background pressures. Loading of tin-doped indium oxide (ITO) nanoparticles also enhanced the performance of BVO, and increased the Z-scheme OWS activity. The fabricated sheet exhibited an optimal STH efficiency of 0.23% during Z-scheme OWS reaction in pure water without stirring. This work demonstrates the rational assembly of photocatalyst sheet systems incorporating a long-wavelength-responsive oxysulfide photocatalyst with low-cost carbon materials-based mediators and superior co-catalysts loading strategy, highlighting the potential for scalable hydrogen production via photocatalytic OWS.