Photosystem I-inspired artificial cell for catalytic hydrogen production driven by lanthanum(III) tungstate

Abstract

Some photosynthetic organisms, including cyanobacteria and green algae, use photosystem-I (PSI) electrons to reduce H⁺ ions into H₂ molecules (light-to-chemical energy conversion mediated by hydrogenase enzymes). Innovative artificial photosynthesis technologies have been proposed to overcome important limitations of this natural process (e.g., enzyme inactivation and competing reduction reactions), but they still demand more efficient, stable, and low-cost electrode materials as progress requirements. This article addresses a series of physicochemical features and properties of lanthanum(III) tungstate – La₂(WO₄)₃, demonstrating great potential to produce H₂ in a PSI-inspired photoelectrochemical cell. La₂(WO₄)₃ was prepared by hydrothermal synthesis, resulting in American football-like structures with high surface area and well-ordered crystalline arrangement. This p-type semiconductor was also susceptible to photoexcitation (E_gap = 4.05 eV) by ultraviolet radiation, boosting the hydrogen evolution reaction (HER) kinetics after its immobilization on Nafion®/fluorine-doped tin oxide glass substrate (NF/FTO). Using La₂(WO₄)₃/NF/FTO as a reactor photocathode, the generated and accumulated electrons move towards its surface, facilitating energetically unfavorable reduction reactions, such as HER. Regarding the device performance in 0.1 mol L^‒1 Na₂SO₄ (pH = 11 at 25 °C), an appreciable reaction yield (150 mL h^‒1 cm^‒2) was obtained, provided by the low overpotential (η = ‒0.41 V to reach 10 mA cm^‒2) and high exchange current density (j₀ = 2.89×10⁻⁵ mA cm⁻²) achieved, although it can be made even better by using SO₃^2‒ as a sacrificial reducing agent (192 mL h^‒1 cm^‒2). Not least, this research still supports the rational design of (photo)electrochemical cells developed for energy conversion and/or related processes.