Design flexible LuH3 monolayer as an efficient water-splitting photocatalyst across a broad light spectrum

Abstract

Photocatalytic water splitting has attracted extensive attention for its bright prospects in producing clean hydrogen energy. To realize efficient solar-to-hydrogen energy conversion, it is important to explore a photocatalyst with high electron–hole separation and wide-range solar absorption. Herein, a novel two-dimensional metal-hydride, LuH₃, is designed and its viability as an efficient photocatalyst for overall water splitting is evaluated in the present work. It reveals that LuH₃ monolayer is an isotropic semiconductor with a direct band gap of 2.56 eV, decreased to 1.872 eV in a bilayer, exhibiting strong absorption efficiency for ultraviolet, visible, and near-infrared regions. Besides, it has favorable valence and conduction band positions for water redox reactions of O₂/H₂O and H${}^{+}$${}^{+}$/H₂, high carrier mobility, and significant charge separation capability due to the orientation-dependent distribution in band edges, which play vital roles to enhance photocatalytic performance. The higher partial charge densities on H${}_{1b}$${}_{1b}$ and H${}_{2d}$${}_{2d}$ in HOMO lead to a more potent oxidation reaction, facilitating the reduction reaction and the production of hydrogen. In particular, LuH₃ monolayer is flexible and sensitive to external stress. Applying both isotropic and uniaxial strain has a limited impact on achieving favorable band alignments with water redox potentials, providing distinct opportunities for various applications. In both acidic and alkaline environments, LuH₃ monolayer shows significant potential for efficient photocatalysis in the context of overall water splitting. Furthermore, LuH3, a van der Waals material, can exfoliate from multilayered or bulk forms with a cleavage energy of 1.07 J/m², which is three times higher than the experimentally measured 0.37 J/m² for graphite. These findings highlight the potential of LuH₃ monolayer as an efficient solar-spectrum water-splitting photocatalyst, with implications for sustainable energy conversion technologies utilizing solar energy for clean and renewable hydrogen fuel generation.