Pentagonal PdTe2 Monolayer for Sustainable Solar-driven Hydrogen Production

This investigation demonstrates that the pentagonal PdTe$_2$ (penta-PdTe$_2$) monolayer is a highly tunable two-dimensional (2D) photocatalyst, characterized by a bandgap of 1.87~eV and high hole mobility. Using density functional theory (DFT) calculations with the HSE06 functional, we show that tensile strain engineering, particularly at $+2%$ and $+3%$, is essential for enabling spontaneous water splitting. At these strain values, the valence-band maximum (VBM) and conduction-band maximum (CBM) straddle the water redox potentials ($\mathrm{H^+/H_2}$ and $\mathrm{O_2/H_2O}$) under both acidic ($\mathrm{pH}=0$) and neutral ($\mathrm{pH}=7$) conditions. The monolayer's low hole effective mass facilitates rapid charge extraction, mitigating electron--hole recombination and promoting the oxygen evolution reaction (OER) more effectively than many hexagonal and pentagonal counterparts. The Gibbs free energy ($\Delta G$) pathways indicate that the overpotentials for the hydrogen evolution reaction (HER) and OER are highly sensitive to mechanical deformation, specifically biaxial strain. In particular, a tensile strain of $+3%$ yields an optimized balance of overpotentials, with $\eta_{\mathrm{HER}} = 0.70~\mathrm{V}$ at $\mathrm{pH}=0$ and $\eta_{\mathrm{OER}} = 0.72~\mathrm{V}$ at $\mathrm{pH}=7$. Finally, integrating optical absorption with thermodynamic driving forces results in a solar-to-hydrogen (STH) efficiency of $20.40%$ at $\mathrm{pH}=7$. This performance exceeds that of several previously reported two-dimensional catalysts, positioning penta-PdTe$_2$ as a superior candidate for sustainable, solar-driven hydrogen production.