Unveiling the HER potential of TM-substituted PdTe₂ monolayers: a first-principles study

In this study, we utilize density functional theory to study the catalytic capability of a pentagonal PdTe₂ monolayer toward the hydrogen evolution reaction (HER). The pristine PdTe₂ sheet, although structurally stable and semiconducting with a 1.27 eV bandgap, exhibits a high overpotential (1.38 V), indicating limited HER activity. To overcome this limitation, we employed a transition metal substitution strategy by replacing a Pd atom with Mo, Ti, Ru, Ir, and Cr. Among these, Mo and Ti substitutions significantly reduce the overpotential to 50 mV and 90 mV, respectively, values that are comparable to that of Pt (the benchmark HER catalyst), and position them near the peak of the HER volcano plot. Phonon spectra validate the dynamical stability of the pristine and doped systems, while AIMD simulations at 300 K validate their thermal robustness. Total and partial density of states (TDOS/PDOS) and band structure analyses reveal that Mo and Ti substitution induces spin polarization, enhances metallicity, and enhances the density of electronic states at the Fermi level, all of which are favourable for the HER. Furthermore, the work function analysis shows a downward shift after doping, facilitating electron transfer. Kinetic analysis of the HER mechanism reveals that the Volmer step has an activation energy barrier of 0.93 eV, whereas the Tafel step proceeds with a lower barrier of 0.65 eV, highlighting favourable reaction kinetics. These findings suggest that Mo- and Ti-substituted PdTe₂ monolayers are promising candidates for efficient and stable HER electrocatalysts, potentially rivalling noble metal-based systems.