Hydrogen-Evolution Reaction in Two-Dimensional PdS2 by Phase and Defect Engineering

The hydrogen-evolution reaction is an essential step in the electrochemical production of hydrogen without the emission of greenhouse gases. For this reaction, alternative catalyst materials that can replace the platinum of current catalysts are needed. Recent alternatives include two-dimensional materials such as transition metal dichalcogenides. Here, we show the electronic and electrochemical properties of the two-dimensional material palladium disulfide (${\mathrm{Pd}\mathrm{S}}_{2}$) with two crystal structures (phases) and the formation of native point defects. We analyze the differences between the pentagonal ($P$-${\mathrm{Pd}\mathrm{S}}_{2}$) phase and the octahedral ($1T$-${\mathrm{Pd}\mathrm{S}}_{2}$) phase, point defects and the Gibbs free energies for hydrogen adsorption from first-principles calculations. Our results show that the $1T$-${\mathrm{Pd}\mathrm{S}}_{2}$ phase has better catalytic activity than the $P$-${\mathrm{Pd}\mathrm{S}}_{2}$ phase in the pristine basal plane. In addition, the point defects of lower formation energy in the $1T$-${\mathrm{Pd}\mathrm{S}}_{2}$ phase, the $S$ vacancies, further improve the catalytic activity for hydrogen production.