“Inverse strain effect in atomic scale”—Enhanced hydrogen evolution activity and durability in Cu-substituted palladseite

Abstract

Since the preceding decade, strain engineering has been playing a vital role in modifying the activity of electrocatalysts. Incorporation of tensile strain into a Pd-based system usually requires substitution with larger atoms (usually a third row expensive transition metals). This work provides a unique strategy of introducing tensile strain by the substitution of small and low cost copper atoms (inverse strain effect) at the palladium sites of Pd₁₇Se₁₅. The Pd atom being in the +2 oxidation state adsorbs hydrogen very weakly, and Se, in its elemental state, binds weakly to H* adsorbate. However, the presence of Pd modulates the electronic structure of Se to have ΔG_H* close to 0 and favors the progress of the reaction. Cu substitution further lowers ΔG_H*, thus favoring the reaction. This unique synergistic effect between the two processes is accountable for better activity, high stability of 30 000 cycles and significantly high turnover frequency of 126.3 s^–1 for (CuPd)₁₇Se₁₅.