Metastable Phase Engineering of Core@Shell RuFe@Ru for Boosting Hydrogen Evolution.

Phase engineering and the construction of core-shell structures of noble nanomaterials are powerful strategies for regulating their functional properties. In this work, we operated phase engineering on a catalyst with a core@shell structure, where the core is a metastable face-centered-cubic (fcc) RuFe alloy and the shell is metastable Ru (fcc RuFe@fcc Ru). Corresponding characterizations and electrochemical analyses reveal that the catalytic performance is highly dependent on both the core@shell structure and the crystal phase. fcc RuFe@fcc Ru delivers a superior hydrogen evolution reaction (HER) performance compared to the hexagonal-close-packed (hcp) phase with a core@shell RuFe@Ru structure (hcp RuFe@hcp Ru) and hcp RuFe alloy (hcp RuFe). Density functional theory calculations reveal that both the core@shell structure and the metastable fcc phase effectively modulate the adsorption strength of intermediate species, leading to a reduction in the reaction free energy of the thermodynamically most unfavorable reaction step, thereby enhancing the HER performance.