Ruthenium (Ru) is one of the most promising metals for its versatility in driving a wide range of catalytic reactions.However,owing to the intrinsic preference of hexagonal close-packed (hcp) phase for bulk Ru,currently,it is still challenging to construct Ru-based nanomaterials with face-centered-cubic (fcc) phase for optimizing their performance towards potential applications.Herein,we report a facile wet-chemical method to directly create unconventionalfcc-structured Ru-copper hollow urchin-like nanospheres (fcc-RuCu HUNSs) as a class of efficient pH-universal hydrogen evolution reaction (HER) electrocatalyst.In-terestingly,this synthetic strategy can be expanded to prepare otherfcc-Ru-based alloy nanomaterials.Significantly,the novel fcc-RuCu HUNSs exhibit superior HER performance with the overpotential of only 25,34,40,and 26 mV to reach the current density of 10 mAcm-2 in 0.5 M H2SO4,0.05 M H2SO4,0.1 M KOH,and 1 M KOH,respectively,much lower than those of hcp-RuCu HUNSs and commercial Pt/C.Density functional theory (DFT) calculations further indicate that their excellent pH-universal HER performance results from the optimized adsorption free energy of H and work functions.Our work highlights the importance of phase control to design high-efficiency nanocatalysts for relevant catalytic reactions in energy conversion.