The metal-nanocluster-catalyzed hydrogen evolution through water splitting has received great interest in the implementation of the hydrogen economy. However, the general and efficient production of well-defined and ligand-free metal nanoclusters (NCs) with precise sizes for efficient hydrogen evolution in various electrolytes remains a formidable challenge. We report here on the synthesis of well-distributed and ligand-free metal NCs (Rh, Ru, Ir) with monodispersity using nitrogen-doped hollow carbon spheres (NHCSs) as support matrices. The metal NCs (MNCs) with diameters less than 2.0 nm (1.97 ± 0.57 nm for Rh NCs, 1.48 ± 0.45 nm for Ru NCs, and 1.34 ± 0.69 nm for Ir-NCs) are evenly distributed over NHCSs. Among the catalysts, Rh / NHCS show not only excellent electrocatalytic activity for the hydrogen evolution reaction (HER) (10 mV in 0.5 M H2SO4, 7 mV in 1.0 M PBS and 6 mV in 1.0 M KOH), but also high stability and long run-time stability over the entire pH range, which outperforms commercial Pt / C and most of the previously reported results. This catalyst can now be used for HER in natural seawater with high activity, stability and long-term stability. This work proposes a simple and effective method for the production of highly dispersed MNCs with high performance for the pH-universal water / seawater splitting.