Zbynek Novotny -Department of Physics, University of Zurich, Winterthurerstrasse 190, Zurich, 8057, Switzerland, E-mail: zbynek.novotny@pnnl.gov Molybdenum sulfide serves as an effective non-precious metal catalyst for hydrogen evolution, primarily active at edge sites with unsaturated molybdenum sites or terminal disulphides. To improve the activity at low loading density, two molybdenum sulfide clusters, [Mo3S4] 4+ and [Mo3S13] 2-, were investigated. The Mo3Sx molecular catalysts were heterogenized on Sb2Se3 with a simple soaking treatment, resulting in a thin catalyst layer of only a few nanometers that gave up to 20 mA cm -2 under one sun illumination. Both [Mo3S4] 4+ and [Mo3S13] 2-exhibit catalytic activities on Sb2Se3 through a simple soaking process, with [Mo3S13] 2-emerging as the superior catalyst, demonstrating enhanced photovoltage and average faradaic efficiency of 100% for hydrogen evolution. This superiority is attributed to the effective loading and higher catalytic activity of [Mo3S13] 2-on the Sb2Se3 surface, validated by X-ray photoelectron and Raman spectroscopy.