Display omitted •We propose a new concept of healing catalyst film made of passivating additives and high catalytic activity building blocks.•Defects passivation is achieved by strong adsorption of Mo (oxo)- thio monomers on the defects of the photoactive substrate.•Catalytic activity arises from polynuclear Mo oxo-thio complexes included in the Mo oxo thio complexes distribution.•H2 generation with photocurrents up to 2 nmA cm-2 are achieved on 2D WSe2 photocathodes using this healing catalyst film. 2D semiconducting nanosheets of Transition Metal Dichalcogenides are attractive materials for solar energy conversion because of their unique absorption properties. Here, we show that Mo thio- and oxo-thio-complexes anchored on 2D p-WSe2 nanosheets considerably boost water splitting under visible light irradiation with photocurrent density up to 2.0 mA cm−2 at -0.2 V/NHE. Besides developing high electro-catalytic activity, the Mo-complexes film is also shown to be capable of healing surface defects. We propose that the observed healing of surface defects arises from the strong adsorption on point defects of the 2D WSe2 substrate of Mo complexes such as (MoS4)2-, (MoOS3)2-, (Mo2S6O2)2- as supported by DFT calculations. In addition, the thio-, oxo-thio Mo complexes films are shown to enhance charge carrier separation and migration favouring the hydrogen evolution reaction, putting forward the use of thio-, oxo-thio-Mo complexes as a multicomponent passivation layer exhibiting multiple properties.