Monomeric (VO2+) and dimeric mixed valence (V2O33+) vanadium species at the surface of shape controlled TiO2 anatase nano crystals

•The coordination of vanadyl species on the different facets of TiO2 anatase is resolved.•Tetrahedrally coordinated vanadyl ions at the TiO2(101) surface and square pyramidal vanadyls at the (001) termination are identified by DFT.•The existence of dinuclear V4+-O-V5+ mixed valence structures is confirmed by ENDOR/HYSCORE techniques.•17O surface enrichment provides insights in the metal-oxide bond interaction through 17O hyperfine interactions.