Incorporating metal Co into CoMoO4/Co2Mo3O8 heterointerfaces with rich-oxygen vacancies for efficient hydrogen evolution catalysis.

• The CoMoO 4 /Co 2 Mo 3 O 8 with rich-oxygen vacancies (V o) incorporated by Co nanoparticles is designed. • The Co@CoMoO 4 /Co 2 Mo 3 O 8 -V o is helpful for H* adsorption and interfacial electron transferring. • The vacancies can optimize the binding energy of intermediates on CoMoO 4 /Co 2 Mo 3 O 8 interfaces. • The Co@CoMoO 4 /Co 2 Mo 3 O 8 -V o shows excellent HER electrocatalytic performance. Realizing synergetic effect of multiple factors is critical to develop an optimal catalyst. Bimetallic oxides have shown great potential for catalytic hydrogen evolution from water splitting in alkaline media because their oxygen species are beneficial for water adsorption and can get unique d electron configurations to optimize the binding strength of intermediates. Here bimetallic oxide heterointerface CoMoO 4 /Co 2 Mo 3 O 8 with rich-oxygen vacancies (V o) incorporated by the monodisperse small-size cobalt (Co) nanoparticles (Co@CoMoO 4 /Co 2 Mo 3 O 8 -V o) is designed for hydrogen evolution reaction (HER) in alkaline media. The charge redistribution occurs at the CoMoO 4 /Co 2 Mo 3 O 8 interface because of incorporation of Co, and this will be helpful for H* adsorption and interfacial electron transferring. Meanwhile, the rich-oxygen vacancies can well optimize the binding energy of intermediate species on CoMoO 4 /Co 2 Mo 3 O 8 interface and thus will facilitate the sluggish HER in alkaline media. Because of the synergistic effects of metallic Co, CoMoO 4 /Co 2 Mo 3 O 8 interfaces and rich-oxygen vacancies, the Co@CoMoO 4 /Co 2 Mo 3 O 8 -V o catalyst shows superior electrocatalytic activity for HER in alkaline media with a low overpotential of 60 mV at 10 mA cm−2, a small Tafel slop of 52 mV dec-1, and excellent durability with ∼ 2% degradation after 24 h test. This work will provide a new strategy to enhance HER catalytic performance of bimetallic oxides in alkaline media. [ABSTRACT FROM AUTHOR]