The　use　of　high-valent　metal　compounds　as　efficient　electrocatalysts　for　the　hydrogen　evolution　reaction　(HER)　is　rare.　Herein,　we　report　that　in　situ　electrochemical　activation　is　an　effective　strategy　to　achieve　outstanding　catalytic　activity　of　TiO2-coated　Co3O4　nanowires　(TiO2@Co3O4)　in　the　alkaline　HER.　The　activated　TiO2@Co3O4　affords　a　current　density　of　20　mA　cm−2　at　a　relatively　small　overpotential　(49　mV),　a　performance　that　is　superior　to　that　of　commercially　available　Pt/C　(20%)　and　those　of　most　electrocatalysts　for　the　alkaline　HER.　＇Pseudo　in　situ＇　spectral　characterization　and　density　functional　theory　calculations　suggest　that　the　in　situ　reduction　of　Co　during　the　HER　results　in　interstitial　Co　defects　(Coi)　in　the　TiO2.　In　the　activated　TiO2@Co3O4,　water　dissociation　is　efficient　at　the　Co3O4/TiO2　interface,　the　Coi　defects　promote　the　desorption　of　the　intermediate　hydroxyl　groups　from　the　TiO2,　and　the　Tafel　step　is　exothermic　on　Co3O4.　Several　steps　of　the　HER　process　are　therefore　energetically　favorable　with　activated　TiO2@Co3O4.　The　strategy　of　TiO2　coating　and　in　situ　electrochemical　activation　is　also　shown　to　promote　the　alkaline　HER　activity　of　Co(OH)2　©　2022　The　Royal　Society　of　Chemistry