Surface reconstruction engineering of twinned Pd2CoAg nanocrystals by atomic vacancy inducement for hydrogen evolution and oxygen reduction reactions

•Co addition increases atomic vacancies of Pd2Ag twinned interface and forms oxygen vacancies on CoOx surface.•Synergistic effect of surface atomic vacancies and metal twinned interfaces of v-Pd2CoAg tunes its surface charge-density distribution electrocatalysts.•v-Pd2CoAg possesses remarkable high HER and ORR catalytic activity and stability.•Unsaturated metal sites for O or H activation are simultaneously produced, resulting in great increase in activity.