Crystal phase can greatly affect the physicochemical properties and applications of nanomaterials.However,it still remains a great challenge to synthesize nanostructures with the same composition and morphology but different phases in order to explore the phase-dependent properties and applications.Herein,we report the crystal phase-controlled synthesis of PtCu alloy shells on 4H Au nanoribbons (NRBs),referred to as 4H-Au NRBs,to form the 4H-Au@PtCu core-hell NRBs.By tuning the thickness of PtCu,4H-PtCu and face-centered cubic (fcc) phase PtCu (fcc-PtCu) alloy shells are successfully grown on the 4H-Au NRB cores.This thickness-dependent phase-controlled growth strategy can also be used to grow PtCo alloys with 4H or fcc phase on 4H-Au NRBs.Significantly,when used as electrocatalysts for the ethanol oxidation reaction (EOR) in alkaline media,the 4H-Au@4H-PtCu NRBs show much better EOR performance than the 4H-Au@fcc-PtCu NRBs,and both of them possess superior performance compared to the commercial Pt black.Our study provides a strategy on phase-controlled synthesis of nanomaterials used for crystal phase-dependent applications.