Probing the surface sensitivity of dimethyl ether oxidation on epitaxially-grown PtRh(1 0 0) alloys: Insights into the challenge of improving on Pt(1 0 0)

•PLD was employed to achieve epitaxial growth of (1 0 0) PtRh alloys on MgO(1 00 ).•XRD pole figures confirm the cube-on-cube growth of the alloy film.•Rh-rich alloys feature the earliest onset for electrochemical CO oxidation.•DME oxidation activity typical of Pt(1 0 0) is rapidly lost as %Rh increases.•(Sub)surface Rh induces an anticipation of the onset of DME oxidation.