Structures of copper and halide (chloride, bromide or iodide) in a sulfuric acid solution on Pt(111), Pt(100) and Au(111) single-crystal electrode surfaces were systematically investigated by in-situ scanning tunneling microscopy. A (4 X 4) structure was imaged after the first cathodic current peak for Cu + Cl on Pt(111). Distorted (4 x 4) and (root 3 x root 3)R30 degrees structures were found after the first and the second peaks, respectively, for Cu + Br on Pt(111). For Cu + I on Pt(111), a (root 3 x root 3)R30 degrees structure was observed after the copper deposition peak. A c(2 x 2) structure was obtained for Cu + Cl, Cu + Br and Cu + I on Pt(100). On a Au(111) surface, a (5 X 5) structure was observed for Cu + Cl after both the first and the second cathodic current peaks. For Cu + Br on Au(111), (root 7 X root 7)R19.1 degrees was found after the first peak, and (4 x 4) structures were imaged after both the second and third peaks. A (3 X 3) image was obtained for Cu + I after a single peak on Au(111). Structural models for the copper and the halide layers are discussed based on the adsorbate-substrate interaction at these surfaces. Coadsorption structures on platinum surfaces are understandable as those of halide adsorption on a pseudomorphic copper (1 X 1) layer on platinum, while on Au(111) the coadsorption layer is interpreted as an ultrathin crystal of CuX(X = Cl, Br, I).