Fig. 2: Structural and compositional characterization of CuWO₄ catalyst.

a XRD pattern. Inset: crystal structure of CuWO₄. b, c XPS spectra of Cu 2p (b) and W 4 f (c). d SEM image. e TEM and atomic-resolution HAADF-STEM image with line profile of the corresponding area. f Atomic structure of CuWO₄ (111) facet.