Fig. 5: Changes in valence states and composition after the electrochemical stress test at pH = 0.

a High resolution XPS core-level spectra of Sb 3d/O 1 s, Sn 3d, Mo 3d, and W 4 f after the 500 CV test at different pH in the electrolyte, pH = 0 (open squares), pH = 1 (open circles), and pH = 2 (open triangles). b Schematic representation of the change in the MO composition after the electrochemical stress test at pH = 0.