Fig. 4: The lattice distortion of WO₃ nanosheets under various electrolytes.

a Transport energy barrier of the embedded K⁺ ions across the different layers of WO₃ nanosheets from surface to subsurface to bulk, showing that the transport energy would rapidly rise when K⁺ ions are inserted into the first and second layers. b XRD patterns of the coloured WO₃ with various thicknesses embedded with H⁺ (left panel), Li⁺ (middle panel), and Na⁺ (right panel) ions, displaying that thinner nanosheets inserted with smaller anode ions produce more radical phase transitions. c iDPC images of the coloured H_xWO₃ (left panel), Li_xWO₃ (middle panel), and Na_xWO₃ (right panel) nanosheets with a thickness of 15 nm, demonstrating that the embedded H⁺, Li⁺, and Na⁺ ions (as revealed by red circles) induce the lattice distortion of the corner-sharing connected WO₃ structures to form polarons, respectively. d Effect of the radius of ions on the crystal symmetry and band gap, showing that the symmetry-dependent band gap is reduced under the electrolyte with smaller anode ions.