Potassium metal

A homogenously ground mixture of WO₃ powder (0.5 g; Sigma-Aldrich, Milwaukee, WI, USA), potassium metal (0.39 g; Sigma-Aldrich, Milwaukee, WI, USA), naphthalene (1.28 g; Sigma-Aldrich, Milwaukee, WI, USA), and tetrahydrofuran (10 mL; Sigma-Aldrich, Milwaukee, WI, USA) was reacted for 3 h. During the reaction, K⁺ intercalated into layers of bulk WO₃ and expanded the bulk of WO₃. The intercalated compounds of WO₃ were stirred and sonicated in NMP (30 mL; Sigma-Aldrich, Milwaukee, WI, USA) for 30 min at 10 °C and 40~50 °C for the exfoliation of large and small WO₃ nanosheets, respectively. In theory, increased energy has the potential to enhance the fragmentation of atomic layers, leading to a significant reduction in the lateral size of the nanosheets [25 ]. Exfoliation achieved through gentle stirring at a low temperature can prevent in-plane damage, resulting in the formation of larger nanosheets in the solution [26 (link)]. Following centrifugation at 1500 rpm for 30 min, a uniformly dispersed yellowish supernatant containing exfoliated WO₃ nanosheets was collected by discarding the precipitate of unexfoliated WO₃ nanosheets. For comparison, the exfoliated WO₃ powder in NMP without intercalation was also prepared. The corresponding preparation process is illustrated in Figure 1.