Sodium Dodecyl Sulfate-Adjusted Phase Composition of Hydrated Tungsten Oxides as Stable Self-Supporting Electrodes...

High pseudocapacitive activity of hydrated tungsten oxides (WO₃·xH₂O, x = 1 or 2) makes them promising materials for supercapacitors (SCs). During their synthesis, additives such as complexing agents and surfactants generally can only affect the morphology and/or size of the products. Here, we demonstrate that not only morphology and size of WO₃·xH₂O were affected, its phase composition could also change from WO₃·2H₂O to WO₃·H₂O simply by increasing the amount of sodium dodecyl sulfate (SDS) during its anodization synthesis. To the best of our knowledge, such a phenomenon has not been reported before. In addition, SDS introduced a special structure to the products, i.e., WO₃·xH₂O nanoplatelets constructed from nanoparticle multilayers with abundant nanogaps between the multilayers, which further arranged into nanoflowers with increased amounts of SDS. Benefiting from such a structure, low internal resistance, enhanced stability, and fast redox kinetics, the as-obtained WO₃·xH₂O/W-3 self-supporting electrode showed a high volumetric specific capacitance of 1402.92 F cm^-3 and good cycling stability (a capacity retention of 106% after 10 000 cycles). In addition, an all-solid-state asymmetric SC device based on WO₃·xH₂O/W-3 delivered high a volumetric energy density of 44.0 mW h cm^-3 at 0.5 W cm^-3. Our method demonstrates a potential way to fabricate excellent self-supporting electrodes for SCs.