Highly Crystalline Mesoporous Phosphotungstic Acid: A High-Performance Electrode Material for Energy-Storage Applications.

Heteropoly acids (HPAs) are unique materials with interesting properties, including high acidity and proton conductivity. However, their low specific surface area and high solubility in polar solvents make them unattractive for catalytic or energy applications. This obstacle can be overcome by creating nanoporosity within the HPA. We synthesized mesoporous phosphotungstic acid (mPTA) with a spherical morphology through the self-assembly of phosphotungstic acid (PTA) with a polymeric surfactant as stabilized by KCl and hydrothermal treatment. The mPTA nanostructures had a surface area of 93 m2  g-1 and a pore size of 4 nm. Their high thermal stability (ca. 450 °C) and lack of solubility in ethylene carbonate/diethyl carbonate (EC/DEC) electrolyte are beneficial for lithium-ion batteries (LIBs). Optimized mPTA showed a reversible capacity of 872 mAh g-1 at 0.1 A g-1 even after 100 cycles for LIBs, as attributed to a super-reduced state of HPA and the storage of Li ions within the mesochannels of mPTA.