Bifuntional Materials Containing Preyssler‐type Polyoxometalates and Iron Phenanthroline Stabilized with Poly (Allylamine Hydrochloride) for Electrochromic Energy Storage Devices

Abstract Electrochromic supercapacitors have received extensive attention owing to their ability to combine electrochromism and energy storage properties. In this paper, a bifunctional electrode material based on Preyssler‐type tungstophosphate (P 5 W 30 ), polyelectrolyte poly(allylamine hydrochloride) chain (PAH) modified by the iron complex (Fe(phen) 3 ) was synthesized by Layer‐by‐Layer method (LbL). Compared with the film without PAH, the composite film displays large optical contrast (35.17 %), fast response time (2.49/0.90 s for coloring/bleaching), great coloration efficiency (94.73 cm 2 ⋅ C −1 ) and high specific capacitance (10.45 mF cm −2 ). Moreover, the good cycling stability (83.66 % retention of the original optical modulation after 1500 cycles, capacity retention rate is 91.46 % after 500 cycles) is achieved. In addition, the composite film is also able to visually detect the energy storage level through reversible and rapid color changes, and further use it to assemble device. This work provides an promising candidate for electrochromic and energy storage devices.