PANI/MoO3-x shell-core composites with enhanced rate and cycling performance for flexible solid-state supercapacitors and electrochromic applications

Polyaniline (PANI) as a bi-functional electrode material for electrochemical energy storage and electrochromism demonstrates potential applications in developing integrated and flexible energy storage devices due to its high theoretical specific capacitance, mechanical flexibility and multicolored changes. However, the buried active sites and the structural failure caused by volume expansion/contraction during charge-discharge cycles reduce its rate performance and cycling stability. In this work, PANI/molybdenum oxide with oxygen vacancies (PANI/MoO3-x) shell-core structure composites were synthesized by a facile in situ oxidative polymerization method in which PANI nanorods were uniformly grown on the surface of MoO3-x nanobelts to promote the charge transmission and minimize the volume change of PANI. The ratio-optimized PANI/MoO3-x-2 exhibits specific capacitances of 606 F g(-1) at 1 A g(-1) and 424 F g(-1) even at 20 A g(-1), superior to the previous PANI-based or MoO3-based composites. Moreover, PANI/MoO3-x-2 presents 80.1% capacitance retention after 2000 cycles and the optical contrast of 33% at a wavelength of 732 nm, showing good cycling and electrochromic performance. The assembled PANI/MoO3-x-2//PANI/MoO3-x-2 flexible solid-state supercapacitor with the PVA/H2SO4 gel electrolyte displays relatively higher energy/power density than the reported PANI or metal oxide-based flexible symmetric supercapacitors. Furthermore, the flexible solid-state supercapacitor does not show the obvious capacitance loss after 100 bending cycles of 180 degrees, demonstrating good flexibility. The PANI/MoO3-x shell-core composites show great potential in flexible and electrochromic energy storage devices.