NiFe-LDH and PPy-reinforced PVA conductive hydrogels for all-in-one high-performance supercapacitors

Abstract

The quasi-solid-state flexible supercapacitor has been successfully built by freezing-thawing method and in-situ polymerization. The high redox activity nickel-iron layered double hydroxide (NiFe-LDH) provides certain pseudocapacitance, interacts with high conductivity reduced graphene oxide (RGO), and avoids the activity structural collapse and agglomeration. Polyvinyl alcohol (PVA) serves as a flexible framework with uniform cross-linking between the components, facilitated by the presence of abundant hydrogen bonds. Polypyrrole (PPy) is further polymerized in-situ into PVA/RGO/NiFe-LDH to improve its electrochemical performance and flexibility. The PVA/RGO/NiFe-LDH0.40/PPy hydrogel electrodes exhibit a high area specific capacitance of 729 mF/cm2 at 1 mA/cm2. The elongation at break of the electrodes is up to 749 %, which reflects excellent tensile properties. The quasi-solid-state flexible supercapacitor has been built using PVA/H2SO4 as the gel electrolyte and PVA/RGO/NiFe-LDH0.40/PPy as the electrodes. The device exhibits a high energy density of 15.9 µWh/cm2 at a power density of 0.19 mW/cm2 and the capacitance retention of 96.7 % after 10,000 charge-discharge cycles.