Mixed-valence iron phosphate: Superhydrophilic multi-plated microflakes towards symmetric supercapacitor

Abstract

Mixed valance state iron phosphate microflakes have been successfully grown by using binder-free, simple, and low-cost chemical bath deposition (CBD) method. Interestingly, grown microflakes embedded with layered flakes platelets are responsible for capillary action to exhibit a superhydrophilic nature. Iron phosphate includes two-oxidation (Fe+2 and Fe+3) states of cation and unique surface architecture that will play important role in the charge storage by providing more redox-active centres which motivated us to employ as liquid configured supercapacitive electrode. To get insight, structural, valence state, surface morphological, and wettability investigations have been performed through XRD, XPS, SEM, HR-TEM, and contact angle measurements. Multilayer hierarchical iron phosphate pseudocapacitive electrode exhibited specific capacitance of 927 F/g and specific capacity of 668 C/g at a 3 mV/s scan rate through cyclic voltammetry and excellent coulombic efficiency through galvanostatic charge-discharge with 96.7% stability at 4000 cycles in KOH electrolyte. First-ever fabricated liquid configured symmetric supercapacitor device based on iron phosphate electrode yield capacitance of 80 F/g and specific capacity of 104 C/g at the scan rate of 10 mV/s with cycling stability of 80% after 2500 cycles forming basis for future practical applications.