Phosphate ion and oxygen defect-modulated nickel cobaltite nanowires: a bifunctional cathode for flexible hybrid supercapacitors and microbial fuel cells

Abstract

The exploration of efficient and cost-effective cathodes for flexible hybrid supercapacitors (HSCs) and microbial fuel cells (MFCs) is highly desirable but challenging.

Harvesting Electricity by Harnessing Nature: Bioelectricity, Triboelectricity, and Method of Storage

“…Supercapacitors are prized for their high power densities but deliver lower energy densities than batteries. Hence, many researchers have focused on enhancing supercapacitor energy densities via enormous advances in nanostructured materials and functional electrolytes [61][62][63][64][65][66][67][68][69][70][71]. Also, current collector flexibility and conductivity are critical to achieving high energy densities in flexible supercapacitors.…”

“…Moreover, cost-effective novel device manufacturing techniques have been adopted to provide good architectural flexibility. Hence, proper selection of electroactive materials and current collectors can be combined with smart design of device structures and fabrication methods to substantially affect the energy densities of supercapacitors [61][62][63][64][65][66][67][68]. In 2014, Yang et al developed a cost-effective, high-performance, solid-state flexible ASC by assembling α-MnO2 nanowires (NWs) and amorphous Fe2O3 nanotubes (NTs) on a flexible carbon fabric with a PVA-LiCl gel electrolyte [61].…”

“…In 2015, Chen et al achieved a high energy density of 99.26 Wh kg -1 by developing a flexible all-solid-state ASC that used carbon clothsupported NiMoO4/PANI and active carbon (AC) electrodes and a PVA-KOH gel electrolyte [63]. In 2016, Qiu et al prepared a flexible, high-energy-density (3.6 × 10 −2 mWh•cm −2 ) solid-state ASC by sandwiching Dacron cloth-supported Cu(OH)2 nanobelt arrays (positive electrode) between two carbon nanofiber (CNF) matrices (negative electrodes) and using KOH-PVA as the gel electrolyte [64]. In 2017, Zhu et al achieved a high energy density of 46 Wh kg -1 by developing wearable, high-performance symmetric supercapacitors (SSCs) based on silver-sputtered textiles using a FeCo2S4-NiCo2S4 composite and PVA-KOH gel electrolyte [65].…”

“…To enhance supercapacitor energy densities, substantial efforts have been made to fabricate hybrid supercapacitors (HSCs) by developing high-performance battery and supercapacitor materials [64,68]. For instance, in 2020, Zhao et al fabricated a carbon clothsupported flexible HSC by combining NiCoP nanoflake-surrounded CNT nanoarrays (NiCoP/CNT) with N-doped, carbon-coated CNT nanoarrays (CNT@N-C) as battery-type and supercapacitor electrode materials, and applying a PVA-KOH gel electrolyte [68].…”

“…The as-developed flexible HSC device exhibited a high energy density of 138.7 Wh kg −1 , which is clearly superior to those of recently developed ASC or SSC devices and indicates potential for practical application. Recently, Qiu et al synthesized a flexible, solid-state HSC composed of phosphate ions, an oxygen-deficient modulated nickel cobaltite nanowire (PNCOx NW) cathode, an as-prepared 3D porous graphene gel (3DPG) anode, and a PVA-LiCl gel electrolyte [64]. The as-fabricated PNCOx//3DPG-HSC exhibited a relatively high maximum energy density of 211 W h kg −1 , which is better than recently reported SSC and ASC devices and batteries [61][62][63][64][65][66][67]69,70].…”