Semiconducting cobalt tungstate flanked by carbon (CoWO4@C) polyhedral microstructures with smooth facets and zinc
ferrite
(ZnFe2O4) polydisperse interconnected nanoparticles
via intrinsic mechanisms of hole polaron transfer from Co3+ to Co2+ sites and electron hopping between Fe2+ and Fe3+ states, respectively, were endowed with high
room-temperature electrical conductivities (>0.9 mS cm–1), thus enabling the fabrication of a high-performance asymmetric
supercapacitor (ASC) possessing an outstanding rate capability as
well as a good trade-off between power (P) and energy
(E) densities. Furthermore, electrochemical response
comparison of CoWO4@C//ZnFe2O4 ASCs
encompassing three different electrolytes (aqueous KOH, KOH–PEO
gel, and KOH–PVA gel) revealed that the KOH–PEO gel
cell outperformed the other two ASCs, with a specific capacity (SC)
of 339 F g–1 (at 1 A g–1) and E
max and P
max of
105 Wh kg–1 and 3.2 kW kg–1 achieved
over an operational voltage window of 1.5 V while retaining 97% of
the original SC after 10,000 cycles. With KOH and KOH–PVA gel,
while the P
max remained the same, SCs
of 300 and 322 F g–1 and E
max’s of 93 and 100 Wh kg–1 were obtained.
The high ionic conductivity (81.6 mS cm–1) of the
KOH-PEO gel is attributed to the hydrogen bonded networked structure
of the gel with free spaces that allows ions to move freely within
the polymer matrix. Further, the oxygens along the polymer chains
ensure a high dissociation of KOH. The gel also serves as an ion-reservoir
and these factors cumulatively resulted in the enhanced performance
of the ASC. This study showcases that scalable, low-cost, leak-proof
supercapacitors can be fabricated using environmentally friendly electroactive
materials that can be synthesized easily using simple wet chemistry
techniques.
The technological importance of cost-effective zinc-doped nickel oxide (Zn:NiO) coatings is demonstrated by applying them to energy saving-electrochromic devices (ECDs) as well as energy storing-asymmetric supercapacitors (ASCs). These devices encompass an inexpensive nonaqueous gel electrolyte of ZnCl 2 /γ-butyrolactone/ ferrocene (Fc)/poly(vinyl butyral), where Fc serves as a redox mediator and accelerates charge transfer and transport kinetics, enhancing both ion-storage and optical modulation responses. This report showcases the prowess of a simple doping and a redox-gel in an unprecedented manner, wherein the improved dc and ac electrical conduction by an order of magnitude, the star-like morphology of Zn:NiO compared to NiO microflowers, and the high conductivity of the gel (33 mS cm −1 ) come to the fore in an ASC [with activated carbon (AC) derived from corncobs as the anode, Zn:NiO//AC], which delivers a very high specific capacitance (SC) of 460 F g −1 (at 1.25 A g −1 ), comparable to expensive rare oxides, a battery like energy density of 164 W h kg −1 (at 1 kW kg −1 ), and a cycle life of 10,000 cycles with 95% SC retention. The potential of Zn doping is further showcased through the panchromatic visible light modulation of the Zn:NiO//WO 3 ECD, switching reversibly between the colorless and the dark black−brown states, accompanied by a remarkably high integrated transmission modulation (ΔT 400−900nm ) of 60.2%, sustained over 3500 cycles with no performance loss, and color/bleach times of 10 s/5 s, most suitable for smart window applications.
The Zn-ion hybrid supercapacitor-battery (ZHSB) type storage device combines the advantage of high power density of a supercapacitor and the high energy density of a battery. This work reports the...
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