RESUMO
Transition-metal-based layered triple hydroxides (LTHs) are evolving as potential positrode candidates for high-performance supercapacitors; however, their phase stabilization is still critical. Alongside, the availability of limited negatrodes pushes research toward exploring novel alternatives in order to minimize performance limitation issues in the fabricated supercapacitors. Herein, a facile strategy for stabilizing freestanding MnCuCo-LTH-based positrode possessing intermingled nanodisk-needle-like morphology is reported. Alongside, novel high-surface-area negatrodes based on Mn1Fe2S2 exhibiting porous microthorn-like morphology are also optimized. MnCuCo_LTH and Mn1Fe2S2 exhibit remarkably high specific capacities of â¼494 mAh g-1 (â¼2540 F g-1) and â¼429 mAh g-1 (â¼1546 F g-1), respectively, at 1 A g-1. The fabricated quasi-solid-state supercapacitor equipped with a poly(vinyl alcohol) (PVA)-KOH gel electrolyte displays a high specific capacity of â¼144 mAh g-1 and a specific capacitance of â¼325 F g-1 at 1 A g-1. The ultrahigh energy cum power traits of â¼105 Wh kg-1 (1 A g-1) and â¼8370 W kg-1 (at 10 A g-1) establish an asymmetric supercapacitor as a high-performance energy storage device. This device shows an appreciably high cycling life with a capacitance retention of â¼93% after 10â¯000 consecutive cycles, at 10 A g-1. This approach provides a neoteric foresight for developing high-performance advanced energy storage devices equipped with cheaper and eco-friendly components.
RESUMO
Introducing defects and in situ topotactic transformation of the electrocatalysts generating heterostructures of mixed-metal oxides(hydroxides) that are highly active for oxygen evolution reaction (OER) in tandem with metals of low hydrogen adsorption barrier for efficient hydrogen evolution reaction (HER) is urgently demanded for boosting the sluggish OER and HER kinetics in alkaline media. Ascertaining that, metal-organic-framework-derived freestanding, defect-rich, and in situ oxidized Fe-Co-O/Co metal@N-doped carbon (Co@NC) mesoporous nanosheet (mNS) heterostructure on Ni foam (Fe-Co-O/Co@NC-mNS/NF) is developed from the in situ oxidation of micropillar-like heterostructured Fe-Co-O/Co@NC/NF precatalyst. The in situ oxidized Fe-Co-O/Co@NC-mNS/NF exhibits excellent bifunctional properties by demanding only low overpotentials of 257 and 112 mV, respectively, for OER and HER at the current density of 10 mA cm-2 , with long-term durability, attributed to the existence of oxygen vacancies, higher specific surface area, increased electrochemical active surface area, and in situ generated new metal (oxyhydr)oxide phases. Further, Fe-Co-O/Co@NC-mNS/NF (+/-) electrolyzer requires only a low cell potential of 1.58 V to derive a current density of 10 mA cm-2 . Thus, the present work opens a new window for boosting the overall alkaline water splitting.
RESUMO
Fabrication of hierarchical nanosheet arrays of 1T phase of transition-metal dichalcogenides is indeed a critical task, but it holds immense potential for energy storage. A single-step strategy is employed for the fabrication of stable 1T-Mnx Mo1- x S2- y Sey and MoFe2 S4- z Sez hierarchical nanosheet arrays on carbon cloth as positive and negative electrodes, respectively. The flexible asymmetric supercapacitor constructed with these two electrodes exhibits an excellent electrochemical performance (energy density of ≈69â¯Wh kg-1 â¯at a power density of 0.985â¯kWâ¯kg-1 ) with ultralong cyclic stability of ≈83.5% capacity retention, after 10 000 consecutive cycles. Co-doping of the metal and nonmetal boosts the charge storage ability of the transition-metal chalcogenides following enrichment in the metallic 1T phase, improvement in the surface area, and expansion in the interlayer spacing in tandem, which is the key focus of the present study. This study explicitly demonstrates the exponential enhancement of specific capacity of MoS2 following intercalation and doping of Mn and Se, and Fe2 S3 following doping of Mo and Se could be an ideal direction for the fabrication of novel energy-storage materials with high-energy storage ability.
RESUMO
Hollow-structured Fex Co2-x P, Fex Co3-x O4 , and Prussian blue analogue (FeCo-PBA) microbuilding arrays on Ni foam (NF) are derived from Co-based metal-organic frameworks (Co-MOF) using a simple room temperature and post-heat-treatment route. Among them, Fex Co2-x P/NF shows excellent bifunctional catalytic activities by demonstrating very low oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) overpotentials of 255/114â mV at a current density of 20/10â mA cm-2 respectively, whereas Fex Co3-x O4 /NF and FeCo-PBA/NF demand higher overpotentials. Remarkably, for water electrolysis, Fex Co2-x P/NF requires only 1.61â V to obtain 10â mA cm-2 . In contrast to water electrolysis, urea electrolysis reduces overpotential and simultaneously purifies the urea-rich wastewater. The urea oxidation reaction at the Fex Co2-x P/NF anode needs just 1.345â V to achieve 20â mA cm-2 , which is 140â mV less than the 1.48â V potential required for OER. Moreover, the generation of H2 through urea electrolysis needs only 1.42â V to drive 10â mA cm-2 .