MnO2 has been widely studied as the pseudo-capactive electrode material of high-performance supercapacitors for its large operating voltage, low cost, and environmental friendliness. However, it suffers from low conductivity and being hardly handle as the electrodes of supercapacitors especially with flexibility, which largely limit its electrochemical performance and application. Herein, we report a novel ternary composite paper composed of reduced graphene sheet (GR)-patched carbon nanotube (CNT)/MnO2, which has controllable structures and prominent electrochemical properties for a flexible electrode of the supercapacitor. The composite paper was prepared by electrochemical deposition of MnO2 on a flexible CNT paper and further adsorption of GR on its surface to enhance the surface conductivity of the electrode and prohibit MnO2 nanospheres from detaching with the electrode. The presence of GR was found remarkably effective in enhancing the initial electrochemical capacitance of the composite paper from 280 F/g to 486.6 F/g. Furthermore, it ensures the stability of the capacitance after a long period of charge/discharge cycles. A flexible CNT/polyaniline/CNT/MnO2/GR asymmetric supercapacitor was assembled with this composite paper as an electrode and aqueous electrolyte gel as the separator. Its operating voltage reached 1.6 V, with an energy density at 24.8 Wh/kg. Such a composite structure derived from a multiscale assembly can offer not only a robust scaffold loading MnO2 nanospheres but also a conductive network for efficient ionic and electronic transport; thus, it is potentially promising as a novel electrode architecture for high-performance flexible energy storage devices.
Rechargeable zinc–air batteries constitute promising next‐generation energy storage devices due to their intrinsic safety, low cost, and feasibility to realize high cycling current density and long cycling lifespan. Nevertheless, their cathodic reactions involving oxygen reduction and oxygen evolution are highly sluggish in kinetics, requiring high‐performance noble‐metal‐free bifunctional electrocatalysts that exceed the current noble‐metal‐based benchmarks. Herein, a noble‐metal‐free bifunctional electrocatalyst is fabricated, which demonstrates ultrahigh bifunctional activity and renders excellent performance in rechargeable zinc–air batteries. Concretely, atomic Co–N–C and NiFe layered double hydroxides (LDHs) are respectively selected as oxygen reduction and evolution active sites and are further rationally integrated to afford the resultant CoNC@LDH composite electrocatalyst. The CoNC@LDH electrocatalyst exhibits remarkable bifunctional activity delivering an indicator ΔE of 0.63 V, far exceeding the noble‐metal‐based Pt/C+Ir/C benchmark (ΔE = 0.77 V) and most reported electrocatalysts. Correspondingly, ultralong lifespan (over 3600 cycles at 10 mA cm−2) and excellent rate performances (cycling current density at 100 mA cm−2) are achieved in rechargeable zinc–air batteries. This work highlights the current advances of bifunctional oxygen electrocatalysis and endows high‐rate and long‐cycling rechargeable zinc–air batteries for efficient sustainable energy storage.
Aqueous metal–air batteries are promising next-generation energy storage and supply technologies due to advantages of high energy density and intrinsic safety. As an abundant natural resource, applying seawater-based electrolytes is...
The rechargeable zinc–air battery (ZAB) is a promising energy storage technology owing to its high energy density and safe aqueous electrolyte, but there is a significant performance bottleneck. Generally, cathode reactions only occur at multiphase interfaces, where the electrocatalytic active sites can participate in redox reactions effectively. In the conventional air cathode, the 2D multiphase interface on the surface of the gas diffusion layer (GDL) inevitably results in an insufficient amount of active sites and poor interfacial contact, leading to sluggish reaction kinetics. To address this problem, a 3D multiphase interface strategy is proposed to extend the reactive interface into the interior of the GDL. Based on this concept, an asymmetric air cathode is designed to increase the accessible active sites, accelerate mass transfer, and generate a dynamically stabilized reactive interface. With a NiFe layered‐double‐hydroxide electrocatalyst, ZABs based on the asymmetric cathode deliver a small charge/discharge voltage gap (0.81 V at 5.0 mA cm−2), a high power density, and a stable cyclability (over 2000 cycles). This 3D reactive interface strategy provides a feasible method for enhancing the air cathode kinetics and further enlightens electrode designs for energy devices involving multiphase electrochemical reactions.
Despite
their high theoretical capacity density (1675 mAh g–1), the application of Li–S batteries has been
seriously hindered by the shuttle effect of polysulfides. Here, inspired
by the working principle of natural spider webs, we synthesized a
spider-web-like nanocomposite in which many hollow mesoporous silica
(mSiO2) nanospheres/Co nanoparticles were threaded by interconnected
nitrogen-doped carbon nanotubes (NCNTs). Then the nanocomposite (denoted
as Co/mSiO2–NCNTs) was coated on the commercial
separator by a simple infiltration to mitigate the above issue. The
intimate combination of three-dimensional conductive networks (NCNTs)
with abundant polysulfide adsorbent sites (SiO2 and N)/polysulfide
conversion catalysts (Co and Co–N
x
species) allows the Co/mSiO2–NCNTs coating layer
to not only effectively capture polysulfides via both physical confinement
and chemical bonding but also accelerate the redox kinetics of polysulfides
significantly. Furthermore, the combination of ex situ experiment and theoretical calculation demonstrates that the reversible
adsorption/desorption of polysulfides on mSiO2 nanospheres
benefits uniform deposition of Li2S2/Li2S on the conductive networks, which contributes to long-term
cycling stability. As a result, Li–S batteries with Co/mSiO2–NCNTs-coated separators exhibited both excellent cycling
stability and rate performance.
Zinc–air batteries deliver great potential as emerging energy storage systems but suffer from sluggish kinetics of the cathode oxygen redox reactions that render unsatisfactory cycling lifespan. The exploration on bifunctional electrocatalysts for oxygen reduction and evolution constitutes a key solution, where rational design strategies to integrate various active sites into a high‐performance air cathode remain insufficient. Herein, a multiscale construction strategy is proposed to rationally direct the fabrication of bifunctional oxygen electrocatalysts for long‐lifespan rechargeable zinc–air batteries. NiFe layered double hydroxides and cobalt coordinated framework porphyrin are selected as the active sites considering their high intrinsic activity at the molecular level, and the active sites are successively integrated on three‐dimensional conductive scaffolds at mesoscale to strengthen ion transportation. Consequently, the multiscale constructed electrocatalyst exhibits excellent bifunctional performance (ΔE = 0.68 V), which is even better than that of the noble metal based benchmarks. The corresponding air cathodes endow zinc–air batteries with a reduced voltage gap of 0.74 V, a high power density of 185.0 mW cm−2, and an ultralong lifespan of more than 2400 cycles at 5.0 mA cm−2. This work demonstrates a feasible strategy to rationally integrate various active sites to construct multifunctional electrocatalysts for energy‐related processes.
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