Electrocatalysis is critical to the performance displayed by sulfur cathodes. However, the constituent electrocatalysts and the sulfur reactants have vastly different molecular sizes, which ultimately restrict electrocatalysis efficiency and hamper device performance. Herein, the authors report that aggregates of cobalt single‐atom catalysts (SACs) attached to graphene via porphyrins can overcome the challenges associated with the catalyst/reactant size mismatch. Atomic‐resolution transmission electron microscopy and X‐ray absorption spectroscopy measurements show that the Co atoms present in the SAC aggregates exist as single atoms with spatially resolved dimensions that are commensurate the sulfur species found in sulfur cathodes and thus fully accessible to enable 100% atomic utilization efficiency in electrocatalysis. Density functional theory calculations demonstrate that the Co SAC aggregates can interact with the sulfur species in a synergistic manner that enhances the electrocatalytic effect and promote the performance of sulfur cathodes. For example, Li–S cells prepared from the Co SAC aggregates exhibit outstanding capacity retention (i.e., 505 mA h g–1 at 0.5 C after 600 cycles) and excellent rate capability (i.e., 648 mA h g−1 at 6 C). An ultrahigh area specific capacity of 12.52 mA h cm−2 is achieved at a high sulfur loading of 11.8 mg cm–2.
Lithium (Li) metal is regarded as the ultimate anode material for use in Li batteries due to its high theoretical capacity (3860 mA h g À 1 ). However, the Li dendrites that are generated during iterative Li plating/stripping cycles cause poor cycling stability and even present safety risks, and thus severely handicap the commercial utility of Li metal anodes. Herein, we describe a graphene and carbon nanotube (CNT)based Li host material that features vertically aligned channels with attached ZnO particles (
Two-dimensional
(2D) organic materials hold great promise for use
in a multitude of contemporary applications due to their outstanding
chemical and physical properties. Herein, 2D sheets of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)
(PEDOT:PSS) are prepared from a commercially available PEDOT:PSS suspension
using ice as a template. The 2D PEDOT:PSS sheets grow in the boundaries
of ice crystals as the polymers are “squeezed” out of
the suspension when the water solidifies. The mechanical robustness
of the sheets can be enhanced by incorporating WO3 nanowires,
and the PSS component can be conveniently removed with a concentrated
solution of H2SO4 to afford stable suspensions
of PEDOT or WO3@PEDOT sheets, either of which can be converted
into flexible films with tunable thicknesses via filtration.
Swagelok- or pouch-type supercapacitor devices prepared from the WO3@PEDOT films exhibit outstanding energy-storage characteristics,
including high rate capability, thickness-independent energy storage
(e.g., 701 mF cm–2 is achieved with a 1-mm-thick film), high resistance toward mechanical
deformation, and good cycling stability. Additionally, a high energy
density of 0.083 mWh cm–2 is measured for a device
prepared using a 1-mm-thick film at a high power density of 10 mW
cm–2. The methodology described establishes an efficient
and readily scalable approach for accessing 2D organic sheets.
Red
phosphorus (RP) is a promising anode material for use in lithium-ion
batteries (LIBs) due to its high theoretical specific capacity (2596
mA h g–1). However, the practical use of RP-based
anodes has been challenged by the material’s low intrinsic
electrical conductivity and poor structural stability during lithiation.
Here, we describe a phosphorus-doped porous carbon (P-PC) and disclose
how the dopant improves the Li storage performance of RP that was
incorporated into the P-PC (designated as RP@P-PC). P-doping porous
carbon was achieved using an in situ method wherein the heteroatom
was added as the porous carbon was being formed. The phosphorus dopant
effectively improves the interfacial properties of the carbon matrix
as subsequent RP infusion results in high loadings, small particle
sizes, and uniform distribution. In half-cells, an RP@P-PC composite
was found to exhibit outstanding performance in terms of the ability
to store and utilize Li. The device delivered a high specific capacitance
and rate capability (1848 and 1111 mA h g–1 at 0.1
and 10.0 A g–1, respectively) as well as excellent
cycling stability (1022 mA h g–1 after 800 cycles
at 2.0 A g–1). Exceptional performance metrics were
also measured when the RP@P-PC was used as an anode material in full
cells that contained lithium iron phosphate as the cathode material.
The methodology described can be extended to the preparation of other
P-doped carbon materials that are employed in contemporary energy
storage applications.
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