Current,
there is an urgent demand for electrode materials with
superior electrochemical performances for the development of supercapacitors.
A nitrogen-doped carbon skeleton (NCS) assembled by carbon nanotubes
and graphene layers is designed and synthesized utilizing a layer-shaped
humate-based zeolitic imidazolate framework (ZIF) (HA-CoFe-ZIF) as
a template in this work. The synthesized NCS is mainly composed of
graphitized carbon with a few hydroxyl groups on its surface, synchronously
doped by 9.5 at % nitrogen in the state of pyridinic N and pyrrolic
N. The rich mesoporous structure entitles it to a high Brunauer–Emmett–Teller
(BET) specific surface area of 427 m2 g–1 and suitable BET average pore diameter of 3.14 nm. The NCS has a
high capacity of 324 F g–1 at 1 A g–1, good rate capability (capacitance retention of 71% from 5 to 100
A g–1), and excellent cycling stability (capacitance
retention of 96 and 87% after 5000 and 10 000 cycles, respectively).
The fabricated NCS//AC asymmetric supercapacitor also exhibits a high
capacity of 93 F g–1 at 1 A g–1, large energy density of 10.3 Wh kg–1 at 331 W
kg–1, and good cycling performance (capacitance
retention of 88% after 5000 cycles). Our elaborately designed NCS
materials exhibit multiple structural advantages including rich mesoporous
structure, various graphitic carbon, and high-dosage nitrogen doping,
resulting in high capacitance performances. This humate-based metal–organic
framework (MOF)-derived strategy provides a good idea for the synthesis
of high-performance carbon skeleton materials applied to energy storage.
A humate‐layer‐based bimetal organic framework (HA‐NiCo‐BPDC) material is successfully synthesized using humate layers obtained by ultrasonic‐hydrothermal peeling as a substrate and BPDC as a ligand via a hydrothermal approach. It exhibits a porous composite structure in which flower‐like NiCo‐BPDC nanosheets are loaded on humate layers, originating a guiding effect of humate layers on the NiCo‐BPDC growth. HA‐NiCo‐BPDC owns a similar crystal structure to NiCo‐BPDC, in which humate and BPDC ions have coordinated with nickel or cobalt ions to form carboxylates. Nickel and cobalt ions present positive divalent states, and they have close ability to coordinate with BPDC or humate ions. Owing to unique hierarchical architectures and fascinating synergetic effects between NiCo‐BPDC nanosheets and humate layers, HA‐NiCo‐BPDC has high specific capacitance and rate capability, and low internal resistance and charge transfer resistance. It exhibits better rate capability than NiCo‐BPDC and larger specific capacitance than HA−Ni(Co)‐BPDC. Moreover, HA‐NiCo‐BPDC//rGO asymmetric supercapacitor has wide operating potential window, high energy density and cycling stability. All those show that HA‐NiCo‐BPDC composites are a promising electrode material for supercapacitors. This study exploits a novel way for value‐added applications of humates and their natural sources “humic acids”.
Metal
organic frameworks (MOFs) have good porosity and adjustable
morphology, which are always used as excellent sacrificial templates
to derive high-performance layered double hydroxides (LDHs). Here,
a humate-based ZIF-67 (HA–ZIF-67) template is first prepared
by a natural precipitation method using humates as a substrate. And
a humate-based NiCo–LDH (HA–NiCo–LDH) composite
material is then successfully prepared via a solvothermal approach
with ethanol as a protic solvent. Due to the special composite structure
including NiCo–LDH nanocages assembled by interlaced nanosheets,
suitable incorporation of layered humate substrate with graphitized
microdomains and rich mesopores, the HA–NiCo–LDH exhibits
a low resistance during the ionic diffusion, charge transfer, and
electron conduction process, a large capacity of 1083 C g–1 (0.5 A g–1), and an excellent cycle stability
with a capacity retention of 77% over 10000 GCD loops at 5 A g–1. The assembled asymmetric supercapacitor of the HA–NiCo–LDH//AC
also has a decent capacity retention of 52% of initial value with
the current density increasing from 0.5 to 10 A g–1, and a large energy density of 44.9 Wh kg–1 at
a power density of 348 W kg–1. Its capacity retention
is still high to 98% at 5 A g–1 over 5000 GCD loops.
Hence, the moderate incorporation of humates is of great significance
for practical applications of the NiCo–LDH in supercapacitors.
To improve electrocatalytic performances of Pt-based catalysts toward methanol oxidation reaction (MOR) and reduce the consumption of Pt, we report a novel strategy for preparing a PtCo/NCS catalyst with bimetallic PtCo nanoparticles supported on the nitrogen-doped carbon skeleton (NCS) derived from ulmic-acid -based ZIF-67 (UA-ZIF-67) template. The synthesized optimal NCS has rich mesoporous structure with a BET specific surface area of 451 m 2 g À 1 and average pore diameterof 4.5 nm, possesses graphitic structure containing some CNTs and many graphene layers, and is doped by 8.16 at% nitrogen in the form of pyridine N and pyrrole N. In the optimum PtCo/NCS, metallic Pt and Co nanoparticles with an average size of 3.0 � 0.5 nm are uniformly supported on the NCS. This PtCo/NCS catalyst shows a high electrocatalytic activity and stability for MOR due to its high electrochemically active specific surface area (ECSA) value, current density, steady-state current and current retention. The results are attributed to small highly-dispersed PtCo nanoparticles with good synergistic effects of bimetallic active components supported on the NCS possessing CNTs and graphene layers, suitable nitrogen doping and well-matched hierarchical pore structure.These findings will provide a new insight in designing and synthesizing high-performance electrocatalysts.
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