Weiwei Qian

Renewable graphene-like nitrogen-doped carbon nanosheets as supercapacitor electrodes with integrated high energy–power properties

The development of supercapacitors with integrated high energy–power properties coupled with long cyclic life is an urgent demand in the energy storage field. The key to the assembly of such devices is to design and fabricate novel high-performance electrode materials in conjunction with matched electrolytes. In this study, a renewable graphene-like nitrogen-doped carbon nanosheet (RGNC-NS) has been constructed by using simultaneous carbonization and auto-activation followed by ultrasonic-assisted liquid exfoliation from natural layered shrimp shells. The final RGNC-NS had an optimum integration of graphene-like nanostructures (∼5 nm thick), large specific surface area (1946 m2 g−1), and rich nitrogen doping (8.75 wt%), resulting in high conductivity (7.8 S cm−1) and good surface wettability with an electrolyte. The RGNC-NS as a supercapacitor electrode exhibited an excellent rate capability with an ultrahigh capacitance of 322 F g−1 at 0.5 A g−1 and 241 F g−1 at 100 A g−1 (75% retention), as well as a long cyclic stability of 98.3% capacitance retention after 20 000 cycles at 10 A g−1 in 6 M KOH. Moreover, the RGNC-NS in a mixed ionic liquid electrolyte displayed an integrated high energy–power density of 30 W h kg−1 energy density at 64 000 W kg−1 power density and 93.2% capacitance retention after 8000 cycles at 5 A g−1.

Biomass‐Derived Porous Carbon with Micropores and Small Mesopores for High‐Performance Lithium–Sulfur Batteries

Biomass-derived porous carbon BPC-700, incorporating micropores and small mesopores, was prepared through pyrolysis of banana peel followed by activation with KOH. A high specific BET surface area (2741 m2  g-1 ), large specific pore volume (1.23 cm3  g-1 ), and well-controlled pore size distribution (0.6-5.0 nm) were obtained and up to 65 wt % sulfur content could be loaded into the pores of the BPC-700 sample. When the resultant C/S composite, BPC-700-S65, was used as the cathode of a Li-S battery, a large initial discharge capacity (ca. 1200 mAh g-1 ) was obtained, indicating a good sulfur utilization rate. An excellent discharge capacity (590 mAh g-1 ) was also achieved for BPC-700-S65 at the high current rate of 4 C (12.72 mA cm-2 ), showing its extremely high rate capability. A reversible capacity of about 570 mAh g-1 was achieved for BPC-700-S65 after 500 cycles at 1 C (3.18 mA cm-2 ), indicating an outstanding cycling stability.

Unique 1D Co3O4 crystallized nanofibers with (220) oriented facets as high-performance lithium ion battery anode material

A novel one-step hydrothermal and calcination strategy was developed to synthesize the unique 1D oriented Co3O4 crystal nanofibers with (220) facets on the carbon matrix derived from the natural, abundant and low cost wool fibers acting as both carbon precursor and template reagent. The resultant W2@Co3O4 nanocomposite exhibited very high specific capacity and favorable high-rate capability when used as anode material of lithium ion battery. The high reversible Li+ ion storage capacity of 986 mAh g−1 was obtained at 100 mA g−1 after 150 cycles, higher than the theoretical capacity of Co3O4 (890 mAh g−1). Even at the higher current density of 1 A g−1, the electrode could still deliver a remarkable discharge capacity of 720 mAh g−1 over 150 cycles.

Graphene-based carbon coated tin oxide as a lithium ion battery anode material with high performance

In this study, we synthesized an excellent ternary graphene-based carbon coated SnO2 (rGO/PC/SnO2) nanocomposite anode for lithium ion batteries (LIBs), in which carbon-coated SnO2 nanoparticles homogeneously grow on the surface of reduced graphene oxide (rGO) using glucose as the soft templating agent. Using glucose can limit the growth of the SnO2 particles; as a result, the size of the SnO2 particles would be relatively uniform. Moreover, the carbon coated on the surface of SnO2 particles can effectively prevent their agglomeration on the surface of rGO and limit their volume expansion during charge–discharge cycles. The porous structure of the rGO/PC/SnO2 nanocomposite can effectively accommodate the severe volume variation upon cycling and provide additional contact areas between the active material and the electrolyte. Significantly, the rGO/PC/SnO2 anode delivers an initial specific discharge capacity of 2238.2 mA h g−1 and retains 1467.8 mA h g−1 after 150 cycles at a current density of 0.1C (1C = 782 mA g−1). Even at the high specific current of 1C after 200 cycles, the reversible specific capacity is still as high as 618.3 mA h g−1. The rGO/PC/SnO2 anode exhibits excellent rate performances and possesses a reversible specific capacity of 445.9 mA h g−1 at 5C implying its good structural stability.

One-pot in situ chemical reduction of graphene oxide and recombination of sulphur as a cathode material for a Li–S battery

Li–S batteries with a high theoretical specific capacity and energy density are poised to be one of the most promising next generation systems; however, the complex preparation process of the cathode material and low cyclic stability, particularly at high current density, have limited their practical applications. Herein, we report a facile and eco-friendly one-pot strategy for the chemical reduction of graphene oxide and recombination of sulphur as the cathode material for a Li–S battery. The optimized rGO/S-3 composite material possesses a porous morphology with pore walls made of the rGO and sulphur composite. The sulphur content is about 73.5 wt%, the particle size is about 8–15 nm, and the particles are distributed evenly on the layer of rGO, wherein the thickness of rGO is about 3–4 nm, corresponding to 8–10 monolayer graphenes. The rGO/S-3 composite electrode presents a high initial discharge capacity of 1012 and 474 mA h g−1 at 1C and 10C, respectively. The discharge capacity of 451 mA h g−1 was preserved after 1200 cycles at 1C. Even though the current density increased to 10C, a discharge capacity of 237 mA h g−1 may be obtained after 400 cycles.

Low content Pt nanoparticles anchored on N-doped reduced graphene oxide with high and stable electrocatalytic activity for oxygen reduction reaction

A novel kind of Pt/N-rGO hybrid possessing of low content 5.31 wt.% Pt anchored on the surface of nitrogen doped reduced graphene oxide (N-rGO) evenly was prepared. The Pt has uniformed 2.8 nm diameter and exposed (111) crystal planes; meanwhile, the N works as the bridge between Pt and rGO with the Pt-N and N-C chemical bonds in Pt/N-rGO. The Pt/N-rGO material has a very high electrocatalytic activity in oxygen reduction reaction with the mass catalytic activity more than 1.5 times of the commercial Pt/C due to the synergistic catalytic effect of both N-doped carbon matrix and Pt nanoparticles. Moreover, the Pt/N-rGO exhibits an excellent stability with hardly loss (only 0.4%) after accelerated durability tests of 5000 cycles based on the stable Pt-N-C chemical bonds in Pt/N-rGO, which can prevent the detachment, dissolution, migration and aggregation of Pt nanoparticles on the matrix during the long-term cycling.

Unusual Mesoporous Carbonaceous Matrix Loading with Sulfur as the Cathode of Lithium Sulfur Battery with Exceptionally Stable High Rate Performance

Unusual three-dimensional mesoporous carbon/reduced graphene oxide (MP-C/rGO) matrix possessing graphene nanolayer pore walls built up by three to five graphene monosheets and some carbon particles with the sizes of about 5 nm located between the graphene nanolayers was prepared by facile freeze-drying and then carbonization of the poly(vinyl alcohol) and graphene oxide mixture. The mesoporous carbonaceous MP-C/rGO sample has a high specific surface area of 661.6 m2 g-1, large specific pore volume of 1.54 m3 g-1, and focused pore size distribution of 2-10 nm. About 64 wt % sulfur could be held in the pores of the MP-C/rGO matrix. As the cathode of a Li-S battery, the MP-C/rGO/S composite showed excellent electrochemical property including a high initial specific capacity of 919 mA h g-1 at 1 C with the capacity retention ratio of 63.3% and the Coulombic efficiency above 90% after 500 cycles. Meanwhile, the initial specific capacity of 602 mA h g-1 at 5 C and remaining capacity of 391 mA h g-1 after 500 cycles with an outstanding Coulombic efficiency of 97% indicate its exceptionally stable rate performance.

Binary Hierarchical Porous Graphene/Pyrolytic Carbon Nanocomposite Matrix Loaded with Sulfur as a High-Performance Li–S Battery Cathode

A N,O-codoped hierarchical porous nanocomposite consisting of binary reduced graphene oxide and pyrolytic carbon (rGO/PC) from chitosan is fabricated. The optimized rGO/PC possesses micropores with size distribution concentrated around 1.1 nm and plenty of meso/macropores. The Brunauer-Emmett-Teller specific surface area is 480.8 m2 g-1, and it possesses impressively large pore volume of 2.14 cm3 g-1. On the basis of the synergistic effects of the following main factors: (i) the confined space effect in the hierarchical porous binary carbonaceous matrix; (ii) the anchor effects by strong chemical bonds with codoped N and O atoms; and (iii) the good flexibility and conductivity of rGO, the rGO/PC/S holding 75 wt % S exhibits high performance as Li-S battery cathode. Specific capacity of 1625 mA h g-1 can be delivered at 0.1 C (1 C = 1675 mA g-1), whereas 848 mA h g-1 can be maintained after 300 cycles at 1 C. Even at high rate of 5 C, 412 mA h g-1 can be restrained after 1000 cycles.

Ultrahigh Oxygen Reduction Reaction Electrocatalytic Activity and Stability over Hierarchical Nanoporous N-doped Carbon

Hierarchical nanoporous N-doped carbon ZNC-1000 was prepared by facile pyrolysis of well-designed nanosized ZIF-8 precursor with optimized reaction temperature and time. It possesses large surface areas leading to sufficient exposed electrochemical active sites. Meanwhile, its moderate graphitization degree and suitable nanosized hierarchical porosity distributions would lead to the sufficient interaction between O2 and the electrocatalyst surface which would benefit the transports of electrons and the electrolyte ions for ORR. As an electrocatalyst for oxygen reduction reaction, the ZNC-1000 presents a better catalytic property than the commercial Pt/C with 6/1 mV positive shifts for onset/half-wave potentials and 1.567 mA cm−2 larger for limiting current density respectively. The stability of ZNC-1000 is also much better than that of Pt/C with negative shifts of 0/−2 mV (vs 5/31 mV) for onset/half-wave potentials and 6.0% vs 29.2% loss of limiting current density after 5000 cycles of accelerated durability test, as well as the relative current of 87.5% vs 40.2% retention after 30,000 s continuous chronoamperometric operation.