Xiaoliang Yu

Macroscopic 3D Porous Graphitic Carbon Nitride Monolith for Enhanced Photocatalytic Hydrogen Evolution

A macroscopic 3D porous graphitic carbon nitride (g-CN) monolith is prepared by the one-step thermal polymerization of urea inside the framework of a commercial melamine sponge and exhibits improved photocatalytic water-splitting performance for hydrogen evolution compared to g-CN powder due to the 3D porous interconnected network, larger specific surface area, better visible light capture, and superior charge-separation efficiency.

Nitrogen-enriched electrospun porous carbon nanofiber networks as high-performance free-standing electrode materials

Nitrogen-enriched porous carbon nanofiber networks (NPCNFs) were successfully prepared by using low-cost melamine and polyacrylonitrile as precursors via electrospinning followed by carbonization and NH3 treatments. The NPCNFs exhibited inter-connected nanofibrous morphology with a large specific surface area, well-developed microporous structure, relatively high-level nitrogen doping and great amount of pyridinic nitrogen. As free-standing new anode materials in lithium-ion batteries (LIBs), the NPCNFs showed ultrahigh capacity, good cycle performance and superior rate capability with a reversible capacity of as high as 1323 mA h g−1 at a current density of 50 mA g−1. These attractive characteristics make the NPCNFs materials very promising anode candidates for high-performance LIBs and, as free-standing electrode materials to be used in other energy conversion and storage devices.

Facile synthesis of nitrogen-doped carbon nanosheets with hierarchical porosity for high performance supercapacitors and lithium–sulfur batteries

Magnesium citrate and potassium citrate are two commonly used food additives in our daily life. Herein, we prepared nitrogen-doped hierarchical porous carbon nanosheets (N-HPCNSs) through direct pyrolysis of their mixtures and subsequent NH3 treatment. The as-prepared N-HPCNS shows hierarchical porosity (specific surface area of 1735 m2 g−1 and pore volume of 1.71 cm3 g−1), and a moderate nitrogen doping of 1.7%. Moreover, it can be effectively applied in various energy storage/conversion systems. When used as supercapacitor electrodes, it shows a high specific capacitance of 128 F g−1 in organic electrolytes and retains 45% of the original capacitance even at an ultrahigh current density of 100 A g−1. It can also serve as an effective sulfur carrier in lithium–sulfur batteries. The N-HPCNS/sulfur cathode shows high discharge capacities of 1209 mA h g−1 at 0.2C and 493 mA h g−1 even at 4C. Over 500 charge/discharge cycles at 1C, it still retains a high discharge capacity of 486 mA h g−1 with an ultralow capacity loss of 0.051% per cycle and a high average coulombic efficiency of 99.4%.

Nitrogen-rich hierarchical porous hollow carbon nanofibers for high-performance supercapacitor electrodes

Nitrogen-rich hierarchical porous hollow carbon nanofibers (HPCNFs) were synthesized by concentric electrospinning and subsequent KCl/K2CO3 activation. The obtained HPCNFs have quite high nitrogen content (14.4 wt%) and rational hierarchical porous structure, thus exhibiting a high specific capacitance of 293 F g−1, a superior specific areal capacitance of 40 μF cm−2 at 0.2 A g−1 and an excellent rate capability of 62.8% (185 F g−1) at 50 A g−1 in 6 M KOH electrolyte.

Silicon-Encapsulated hollow carbon nanofiber networks as binder-free anodes for lithium ion battery

Silicon-encapsulated hollow carbon nanofiber networks with ample space around the Si nanoparticles (hollow Si/C composites) were successfully synthesized by dip-coating phenolic resin onto the surface of electrospun Si/PVA nanofibers along with the subsequent solidification and carbonization. More importantly, the structure and Si content of hollow Si/C composite nanofibers can be effectively tuned by merely varying the concentration of dip solution. As-synthesized hollow Si/C composites show excellent electrochemical performance when they are used as binder-free anodes for Li-ion batteries (LIBs). In particular, when the concentration of resol/ethanol solution is 3.0%, the product exhibits a large capacity of 841mAh g-1 in the first cycle, prominent cycling stability, and good rate capability. The discharge capacity retention of it was ∼90%, with 745mAh g-1 after 50 cycles. The results demonstrate that the hollow Si/C composites are very promising as alternative anode candidates for high-performance LIBs.

Flour food waste derived activated carbon for high-performance supercapacitors

It is of great importance to develop electrode materials at a low cost for constructing high-performance electrochemical energy storage systems. Herein, we employed flour food waste residue as a raw material to prepare porous carbon based supercapacitor electrodes through the carbonization and subsequent KOH activation process. The as-prepared biomass-derived activated carbon exhibits an interconnected porous network with numberous open micropores and appropriate mesopores. Meanwhile, its moderate total pore volume results in a high mass density of 0.86 g cm−3. When used as supercapacitor electrodes in an aqueous solution of KOH (6 mol L−1), the porous carbon material shows a high specific capacitance (278 F g−1, 241 F cm−3) and good cycling stability with 95% capacitance retention over 3000 cycles at a current density of 2 A g−1. Furthermore, even at an ultrahigh current density of 100 A g−1 (charge/discharge completed within 3 s), it still maintains a high specific capacitance of 142 F g−1 (122 F cm−3).

Nitrogen-enriched hierarchical porous carbon with enhanced performance in supercapacitors and lithium–sulfur batteries

It is quite desirable but challenging to prepare highly active materials for various energy storage applications at low cost. Here, an efficient strategy to produce nitrogen-enriched hierarchical porous carbon (N-HPC) is reported by facile pyrolysis of magnesium citrate and subsequent NH3 treatment. As-prepared N-HPC presents a developed hierarchical micro- and trimodal meso-porosity with a high specific surface area of 1290 m2 g−1 and pore volume of 3.04 cm3 g−1. It also shows an abundant nitrogen doping of 3.6%. When used for electrochemical electrodes in supercapacitors and lithium–sulfur (Li–S) batteries, significantly enhanced performances have been obtained compared with commercially available activated carbon. In supercapacitor testing, the N-HPC electrode shows a specific capacitance of 101 F g−1 in a nonaqueous electrolyte. And the capacitance retains 67% even at a 200-fold charge/discharge rate. Moreover, its performance in Li–S batteries is more outstanding. It enables a very high sulfur loading (76.2% by weight) and the resulting N-HPC/S cathode shows high discharge capacities of 1153 mA h g−1sulfur (or 702 mA h g−1electrode) at 0.2C and 671 mA h g−1 even at 4C. And it still remains 600 mA h g−1 over 300 charge/discharge cycles at 1C with an average coulombic efficiency of 99.0%.

A High Performance Lithium-Ion Capacitor with Both Electrodes Prepared from Sri Lanka Graphite Ore

The natural Sri Lanka graphite (vein graphite) is widely-used as anode material for lithium-ion batteries (LIBs), due to its high crystallinity and low cost. In this work, graphitic porous carbon (GPC) and high-purity vein graphite (PVG) were prepared from Sri Lanka graphite ore by KOH activation, and high temperature purification, respectively. Furthermore, a lithium-ion capacitor (LIC) is fabricated with GPC as cathode, and PVG as anode. The assembled GPC//PVG LIC shows a notable electrochemical performance with a maximum energy density of 86 W·h·kg−1 at 150 W·kg−1, and 48 W·h·kg−1 at a high-power density of 7.4 kW·kg−1. This high-performance LIC based on PVG and GPC is believed to be promising for practical applications, due to its low-cost raw materials and industrially feasible production.