hua Lu

A Graphene-like Oxygenated Carbon Nitride Material for Improved Cycle-Life Lithium/Sulfur Batteries.

Novel sulfur (S) anchoring materials and the corresponding mechanisms for suppressing capacity fading are urgently needed to advance the performance of Li/S batteries. Here, we designed and synthesized a graphene-like oxygenated carbon nitride (OCN) host material that contains tens of micrometer scaled two-dimensional (2D) rippled sheets, micromesopores, and oxygen heteroatoms. N content can reach as high as 20.49 wt %. A sustainable approach of one-step self-supporting solid-state pyrolysis (OSSP) was developed for the low-cost and large-scale production of OCN. The urea in solid sources not only provides self-supporting atmospheres but also produces graphitic carbon nitride (g-C3N4) working as 2D layered templates. The S/OCN cathode can deliver a high specific capacity of 1407.6 mA h g(-1) at C/20 rate with 84% S utilization and retain improved reversible capacity during long-term cycles at high current density. The increasing micropores, graphitic N, ether, and carboxylic O at the large sized OCN sheet favor S utilization and trapping for polysulfides.

Biomass chitosan derived cobalt/nitrogen doped carbon nanotubes for the electrocatalytic oxygen reduction reaction

Carbon nanomaterials derived from biomass are considered as important sustainable energy carriers. In this study, we report an approach to synthesize cobalt/nitrogen doped carbon nanotubes (Co-NCNTs) for high oxygen reduction reaction (ORR) activity by cobalt catalyzed carbonization of biomass chitosan. It is found that the existence of cobalt results in the transition of graphene-like carbon nanosheets to tubular graphitic carbons. Moreover, a strong chemical bonding of cobalt with nitrogen and carbon in Co-NCNTs is found, which is important for enhancing the ORR activity. The Co-NCNT catalyst under optimized synthetic conditions displays attractive ORR activity superior to those of commercial Pt/C catalysts. Furthermore, the mechanism behind the enhanced ORR activity has also been studied. This study provides a feasible synthesis approach for the scalable production of biomass derived high performance carbon based ORR catalysts.

Residual oxygen groups in nitrogen-doped graphene to enhance the capacitive performance

Nitrogen-doped graphene (NG) was obtained from a facile and eco-friendly hydrothermal reaction and used as electrode materials for supercapacitors. The textural and chemical properties could be easily tuned by adjusting the basicity of the reaction environment. As the basic reaction conditions became stronger, the sheets of NG tended to stack together, the content of residual oxygen groups increased, but the nitrogen content decreased, which affected the electrochemical performance. The NG synthesized under a weak basic environment shows great pseudocapacitance and the largest electrochemical performance in a 6 mol L−1 KOH aqueous electrolyte when measured in a three-electrode system, which can be attributed to its randomly distributed and loosely stacked structure and high amount of residual oxygen atoms (12.8 at%). Furthermore, it presented excellent cycling stability with a capacitance retention ratio of 92.86% at the current densities of 5 A g−1 after 10u2006000 charge–discharge cycles in two-electrode configuration, which kept stable after 5000 cycles. These results implied that the NG sheets obtained by this simple eco-friendly approach are suitable for high performance supercapacitor applications.

Phosphoric acid-assisted synthesis of layered MoS2/graphene hybrids with electrolyte-dependent supercapacitive behaviors

A reformative graphene-supported MoS2 hybrid has been synthesized by a phosphoric acid (H3PO4)-assisted hydrothermal process. The effect of H3PO4 on the growth, morphology, structure, and composition of the MoS2/graphene hybrid has been explored by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results indicate that H3PO4 can control the process of both the reduction of graphene oxide and the crystallization of MoS2. The electrochemical performance suggests that involvement of H3PO4 in the reaction bestows the hybrid with electrolyte-dependent capacitive behaviors in which contribution from electric double-layer capacitance (EDLC) and pseudocapacitance can be distinguished in acidic and alkaline electrolytes, respectively. While the quasi-EDLC behavior of the hybrid dominates in an alkaline electrolyte (258 F g−1 at 2 A g−1), the pseudocapacitance of the hybrid in an acidic electrolyte can be significantly enhanced due to oxygen-containing groups and Mo active in the total capacitance value (351 F g−1 at 2 A g−1). Moreover, a superior cycling performance and quick frequency response of the hybrid reinforces its potential for supercapacitor applications.