Zhixiao Xu

Nitrogen-Doped Porous Carbon Superstructures Derived from Hierarchical Assembly of Polyimide Nanosheets

3D carbon superstructures are fabricated through the hierarchical assembly of polyimide nanosheets and thermal treatment. Benefiting from the ultrahigh surface area and the hierarchically porous structure, along with the well-distributed highly electroactive sites, the flower-like carbon material exhibits outstanding catalytic activity toward the oxygen reduction reaction and also serves as a highly stable electrode material in supercapacitors.

Highly Crumpled Hybrids of Nitrogen/Sulfur Dual-Doped Graphene and Co9S8 Nanoplates as Efficient Bifunctional Oxygen Electrocatalysts

A bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly attractive for the manufacture of clean energy conversion devices. In this work, highly crumpled hybrid of nitrogen and sulfur dual-doped graphene and quasi-hexagonal Co9S8 nanoplates (Co9S8/NSGg-C3N4) is fabricated via a facile ionic assembly approach. The unique structure of Co9S8/NSGg-C3N4 renders it high specific surface area (288.3 m2 g-1) and large pore volume (1.32 cm3 g-1). As the electrocatalyst for ORR, Co9S8/NSGg-C3N4 demonstrates excellent performance with the onset potential of -0.02 V vs Ag/AgCl and the limited current density of 6.05 mA cm-2 at -0.9 V vs Ag/AgCl. Co9S8/NSGg-C3N4 also presents outstanding catalytic activity toward OER by delivering a limited current density of 48 mA cm-2 at 1 V vs Ag/AgCl. The bifunctional catalytic behaviors of Co9S8/NSGg-C3N4 enable the assembly of a rechargeable Zn-air battery with it as the cathode catalyst, which exhibits stable discharge/charge voltage plateaus upon long time cycling over 50 h.

A facile self-assembly strategy towards naphthalene diimide/graphene hybrids as high performance organic cathodes for lithium-ion batteries

A two-dimensional hybrid of naphthalene diimide and reduced graphene oxide (NDI–RGO) has been constructed by a facile self-assembly strategy. In the resulting hybrid, the non-covalent interactions between NDI and RGO enable the uniform distribution of NDI on the surface of RGO. As the cathode material in lithium ion batteries, NDI–RGO shows excellent revisable capacity and rate capability.

Bottom-up fabrication of nitrogen-doped mesoporous carbon nanosheets as high performance oxygen reduction catalysts

Nitrogen-doped mesoporous carbon nanosheets (NMCNs) with uniform hexagonal structures are fabricated via the thermal treatment of polyaniline enwrapped cobalt hydroxide (Co(OH)2) nanosheets and the subsequent acid etching of the resulting composites. It is found that the morphologies, poroisties and compositions of the NMCNs are greatly dependent on the ratio of the added aniline and Co(OH)2 nanosheets, which can in turn affect the electrochemical behavior of the NMCNs. As the electrocatalyst for oxygen reduction reaction in alkaline media, the NMCNs obtained with the aniline/Co(OH)2 ratio of ∼1.2 manifest excellent perfromance with the onset potential of -0.119V, the half-wave potential of -0.182V and the limiting current density of 5.06mAcm-2, which are superior to most of the previously reported N-doped porous carbon nanosheets.

Template-directed approach to two-dimensional molybdenum phosphide–carbon nanocomposites with high catalytic activities in the hydrogen evolution reaction

We first developed a new two-dimensional graphene-based Schiff-base porous polymer by the condensation of melamin, 1,4-phthalaldehyde and aminated graphene oxide. Then, we prepared a new family of two-dimensional molybdenum phosphide-containing porous carbons (TPC–MoPs) by using the as-prepared two-dimensional porous polymer (TPP) as a two-dimensional template, and low-cost diammonium phosphate and ammonium molybdate as precursors through stepwise self-assembly and pyrolysis. The resulting TPC–MoPs featured layered and porous structures with high specific surface areas of up to 72 m2 g−1. The unique mophology characteristics render such kinds of materials with increased active catalytic sites and better conductivity, as compared with the other MoPs-based composites. As a consequence, the as-prepared composites exhibit superior electrocatalytic performance in the hydrogen evolution reaction (HER) under acidic conditions, with a Tafel slope of 68.5 mV dec−1, a low onset overpotential of 65 mV (versus the reversible hydrogen electrode), and a large exchange current density (j0) of 0.144 mA cm−2.

Perylene diimide-diamine/carbon black composites as high performance lithium/sodium ion battery cathodes

The electrochemical performances of three in situ synthesized composites of perylene diimide-diamine and carbon black (PDI-DA/CBs) and their mechanically mixed analogs are compared as the cathode materials in both lithium ion batteries (LIBs) and sodium ion batteries (SIBs). Benefiting from the fabrication strategy and variable structures, the composite containing ethylene diamine units exhibits an excellent reversible capacity of ∼100 mA h g−1 at an ultrahigh current density of 5.0 A g−1 in LIBs and a high capacity over 90 mA h g−1 at 2.0 A g−1 in SIBs.

Magnesium ion based organic secondary batteries

A magnesium ion based organic secondary battery (MIOB) is fabricated by using polytriphenylamine as the cathode, perylene diimide–ethylene diamine as the anode and an anhydrous acetonitrile solution of magnesium perchlorate as the electrolyte. Based on a dual-ion battery mechanism, the MIOB manifests high capacities and good cycling stability. Moreover, the good electrochemical properties of the MIOB can still be reserved even at low temperatures and in flexible pouch cells. The excellent battery performance of the MIOB can be attributed to the synergistic effect of the dual-ion energy storage mechanism and the utilization of organic electrode materials.

Anion-induced self-assembly of positively charged polycyclic aromatic hydrocarbons towards nanostructures with controllable two-dimensional morphologies

A controllable self-assembly strategy of positively charged polycyclic aromatic hydrocarbons (PCPAH) towards the formation of rectangle sheets and ribbon-like nanostructures has been achieved by choosing divalent anions with different sizes. In contrast, only rod-like nanostructures are obtained from PCPAH with univalent anions. It is revealed that the divalent anions play a key role in guiding the packing of PCPAH, which provides an unprecedented route to fabricate two-dimensional nanostructures.