Yuezeng Su

Polyaniline‐Coupled Multifunctional 2D Metal Oxide/Hydroxide Graphene Nanohybrids

Owing to their unique properties compared with conventional bulk analogues, two-dimensional (2D) nanomaterials, having nano-scale thickness and infinite length, are attracting increasing attention for their potential application in the fields of electronics, sensing, energy storage, and conversion. In particular, transition-metal chalcogenides and metal oxide nanosheets are highly promising functional 2D nanomaterials, however, their synthesis in a large scale remains a great challenge. Graphene, a 2D “aromatic” monolayer of carbon material having an ultralight weight, high surface area, and electric conductivity, has emerged as an ideal substrate for the growth and anchoring of functional nanomaterials, such as metal oxide/hydroxide nanoparticles (MO/MH NPs). 17–19] The strong coupling between MO/MH NPs and graphene in a confined 2D manner gives nanohybrids with unique structural features and synergistic physical and electrochemical properties derived from both counterparts. Along this line, numerous 2D functional nanohybrids comprising MO/MH NPs and graphene have been successfully constructed. Nevertheless, owing to the general incompatibility between graphene and inorganic NPs under synthetic conditions, the growth of MO/MH NPs on a graphene substrate with uniform morphology, controllable particle size, and enhanced coupling effects constitutes a highly desirable synthetic target. Polyaniline (PANI) is a typical low-cost conducting polymer that can be readily shaped into multiform morphologies, such as fibers/tubes, dots/shells, and other oriented nanostructures. Hydrothermal treatment has proven to be an excellent strategy for fabricating PANI NPs. Therefore, given that the protonated nitrogen atoms in PANI can bind with metal ions and mediate their hydrolysis process during hydrothermal treatment, we imagined that graphene-supported PANI nanosheets can facilitate the growth of MO and MH nanocrystals, and thus give rise to ternary nanohybrid sheets with a uniform distribution of hybrid NPs. Herein, we demonstrate an efficient and universal strategy for the controlled growth of MO/MH (such as Co3O4, Fe2O3, and Ni(OH)2) NPs on graphene to construct unique 2D nanohybrids employing PANI as the coupling linker between the two components. These nanohybrids have a welldefined 2D morphology, confined MO/MH NPs within the PANI nanostructures, controllable particle size, and high specific surface areas. The fabricated ternary hybrids of graphene, PANI, and Co3O4 (G-PANI-Co3O4) with a particle size of 6 to 10 nm deliver excellent rate capability and cycle performance when used as electrode materials for supercapacitors. Further, thermal treatment of G-PANI-MOs/MHs under inert gas yields nitrogen-doped carbon nanosheets integrated with size-controlled metal NPs (GNC-M). For example, N-doped carbon nanosheets supported by 3 to 5 nm sized cobalt NPs (GNC-Co) are synthesized by pyrolysis of GPANI-Co3O4. The GNC-Co nanohybrids exhibit outstanding catalytic behavior for the oxygen-reduction reaction (ORR). The overall synthetic strategy of 2D ternary graphene, PANI, and MO/MH (G-PANI-MOs/MHs)-coupled nanohybrids is illustrated in Figure 1a. First, graphene oxide (GO) nanosheets were functionalized with polyaniline by in situ polymerization of aniline in a GO suspension, which led to the formation of GO-based polyaniline (GO-PANI) nanosheets after centrifugation. Second, at pH 7 the GO-PANI nanosheets were mixed with the corresponding metal salts as the precursors of MO/MH followed by hydrothermal treatment. During this process, PANI particles formed on the graphene surface, while MO/MH NPs grew simultaneously and were confined within the PANI nanostructures. Specifically, G-PANI-Co3O4 (1:3), G-PANI-Co3O4 (1:10), and GPANI-Co3O4 (1:20) were fabricated using GO-PANI with different GO to aniline weight ratios of 1:3, 1:10, and 1:20 respectively, in the first step of the synthesis. By the similar means, graphene decorated with PANI-Fe2O3 hybrid NPs (GPANI-Fe2O3 (1:10)) and PANI-Ni(OH)2 hybrid NPs (GPANI-Ni(OH)2 (1:10)) were also synthesized. For comparison, GO-PANI nanosheets were directly treated under the same conditions with no addition of metal salts, the composites obtained were named G-PANI. The morphology and microstructures of as-prepared GOPANI, G-PANI, G-PANI-Co3O4 (1:3), G-PANI-Co3O4 (1:10), [*] S. Li, Dr. Y. Su School of Aeronautics and Astronautics Shanghai Jiao Tong University 800 Dongchuan Road, Shanghai 200240 (P.R. China) E-mail: yzsu@sjtu.edu.cn

Compact Coupled Graphene and Porous Polyaryltriazine‐Derived Frameworks as High Performance Cathodes for Lithium‐Ion Batteries

It is highly desirable to develop electroactive organic materials and their derivatives as green alternatives of cathodes for sustainable and cost-effective lithium-ion batteries (LIBs) in energy storage fields. Herein, compact two-dimensional coupled graphene and porous polyaryltriazine-derived frameworks with tailormade pore structures are fabricated by using various molecular building blocks under ionothermal conditions. The porous nanosheets display nanoscale thickness, high specific surface area, and strong coupling of electroactive polyaryltriazine-derived frameworks with graphene. All these features make it possible to efficiently depress the dissolution of redox moieties in electrolytes and to boost the electrical conductivity of whole electrode. When employed as a cathode in LIBs, the two-dimensional porous nanosheets exhibit outstanding cycle stability of 395 mAh g(-1) at 5 A g(-1) for more than 5100 cycles and excellent rate capability of 135 mAh g(-1) at a high current density of 15 A g(-1).

Molybdenum Carbide-Embedded Nitrogen-Doped Porous Carbon Nanosheets as Electrocatalysts for Water Splitting in Alkaline Media

Molybdenum carbide (Mo2C) based catalysts were found to be one of the most promising electrocatalysts for hydrogen evolution reaction (HER) in acid media in comparison with Pt-based catalysts but were seldom investigated in alkaline media, probably due to the limited active sites, poor conductivity, and high energy barrier for water dissociation. In this work, Mo2C-embedded nitrogen-doped porous carbon nanosheets (Mo2C@2D-NPCs) were successfully achieved with the help of a convenient interfacial strategy. As a HER electrocatalyst in alkaline solution, Mo2C@2D-NPC exhibited an extremely low onset potential of ∼0 mV and a current density of 10 mA cm-2 at an overpotential of ∼45 mV, which is much lower than the values of most reported HER electrocatalysts and comparable to the noble metal catalyst Pt. In addition, the Tafel slope and the exchange current density of Mo2C@2D-NPC were 46 mV decade-1 and 1.14 × 10-3 A cm-2, respectively, outperforming the state-of-the-art metal-carbide-based electrocatalysts in alkaline media. Such excellent HER activity was attributed to the rich Mo2C/NPC heterostructures and synergistic contribution of nitrogen doping, outstanding conductivity of graphene, and abundant active sites at the heterostructures.

Metal–Nitrogen Doping of Mesoporous Carbon/Graphene Nanosheets by Self‐Templating for Oxygen Reduction Electrocatalysts

We demonstrate a general and efficient self-templating strategy towards transition metal-nitrogen containing mesoporous carbon/graphene nanosheets with a unique two-dimensional (2D) morphology and tunable mesoscale porosity. Owing to the well-defined 2D morphology, nanometer-scale thickness, high specific surface area, and the simultaneous doping of the metal-nitrogen compounds, the as-prepared catalysts exhibits excellent electrocatalytic activity and stability towards the oxygen reduction reaction (ORR) in both alkaline and acidic media. More importantly, such a self-templating approach towards two-dimensional porous carbon hybrids with diverse metal-nitrogen doping opens up new avenues to mesoporous heteroatom-doped carbon materials as electrochemical catalysts for oxygen reduction and hydrogen evolution, with promising applications in fuel cell and battery technologies.

Graphene-directed two-dimensional porous carbon frameworks for high-performance lithium–sulfur battery cathodes

Graphene-directed two-dimensional (2D) nitrogen-doped porous carbon frameworks (GPF) as the hosts for sulfur were constructed via the ionothermal polymerization of 1,4-dicyanobenzene directed by the polyacrylonitrile functionalized graphene nanosheets. As cathodes for lithium–sulfur (Li–S) batteries, the prepared GPF/sulfur nanocomposites exhibited a high capacity up to 962 mA h g−1 after 120 cycles at 2 A g−1. A high reversible capacity of 591 mA h g−1 was still retained even at an extremely large current density of 20 A g−1. Such impressive electrochemical performance of GPF should benefit from the 2D hierarchical porous architecture with an extremely high specific surface area, which could facilitate the efficient entrapment of sulfur and polysulfides and afford rapid charge transfer, fast electronic conduction as well as intimate contact between active materials and the electrolyte during cycling.

Nitrogen-doped carbon-encapsulated SnO2–SnS/graphene sheets with improved anodic performance in lithium ion batteries

A dual-doping approach for nitrogen-doped carbon-coated SnO2–SnS/graphene nanosheets (N–C@SnO2–SnS/GN) has been developed, using hydrothermal carbonization of sucrose with SnO2-decorated graphene and ammonium thiocyanate and a subsequent thermal treatment. The resulting hybrid manifests a typical two-dimensional core–shell architecture, with a N-doped carbon coating over the SnS- and SnO2-decorated graphene nanosheets. Used as the anode material in lithium ion batteries (LIBs), N–C@SnO2–SnS/GN delivers a high specific capacity of 1236 mA h g−1 at a current density of 0.1 A g−1 after 110 cycles, which outperforms most state-of-the-art tin-based LIB anodes with core–shell structures.

Semiconducting single-walled carbon nanotubes synthesized by S-doping

An approach was presented for synthesis of semiconducting single-walled carbon nanotubes (SWNTs) by sulfur (S) doping with the method of graphite arc discharge. Raman spectroscopy, UV-vis-NIR absorption spectroscopy and electronic properties measurements indicated the semconducting properties of the SWNTs samples. Simulant calculation indicated that S doping could induce convertion of metallic SWNTs into semiconducting ones. This strategy may pave a way for the direct synthesis of pure semiconducting SWNTs.

Boron‐Doped, Carbon‐Coated SnO2/Graphene Nanosheets for Enhanced Lithium Storage

Heteroatom doping is an effective method to adjust the electrochemical behavior of carbonaceous materials. In this work, boron-doped, carbon-coated SnO2 /graphene hybrids (BCTGs) were fabricated by hydrothermal carbonization of sucrose in the presence of SnO2/graphene nanosheets and phenylboronic acid or boric acid as dopant source and subsequent thermal treatment. Owing to their unique 2D core-shell architecture and B-doped carbon shells, BCTGs have enhanced conductivity and extra active sites for lithium storage. With phenylboronic acid as B source, the resulting hybrid shows outstanding electrochemical performance as the anode in lithium-ion batteries with a highly stable capacity of 1165 mA h g(-1) at 0.1 A g(-1) after 360 cycles and an excellent rate capability of 600 mA h g(-1) at 3.2 A g(-1), and thus outperforms most of the previously reported SnO2-based anode materials.

An interfacial engineering approach towards two-dimensional porous carbon hybrids for high performance energy storage and conversion

In order to improve the performance and fundamental understanding of conducting polymers, development of new nanotechnologies for engineering aggregated states and morphologies is one of the central focuses for conducting polymers. In this work, we demonstrated an interfacial engineering method for the rational synthesis of a two-dimensional (2D) polyaniline (PANI) nano-array and its corresponding nitrogen-doped porous carbon nanosheets. Not only was it easy to produce a sandwich-like 2D morphology, but also the thickness, anchored ions and produced various metal phosphides were easily and rationally engineered by controlling the composition of the aqueous layer. The novel structural features of these hybrids enabled outstanding electrochemical capacitor performance. The specific capacitance of the as-produced diiron phosphide embedded nitrogen-doped porous carbon nanosheets was calculated to be as high as 1098 F g−1 at 1 A g−1 and an extremely high specific capacitance of 611 F g−1 at 10 A g−1, outperforming state-of-the-art performance among porous carbon and metal-phosphide-based supercapacitors. We believe that this interfacial approach can be extended to the controllable synthesis of various 2D material coupled sandwich-like hybrid materials with potential applications in a wide range of areas.

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.