Chenbao Lu

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.

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.

Cobalt/nitrogen co-doped porous carbon nanosheets as highly efficient catalysts for the oxygen reduction reaction in both basic and acidic media

Porous carbon materials have been widely developed as catalysts for the oxygen reduction reaction (ORR) under basic conditions but very few under acidic conditions. In this work, two-dimensional (2D) cobalt/nitrogen co-doped porous carbon nanosheets were prepared as catalysts for the ORR under both basic and acidic conditions by using a cobalt porphyrin based 2D conjugated microporous polymer as a precursor. Remarkably, the as-prepared porous carbon nanosheets exhibited excellent electrochemical catalytic performance for the ORR, with a low half-wave potential (E1/2) at −0.146 V in 0.1 M KOH and 0.54 V in 0.5 M H2SO4 (versus Ag/AgCl) as well as a dominant four-electron transfer mechanism (n = 3.8 at −0.28 V in 0.1 M KOH; n = 3.8 at 0.55 V in 0.5 M H2SO4). The high catalytic ORR performance can be attributed to the high activity of CoNx active sites as well as the high specific surface area that derived from the cobalt porphyrin blocks among the conjugated microporous polymer nanosheets. Its believed that this method opens up new avenues for metal/heteroatom co-doped porous carbon materials with promising performance for energy storage and conversion.

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.

Cobaloxime anchored MoS2 nanosheets as electrocatalysts for the hydrogen evolution reaction

Molybdenum disulfide (MoS2) has emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER). However, the catalytic performance of pure MoS2 is not as good as expected due to the limited active sites at the surface. Herein, cobaloxime anchored MoS2 nanosheets (MoS2–Co(dmgBF2)2) were successfully developed as electrocatalysts for the HER in acidic media. Remarkably, MoS2–Co(dmgBF2)2 delivered a current density of 10 mA cm−2 at a low overpotential of approximately 103 mV versus the reversible hydrogen electrode, which is much lower than the values of most reported MoS2-based HER electrocatalysts. In addition, the Tafel slope and the exchange current density of MoS2–Co(dmgBF2)2 were calculated to be 45 mV dec−1 and 64.5 μA cm−2, respectively. Such superior HER activity can be attributed to the abundant active sites from both the edges and the modified basal planes. We believe that this approach not only provides a new method to functionalize MoS2 through coordination, but also offers a new approach to integrate homogeneous and heterogeneous catalysts for the HER.

Polymer nanosheets derived porous carbon nanosheets as high efficient electrocatalysts for oxygen reduction reaction

Porous carbon nanosheets and corresponding heteroatom doped porous carbon nanosheets have shown great potential as active materials for energy conversion and storage in recent years. However, it remains great challenge to prepare such kind of new two-dimensional (2D) polymer nanosheets without using any templates. In this work, thiadiazole-containing expanded heteroazaporphyrinoid was designed as the building blocks for preparation of free-standing N/S-containing polymer nanosheets (PN) without using any templates. Most importantly, such PN can coordinate with transition metal ions to prepare Fe, N, and S containing PN-Fe. By using these PN-Fe as precursors, Fe/N/S co-doped porous carbon nanosheets (PCN-FeNS) can be facilely prepared by direct pyrolysis under inert condition. The N and S contents of PCN-FeNS can reach up to 6.4 at.% and 0.8 at.%, respectively. For proof-of-concept, PCN-FeNS were further used as electrochemical catalysts for oxygen reduction reaction (ORR) in both alkaline and neutral media. Benefiting from the high surface area and rich-doping character, PCN-FeNS exhibited relatively high half-wave potential of down to 0.71 V, via a four-electron transfer mechanism (n = 3.87 at 0.65 V), as well as high diffusion limiting current density (JL = 5.02 mA cm-2), which are comparable to commercial precious metal based electrocatalysts. This study not only offers a new method to prepare conjugated polymer nanosheets, but also provides a new strategy to fabricate Fe/N/S co-doped porous carbon nanosheets for versatile energy-related applications.

S-enriched porous polymer derived N-doped porous carbons for electrochemical energy storage and conversion

Porous polymers have been recently recognized as one of the most important precursors for fabrication of heteroatom-doped porous carbons due to the intrinsic porous structure, easy available heteroatom-containing monomers and versatile polymerization methods. However, the heteroatom elements in as-produced porous carbons are quite relied on monomers. So far, the manipulating of heteroatom in porous polymer derived porous carbons are still very rare and challenge. In this work, a sulfur-enriched porous polymer, which was prepared from a diacetylene-linked porous polymer, was used as precursor to prepare S-doped and/or N-doped porous carbons under nitrogen and/or ammonia atmospheres. Remarkably, S content can sharply decrease from 36.3% to 0.05% after ammonia treatment. The N content and specific surface area of as-fabricated porous carbons can reach up to 1.32% and 1508 m2∙g–1, respectively. As the electrode materials for electrical double-layer capacitors, as-fabricated porous carbons exhibit high specific capacitance of up to 431.6 F∙g–1 at 5 mV∙s–1 and excellent cycling stability of 99.74% capacitance retention after 3000 cycles at 100 mV∙s–1. Furthermore, as the electrochemical catalysts for oxygen reduction reaction, as-fabricated porous carbons presented ultralow half-wave-potential of 0.78 V versus RHE. This work not only offers a new strategy for manipulating S and N doping features for the porous carbons derived from S-containing porous polymers, but also paves the way for the structureperformance interrelationship study of heteroatoms codoped porous carbon for energy applications.