Xizhang Wang

Nitrogen‐Doped Carbon Nanocages as Efficient Metal‐Free Electrocatalysts for Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is one of the most crucial factors limiting the performance of proton exchange membrane fuel cells due to its slow kinetics. [ 1 , 2 ] The development of effi cient ORR electrocatalysts is thus of great signifi cance. Today, platinum is usually used as the electrocatalyst for ORR; however, the large-scale application of fuel cells is hampered by the its scarcity and high cost. [ 3 ] In addition, Pt-based catalyst is sensitive to deactivation in the presence of CO, methanol and also susceptible to time-dependent drift. [ 1 ] Hence, great efforts have been devoted to exploring the advanced ORR catalysts to rival the commercial Pt/C catalyst in activity and durability with reduced Pt loading, [ 1 , 4–6 ] or nonprecious metals, [ 7–10 ] or even metalfree species. [ 11–16 ] Compared to Pt-based catalysts, metal-free catalysts have several noteable advantages, in that they do not suffer CO poisoning or crossover effects, have long-term operational stability, and are relatively cost-effective. Following the breakthrough in discovering the metal-free catalyst of PEDOT for ORR, [ 11 ] heteroatom-doped carbon nanotubes (CNTs) were demonstrated to be a new kind of promising metal-free electrocatalyst. Doping with either electron-rich nitrogen [ 12 ] or electrodefi cient boron [ 13 ] can transform CNTs into superb metal-free ORR catalysts, and the co-doping can provide further space for performance optimization, [ 14 ] which forms a scientifi cally interesting and technologically important subject today. However, there are still some key issues to address. First, enhancing the catalytic activity by increasing the specifi c surface area is an important challenge. This has proven to be diffi cult for doped CNTs, [ 17 , 18 ] although undoped CNTs have been prepared with high specifi c surface areas ( > 1200 m 2 g − 1 ) in the case of singlewalled CNTs. [ 19 ] In addition, the origin of the ORR activity for doped CNTs is still a matter of controversy and need to be further clarifi ed. [ 10 , 12 , 20–22 ] Since the metal impurities with ORR activity, i.e., the residue from the catalyst used in the growth of

Can Boron and Nitrogen Co-doping Improve Oxygen Reduction Reaction Activity of Carbon Nanotubes?

Two kinds of boron and nitrogen co-doped carbon nanotubes (CNTs) dominated by bonded or separated B and N are intentionally prepared, which present distinct oxygen reduction reaction (ORR) performances. The experimental and theoretical results indicate that the bonded case cannot, while the separated one can, turn the inert CNTs into ORR electrocatalysts. This progress demonstrates the crucial role of the doping microstructure on ORR performance, which is of significance in exploring the advanced C-based metal-free electrocatalysts.

Carbon Nanocages as Supercapacitor Electrode Materials

Supercapacitor electrode materials: Carbon nanocages are conveniently produced by an in situ MgO template method and demonstrate high specific capacitance over a wide range of charging-discharging rates with high stability, superior to the most carbonaceous supercapacitor electrode materials to date. The large specific surface area, good mesoporosity, and regular structure are responsible for the excellent performance.

Hydrophilic Hierarchical Nitrogen-Doped Carbon Nanocages for Ultrahigh Supercapacitive Performance.

The synergism of large surface area, multiscale porous structure, and good conductivity endows hierarchical carbon nanocages with high-level supercapacitive performances. Further nitrogen doping greatly improves the hydrophilicity, which boosts the supercapacitive performances to an ultrahigh specific capacitance of up to 313 F g(-1) at 1 A g(-1).

Facile Construction of Pt–Co/CNx Nanotube Electrocatalysts and Their Application to the Oxygen Reduction Reaction

A straight forward method for immobilizing Pt-Co alloyed nanoparticles onto nitrogen-doped CNx nanotubes is presented. The as-prepared electrocatalysts exhibit good performance for oxygen reduction reaction in acidic medium arising from the high-dispersion and alloying effect of the Pt-Co nanoparticles and the intrinsic catalytic capacity of the CNx nanotubes.

CNx nanofibers converted from polypyrrole nanowires as platinum support for methanol oxidation

A new kind of carbon nitride (CNx) nanofiber has been prepared by the calcination of polypyrrole nanowires at 800 °C. The product maintained a wire-like morphology during calcination, and the pyrrolic nitrogen in the polypyrrole nanowires gradually changed to pyridinic and graphitic nitrogen as annealing temperature increased. These CNx nanofibers, prepared at 800 °C, have a nitrogen concentration of about 10%. Pt nanoparticles with average size of ∼3 nm could therefore be easily immobilized onto the CNx nanofibers because of the inherent chemical activity arising from the nitrogen incorporation. The Pt/CNx composite catalyst thus obtained has a large electrochemically active area and gives good electrocatalytic performance for methanol oxidation, both in activity and stability, suggesting it has potential application in fuel cells.

CNx nanotubes as catalyst support to immobilize platinum nanoparticles for methanol oxidation

Pt nanoparticles with sizes of 3–9 nm were well dispersed on carbon nitride (CNx) nanotubes without needing pre-surface modification on the CNx nanotubes due to the inherent chemical activity. The products were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. All the experimental results revealed that Pt nanoparticles were immobilized on the CNx nanotubes due to the N-participation in the connection of Pt species with the support. The electrocatalytic property of the as-prepared Pt/CNx catalyst in methanol oxidation was examined by cyclic voltammetry. The results reveal that the so-constructed Pt/CNx catalyst has obvious catalytic activity, suggesting potential applications in fuel cells.

Porous 3D Few‐Layer Graphene‐like Carbon for Ultrahigh‐Power Supercapacitors with Well‐Defined Structure–Performance Relationship

3D few-layer graphene-like carbon with hierarchical open porous architecture is obtained by a new in situ Cu template method, leading to top-level supercapacitive performance, especially state-of-the-art power density. An effective new approach is demonstrated, which can extend the understanding of structure-performance relationships for many electrochemical energy-storage systems and form a significant complement to classical electrochemical impedance spectroscopy.

Extended vapor–liquid–solid growth and field emission properties of aluminium nitride nanowires

Hexagonal AlN (h-AlN) nanowires with an average diameter of around 15 nm have been prepared by an extended vapor–liquid–solid growth technique and characterized by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray analysis, Raman spectroscopy and field emission measurements. This preparation is a rather simple route for bulk fabrication of h-AlN nanowires. The promising field emission property observed for h-AlN nanowires points to the important application potential of this material.

Mesostructured NiO/Ni composites for high-performance electrochemical energy storage

Electrochemical energy storage (EES) devices combining high energy density with high power density are necessary for addressing the growing energy demand and environmental crisis. Nickel oxide (NiO) is a promising electrode material for EES owing to the ultrahigh theoretical specific capacity, but the practical values are far below the theoretical limit to date, with inferior rate and cycling performances. Herein, we report the novel mesostructured NiO/Ni composites, which consist of hetero-NiO/Ni components at nanoscale while displaying 3D porous architectures at mesoscale, with adjustable metallic Ni content in a wide range. The unique mesostructure boosts the EES performance of NiO to its theoretical limit with the ultrahigh specific capacity, high rate capability and stability. The superior performance is well correlated with the synergism of the high accessibility to electrolyte, short solid-state ion diffusion length, and much enhanced conductivity of the mesostructured NiO/Ni composites. This study demonstrates a new strategy likely applicable to other transition metal oxides in maximizing their potential in energy storage, i.e. by constructing the similar mesostructured metal-oxide/metal composites.