MOF-derived nitrogen-doped porous carbon nanofibers with interconnected channels for high-stability Li+/Na+ battery anodes.

Heteroatom-doped porous carbon materials have been widely used as anode materials for Li-ion and Na-ion batteries, however, improving the specific capacity and long-term cycling stability of ion batteries remains a major challenge. Here, we report a facile based metal-organic framework (MOFs) strategy to synthesize nitrogen-doped porous carbon nanofibers (NCNFs) with a large number of interconnected channels that can increase the contact area between the material and the electrolyte, shorten the diffusion distance between Li+/Na+ and the electrolyte, and relieve the volume expansion of the electrode material during cycling; the doping of nitrogen atoms can improve the conductivity and increase the active sites of the carbon material, can also affect the microstructure and electron distribution of the electrode material, thereby improving the electrochemical performance of the material. As expected, the obtained NCNFs-800 exhibited excellent electrochemical performance with high reversible capacity (for Li+ battery anodes: 1237 mA h g-1 at 100 mA g-1 after 200 cycles, for Na+ battery anodes: 323 mA h g-1 at 100 mA g-1 after 150 cycles) and long-term cycling stability (for Li+ battery anodes: 635 mA h g-1 at 2 A g-1 after 5000 cycles, for Na+ battery anodes: 194 mA h g-1 at 2 A g-1 after 5000 cycles).

Optimizing the Interlayer Spacing of Heteroatom-Doped Carbon Nanofibers toward Ultrahigh Potassium-Storage Performances.

Precise control over the interlayer spacing for K+ intercalation is an effective approach to boost the potassium-storage performances in carbonaceous materials. Herein, we first found that the optimal interlayer spacing for K+ intercalation is around 0.38 nm for N, O codoped carbon nanofibers (NOCNs), displaying a reversible capacity of 627 mAh g-1 at 0.1 A g-1 after 200 cycles, excellent rate capability (123 mAh g-1 at 20 A g-1), and ultrastable cycling stability (262 mAh g-1 at 5 A g-1 after 10 000 cycles). Such good potassium-storage performances have never been reported in carbonaceous materials. The theoretical calculations and electrochemical studies reveal that the optimal interlayer spacing and N, O heteroatom-induced active sites work together to provide an intercalation-adsorption mechanism for storing K+ in carbonaceous materials. This work facilitates the understanding of the role of the critical interlayer spacing for K+ intercalation in carbonaceous materials.

Heteroatom-doped carbon materials with interconnected channels as ultrastable anodes for lithium/sodium ion batteries.

Carbon materials have been extensively investigated as promising negative electrode materials for lithium/sodium ion batteries. However, most common carbon materials always suffer from limitations in regards to high reversible capacity and long-term cycling stability because of their low theoretical specific capacities and sluggish kinetics. Herein, we report a facile MOF-derived strategy for the synthesis of nitrogen/oxygen co-doped porous carbon polyhedra (NOPCP) with abundant channel-connected cavities with their inner surface decorated with a large number of N and O atoms, which can provide a large number of active sites (defects and edge doping sites) for the sorption of Li+/Na+. These cavities can also be considered as "ponds" where the electrolyte is stored, which shortens the diffusion distance of ions during the discharge/charge process. When evaluated as an anode material for LIBs, NOPCP-600 delivers a high reversible capacity of 1663 mA h g-1 at 0.1 A g-1 after 120 cycles and superior cycling stability with a capacity of 667 mA h g-1 after 1000 cycles at 2 A g-1. For SIBs, NOPCP-600 delivers a high reversible capacity of 313 mA h g-1 at 0.1 A g-1 after 100 cycles and an excellent long-term cycling stability of 228 mA h g-1 at 1 A g-1 after 2000 cycles.

Synergistic Tuning of the Electronic Structure of Mo2C by P and Ni Codoping for Optimizing Electrocatalytic Hydrogen Evolution.

Developing earth-abundant and highly efficient nonprecious metal catalysts for hydrogen evolution reaction (HER) is critical for the storage and conversion of renewable energy sources. Molybdenum carbide (Mo2C) has been extensively investigated as one of the most promising nonprecious electrocatalysts for boosting HER because of its low cost, high electrical conductivity, good chemical structure, and similar electronic structure to that of Pt. However, Mo2C always exhibits the negative hydrogen-binding energy, which can largely prevent adsorbed H desorption during the HER process. Herein, we report P- and Ni-dual-doped Mo2C in porous nitrogen-doped carbon (P/Ni-Mo2C) as an electrocatalyst for the HER, exhibiting excellent activity and durability with a low overpotential of 165 mV at 10 mA cm-2 in alkaline electrolyte. Density functional theory (DFT) calculations proved that P and Ni acted as the anion and cation, respectively, to synergistically tune the electronic properties of Mo2C to decrease the negative hydrogen-binding energy, endowing the catalyst with excellent catalytic performance for the HER.

NiRu nanoparticles encapsulated in a nitrogen-doped carbon matrix as a highly efficient electrocatalyst for the hydrogen evolution reaction.

The design and fabrication of low-cost, efficient, and robust electrocatalysts for the hydrogen evolution reaction (HER) is of great importance in accelerating the development of water electrolysis technology. Herein, NiRu alloy nanostructures embedded in a nitrogen-doped carbon matrix (NiRu@NC) have been fabricated through a facile metal-organic framework-derived (MOF-derived) strategy. Benefiting from their advantages in the unique structures and components, the resulting NiRu@NC possesses excellent activity and durability towards the HER, which exhibits low overpotentials of 85 and 53 mV at a current density of 10 mA cm-2 in acidic and alkaline electrolytes, respectively. Furthermore, NiRu2@NC-600 also exhibits excellent hydrogen oxidation reaction (HOR) activity in an alkaline electrolyte. Therefore, this work provides a facile MOF-derived strategy for the design and synthesis of low-cost and efficient electrocatalysts for the HER.

Porous CuO@C composite as high-performance anode materials for lithium-ion batteries.

Though carbon matrices could effectively improve the electrical conductivity and accommodate the volume expansion of CuO-based anode materials for lithium ion batteries (LIBs), achieving an optimized utilization ratio of the active CuO component remains a big challenge. In this work, we developed a metal-organic framework (MOF)-derived strategy to synthesize ultrafine CuO nanoparticles embedded in a porous carbon matrix (CuO@C). Benefiting from its unique structure, the resulting CuO@C exhibits a high reversible capacity of 1024 mA h g-1 at 100 mA g-1 after 100 cycles and a long-term cycling stability with a reversible capacity of 613 mA h g-1 at 500 mA g-1 over 700 cycles. The outstanding Li-storage performances can be attributed to its porous carbon matrix and ultrafine CuO nanoparticles with more exposed active sites for electrochemical reactions.

MOF-derived hollow NiCo2O4 nanowires as stable Li-ion battery anodes.

Although binary metal oxides with high theoretical specific capacities and power densities are widely investigated as promising anode materials for lithium-ion batteries (LIBs), their poor cycling stability and huge volume expansion largely limit their extensive application in practical electrode materials. Herein, we report a facile strategy to synthesize hollow NiCo2O4 nanowires through direct calcination of binary metal-organic frameworks (MOFs) in air. When evaluated as an anode material for LIBs, NiCo2O4 nanowires deliver a reversible capacity of 1310 mA h g-1 at a current density of 100 mA g-1 after 100 cycles. Even at a high current density of 1 A g-1, NiCo2O4 nanowires exhibit long-term cycling stability with a capacity of 720 mA h g-1 after 1000 cycles. The outstanding lithium-storage performance can be attributed to the unique structures with 1D porous channels, which are beneficial for the fast transfer of Li+ ions and electrolyte and alleviate the strain caused by the volume expansion during cycling processes.