Jiantao Li

Low-crystalline iron oxide hydroxide nanoparticle anode for high-performance supercapacitors

Carbon materials are generally preferred as anodes in supercapacitors; however, their low capacitance limits the attained energy density of supercapacitor devices with aqueous electrolytes. Here, we report a low-crystalline iron oxide hydroxide nanoparticle anode with comprehensive electrochemical performance at a wide potential window. The iron oxide hydroxide nanoparticles present capacitances of 1,066 and 716 F g−1 at mass loadings of 1.6 and 9.1 mg cm−2, respectively, a rate capability with 74.6% of capacitance retention at 30 A g−1, and cycling stability retaining 91% of capacitance after 10,000 cycles. The performance is attributed to a dominant capacitive charge-storage mechanism. An aqueous hybrid supercapacitor based on the iron oxide hydroxide anode shows stability during float voltage test for 450 h and an energy density of 104 Wh kg−1 at a power density of 1.27 kW kg−1. A packaged device delivers gravimetric and volumetric energy densities of 33.14 Wh kg−1 and 17.24 Wh l−1, respectively.

General Oriented Formation of Carbon Nanotubes from Metal–Organic Frameworks

Carbon nanotubes (CNTs) are of great interest for many potential applications because of their extraordinary electronic, mechanical and structural properties. However, issues of chaotic staking, high cost and high energy dissipation in the synthesis of CNTs remain to be resolved. Here we develop a facile, general and high-yield strategy for the oriented formation of CNTs from metal-organic frameworks (MOFs) through a low-temperature (as low as 430 °C) pyrolysis process. The selected MOF crystals act as a single precursor for both nanocatalysts and carbon sources. The key to the formation of CNTs is obtaining small nanocatalysts with high activity during the pyrolysis process. This method is successfully extended to obtain various oriented CNT-assembled architectures by modulating the corresponding MOFs, which further homogeneously incorporate heteroatoms into the CNTs. Specifically, nitrogen-doped CNT-assembled hollow structures exhibit excellent performances in both energy conversion and storage. On the basis of experimental analyses and density functional theory simulations, these superior performances are attributed to synergistic effects between ideal components and multilevel structures. Additionally, the appropriate graphitic N doping and the confined metal nanoparticles in CNTs both increase the densities of states near the Fermi level and reduce the work function, hence efficiently enhancing its oxygen reduction activity. The viable synthetic strategy and proposed mechanism will stimulate the rapid development of CNTs in frontier fields.

Porous Nickel–Iron Selenide Nanosheets as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction

Exploring non-noble and high-efficiency electrocatalysts is critical to large-scale industrial applications of electrochemical water splitting. Currently, nickel-based selenide materials are promising candidates for oxygen evolution reaction due to their low cost and excellent performance. In this work, we report the porous nickel-iron bimetallic selenide nanosheets ((Ni0.75Fe0.25)Se2) on carbon fiber cloth (CFC) by selenization of the ultrathin NiFe-based nanosheet precursor. The as-prepared three-dimensional oxygen evolution electrode exhibits a small overpotential of 255 mV at 35 mA cm(-2) and a low Tafel slope of 47.2 mV dec(-1) and keeps high stability during a 28 h measurement in alkaline solution. The outstanding catalytic performance and strong durability, in comparison to the advanced non-noble metal catalysts, are derived from the porous nanostructure fabrication, Fe incorporation, and selenization, which result in fast charge transportation and large electrochemically active surface area and enhance the release of oxygen bubbles from the electrode surface.

Interface-modulated approach toward multilevel metal oxide nanotubes for lithium-ion batteries and oxygen reduction reaction

Metal oxide hollow structures with multilevel interiors are of great interest for potential applications such as catalysis, chemical sensing, drug delivery, and energy storage. However, the controlled synthesis of multilevel nanotubes remains a great challenge. Here we develop a facile interface-modulated approach toward the synthesis of complex metal oxide multilevel nanotubes with tunable interior structures through electrospinning followed by controlled heat treatment. This versatile strategy can be effectively applied to fabricate wire-in-tube and tube-in-tube nanotubes of various metal oxides. These multilevel nanotubes possess a large specific surface area, fast mass transport, good strain accommodation, and high packing density, which are advantageous for lithium-ion batteries (LIBs) and the oxygen reduction reaction (ORR). Specifically, shrinkable CoMn2O4 tube-in-tube nanotubes as a lithium-ion battery anode deliver a high discharge capacity of ~565 mAh·g−1 at a high rate of 2 A·g−1, maintaining 89% of the latter after 500 cycles. Further, as an oxygen reduction reaction catalyst, these nanotubes also exhibit excellent stability with about 92% current retention after 30,000 s, which is higher than that of commercial Pt/C (81%). Therefore, this feasible method may push the rapid development of one-dimensional (1D) nanomaterials. These multifunctional nanotubes have great potential in many frontier fields.

Highly Durable Na2V6O16·1.63H2O Nanowire Cathode for Aqueous Zinc-Ion Battery

Rechargeable aqueous zinc-ion batteries are highly desirable for grid-scale applications due to their low cost and high safety; however, the poor cycling stability hinders their widespread application. Herein, a highly durable zinc-ion battery system with a Na2V6O16·1.63H2O nanowire cathode and an aqueous Zn(CF3SO3)2 electrolyte has been developed. The Na2V6O16·1.63H2O nanowires deliver a high specific capacity of 352 mAh g-1 at 50 mA g-1 and exhibit a capacity retention of 90% over 6000 cycles at 5000 mA g-1, which represents the best cycling performance compared with all previous reports. In contrast, the NaV3O8 nanowires maintain only 17% of the initial capacity after 4000 cycles at 5000 mA g-1. A single-nanowire-based zinc-ion battery is assembled, which reveals the intrinsic Zn2+ storage mechanism at nanoscale. The remarkable electrochemical performance especially the long-term cycling stability makes Na2V6O16·1.63H2O a promising cathode for a low-cost and safe aqueous zinc-ion battery.

General Oriented Synthesis of Precise Carbon-Confined Nanostructures by Low-Pressure Vapor Superassembly and Controlled Pyrolysis

Earth-abundant metal-based nanostructured materials have been widely studied for potential energy conversion and storage. However, controlled synthesis of functional nanostructures with high electron conductivity, high reaction activity, and structural stability is still a formidable challenge for further practical applications. Herein, for the first time, we develop a facile, efficient, and general method for the oriented synthesis of precise carbon-confined nanostructures by low-pressure vapor superassembly of a thin metal-organic framework (MOF) shell and subsequent controlled pyrolysis. The selected nanostructured metal oxide precursors not only act as metal ion sources but also orient the superassembly of gaseous organic ligands through the coordination reactions under the low-pressure condition, resulting in the formation of a tunable MOF shell on their surfaces. This strategy is further successfully extended to obtain various precise carbon-confined nanostructures with diverse compositions and delicate morphologies. Notably, these as-prepared carbon-confined architectures exhibit outstanding electrochemical performances in water splitting and lithium storage. The remarkable performances are mainly attributed to the synergistic effect from appropriate chemical compositions and stable carbon-confined structures. This synthetic approach and proposed mechanism open new avenues for the development of functional nanostructured materials in many frontier fields.

Facet-Selective Deposition of FeOx on α-MoO3 Nanobelts for Lithium Storage

One-dimensional heterostructures have attracted significant interests in various applications. However, the selective deposition of shell material on specific sites of the backbone material remains a challenge. Herein, a facile facet-selective deposition strategy has been developed for the construction of heterostructured α-MoO3@FeOx nanobelts. Because of the anisotropic feature of α-MoO3 nanobelts, the FeOx nanoparticles selectively deposit on the edges of α-MoO3 nanobelts, that is, the {100} and {001} facets. Such a heterostructure facilitates the electron transfer in lithium storage. As a result, the α-MoO3@FeOx nanobelts exhibit high capacities of 913 mA h g-1 after 100 cycles at 200 mA g-1 and 540 mA h g-1 after 100 cycles at 1000 mA g-1. The facet-selective deposition strategy developed here would be extended to the construction of other novel heterostructures with fascinating physical/chemical properties and wide potential applications.

High-Performance Na–O2 Batteries Enabled by Oriented NaO2 Nanowires as Discharge Products

Na-O2 batteries are emerging rechargeable batteries due to their high theoretical energy density and abundant resources, but they suffer from sluggish kinetics due to the formation of large-size discharge products with cubic or irregular particle shapes. Here, we report the unique growth of discharge products of NaO2 nanowires inside Na-O2 batteries that significantly boosts the performance of Na-O2 batteries. For this purpose, a high-spin Co3O4 electrocatalyst was synthesized via the high-temperature oxidation of pure cobalt nanoparticles in an external magnetic field. The discharge products of NaO2 nanowires are 10-20 nm in diameter and ∼10 μm in length, characteristics that provide facile pathways for electron and ion transfer. With these nanowires, Na-O2 batteries have surpassed 400 cycles with a fixed capacity of 1000 mA h g-1, an ultra-low over-potential of ∼60 mV during charging, and near-zero over-potential during discharging. This strategy not only provides a unique way to control the morphology of discharge products to achieve high-performance Na-O2 batteries but also opens up the opportunity to explore growing nanowires in novel conditions.

Oxygen Vacancy-Determined Highly Efficient Oxygen Reduction in NiCo2O4/Hollow Carbon Spheres

Rationally generating oxygen vacancies in electrocatalysts is an important approach to modulate the electrochemical activity of a catalyst. Herein, we report a remarkable enhancement in oxygen reduction reaction (ORR) activity of NiCo2O4 supported on hollow carbon spheres (HCS) achieved through generating abundant oxygen vacancies within the surface lattice. This catalyst exhibits enhanced ORR activity (larger limiting current density of ∼-5.8 mA cm-2) and higher stability (∼90% retention after 40 000 s) compared with those of NiCo2O4/HCS and NiCo2O4. The results of X-ray photoelectron spectroscopy (XPS) characterizations suggest that the introduction of oxygen vacancies optimizes the valence state of active sites. Furthermore, we carried out density functional theory (DFT) calculations to further confirm the mechanism of oxygen vacancies, and results show that oxygen vacancies enhance the density of states (DOS) near the Fermi level, decrease work function, and lower the calculated overpotential of NiCo2O4.

Porous nitrogen-doped carbon/MnO coaxial nanotubes as an efficient sulfur host for lithium sulfur batteries

As a promising candidate for next generation energy storage devices, lithium sulfur (Li-S) batteries still confront rapid capacity degradation and low rate capability. Herein, we report a well-architected porous nitrogen-doped carbon/MnO coaxial nanotubes (MnO@PNC) as an efficient sulfur host material. The host shows excellent electron conductivity, sufficient ion transport channels and strong adsorption capability for the polysulfides, resulting from the abundant nitrogen-doped sites and pores as well as MnO in the carbon shell of MnO@PNC. The MnO@PNC-S composite electrode with a sulfur content of 75 wt.% deliveries a specific capacity of 802 mAh·g–1 at a high rate of 5.0 C and outstanding cycling stability with a capacity retention of 82% after 520 cycles at 1.0 C.