WC Nanocrystals Grown on Vertically Aligned Carbon Nanotubes: An Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction

Single nanocrystalline tungsten carbide (WC) was first synthesized on the tips of vertically aligned carbon nanotubes (VA-CNTs) with a hot filament chemical vapor deposition (HF-CVD) method through the directly reaction of tungsten metal with carbon source. The VA-CNTs with preservation of vertical structure integrity and alignment play an important role to support the nanocrystalline WC growth. With the high crystallinity, small size, and uniform distribution of WC particles on the carbon support, the formed WC–CNTs material exhibited an excellent catalytic activity for hydrogen evolution reaction (HER), giving a η₁₀ (the overpotential for driving a current of 10 mA cm^–2) of 145 mV, onset potential of 15 mV, exchange current density@ 300 mV of 117.6 mV and Tafel slope values of 72 mV dec^–1 in acid solution, and η₁₀ of 137 mV, onset potential of 16 mV, exchange current density@ 300 mV of 33.1 mV and Tafel slope values of 106 mV dec^–1 in alkaline media, respectively. Electrochemical stability test further confirms the long-term operation of the catalyst in both acidic and alkaline media

M₃C (M: Fe, Co, Ni) Nanocrystals Encased in Graphene Nanoribbons: An Active and Stable Bifunctional Electrocatalyst for Oxygen Reduction and Hydrogen Evolution Reactions

Transition metal carbide nanocrystalline M₃C (M: Fe, Co, Ni) encapsulated in graphitic shells supported with vertically aligned graphene nanoribbons (VA-GNRs) are synthesized through a hot filament chemical vapor deposition (HF-CVD) method. The process is based on the direct reaction between iron group metals (Fe, Co, Ni) and carbon source, which are facilely get high purity carbide nanocrystals (NCs) and avoid any other impurity at relatively low temperature. The M₃C-GNRs exhibit superior enhanced electrocatalystic activity for oxygen reduction reaction (ORR), including low Tafel slope (39, 41, and 45 mV dec^–1 for Fe₃C-GNRs, Co₃C-GNRs, and Ni₃C-GNRs, respectively), positive onset potential (∼0.8 V), high electron transfer number (∼4), and long-term stability (no obvious drop after 20 000 s test). The M₃C-GNRs catalyst also exhibits remarkable hydrogen evolution reaction (HER) activity with a large cathodic current density of 166.6, 79.6, and 116.4 mA cm^–2 at an overpotential of 200 mV, low onset overpotential of 32, 41, and 35 mV, small Tafel slope of 46, 57, and 54 mV dec^–1 for Fe₃C-GNRs, Co₃C-GNRs, and Ni₃C-GNRs, respectively, as well as an excellent stability in acidic media

Hydrothermally Formed Three-Dimensional Nanoporous Ni(OH)₂ Thin-Film Supercapacitors

A three-dimensional nanoporous Ni(OH)₂ thin-film was hydrothermally converted from an anodically formed porous layer of nickel fluoride/oxide. The nanoporous Ni(OH)₂ thin-films can be used as additive-free electrodes for energy storage. The nanoporous layer delivers a high capacitance of 1765 F g^–1 under three electrode testing. After assembly with porous activated carbon in asymmetric supercapacitor configurations, the devices deliver superior supercapacitive performances with capacitance of 192 F g^–1, energy density of 68 Wh kg^–1, and power density of 44 kW kg^–1. The wide working potential window (up to 1.6 V in 6 M aq KOH) and stable cyclability (∼90% capacitance retention over 10 000 cycles) make the thin-film ideal for practical supercapacitor devices

Three-Dimensional Nanoporous Fe₂O₃/Fe₃C‑Graphene Heterogeneous Thin Films for Lithium-Ion Batteries

Three-dimensional self-organized nanoporous thin films integrated into a heterogeneous Fe₂O₃/Fe₃C-graphene structure were fabricated using chemical vapor deposition. Few-layer graphene coated on the nanoporous thin film was used as a conductive passivation layer, and Fe₃C was introduced to improve capacity retention and stability of the nanoporous layer. A possible interfacial lithium storage effect was anticipated to provide additional charge storage in the electrode. These nanoporous layers, when used as an anode in lithium-ion batteries, deliver greatly enhanced cyclability and rate capacity compared with pristine Fe₂O₃: a specific capacity of 356 μAh cm^–2 μm^–1 (3560 mAh cm^–3 or ∼1118 mAh g^–1) obtained at a discharge current density of 50 μA cm^–2 (∼0.17 C) with 88% retention after 100 cycles and 165 μAh cm^–2 μm^–1 (1650 mAh cm^–3 or ∼518 mAh g^–1) obtained at a discharge current density of 1000 μA cm^–2 (∼6.6 C) for 1000 cycles were achieved. Meanwhile an energy density of 294 μWh cm^–2 μm^–1 (2.94 Wh cm^–3 or ∼924 Wh kg^–1) and power density of 584 μW cm^–2 μm^–1 (5.84 W cm^–3 or ∼1834 W kg^–1) were also obtained, which may make these thin film anodes promising as a power supply for micro- or even nanosized portable electronic devices

Three-Dimensional Thin Film for Lithium-Ion Batteries and Supercapacitors

Three-dimensional heterogeneously nanostructured thin-film electrodes were fabricated by using Ta₂O₅ nanotubes as a framework to support carbon-onion-coated Fe₂O₃ nanoparticles along the surface of the nanotubes. Carbon onion layers function as microelectrodes to separate the two different metal oxides and form a nanoscale 3-D sandwich structure. In this way, space-charge layers were formed at the phase boundaries, and it provides additional energy storage by charge separation. These 3-D nanostructured thin films deliver both excellent Li-ion battery properties (stabilized at 800 mAh cm^–3) and supercapacitor (up to 18.2 mF cm^–2) performance owing to the synergistic effects of the heterogeneous structure. Thus, Li-ion batteries and supercapacitors are successfully assembled into the same electrode, which is promising for next generation hybrid energy storage and delivery devices

Boron- and Nitrogen-Doped Graphene Quantum Dots/Graphene Hybrid Nanoplatelets as Efficient Electrocatalysts for Oxygen Reduction

The scarcity and high cost of platinum-based electrocatalysts for the oxygen reduction reaction (ORR) has limited the commercial and scalable use of fuel cells. Heteroatom-doped nanocarbon materials have been demonstrated to be efficient alternative catalysts for ORR. Here, graphene quantum dots, synthesized from inexpensive and earth-abundant anthracite coal, were self-assembled on graphene by hydrothermal treatment to form hybrid nanoplatelets that were then codoped with nitrogen and boron by high-temperature annealing. This hybrid material combined the advantages of both components, such as abundant edges and doping sites, high electrical conductivity, and high surface area, which makes the resulting materials excellent oxygen reduction electrocatalysts with activity even higher than that of commercial Pt/C in alkaline media

Lithium Batteries with Nearly Maximum Metal Storage

The drive for significant advancement in battery capacity and energy density inspired a revisit to the use of Li metal anodes. We report the use of a seamless graphene–carbon nanotube (GCNT) electrode to reversibly store Li metal with complete dendrite formation suppression. The GCNT-Li capacity of 3351 mAh g^–1_GCNT‑Li approaches that of bare Li metal (3861 mAh g^–1_Li), indicating the low contributing mass of GCNT, while yielding a practical areal capacity up to 4 mAh cm^–2 and cycle stability. A full battery based on GCNT-Li/sulfurized carbon (SC) is demonstrated with high energy density (752 Wh kg^–1 total electrodes, where total electrodes = GCNT-Li + SC + binder), high areal capacity (2 mAh cm^–2), and cyclability (80% retention at >500 cycles) and is free of Li polysulfides and dendrites that would cause severe capacity fade

Growing Carbon Nanotubes from Both Sides of Graphene

The design and synthesis of hybrid structures between graphene and carbon nanotubes is an intriguing topic in the field of carbon nanomaterials. Here the synthesis of vertically aligned CNT carpets underneath graphene and from both sides of graphene is described with continuous ordering over a large area. Scanning electron microscopy and Raman spectroscopic characterizations show that CNT carpets grow underneath graphene through a base-growth mechanism, and grow on top of graphene through a tip-growth mechanism. Good electrical contact is observed from the top CNT carpets, through the graphene layer, to the bottom CNT carpets. This sandwich-like CNT/graphene/CNT hybrid structure could provide an approach to design and fabricate multilayered graphene/CNTs materials, as well as potential applications in the fields of nanomanufacturing and energy storage

Hydrogen Diffusion and Stabilization in Single-Crystal VO₂ Micro/Nanobeams by Direct Atomic Hydrogenation

We report measurements of the diffusion of atomic hydrogen in single crystalline VO₂ micro/nanobeams by direct exposure to atomic hydrogen, without catalyst. The atomic hydrogen is generated by a hot filament, and the doping process takes place at moderate temperature (373 K). Undoped VO₂ has a metal-to-insulator phase transition at ∼340 K between a high-temperature, rutile, metallic phase and a low-temperature, monoclinic, insulating phase with a resistance exhibiting a semiconductor-like temperature dependence. Atomic hydrogenation results in stabilization of the metallic phase of VO₂ micro/nanobeams down to 2 K, the lowest point we could reach in our measurement setup. Optical characterization shows that hydrogen atoms prefer to diffuse along the <i>c</i> axis of rutile (<i>a</i> axis of monoclinic) VO₂, along the oxygen “channels”. Based on observing the movement of the hydrogen diffusion front in single crystalline VO₂ beams, we estimate the diffusion constant for hydrogen along the <i>c</i> axis of the rutile phase to be 6.7 × 10^–10 cm²/s at approximately 373 K, exceeding the value in isostructural TiO₂ by ∼38×. Moreover, we find that the diffusion constant along the <i>c</i> axis of the rutile phase exceeds that along the equivalent <i>a</i> axis of the monoclinic phase by at least 3 orders of magnitude. This remarkable change in kinetics must originate from the distortion of the “channels” when the unit cell doubles along this direction upon cooling into the monoclinic structure. Ab initio calculation results are in good agreement with the experimental trends in the relative kinetics of the two phases. This raises the possibility of a switchable membrane for hydrogen transport

Targeted delivery of doxorubicin by CSA-binding nanoparticles for choriocarcinoma treatment

<p>Gestational trophoblastic neoplasia (GTN) can result from the over-proliferation of trophoblasts. Treatment of choriocarcinoma, the most aggressive GTN, currently requires high doses of systemic chemotherapeutic agents, which result in indiscriminate drug distribution and severe toxicity. To overcome these disadvantages and enhance the chemotherapeutic efficacy, chondroitin sulfate A (CSA)-binding nanoparticles were developed for the targeted delivery of doxorubicin (DOX) to choriocarcinoma cells using a synthetic CSA-binding peptide (CSA-BP), derived from malarial protein, which specifically binds to the CSA exclusively expressed in the placental trophoblast. CSA-BP-conjugated nanoparticles rapidly bonded to choriocarcinoma (JEG3) cells and were efficiently internalized into the lysosomes. Moreover, CSA-BP modification significantly increased the anti-cancer activity of the DOX-loaded nanoparticles <i>in vitro</i>. Intravenous injections of CSA-BP-conjugated nanoparticles loaded with indocyanine green (CSA-INPs) were rapidly localized to the tumor. The CSA-targeted nanoparticles loaded with DOX (CSA-DNPs) strongly inhibited primary tumor growth and, more importantly, significantly suppressed metastasis <i>in vivo</i>. Collectively, our results highlight the potential of the CSA-BP-decorated nanoparticles as an alternative targeted delivery system of chemotherapeutic agents for treating choriocarcinoma and for developing new GTN therapies based on drug targeting.</p