8 research outputs found
Enhanced Oxygen Evolution Reaction Electrocatalysis via Electrodeposited Amorphous α‑Phase Nickel-Cobalt Hydroxide Nanodendrite Forests
We demonstrate an
electrodeposition method to rapidly grow novel
three-dimensional nanodendrite forests of amorphous α-phase
mixed nickel-cobalt hydroxides on stainless steel foil toward high
performance electrocatalysis of the oxygen evolution reaction (OER).
The proposed hydrogen bubble-templated, diffusion-limited deposition
process leads to the unprecedented dendritic growth of vertically
aligned amorphous metal hydroxides, induced by the controlled electrolysis
of the tuned water content in the primarily alcohol-based deposition
solution. The hierarchical nature of these binder-free, amorphous
metal hydroxide deposits leads to their superhydrophilic nature and
underwater superaerophobic behavior. The combination of all of these
qualities leads to exemplary catalytic performance. When directly
grown on planar stainless steel substrates, these nanoforests show
high OER activity with overpotentials as low as ∼255 mV to
produce a current density of 10 mA cm<sup>–2</sup> over 10 000
accelerated stability test cycles. This work demonstrates a novel
fabrication technique that can simultaneously achieve a dendritic
hierarchical structure, vertical alignment, superaerophobicity, amorphous
crystal structure, and intimate contact with the substrate that leads
to high catalytic activity with excellent durability
High voltage electrophoretic deposition of aligned nanoforests for scalable nanomanufacturing of electrochemical energy storage devices
High voltage electrophoretic deposition (HVEPD) has been used to obtain forests of aligned multi-walled carbon nanotubes (MWCNTs) on long strips of flexible, conductive substrates. Successful design and integration of a continuous HVEPD setup has enabled scalable fabrication of electrodes for electrochemical energy storage. The mechanism of continuous HVEPD has been investigated to ensure appropriate alignment. Well-aligned forests of MWCNTs were obtained using a conductive holding layer which helped reduce internal resistance and enhance the electrochemical performance of the electrodes. © (2012) Trans Tech Publications, Switzerland
Scalable High-Power Redox Capacitors with Aligned Nanoforests of Crystalline MnO<sub>2</sub> Nanorods by High Voltage Electrophoretic Deposition
It is commonly perceived that reduction–oxidation (redox) capacitors have to sacrifice power density to achieve higher energy density than carbon-based electric double layer capacitors. In this work, we report the synergetic advantages of combining the high crystallinity of hydrothermally synthesized α-MnO<sub>2</sub> nanorods with alignment for high performance redox capacitors. Such an approach is enabled by high voltage electrophoretic deposition (HVEPD) technology which can obtain vertically aligned nanoforests with great process versatility. The scalable nanomanufacturing process is demonstrated by roll-printing an aligned forest of α-MnO<sub>2</sub> nanorods on a large flexible substrate (1 inch by 1 foot). The electrodes show very high power density (340 kW/kg at an energy density of 4.7 Wh/kg) and excellent cyclability (over 92% capacitance retention over 2000 cycles). Pretreatment of the substrate and use of a conductive holding layer have also been shown to significantly reduce the contact resistance between the aligned nanoforests and the substrates. High areal specific capacitances of around 8500 μF/cm<sup>2</sup> have been obtained for each electrode with a two-electrode device configuration. Over 93% capacitance retention was observed when the cycling current densities were increased from 0.25 to 10 mA/cm<sup>2</sup>, indicating high rate capabilities of the fabricated electrodes and resulting in the very high attainable power density. The high performance of the electrodes is attributed to the crystallographic structure, 1D morphology, aligned orientation, and low contact resistance
Electrophoretically‐deposited metal‐decorated CNT nanoforests with high thermal/electric conductivity and wettability tunable from hydrophilic to superhydrophobic
A single‐step, room‐temperature, and scalable electrophoretic deposition process is reported to form nanocomposites on any electrically conductive surface with metal nanoparticle decorated carbon nanotubes (CNTs). The contact angles (CAs) can be easily tuned from ≈60° to 168° by varying the deposition voltage, while hydrophobicity and superhydrophobicity surprisingly arise from the hydrophilic CNTs being deposited. The relatively high voltage tends to vertically align CNTs during deposition, leading to architectural micro/nanoscale roughness on the surface. The combination of the multiscale roughness along with the low surface energy of hydrocarbon functional groups on the CNT surface has enabled facile wettability control, including the Petal and Lotus effects. Further, the relatively vertical orientation of the CNTs, without any coating, allows for current and heat transfer along their axis with superior conductivity. Similar behavior in terms of CA control is seen for all three divalent metal ions in the deposition solution (i.e., Cu2+, Ni2+, and Zn2+) that are used to charge the CNTs while eventually getting co‐deposited. This implies that this method could possibly be extended to other metals by selecting appropriate charging salt. A patterning technique is also demonstrated for facile fabrication of superhydrophobic CNT‐metal islands surrounded by hydrophilic CNT coating
Optofluidic Lasers with Monolayer Gain at the Liquid–Liquid Interface
We
report optofluidic lasers with a monolayer gain material that
self-assembles at the two-phase liquid–liquid interface. The
self-assembly process deterministically introduces the gain at the
surface of a microdroplet optical cavity, where the lasing mode has
maximal interaction with the gain medium. A complete monolayer gain
can be achieved in this surface-gain geometry, giving a surface density
on the order of 10<sup>14</sup> cm<sup>–2</sup>, which proves
to be difficult, if not impossible, to achieve in the monolayer gain
created at the solid–liquid interface via the surface immobilization
method. We demonstrated that the lasing characteristics are drastically
different between the gain material that is confined to the liquid–liquid
interface and that homogeneously distributed in the bulk liquid solution.
Our study reveals the unique capabilities of the surface-gain geometry
optofluidic laser, which can be developed into a novel sensing platform
to study biophysical and biochemical processes at the molecular level
and has vast applications in biomedical diagnostics
Scalable high-power redox capacitors with aligned nanoforests of crystalline MnO \u3c inf\u3e 2 nanorods by high voltage electrophoretic deposition
It is commonly perceived that reduction-oxidation (redox) capacitors have to sacrifice power density to achieve higher energy density than carbon-based electric double layer capacitors. In this work, we report the synergetic advantages of combining the high crystallinity of hydrothermally synthesized α-MnO2 nanorods with alignment for high performance redox capacitors. Such an approach is enabled by high voltage electrophoretic deposition (HVEPD) technology which can obtain vertically aligned nanoforests with great process versatility. The scalable nanomanufacturing process is demonstrated by roll-printing an aligned forest of α-MnO2 nanorods on a large flexible substrate (1 inch by 1 foot). The electrodes show very high power density (340 kW/kg at an energy density of 4.7 Wh/kg) and excellent cyclability (over 92% capacitance retention over 2000 cycles). Pretreatment of the substrate and use of a conductive holding layer have also been shown to significantly reduce the contact resistance between the aligned nanoforests and the substrates. High areal specific capacitances of around 8500 μF/cm2 have been obtained for each electrode with a two-electrode device configuration. Over 93% capacitance retention was observed when the cycling current densities were increased from 0.25 to 10 mA/cm2, indicating high rate capabilities of the fabricated electrodes and resulting in the very high attainable power density. The high performance of the electrodes is attributed to the crystallographic structure, 1D morphology, aligned orientation, and low contact resistance. © 2013 American Chemical Society