10 research outputs found
Mussel-inspired nitrogen-doped graphene nanosheet supported manganese oxide nanowires as highly efficient electrocatalysts for oxygen reduction reaction
Electrocatalysts for oxygen reduction reaction (ORR) play a vital role in determining the performance of fuel cells and metal-air batteries. Carbon nanomaterials doped with heteroatoms are highly attractive by virtue of their excellent electrocatalytic activity, high conductivity and large surface area. This study reports the synthesis of a highly efficient electrocatalyst based on nitrogen-doped (N-doped) graphene nanosheets (NG) using mussel-inspired dopamine as a nitrogen source. Dopamine undergoes oxidative polymerization that can functionalize the surface of graphene and also introduces nitrogen atoms onto the graphene nanosheets upon pyrolysis. N-doping not only leads to improved catalytic activity, but it also provides anchoring sites for the growth of electroactive amorphous manganese oxide nanowires on the graphene nanosheets (NG/MnOx). On the basis of a Koutecky-Levich plot, it is found that the hybrid NG/MnOx catalyst exhibits excellent catalytic activity with a direct four-electron pathway in ORR. Furthermore, the hybrid electrocatalyst possesses superior stability and gives a low yield of peroxide compared to commercial Pt/C catalysts. This suggests that the unique combination of an N-doped graphene support and amorphous MnOx nanowires can synergistically improve the catalytic activity for ORR.close1
Interface Engineering of Hematite with Nacre-like Catalytic Multilayers for Solar Water Oxidation
An efficient water oxidation photoanode based on hematite has been designed and fabricated by tailored assembly of graphene oxide (GO) nanosheets and cobalt polyoxometalates (Co-POM) water oxidation catalysts into a nacre-like multilayer architecture on a hematite photoanode. The deposition of catalytic multilayers provides a high photocatalytic efficiency and photoelectrochemical stability to underlying hematite photoanodes. Compared to the bare counterpart, the catalytic multilayer electrode exhibits a significantly higher photocurrent density and large cathodic shift in onset potential (~ 369 mV) even at neutral pH conditions due to the improved charge transport and catalytic efficiency from the rational and precise assembly of GO and Co-POM. Unexpectedly, the polymeric base layer deposited prior to the catalytic multilayers improves the performance even more by facilitating the transfer of photogenerated holes for water oxidation through modification of the flat band potential of the underlying photoelectrode. This approach utilizing polymeric base and catalytic multilayers provides an insight into the design of highly efficient photoelectrodes and devices for artificial photosynthesis
Design of ITER divertor VUV spectrometer and prototype test at KSTAR tokamak
Design and development of the ITER divertor VUV spectrometer have been performed from the year 1998, and it is planned to be installed in the year 2027. Currently, the design of the ITER divertor VUV spectrometer is in the phase of detail design. It is optimized for monitoring of chord-integrated VUV signals from divertor plasmas, chosen to contain representative lines emission from the tungsten as the divertor material, and other impurities. Impurity emission from overall divertor plasmas is collimated through the relay optics onto the entrance slit of a VUV spectrometer with working wavelength range of 14.6ā32 nm. To validate the design of the ITER divertor VUV spectrometer, two sets of VUV spectrometers have been developed and tested at KSTAR tokamak. One set of spectrometer without the field mirror employs a survey spectrometer with the wavelength ranging from 14.6 nm to 32 nm, and it provides the same optical specification as the spectrometer part of the ITER divertor VUV spectrometer system. The other spectrometer with the wavelength range of 5ā25 nm consists of a commercial spectrometer with a concave grating, and the relay mirrors with the same geometry as the relay mirrors of the ITER divertor VUV spectrometer. From test of these prototypes, alignment method using backward laser illumination could be verified. To validate the feasibility of tungsten emission measurement, furthermore, the tungsten powder was injected in KSTAR plasmas, and the preliminary result could be obtained successfully with regard to the evaluation of photon throughpu
Design of ITER divertor VUV spectrometer and prototype test at KSTAR tokamak
Design and development of the ITER divertor VUV spectrometer have been performed from the year 1998, and it is planned to be installed in the year 2027. Currently, the design of the ITER divertor VUV spectrometer is in the phase of detail design. It is optimized for monitoring of chord-integrated VUV signals from divertor plasmas, chosen to contain representative lines emission from the tungsten as the divertor material, and other impurities. Impurity emission from overall divertor plasmas is collimated through the relay optics onto the entrance slit of a VUV spectrometer with working wavelength range of 14.6ā32 nm. To validate the design of the ITER divertor VUV spectrometer, two sets of VUV spectrometers have been developed and tested at KSTAR tokamak. One set of spectrometer without the field mirror employs a survey spectrometer with the wavelength ranging from 14.6 nm to 32 nm, and it provides the same optical specification as the spectrometer part of the ITER divertor VUV spectrometer system. The other spectrometer with the wavelength range of 5ā25 nm consists of a commercial spectrometer with a concave grating, and the relay mirrors with the same geometry as the relay mirrors of the ITER divertor VUV spectrometer. From test of these prototypes, alignment method using backward laser illumination could be verified. To validate the feasibility of tungsten emission measurement, furthermore, the tungsten powder was injected in KSTAR plasmas, and the preliminary result could be obtained successfully with regard to the evaluation of photon throughpu
Enhanced Photocatalytic Performance Depending on Morphology of Bismuth Vanadate Thin Film Synthesized by Pulsed Laser Deposition
We
have fabricated high quality bismuth vanadate (BiVO<sub>4</sub>) polycrystalline
thin films as photoanodes by pulsed laser deposition
(PLD) without a postannealing process. The structure of the grown
films is the photocatalytically active phase of scheelite-monoclinic
BiVO<sub>4</sub> which was obtained by X-ray diffraction (XRD) analysis.
The change of surface morphology for the BIVO<sub>4</sub> thin films
depending on growth temperature during synthesis has been observed
by scanning electron microscopy (SEM), and its influence on water
splitting performance was investigated. The current density of the
BiVO<sub>4</sub> film grown on a glass substrate covered with fluorine-doped
tin oxide (FTO) at 230 Ā°C was as high as 3.0 mA/cm<sup>2</sup> at 1.23 V versus the potential of the reversible hydrogen electrode
(<i>V</i><sub>RHE</sub>) under AM 1.5G illumination, which
is the highest value so far in previously reported BiVO<sub>4</sub> films grown by physical vapor deposition (PVD) methods. We expect
that doping of transition metal or decoration of oxygen evolution
catalyst (OEC) in our BiVO<sub>4</sub> film might further enhance
the performance
A wafer-scale antireflective protection layer of solution-processed TiO2 nanorods for high performance silicon-based water splitting photocathodes
Sustainable and efficient conversion of solar energy to transportable green energy and storable fuels, hydrogen, represents a solution to the energy crisis and reduces the consumption of fossil fuels, which are mainly responsible for the rise in global temperature. Solar water splitting using semiconductors, such as silicon, is promising to satisfy the global energy demand by producing hydrogen molecules. However, the solar to hydrogen conversion efficiency of a silicon photoelectrode is suppressed by overpotential, high reflectance and/or instability in liquid electrolytes. Herein, we report the synthesis of multifunctional solution-processed TiO2 nanorods on a 4-inch p-silicon wafer with controllable heights and diameters for highly efficient water splitting photocathodes. The solution-processed passivation layer of TiO2 nanorods reduces the overpotential of the silicon photocathode due to its catalytic properties. The TiO2 NRs also dramatically improves the light absorption of silicon due to the antireflective ability of the nanorods. The reflectance of silicon is decreased from 37.5% to 1.4% and enhances the saturated photocurrent density. The Pt-decorated (1-2.5 nm diameter) TiO2 nanorods/p-Si photocathodes show a short circuit current density of up to 40 mA cm(-2), an open circuit voltage similar to 440 mV and incident photon to current conversion efficiency of >90% using 0.5 M H2SO4 electrolyte with simulated 1 sun irradiation. The heterostructure photocathodes are stable for more than 52 h without noticeable degradation and an ideal regenerative cell efficiency of 2.5% is achieved.1118sciescopu
pāp Heterojunction of Nickel Oxide-Decorated Cobalt Oxide Nanorods for Enhanced Sensitivity and Selectivity toward Volatile Organic Compounds
The
utilization of pāp isotype heterojunctions is an effective
strategy to enhance the gas sensing properties of metal-oxide semiconductors,
but most previous studies focused on pān heterojunctions owing
to their simple mechanism of formation of depletion layers. However,
a proper choice of isotype semiconductors with appropriate energy
bands can also contribute to the enhancement of the gas sensing performance.
Herein, we report nickel oxide (NiO)-decorated cobalt oxide (Co<sub>3</sub>O<sub>4</sub>) nanorods (NRs) fabricated using the multiple-step
glancing angle deposition method. The effective decoration of NiO
on the entire surface of Co<sub>3</sub>O<sub>4</sub> NRs enabled the
formation of numerous pāp heterojunctions, and they exhibited
a 16.78 times higher gas response to 50 ppm of C<sub>6</sub>H<sub>6</sub> at 350 Ā°C compared to that of bare Co<sub>3</sub>O<sub>4</sub> NRs with the calculated detection limit of approximately
13.91 ppb. Apart from the pāp heterojunctions, increased active
sites owing to the changes in the orientation of the exposed lattice
surface and the catalytic effects of NiO also contributed to the enhanced
gas sensing properties. The advantages of pāp heterojunctions
for gas sensing applications demonstrated in this work will provide
a new perspective of heterostructured metal-oxide nanostructures for
sensitive and selective gas sensing