Discovering efficient and promising non-noble catalysts toward the alkaline hydrogen evolution reaction (HER) is vital for a clean energy system. Here, we design an efficient alkaline HER ...electrocatalyst, coating of WN nanowire core with a Ni(OH)2 shell supported on a carbon fiber paper (WN-Ni(OH)2). In a 1 M KOH solution, the hierarchical electrocatalyst affords a current density of 20 mA cm–2 at an overpotential of 170 mV and 100 mA cm–2 at 245 mV. The enhanced performance of WN-Ni(OH)2 in the HER is attributed to the synergy between WN and Ni(OH)2: during water dissociation, hydroxyl groups are preferentially adsorbed on WN and hydrogen on Ni(OH)2; meanwhile, Ni(OH)2 could promote hydroxyl group desorption from WN. Thus, the full-surface Volmer reaction kinetics could be enhanced. As a consequence, the WN-Ni(OH)2 has a reduced activation energy of the HER and enhanced intrinsic activity performance. Meanwhile, the hybrid can reach a current density of 100 mA cm–2 at an overpotential of 339 mV for the oxygen evolution reaction (OER), and an overpotential of 510 mV for the full water-splitting reaction. This interfacial cooperation offers a promising bifunctional electrocatalyst, as well as a hopeful strategy for fabricating efficient nitride-based electrocatalysts in alkaline media.
Methanol dehydrogenation is an efficient way to produce syngas with high quality. The current efficiency of sunlight-driven methanol dehydrogenation is poor, which is limited by the lack of excellent ...catalysts and effective methods to convert sunlight into chemicals. Here, we show that atomically substitutional Pt-doped in CeO2 nanosheets (Pts-CeO2) exhibit excellent methanol dehydrogenation activity with 500-hr level catalytic stability, 11 times higher than that of Pt nanoparticles/CeO2. Further, we introduce a photothermal conversion device to heat Pts-CeO2 up to 299°C under 1 sun irradiation owning to efficient full sunlight absorption and low heat dissipation, thus achieving an extraordinarily high methanol dehydrogenation performance with a 481.1 mmol g−1 h−1 of H2 production rate and a high solar-to-hydrogen (STH) efficiency of 32.9%. Our method represents another progress for ambient sunlight-driven stable and active methanol dehydrogenation technology.
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•Atomically substitutional Pt-doped CeO2 is active and robust for CH3OH dehydrogenation•The photothermal conversion device can heat Pts-CeO2 to 299°C under 1 sun irradiation•The joint system achieves a one sun irradiated H2 production rate of 481.1 mmol g−1 h−1•This system delivers a high solar-to-H2 efficiency of 32.9% under one sun irradiation
Catalysis; Chemical Reaction Engineering; Chemistry
ABSTRACT
We perform mode identification for five δ Scuti stars in the Pleiades star cluster, using custom light curves from K2 photometry. By creating échelle diagrams, we identify radial and dipole ...mode ridges, comprising a total of 28 radial and 16 dipole modes across the five stars. We also suggest possible identities for those modes that lie offset from the radial and dipole ridges. We calculate non-rotating stellar pulsation models to verify our mode identifications, finding good agreement within the age and metallicity constraints of the cluster. We also find that for all stars, the least dense models are preferred, reflecting the lower density of these oblate, rotating stars. Three of the five stars show rotationally split multiplets. We conclude that the sample shows promise for asteroseismic rotation rates, masses, and ages with rotating models in the future. Our preliminary modelling also indicates some sensitivity to the helium abundance.
In this work, we present a novel artificial photosynthetic paradigm with square meter (m2) level scalable production by integrating photovoltaic electrolytic water splitting device and solar heating ...CO2 hydrogenation device, successfully achieving the synergy of 1 sun driven 19.4% solar to chemical energy efficiency (STC) for CO production (2.7 times higher than that of large-sized artificial photosynthetic systems) with a low cost (equivalent to 1/7 of reported artificial photosynthetic systems). Furthermore, the outdoor artificial photosynthetic demonstration with 1.268 m2 of scale exhibits the CO generation amount of 258.4 L per day, the STC of ~15.5% for CO production in winter, which could recover the cost within 833 sunny days of operation by selling CO.
Machine learning has been recently applied to solve challenging research problems in the EDA area. The performance of the machine learning algorithms are vulnerable to effects such as the outliers ...and the insignificant features in the input training data set. In this paper, we propose a model averaging method, together with an outlier detection method, to make the machine learning process more robust to such contaminating effects. Results on artificial and chip power estimation data sets show that our method behave much better than the conventional ordinary least square method which is widely used in the machine learning community.
Oxygen evolution reaction (OER) is key for electrochemical water splitting. Catalysts minimized in single-atom level (SACs) anchored on two-dimensional substances are highly active for various ...electrocatalytic reactions, but so far represent the limited performance for OER. Herein we report a general strategy for the fabrication of bi-metal Ni and Fe SACs loaded on graphene to significantly boost the OER activity. Notably, this unique structure of single Ni and Fe atoms co-existed on graphene has a strong synergetic effect, which can substantially elevate the charge transfer of catalysts. As a result, the obtained bi-metal SACs with the appropriate ratio of 4 for single Ni and Fe atoms show a small overpotential of 247 mV at 10 mA·cm−2 of OER current density in KOH electrolyte, outperforming individual-metal Ni (329 mV) or Fe (384 mV) SACs. Furthermore, such catalyst exhibits excellent stability without significant decay with increasing time at high current of 20 mA·cm−2 continuously for 48 h. This work provides a new avenue for regulating the properties of transition metal SACs on graphene for water electrolysis.
ABSTRACT Asteroseismology can precisely characterize stars, but the accuracy of seismic inference is still an open question. In this work, we use three evolved stars, including one late subgiant ...(EPIC 211411922) and two young red giants (EPIC 211409560 and EPIC 211416749) in the open cluster M67 to validate seismic inferences of stellar mass and age. We start by measuring oscillation mode frequencies and identifying acoustic and mixed modes in all three stars. We then fit the stars to determine their masses and ages with a detailed modelling approach. Our age estimates for all stars agree well with the literature consensus age range of M67 (3.0–5.0 Gyr). Mass estimates for EPIC 211411922 and EPIC 211409560 are sensible because they are slightly higher than the typical turn-off mass of the cluster. The inferred mass for EPIC 211416749 is underestimated by 5–10 per cent compared with the turn-off mass, but this could be caused by poor data quality. Our results indicate that the detailed modelling can determine sensible masses and ages for evolved stars near the base of the red giant branch.
c
-axis oriented Bi
1−
x
Pb
x
CuSeO (0 ≤
x
≤ 0.8) single crystalline thin films have been successfully epitaxially grown on SrTiO
3
(001) substrates
via
the pulsed laser deposition technique. ...Detailed X-ray diffraction and transmission electron microscopy measurements reveal the excellent
c
-axis and
ab
-plane texture of the films. As the Pb doping concentration increases, both the resistivity and the Seebeck coefficient decrease due to the increase in hole carrier concentration. The highest power factor of about 1.2 mW m
−1
K
−2
has been achieved in Bi
0.96
Pb
0.06
CuSeO single crystalline thin films at 673 K, which is much higher than those of polycrystalline ceramics with random orientation, suggesting that
c
-axis oriented BiCuSeO-based single crystalline thin films might have great potential for application in thermoelectric thin film devices.
Enhanced thermoelectric performance of
c
-axis oriented Bi
1−
x
Pb
x
CuSeO single crystalline thin films.
ABSTRACT The importance of νmax (the frequency of maximum oscillation power) for asteroseismology has been demonstrated widely in the previous decade, especially for red giants. With the large amount ...of photometric data from CoRoT (Convection, Rotation, and planetary Transits), Kepler, and Transiting Exoplanet Survey Satellite, several automated algorithms to retrieve νmax values have been introduced. Most of these algorithms correct the granulation background in the power spectrum by fitting a model and subtracting it before measuring νmax. We have developed a method that does not require fitting to the granulation background. Instead, we simply divide the power spectrum by a function of the form $\rm \nu ^{-2}$, to remove the slope due to granulation background, and then smooth to measure νmax. This method is fast and simple and avoids degeneracies associated with fitting. The method is able to measure oscillations in 99.9 per cent of previously studied Kepler red giants, with a systematic offset of 1.5 per cent in νmax values that we are able to calibrate. On comparing the seismic radii from this work with Gaia, we see similar trends to those observed in previous studies. Additionally, our values of width of the power envelope can clearly identify the dipole mode suppressed stars as a distinct population, hence as a way to detect them. We also applied our method to stars with low νmax (0.19–18.35 µHz) and found that it works well to correctly identify the oscillations.
Reconfigurable lens provides variable-focus in optics without any moving part. The material for a reconfigurable lens should be deformable in the presence of external stimuli meanwhile maintaining ...its optical transparency for the lens function. This article reports the fabrication and actuation property of the Poly(acrylic acid)-Poly(vinyl alcohol) (PAP) hydrogels for reconfigurable active lens. The PAP hydrogels were prepared by free radical and freeze-thaw technique using N,N1-methylenebisacrylamaide and potassium persulfate/N,N,N1,N1-tetramethylethylenediamene as crosslinker-initiator pair system. The formation of the hydrogels was conformed form Fourier transform infrared spectra and thermogravimetric analysis. The prepared hydrogels were characterized by swelling studies and optical transparency measured with UV-visible spectroscopy and actuation test in the presence of electric field. There is an optimal concentration of acrylic acid concentration that shows maximum displacement output with less optical transparency loss. Displacement output increased with increasing the voltage and the maximum displacement output of 15.5 μm was achieved in the presence of electrical field. This corresponds to 4% strain.
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