Shushuang Li

A high-performance electrocatalyst for oxygen reduction based on reduced graphene oxide modified with oxide nanoparticles, nitrogen dopants, and possible metal-N-C sites

Non-noble metal (NNM) electrocatalysts with performances comparable with or superior to Pt are highly desirable for fuel cells and metal-air batteries, but remain rare. Herein, we report a new NNM electrocatalyst derived from reduced graphene oxide (rGO), dual nitrogen-containing ligands, and iron and cobalt salts. Remarkably, the onset potential and half-wave potential (E1/2) of the obtained electrocatalyst shifts 5 and −23 mV, respectively, relative to commercial Pt/C at a standard loading of 20 μgpt cm−2 toward an oxygen reduction reaction (ORR) in alkaline solutions. Additionally, the electrocatalyst is much better than the Pt/C in terms of durability and tolerance to methanol.

Light-controlled synthesis of uniform platinum nanodendrites with markedly enhanced electrocatalytic activity

AbstractWe report a fast in situ seeding approach based on zinc(II) porphyrin (ZnP) under white light irradiation, leading to uniform spherical platinum nanodendrites with tunable sizes. The platinum nanodendrites exhibit significantly improved electrocatalytic activities toward oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) compared with commercial platinum black.

Controlled synthesis of high metal-loading, Pt-based electrocatalysts with enhanced activity and durability toward oxygen reduction reaction

High metal-loading Pt/C electrocatalysts are much sought after for the fabrication of thin-layered membrane electrode assemblies (MEA) suitable for mass transport and balance control of water and heat. However, such electrocatalysts are still limited to commercial Pt/C, comprised of carbon-supported, 2–5 nm Pt particles without size and size uniformity control, causing poor activity and durability toward oxygen reduction reaction (ORR). Herein, we report the controlled synthesis of 59.9 wt% Pt/C by using metallic ion-containing reversed micelles adsorbed on carbon. Combined with a simple surfactant removal method of washing with water, this unique confining approach enables easy control over the size and size uniformity of the resultant Pt/C, leading to significantly improved activity and durability for ORR compared with commercial 60 wt% Pt/C. The ORR activity enhancement arises from a smaller average size of Pt nanoparticles in combination with a narrower size distribution, with more Pt nanoparticles falling in an optimal size range of 2–4 nm with the highest ORR activity. The narrower size distribution of our Pt/C also makes the Pt nanoparticles resistant to the dissolution–re-deposition Ostwald ripening process, in which small Pt nanoparticles gradually shrink until they disappear, while large ones become bigger and bigger.

Constraining broad-line regions from time lags of broad emission lines relative to radio emission

In this paper, a new method is proposed to estimate the broad-line region sizes of ultraviolet (UV) lines RuvBLR. It is applied to 3C 273. First, we derive the time lags of radio emission relative to broad emission lines Lya and C iv by the z-transformed discrete correlation function (ZDCF) method. The broad lines lag the 5-, 8-, 15-, 22- and 37-GHz emission. The measured lags tuvob are of the order of years. For a given line, tuvob decreases as the radio frequency increases. This trend results from the radiative cooling of relativistic electrons. Both UV lines have a lag of tuvob=-2.74+0.06- 0.25 yr relative to the 37-GHz emission. These results are consistent with those derived from the Balmer lines in Paper I. Secondly, we derive the time lags of the lines Lya, C iv, H, H beta and Ha relative to the 37-GHz emission by the flux randomization/random subset selection (FR/RSS) Monte Carlo method. The measured lags are tob=-3.40+0.31- 0.05, -3.40+0.41- 0.14, -2.06+0.36- 0.92, -3.40+1.15- 0.20 and -3.56+0.35- 0.18 yr for the lines Lya, C iv, H, H beta and Ha, respectively. These estimated lags are consistent with those derived by the ZDCF method within the uncertainties. Based on the new method, we derive RuvBLR= 2.54+0.71- 0.35 to 4.01+0.90- 1.16 and 2.54+0.80- 0.43 to 4.01+0.98- 1.24 light-years for the Lya and C iv lines, respectively. Considering the uncertainties, these estimated sizes are consistent with those obtained in the classical reverberation mapping for the UV and the Balmer lines. This indicates that their emitting regions are not separated so large as in the classical mapping of the UV and optical lines. These results seem to depart from the stratified ionization structures obtained in the classical mapping.

Synthesis of core/shell structured Pd3Au@Pt/C with enhanced electrocatalytic activity by regioselective atomic layer deposition combined with a wet chemical method

We report the synthesis of Pd3Au@Pt/C by atomic layer deposition (ALD) combined with a wet chemical method. Initially, nearly uniform Pd3Au nanoparticles (NPs) (∼4.7 nm) supported on carbon with a loading of ∼20 wt% were prepared by reducing metal complexes confined in reverse micelles adsorbed on carbon. Next, a Pt thin layer (less than 1 nm) was selectively deposited on purified Pd3Au particles instead of on carbon by regioselective ALD that likely arises from the coverage of nucleation sites on carbon by surfactant molecules in conjunction with catalytic decomposition of the Pt precursor on Pd3Au. The resulting core–shell structured material was subject to TEM, HAADF-STEM/EDX, XRD, XPS and electrochemical measurements. Interestingly, Pd3Au@Pt/C demonstrates a significantly improved electrocatalytic activity toward both formic acid oxidation reaction (FAOR) and oxygen reduction reaction (ORR) compared with Pd3Au/C and state-of-the art Pt/C. This study opens up a unique avenue for the synthesis core/shell structured materials with potential applications in catalysis, electrocatalysis, and so on.

One-step synthesis of carbon-supported foam-like platinum with enhanced activity and durability

Carbon black nanoparticles localized in-between liposomal bi-layers provide a unique reaction environment that permits one-step synthesis of carbon-supported foam-like platinum (Pt foam/C) in aqueous solution under ambient conditions. The obtained Pt foam/C was readily purified by simple washing with water and chloroform at room temperature. Unlike commercial Pt/C composed of quasi-spherical nanoparticles, Pt foam/C consists of convoluted dendritic nanosheets. Interestingly, Pt foam/C demonstrated both improved durability and activity toward oxygen reduction reaction (ORR). The improved durability is because of the formation of metastable nano-holes among dendritic branches of Pt foam/C under ripening, preserving the surface area. The activity enhancement of Pt foam/C can be attributed to predominantly exposed Pt {1,1,0} planes that possess the highest ORR activity among all low-indexed Pt crystalline planes. Nano-scale Pt primarily enclosed by {1,1,0} planes has not been reported previously.

Search for Intra-day Optical Variability in Mrk 501

We present our observations of the optical intra-day variability (IDV) in

Graphene supported foam-like platinum electrocatalyst for oxygen reduction reaction

\gamma

Hints of Correlation between Broad-line and Radio Variations for 3C 120

-ray BL Lac object Mrk 501. The observations were run with the 1.02 m and 2.4 m optical telescopes at Yunnan Observatories from 2005 April to 2012 May. The light curve at the

Revisiting Correlations Between Broad-Line and Jet Emission Variations for AGNs: 3C 120 and 3C 273

R