Haijing Yan

Phosphorus-Modified Tungsten Nitride/Reduced Graphene Oxide as a High-Performance, Non-Noble-Metal Electrocatalyst for the Hydrogen Evolution Reaction†

Phosphorus-modified tungsten nitride/reduced graphene oxide (P-WN/rGO) is designed as a high-efficient, low-cost electrocatalyst for the hydrogen evolution reaction (HER). WN (ca. 3 nm in size) on rGO is first synthesized by using the H3[PO4(W3O9)4] cluster as a W source. Followed by phosphorization, the particle size increase slightly to about 4 nm with a P content of 2.52 at %. The interaction of P with rGO and WN results in an obvious increase of work function, being close to Pt metal. The P-WN/rGO exhibits low onset overpotential of 46 mV, Tafel slope of 54 mV dec(-1), and a large exchange current density of 0.35 mA cm(-2) in acid media. It requires overpotential of only 85 mV at current density of 10 mA cm(-2), while remaining good stability in accelerated durability testing. This work shows that the modification with a second anion is powerful way to design new catalysts for HER.

Small-sized and high-dispersed WN from [SiO4(W3O9)4]4− clusters loading on GO-derived graphene as promising carriers for methanol electro-oxidation

The small size and high dispersion of cocatalysts on supports are essential to increase the chance to contact with a Pt catalyst for promoting the synergistic effect. In this paper, we report the synthesis of the small-sized WN nanoparticles (NPs) loading on GO-derived graphene (denoted as graphene for simplicity) by using heteropoly acid H4[SiO4(W3O9)4] (SiW12) clusters as a W source. The SiW12 clusters are anchored on the polyethyleneimine (PEI)-modified GO through a hydrothermal process. After the nitridation with NH3, the small-sized and well dispersed WN NPs of 2–3 nm are obtained. The ternary Pt–WN/graphene catalysts are fabricated by an EG reduction method. The intimate contact and intensive interaction between Pt and WN are verified by TEM, XRD, XPS and XAFS tests. Due to the above characteristics, the Pt–WN/graphene catalyst exhibits a remarkably enhanced activity and durability toward methanol electrocatalytic oxidation. The mass activity of Pt–WN/graphene (531.5 mA mgPt−1) is 2.45, 2.88 and 3.70 times that of Pt/graphene, Pt/C(JM) and Pt/Vulcan catalysts, respectively. Furthermore, the ternary Pt–WN/graphene catalyst shows excellent resistance to CO poisoning and good stability. The high activity of Pt–WN/graphene is mainly attributed to the enhanced synergistic effect benefited from the intimate contact and intensive interaction of Pt with WN NPs.

A hierarchical porous carbon material from a loofah sponge network for high performance supercapacitors

Environmentally friendly, low-cost and renewable biomass is a promising raw material for a high-performance supercapacitor electrode material. Herein, high surface area, hierarchical porous carbon materials were obtained by a carbonization and activation process of a loofah sponge. The specific surface area, pore volume and the pore size distribution of the porous carbon were controlled by adjusting the activation temperature and suitable activation agents. The results show that the carbon materials possess a high proportion of micropores and a few mesoporous structures. Amazingly, among them, the carbon materials prepared at 800 °C with an optimal structure and high surface area (1733 m2 g−1) have an outstanding specific capacitance of 304 F g−1 at a current density of 1 A g−1 and excellent rate capability (60.2% capacitance retention at a current density of 50 A g−1). The enhanced electrochemical performance is attributed to the large surface area, good electrical conductivity, and fast charge transfer. Hierarchical porous carbon materials demonstrate superior good cyclic stability such as high capacitance retention of 98% over 10000 charge–discharge cycles in a 6 M KOH electrolyte. Notably, in the two-electrode symmetric supercapacitors, the energy density could be up to 10 and 64.4 W h kg−1 at a power density of 500 W kg−1 and 11.3 kW kg−1 in aqueous and organic electrolytes, respectively. Our results indicated that the strategies developed here would provide a novel route for the synthesis of porous carbon materials from a low-cost loofah sponge and show the possibility for application in energy storage.

Holey Reduced Graphene Oxide Coupled with an Mo2N–Mo2C Heterojunction for Efficient Hydrogen Evolution

An in situ catalytic etching strategy is developed to fabricate holey reduced graphene oxide along with simultaneous coupling with a small-sized Mo2 N-Mo2 C heterojunction (Mo2 N-Mo2 C/HGr). The method includes the first immobilization of H3 PMo12 O40 (PMo12 ) clusters on graphite oxide (GO), followed by calcination in air and NH3 to form Mo2 N-Mo2 C/HGr. PMo12 not only acts as the Mo heterojunction source, but also provides the Mo species that can in situ catalyze the decomposition of adjacent reduced GO to form HGr, while the released gas (CO) and introduced NH3 simultaneously react with the Mo species to form an Mo2 N-Mo2 C heterojunction on HGr. The hybrid exhibits superior activity towards the hydrogen evolution reaction with low onset potentials of 11 mV (0.5 m H2 SO4 ) and 18 mV (1 m KOH) as well as remarkable stability. The activity in alkaline media is also superior to Pt/C at large current densities (>88 mA cm-2 ). The good activity of Mo2 N-Mo2 C/HGr is ascribed to its small size, the heterojunction of Mo2 N-Mo2 C, and the good charge/mass-transfer ability of HGr, as supported by a series of experiments and theoretical calculations.

Intermittent microwave heating-promoted rapid fabrication of sheet-like Ag assemblies and small-sized Ag particles and their use as co-catalyst of ZnO for enhanced photocatalysis

An easy and rapid intermittent microwave heating (IMH) method was developed for the synthesis of Ag nanostructures with high yields within the short time of 2 minutes. A Ag–DT (dodecanethiol) complex with sheet-like structure was used as precursor. After an IMH treatment of the solid Ag–DT, Ag nanoparticles (NPs) with a small size below 5 nm were obtained. Time-dependent experiments and a series of tests indicated that the Ag NPs were formed and grown in the sheet-like Ag–DT precursor. Specifically, the fewer IMH cycles (less than 3 times) would result in the formation of the sheet-like assemblies of Ag NPs linked by the Ag–DT. The sheet-like assemblies of Ag NPs were rarely observed in previous reports. The Ag NPs with small size below 5 nm would emerge as major products with increasing the number of IMH cycles to 5 times. With further increase of IMH cycles, Ag NPs with a large size of 20 nm were observed. Notably, due to the presence of DT groups on the surface of Ag NCs, the small-sized Ag NPs could directly combine with an oxide (ZnO here) to form Ag–oxide composites with no need for additional modification. The Ag–ZnO composites exhibited enhanced performance for the photocatalytic degradation of dye pollutants over unmodified ZnO and P25 TiO2, demonstrating the large application potential of composites in advanced areas. The IMH strategy developed here will be important for the practical application of Ag-based materials due to the fast synthesis process, high yields benefiting from the solid-based reaction, high stability, as well as the ability of the as-prepared Ag NCs to easily combine with oxide materials to form functional nanocomposites (ZnO here).

A “1-methylimidazole-fixation” route to anchor small-sized nitrides on carbon supports as non-Pt catalysts for the hydrogen evolution reaction

A effective “1-methylimidazole (1-MD)-fixation” strategy was developed to anchor small-sized nitrides on carbon supports. The carbon supports used (CNTs (carbon nanotubes), carbon black, reduced graphene oxides) and nitrides (WN, Mo2N) can be easily tuned. The application of the nitride/CNT hybrids as non-Pt catalysts for the hydrogen evolution reaction (HER) was also demonstrated. It was shown that the performance could be tuned by the kind of the nitride. The combination of WN and Mo2N simultaneously on CNTs can improve the HER performance obviously. It is expected that the present “fixation” route could be useful to anchor small-sized nitrides on carbon supports for application in electrocatalytic fields.

Gelatin-assisted synthesis of ZnS hollow nanospheres: the microstructure tuning, formation mechanism and application for Pt-free photocatalytic hydrogen production

Nano-sized hollow spheres with tunable microstructures are urgently needed for their applications in advanced fields. The ZnS hollow spheres reported previously have usually required a complex multi-step process, and/or large size and/or less tunability in the microstructure. Here, a simple gelatin-assisted hydrothermal reaction of Zn(OAc)2 and thiourea was developed for the synthesis of ZnS hollow nanospheres. The size of the hollow spheres could be controlled below 100 nm with good homogeneity. The presence of gelatin is essential to decrease the size of ZnS particles and to form hollow structures. Only solid spheres with a large size were prepared in the absence of gelatin. The structure of hollow nanospheres could be regulated by altering the reaction parameters. Typically, the size of voids increases with prolonged reaction time. Also, the grain size of the hollow spheres increased with increasing reaction temperature (from about 3 nm to 10 nm) accompanied by a decrease in shell thickness. The results indicated that the hollow structure was formed through an “Ostwald ripening” process. The ZnS hollow nanospheres were used as catalyst for photocatalytic hydrogen production without additional co-catalyst. The maximum H2 production rate reached was 340 μmol h−1 (about 6.8 mmol h g).

Modulation of intestine development by fecal microbiota transplantation in suckling pigs

The present study was conducted to investigate the effects of early fecal microbiota transplantation on gut development in sucking piglets. A total of 24 3 day-old DLY sucking piglets (2.11 ± 0.15) kg were randomly divided into four groups (TMP, YMP, RMP and control group (CON)), which were transplanted with intact fecal microbiota of Tibetan pig (TP), Yorkshire pig (YP), Rongchang pig (RP), and without transplantation, respectively. The whole trial lasted for 56 d. The results are as follows: when compared with the YMP and RMP treatments, TMP and CON had a lower diarrhea index (P < 0.05), TMP and CON had higher GLP-2 and ANG4 mRNA abundances in the ileum (P < 0.05), and the TMP had a higher jejunal villus height: crypt depth and a higher colonic GLP-2 mRNA abundance (P < 0.05). Moreover, when compared with the YMP and RMP treatments, TMP had an enhanced DMT1 mRNA abundance in the duodenum (P < 0.05), TMP and CON had a greater lactase activity and a higher DMT1 mRNA abundance in the jejunum (P < 0.05), and CON had a higher γ-GT activity in the jejunum (P < 0.05). The jejunal Ca2+, Mg2+-ATPase activity in TMP was higher than that in CON, and the jejunal Na+, K+-ATPase activity in TMP was higher than that in the other three treatments (P < 0.05). Besides, when compared with the YMP and RMP treatments, TMP had a lower MDA content and a higher MUC1 mRNA abundance in the jejunum (P < 0.05); CON had a higher SOD activity in the jejunum (P < 0.05), whereas TMP and CON had a higher butyric acid concentration in the colon and a lower LPS content in the serum (P < 0.05). Finally, when compared with the TMP treatment, the other three treatments had an enhanced IL-10 mRNA abundance in the colon (P < 0.05), YMP and CON had higher counts of Escherichia coli in the colonic digesta (P < 0.05), and the CON had lower counts of Lactobacillus spp in the cecal and colonic digesta (P < 0.05). These data indicated that early transplantation of the fecal microbiota from the Yorkshire pigs and Rongchang pigs to DLY suckling piglets would destroy the gut microbiota balance and thus damage intestinal health.

Synergism of molybdenum nitride and palladium for high-efficiency formic acid electrooxidation

The direct formic acid fuel cell (DFAFC) has received increasing attention in the sustainable and clean energy field. However, the high cost, poor durability, and shortage of palladium (Pd) based catalysts for the formic acid oxidation reaction (FAOR) restrict the large-scale application of DFAFC. Herein, molybdenum nitride/reduced graphene oxide (Mo2N/rGO) was designed as an effective cocatalyst of Pd for FAOR based on an assembly-immobilization method. It is shown that the small-sized Mo2N is well dispersed on rGO with high density, which is favorable for the post-loading deposition of Pd onto the rGO to form a strongly coupled Pd–Mo2N structure. The strong interaction between Pd and Mo2N, verified by a series of characterizations, is helpful for promoting the performance of Pd. Electrochemical tests indicate that the Pd–Mo2N/rGO catalyst shows superior activity to other Pd based catalysts, with a current density of 532.7 mA mgPd−1, which is 1.7 and 2.2 times greater than those of Pd/reduced graphene oxide (Pd/rGO) and Pd/Vulcan XC-72 (Pd/VC), respectively. In addition, Pd–Mo2N/rGO exhibits enhanced CO tolerance and good stability. The good performance is mainly ascribed to the intimate contact between Mo2N and Pd which gives enhanced synergistic action. The excellent performance of Pd–Mo2N/rGO makes it a potential electrocatalyst for DFAFC applications.

Layer Stacking-like Iodine and Phosphorus Co-doped C3N4 for Enhanced Visible-light Photocatalytic Hydrogen Evolution

Hetero‐element doping is one of the most effective methods for band gap regulation of semiconductor photocatalysts. Here, a novel layer stacking of iodine and phosphorus co‐doped carbon nitride (I/P‐CN) was prepared from a novel supramolecular precursor. The obtained I/P‐CN exhibits significantly enhanced visible‐light photocatalytic hydrogen production (93.9 μmol h−1) compared with bulk carbon nitride. Moreover, it reveals a consistent cycle stability for photocatalytic application. The marked improvement in photocatalytic activity is the result of iodine and phosphorus co‐doping bringing about a decrease in the band gap and an increase of absorption intensity and width. The unique layer in the stacking structure facilitates an increase in specific surface area and active reaction sites. Our research opens up a new strategy to synthesize multiple elements co‐doped carbon nitride as a promising metal‐free photocatalyst for hydrogen evolution under visible light.