The synergistic effects of alloying on the performance and stability of Co3Mo and Co7Mo6 for the electrocatalytic hydrogen evolution reaction

Metal alloys have become a ubiquitous choice as catalysts for electrochemical hydrogen evolution in alkaline media. However, scarce and expensive Pt remains the key electrocatalyst in acidic electrolytes, making the search for earth-abundant and cheaper alternatives important. Herein, we present a facile and efficient synthetic route towards polycrystalline Co3Mo and Co7Mo6 alloys. The single-phased nature of the alloys is confirmed by X-ray diffraction and electron microscopy. When electrochemically tested, they achieve competitively low overpotentials of 115 mV (Co3Mo) and 160 mV (Co7Mo6) at 10 mA cm−2 in 0.5 M H2SO4, and 120 mV (Co3Mo) and 160 mV (Co7Mo6) at 10 mA cm−2 in 1 M KOH. Both alloys outperform Co and Mo metals, which showed significantly higher overpotentials and lower current densities when tested under identical conditions, confirming the synergistic effect of the alloying. However, the low overpotential in Co3Mo comes at the price of stability. It rapidly becomes inactive when tested under applied potential bias. On the other hand, Co7Mo6 retains the current density over time without evidence of current decay. The findings demonstrate that even in free-standing form and without nanostructuring, polycrystalline bimetallic electrocatalysts could challenge the dominance of Pt in acidic media if ways for improving their stability were found

Synthesis and investigation of low valent transition metal nitrides as electrocatalysts for the hydrogen evolution reaction

With the help of renewable electricity, a device called electrolyser can split water into main components: O2 and H2. Hydrogen is a good fuel and can be used on demand in a range of energy applications as well as feedstock for chemicals. The hydrogen evolution reaction from water is commonly assisted by Pt-group metal electrocatalysts. The high cost of Pt-group metals makes the search for cheaper alternatives important. The presented work aims to assess the suitability of low valent transition metal nitrides as electrocatalysts for the hydrogen evolution reaction (HER) and compare their performance with transition metal alloys. After brief introduction and experimental sections, the synthesis, crystal structure and electronic properties of two common ordered Co-Mo intermetallics (Co3Mo and Co7Mo6) are discussed. These were tested in both acidic and alkaline conditions to have a reliable benchmark for comparison with metal nitrides. Despite relatively good electrocatalytic performance the stability of the intermetallic was found limited which is consistent with previous literature reports. The following chapter is focused on comparison of three isostructural ternary nitrides (Co3Mo3N, Fe3Mo3N and Co6Mo6N) which crystallize in the -carbide structure type. As the focus is given to the comparative investigation a great care was given to isolate them as phase pure materials which was confirmed by Rietveld refinement of PXRD data. The synthesis was carried out by reduction of the relevant metal oxides in H2/N2 gas mixtures while Co6Mo6N was prepared through topotactic reaction from Co3Mo3N in H2/Ar gas mixture. Co3Mo3N delivered a relatively low overpotential of just 108 mV at 10 mA cm-2 while it also showed high current densities when immobilised on Ni-foam substrate. The stability of the nitride was excellent as was evidenced by chronoamperometric studies. Remarkably, Co6Mo6N showed a similar electrocatalytic properties with slightly higher overpotential but poor electrochemical stability. Hence, the initial hypothesis that the introduction of N atoms within the lattice could lead to higher stability was confirmed. Replacing Co for Fe into isostructural Fe3Mo3N on the other hand led to deteriorated performance suggesting that Co sites are catalytically active. This observation was also supported by computational DFT studies presented in this work. Overall, it was shown that low valent nitrides are probably superior catalyst than similar metal alloys. To study the effect of Mo substitution a previously unreported nitride with a composition Co6W6N was isolated. The additional use of urea precursor along with H2/N2 was required with elemental analysis unambiguously pointing out that the resulting compound was pure nitride as no traces of carbon were found. In comparison, isostructural Fe6W6N showed poor electrochemical performance confirming that the Co-sites are probably responsible for catalytic activity in these low valent nitrides. To pursue the hypothesis about crucial role of late transition metals play in catalytic performance Co2Mo3N and the isostructural solid solutions with the compositions Ni2- xFexMo3N (x= 0 – 1.25) were investigated. The substitution of Ni for Fe led to a deterioration in the performance further suggesting that d8 /d9 metals are essential for good electrocatalytic properties. An additional XPS investigation suggested that preserving low oxidation state of the metals is important. As Co2Mo3N showed higher overpotential than Co3Mo3N at a benchmark current density this suggested that higher number of d8 /d9 transition metals per formula unit could be a way forward for improving the catalytic properties. To test the hypothesis that increased number of late transition metal per formula unit would lead to improved catalytic activity several ternary nitrides with anti-perovskite structure were synthesised, including Co3SnN, Fe3SnN, Co3ZnN and Co3InN. These were prepared with the help of melamine as a nitrogen source and were found phase pure according to the Rietveld refinement of the PXRD data. The nitrides showed poor stability in acidic electrolyte but demonstrated a good stability in alkaline conditions. Among these nitrides, despite relatively higher number of Co atoms per formula unit, the lowest overpotential of 128 mV was achieved on Co3InN. However, this was higher than that of 108 mV demonstrated by Co3Mo3N at a benchmark current density of 10 mA cm-2 . From this perspective it was not possible to determine whether increasing the number of late-transition metal sites could lead to an improved catalytic performance. Overall, the results pointed out that ternary low valent transition metal nitrides are promising targets for application in electrocatalytic water splitting. Ni2Mo3N was identified as the most cost-effective material due to a relative simplicity of immobilizing it on a high surface area nickel foam substrate. This creates future opportunities for further research that could lead to an implementation of nitrides in proton exchange electrolysers

Saikosaponins induced hepatotoxicity in mice via lipid metabolism dysregulation and oxidative stress: a proteomic study

Background Radix Bupleuri (RB) has been popularly used for treating many liver diseases such as chronic hepatic inflammation and viral Hepatitis in China. Increasing clinical and experimental evidence indicates the potential hepatotoxicity of RB or prescriptions containing RB. Recently, Saikosaponins (SS) have been identified as major bioactive compounds isolated from RB, which may be also responsible for RB-induced liver injury. Methods Serum AST, ALT and LDH levels were determined to evaluate SS-induced liver injury in mice. Serum and liver total triglyceride and cholesterol were used to indicate lipid metabolism homeostasis. Liver ROS, GSH, MDA and iNOS were used to examine the oxidative stress level after SS administration. Western blot was used to detect CYP2E1 expression. A 8-Plex iTRAQ Labeling Coupled with 2D LC - MS/MS technique was applied to analyze the protein expression profiles in livers of mice administered with different doses of SS for different time periods. Gene ontology analysis, cluster and enrichment analysis were employed to elucidate potential mechanism involved. HepG2 cells were used to identify our findings in vitro. Results SS dose- and time-dependently induced liver injury in mice, indicated by increased serum AST, ALT and LDH levels. According to proteomic analysis, 487 differentially expressed proteins were identified in mice administrated with different dose of SS for different time periods. Altered proteins were enriched in pathways such as lipid metabolism, protein metabolism, macro molecular transportation, cytoskeleton structure and response to stress. SS enhanced CYP2E1 expression in a time and dose dependent manner, and induced oxidative stress both in vivo and in vitro. Conclusion Our results identified hepatotoxicity and established dose-time course-liver toxicity relationship in mice model of SS administration and suggested potential mechanisms, including impaired lipid and protein metabolism and oxidative stress. The current study provides experimental evidence for clinical safe use of RB, and also new insights into understanding the mechanism by which SS and RB induced liver injury

Assembly of Silver Nanoparticles into Hollow Spheres Using Eu(III) Compound based on Trifluorothenoyl-Acetone

The preparation of luminescent silver hollow spheres using Eu(III) compound based on trifluorothenoyl-acetone is described. The structure and size of silver hollow spheres were determined by TEM images. The result shows the formation of hollow structure and average size of the silver hollow spheres (0.9 μm). The silver hollow spheres were further characterized by UV absorption spectrum, SNOM and SEM images, suggesting them to be formed by self-assemble of some isolated silver nanoparticles. The luminescent properties of them were also investigated and they are shown to be high emission strength; moreover, they offer the distinct advantage of a lower packing density compared with other commercial luminescent products

In Situ Synthesis of Reduced Graphene Oxide-Reinforced Silicone-Acrylate Resin Composite Films Applied in Erosion Resistance

The reduced graphene oxide reinforced silicone-acrylate resin composite films (rGO/SAR composite films) were prepared by in situ synthesis method. The structure of rGO/SAR composite films was characterized by Raman spectrum, atomic force microscope, scanning electron microscopy, and thermogravimetric analyzer. The results showed that the rGO were uniformly dispersed in silicone-acrylate resin matrix. Furthermore, the effect of rGO loading on mechanical properties of composite films was investigated by bulge test. A significant enhancement (ca. 290% and 320%) in Young’s modulus and yield stress was obtained by adding the rGO to silicone-acrylate resin. At the same time, the adhesive energy between the composite films and metal substrate was also improved to be about 200%. Moreover, the erosion resistance of the composite films was also investigated as function of rGO loading. The rGO had great effect on the erosion resistance of the composite films, in which the Rcorr (ca. 0.8 mm/year) of composite film was far lower than that (28.7 mm/year) of pure silicone-acrylate resin film. Thus, this approach provides a novel route to investigate mechanical stability of polymer composite films and improve erosion resistance of polymer coating, which are very important to be used in mechanical-corrosion coupling environments

Revealing the activity of Co3Mo3N and Co3Mo3N0.5 as electrocatalysts for the hydrogen evolution reaction

The hydrogen evolution reaction (HER) from water is governed by electrocatalysts used. Multiple factors such as crystal structure, composition and morphology dictate the final catalytic performance. However, as multicomponent materials are developed to replace noble metals in the HER, it has become increasingly difficult to identify intrinsically active materials. Hence, there is an imperative for phase-pure catalysts to be synthetized and tested without obscuring contributions from impurities or substrates. Herein, we demonstrate that phase-pure, unsupported Co3Mo3N achieves a competitively low overpotential (OVP) of 108 ± 8 mV at 10 mA cm‒2 in 0.5 M H2SO4. Density functional theory (DFT) reveals weakly binding metal sites as the catalytic centres for the HER in the nitride. Remarkably, the N-deficient Co3Mo3N0.5 shows similar electrochemical properties but has limited chemical stability under cathodic bias. Thus, even though nitrogen sites play only a minor role in catalytic performance, their occupancy is crucial for the stability of nitride catalysts in the corrosive electrolyte. The composite of Co3Mo3N on Ni-foam sustains 10 ± 0.7 mA cm‒2 at applied potential of just 20 mV over extended time, highlighting the utility of nitrides for future design of stable and active HER catalytic systems

Development and evaluation of the first high-throughput SNP array for common carp (Cyprinus carpio)

BACKGROUND: A large number of single nucleotide polymorphisms (SNPs) have been identified in common carp (Cyprinus carpio) but, as yet, no high-throughput genotyping platform is available for this species. C. carpio is an important aquaculture species that accounts for nearly 14% of freshwater aquaculture production worldwide. We have developed an array for C. carpio with 250,000 SNPs and evaluated its performance using samples from various strains of C. carpio. RESULTS: The SNPs used on the array were selected from two resources: the transcribed sequences from RNA-seq data of four strains of C. carpio, and the genome re-sequencing data of five strains of C. carpio. The 250,000 SNPs on the resulting array are distributed evenly across the reference C.carpio genome with an average spacing of 6.6 kb. To evaluate the SNP array, 1,072 C. carpio samples were collected and tested. Of the 250,000 SNPs on the array, 185,150 (74.06%) were found to be polymorphic sites. Genotyping accuracy was checked using genotyping data from a group of full-siblings and their parents, and over 99.8% of the qualified SNPs were found to be reliable. Analysis of the linkage disequilibrium on all samples and on three domestic C.carpio strains revealed that the latter had the longer haplotype blocks. We also evaluated our SNP array on 80 samples from eight species related to C. carpio, with from 53,526 to 71,984 polymorphic SNPs. An identity by state analysis divided all the samples into three clusters; most of the C. carpio strains formed the largest cluster. CONCLUSIONS: The Carp SNP array described here is the first high-throughput genotyping platform for C. carpio. Our evaluation of this array indicates that it will be valuable for farmed carp and for genetic and population biology studies in C. carpio and related species