Tanyuan Wang

Enhanced electrocatalytic activity for hydrogen evolution reaction from self-assembled monodispersed molybdenum sulfide nanoparticles on an Au electrode

Ultrasmall molybdenum sulfide nanoparticles with diameters of 1.47 ± 0.16 nm were fabricated from bulk MoS2 by a combination of ultrasonication and centrifugation. The nanoparticles were then assembled on an Au surface to form a film with high electrocatalytic activity for hydrogen evolution reaction (HER). A Tafel slope of 69 mV per decade was measured for this film and the onset potential was estimated to be −0.09 V. The small loading (1.03 μg cm−2) and the high current density (0.92 mA cm−2 at η = 0.15 V) demonstrated extremely high catalytic efficiency. X-ray photoelectron spectroscopic results revealed that the assembled nanoparticle film was sulfur enriched with abundant S edges and a structural rearrangement of the S rich particles might occur during the self-assembly process, resulting in significantly enhanced electrocatalytic activity for HER. Electrochemical impedance measurements suggested that the assembling process optimized the conductivity of the nanoparticle film, which contributed to the enhanced HER catalytic activity. Our research has provided a new way to synthesize active molybdenum sulfide nanoparticles for HER and a new approach to achieve enrichment of S edges on molybdenum sulfide, which might have potential use not only for electrocatalytic HER, but also for photoelectrocatalytic HER and plasmon-enhanced water splitting.

Biosensor Based on Ultrasmall MoS2 Nanoparticles for Electrochemical Detection of H2O2 Released by Cells at the Nanomolar Level

Monodispersed surfactant-free MoS2 nanoparticles with sizes of less than 2 nm were prepared from bulk MoS2 by simple ultrasonication and gradient centrifugation. The ultrasmall MoS2 nanoparticles expose a large fraction of edge sites, along with their high surface area, which lead to attractive electrocatalytic activity for reduction of H2O2. An extremely sensitive H2O2 biosensor based on MoS2 nanoparticles with a real determination limit as low as 2.5 nM and wide linear range of 5 orders of magnitude was constructed. On the basis of this biosensor, the trace amount of H2O2 released from Raw 264.7 cells was successfully recorded, and an efficient glucose biosensor was also fabricated. Since H2O2 is a byproduct of many oxidative biological reactions, this work serves as a pathway for the application of MoS2 in the fields of electrochemical sensing and bioanalysis.

Size‐Dependent Enhancement of Electrocatalytic Oxygen‐Reduction and Hydrogen‐Evolution Performance of MoS2 Particles

MoS2 particles with different size distributions were prepared by simple ultrasonication of bulk MoS2 followed by gradient centrifugation. Relative to the inert microscale MoS2, nanoscale MoS2 showed significantly improved catalytic activity toward the oxygen-reduction reaction (ORR) and hydrogen-evolution reaction (HER). The decrease in particle size was accompanied by an increase in catalytic activity. Particles with a size of around 2 nm exhibited the best dual ORR and HER performance with a four-electron ORR process and an HER onset potential of -0.16 V versus the standard hydrogen electrode (SHE). This is the first investigation on the size-dependent effect of the ORR activity of MoS2, and a four-electron transfer route was found. The exposed abundant Mo edges of the MoS2 nanoparticles were proven to be responsible for the high ORR catalytic activity, whereas the origin of the improved HER activity of the nanoparticles was attributed to the plentiful exposed S edges. This newly discovered process provides a simple protocol to produce inexpensive highly active MoS2 catalysts that could easily be scaled up. Hence, it opens up possibilities for wide applications of MoS2 nanoparticles in the fields of energy conversion and storage.

Electrochemically Fabricated Polypyrrole and MoSx Copolymer Films as a Highly Active Hydrogen Evolution Electrocatalyst

DOI: 10.1002/adma.201400265 surface area, as well as good stability. [ 14 ] Moreover, It has been demonstrated that [MoS 4 ] 2− and some other molybdenum sulfi de anions can be doped into PPy during the polymerization process, [ 15 ] which makes it an ideal carrier for MoS x . Herein, we demonstrate a simple way to fabricate polypyrrole/MoS x hybrid (PPy/MoS x ) fi lms by a one-step electrochemical copolymerization. The PPy/MoS x fi lms exhibit an outstanding HER performance that is comparable to that of commercial Pt/C catalysts. The highly active PPy/MoS x fi lms for HER were prepared in 0.1 M NaClO 4 containing 0.5 M pyrrole (Py) and 2 m M

Direct detection of DNA below ppb level based on thionin-functionalized layered MoS2 electrochemical sensors.

A layered MoS2-thionin composite was prepared by sonicating their mixture in an ionic liquid and gradient centrifugation. Because DNA is rarely present in single-stranded form, either naturally or after PCR amplification, the composite was used for fabrication of a double-stranded DNA (dsDNA) electrochemical biosensor due to stable electrochemical response, intercalation, and electrostatic interaction of thionin with DNA. The linear range over dsDNA concentration from 0.09 ng mL(-1) to 1.9 ng mL(-1) is obtained, and moreover, it is suitable for the detection of single-stranded DNA (ssDNA). The biosensor has been applied to the detection of circulating DNA from healthy human serum, and satisfactory results have been obtained. The constructed DNA electrochemical biosensor shows potential application in the fields of bioanalysis and clinic diagnosis. Furthermore, this work proposes a new method to construct electrochemical biosensors based on MoS2 sheets.

Salts of C60(OH)8 Electrodeposited onto a Glassy Carbon Electrode: Surprising Catalytic Performance in the Hydrogen Evolution Reaction

With the energy crisis becoming increasingly serious, hydrogen is proposed as a promising energy carrier substitute to fossil energy. A practical technique to produce hydrogen is the splitting of water by either electrochemical or photochemical methods. Usually, catalysts are widely used to overcome the overpotential for the hydrogen evolution reaction (HER) and to obtain high efficiency. Among the catalysts produced for the HER, Pt, Pd, and Ru show the best performance, but their high cost seriously limits their use. On the other hand, less expensive substitutes using metals such as Ni and Co suffer from corrosion, passivation, and lower catalytic activity. The need for active, stable, and inexpensive electrocatalysts has aroused intensive research interest, resulting in the development of molecular catalysts. Thus far, relatively few molecular catalysts have been studied for the HER in aqueous solutions, and most of catalysts studied consisted of transition metals. Herein, we report a novel molecular catalyst based on carbon: a salt consisting of fullerenol anions electrodeposited onto a glassy carbon electrode (GCE) coated with Nafion in an aqueous solution for the HER. The onset potential was estimated to be 0.11 V (vs. RHE) with low loading and high exchange current density. Polyhydroxylated fullerene (fullerenol) is one of the most studied fullerene derivatives, because of their low biological toxicity and outstanding radical scavenging ability. Various synthetic methods have been reported, but most of them obtained complicated mixtures of fullerenols with different structures, which limited further study of their properties. We have previously reported the preparation of the first isomerically pure multihydroxylated fullerene, C60(OH)8. [6] Its solubility in water is much greater than that of C60 due to the eight hydroxy groups on the carbon cage, which makes it possible to study its electrochemical properties in aqueous solutions; these properties are fundamental for investigating electrocatalysis based on fullerenols. There have been few reports to date about the electrochemical properties of fullerenols in water, therefore, we investigated electrochemical behavior of C60(OH)8 in aqueous solutions. Figure 1 displays a cyclic voltammogram of C60(OH)8 in an aqueous solution of KCl (0.1m). A reduction peak at

Enhanced electrocatalytic activity of MoP microparticles for hydrogen evolution by grinding and electrochemical activation

Transition metal phosphides like CoP, MoP, Ni2P are suggested to be highly efficient catalysts for hydrogen evolution reaction (HER). However, HER-inert oxides would usually form on the surfaces of these phosphides during preparation and long-term storage. In this study, a simple combination method of grinding and electrochemical activation is used to tune the surface states of long-term stored commercial MoP microparticles, which show low activity for HER due to the molybdenum and phosphorus oxides on the surface, resulting in more exposed active sites of MoP and an enhanced catalytic activity for HER with an onset potential of 0.08 V vs. RHE and a Tafel slope of 50 mV dec−1.

Tuning the Catalytic Activity of Graphene Nanosheets for Oxygen Reduction Reaction via Size and Thickness Reduction

Currently, the fundamental factors that control the oxygen reduction reaction (ORR) activity of graphene itself, in particular, the dependence of the ORR activity on the number of exposed edge sites remain elusive, mainly due to limited synthesis routes of achieving small size graphene. In this work, the synthesis of low oxygen content (<2.5±0.2 at. %), few layer graphene nanosheets with lateral dimensions smaller than a few hundred nanometers were achieved using a combination of ionic liquid assisted grinding of high purity graphite coupled with sequential centrifugation. We show for the first time that the graphene nanosheets possessing a plethora of edges exhibited considerably higher electron transfer numbers compared to the thicker graphene nanoplatelets. This enhanced ORR activity was accomplished by successfully exploiting the plethora of edges of the nanosized graphene as well as the efficient electron communication between the active edge sites and the electrode substrate. The graphene nanosheets were characterized by an onset potential of -0.13 V vs Ag/AgCl and a current density of -3.85 mA/cm2 at -1 V, which represent the best ORR performance ever achieved from an undoped carbon based catalyst. This work demonstrates how low oxygen content nanosized graphene synthesized by a simple route can considerably impact the ORR catalytic activity and hence it is of significance in designing and optimizing advanced metal-free ORR electrocatalysts.

Synergistic Catalytic Effect of MoS2 Nanoparticles Supported on Gold Nanoparticle Films for a Highly Efficient Oxygen Reduction Reaction

MoS2 nanoparticles supported on gold nanoparticle films (AuNP/MoS2 films) were constructed by a simple two‐step drop‐casting modification process on a glassy carbon electrode. The films realized a direct four‐electron pathway for the oxygen reduction reaction (ORR) in alkaline media with an onset potential of −0.10 V versus the saturated calomel electrode. The films exhibited superior stability and better electrocatalytic performance than commercial Pt/C. Electrochemical studies and composition characterization illustrated that the enhanced catalytic activity of the AuNP/MoS2 films could be attributed to the synergistic effect of the positive onset potential of the gold nanoparticles for the ORR and the four‐electron oxygen reduction properties of the ultrasmall MoS2 nanoparticles, which is different from gold nanoparticle and MoS2 nanoparticle modified electrodes.

Molybdenum disulfide and Au ultrasmall nanohybrids as highly active electrocatalysts for hydrogen evolution reaction

Molybdenum disulfide (MoS2) is a promising catalyst for hydrogen generation from water splitting. However, there is still a gap compared to electrocatalytic performance of Pt group metals. Herein, we propose a simple solvothermal method to prepare ultrasmall MoS2–Au nanohybrids with average diameters of 2.5 nm. The MoS2–Au nanohybrids exhibit superior HER performance with a low onset potential of 17 mV, a Tafel slope of 40 mV dec−1 and a current density of 10 mA cm−2 at an overpotential of only 66 mV. The enhanced HER catalytic activity is attributed to the doping of gold resulting in a synergistic effect between Au and MoS2, which promotes the activity of the edge sites and enhancement of conductivity. Our work has provided a new approach to synthesize hybridized MoS2 for an enhanced hydrogen evolution reaction (HER).