Gao-Feng Han

Controllable Growth and Transfer of Monolayer MoS2 on Au Foils and Its Potential Application in Hydrogen Evolution Reaction

Controllable synthesis of monolayer MoS2 is essential for fulfilling the application potentials of MoS2 in optoelectronics and valleytronics, etc. Herein, we report the scalable growth of high quality, domain size tunable (edge length from ∼ 200 nm to 50 μm), strictly monolayer MoS2 flakes or even complete films on commercially available Au foils, via low pressure chemical vapor deposition method. The as-grown MoS2 samples can be transferred onto arbitrary substrates like SiO2/Si and quartz with a perfect preservation of the crystal quality, thus probably facilitating its versatile applications. Of particular interest, the nanosized triangular MoS2 flakes on Au foils are proven to be excellent electrocatalysts for hydrogen evolution reaction, featured by a rather low Tafel slope (61 mV/decade) and a relative high exchange current density (38.1 μA/cm(2)). The excellent electron coupling between MoS2 and Au foils is considered to account for the extraordinary hydrogen evolution reaction activity. Our work reports the synthesis of monolayer MoS2 when introducing metal foils as substrates, and presents sound proof that monolayer MoS2 assembled on a well selected electrode can manifest a hydrogen evolution reaction property comparable with that of nanoparticles or few-layer MoS2 electrocatalysts.

Nanoporous gold supported cobalt oxide microelectrodes as high-performance electrochemical biosensors

Tremendous demands for electrochemical biosensors with high sensitivity and reliability, fast response and excellent selectivity have stimulated intensive research on developing versatile materials with ultrahigh electrocatalytic activity. Here we report flexible and self-supported microelectrodes with a seamless solid/nanoporous gold/cobalt oxide hybrid structure for electrochemical nonenzymatic glucose biosensors. As a result of synergistic electrocatalytic activity of the gold skeleton and cobalt oxide nanoparticles towards glucose oxidation, amperometric glucose biosensors based on the hybrid microelectrodes exhibit multi-linear detection ranges with ultrahigh sensitivities at a low potential of 0.26 V (versus Ag/AgCl). The sensitivity up to 12.5 mA mM⁻¹ cm⁻² with a short response time of less than 1 s gives rise to ultralow detection limit of 5 nM. The outstanding performance originates from a novel nanoarchitecture in which the cobalt oxide nanoparticles are incorporated into pore channels of the seamless solid/nanoporous Au microwires, providing excellent electronic/ionic conductivity and mass transport for the enhanced electrocatalysis.

Dendritic, transferable, strictly monolayer MoS2 flakes synthesized on SrTiO3 single crystals for efficient electrocatalytic applications.

Controllable synthesis of macroscopically uniform, high-quality monolayer MoS2 is crucial for harnessing its great potential in optoelectronics, electrocatalysis, and energy storage. To date, triangular MoS2 single crystals or their polycrystalline aggregates have been synthesized on insulating substrates of SiO2/Si, mica, sapphire, etc., via portable chemical vapor deposition methods. Herein, we report a controllable synthesis of dendritic, strictly monolayer MoS2 flakes possessing tunable degrees of fractal shape on a specific insulator, SrTiO3. Interestingly, the dendritic monolayer MoS2, characterized by abundant edges, can be transferred intact onto Au foil electrodes and serve as ideal electrocatalysts for hydrogen evolution reaction, reflected by a rather low Tafel slope of ∼73 mV/decade among CVD-grown two-dimensional MoS2 flakes. In addition, we reveal that centimeter-scale uniform, strictly monolayer MoS2 films consisting of relatively compact domains can also be obtained, offering insights into promising applications such as flexible energy conversion/harvesting and optoelectronics.

Integrated Solid/Nanoporous Copper/Oxide Hybrid Bulk Electrodes for High-performance Lithium-Ion Batteries

Nanoarchitectured electroactive materials can boost rates of Li insertion/extraction, showing genuine potential to increase power output of Li-ion batteries. However, electrodes assembled with low-dimensional nanostructured transition metal oxides by conventional approach suffer from dramatic reductions in energy capacities owing to sluggish ion and electron transport kinetics. Here we report that flexible bulk electrodes, made of three-dimensional bicontinuous nanoporous Cu/MnO2 hybrid and seamlessly integrated with Cu solid current collector, substantially optimizes Li storage behavior of the constituent MnO2. As a result of the unique integration of solid/nanoporous hybrid architecture that simultaneously enhances the electron transport of MnO2, facilitates fast ion diffusion and accommodates large volume changes on Li insertion/extraction of MnO2, the supported MnO2 exhibits a stable capacity of as high as ~1100 mA h g−1 for 1000 cycles, and ultrahigh charge/discharge rates. It makes the environmentally friendly and low-cost electrode as a promising anode for high-performance Li-ion battery applications.

Chemical vapor deposition of monolayer WS2 nanosheets on Au foils toward direct application in hydrogen evolution

Monolayer tungsten disulfide (WS2), a typical member of the semiconducting transition metal dichalcogenide family, has drawn considerable interest because of its unique properties. Intriguingly, the edge of WS2 exhibits an ideal hydrogen binding energy, which makes WS2 a potential alternative to Pt-based electrocatalysts for the hydrogen evolution reaction (HER). Here, we demonstrate for the first time the successful synthesis of uniform monolayer WS2 nanosheets on centimeter-scale Au foils using a facile, low-pressure chemical vapor deposition method. The edge lengths of the universally observed triangular WS2 nanosheets are tunable from ∼100 to ∼1,000 nm. The WS2 nanosheets on Au foils featuring abundant edges were then discovered to be efficient catalysts for the HER, exhibiting a rather high exchange current density of ∼30.20 μA/cm2 and a small onset potential of ∼110 mV. The effects of coverage and domain size (which correlate closely with the active edge density of WS2) on the electrocatalytic activity were investigated. This work not only provides a novel route toward the batch-production of monolayer WS2 via the introduction of metal foil substrates but also opens up its direct application for facile HER.

Facile Synthesis of Non-Graphitizable Polypyrrole-Derived Carbon/Carbon Nanotubes for Lithium-ion Batteries

Graphite is usually used as an anode material in the commercial lithium ion batteries (LIBs). The relatively low lithium storage capacity of 372 mAh g–1 and the confined rate capability however limit its large-scale applications in electrical vehicles and hybrid electrical vehicles. As results, exploring novel carbon-based anode materials with improved reversible capacity for high-energy-density LIBs is urgent task. Herein we present TNGC/MWCNTs by synthesizing tubular polypyrrole (T-PPy) via a self-assembly process, then carbonizing T-PPy at 900 °C under an argon atmosphere (TNGC for short) and finally mixing TNGC with multi-walled carbon nanotubes (MWCNTs). As for TNGC/MWCNTs, the discharge capacity of 561 mAh g−1 is maintained after 100 cycles at a current density of 100 mA g−1. Electrochemical results demonstrate that TNGC/MWCNTs can be considered as promising anode materials for high-energy-density LIBs.

Self-grown Ni(OH)(2) layer on bimodal nanoporous AuNi alloys for enhanced electrocatalytic activity and stability.

Au nanostructures as catalysts toward electrooxidation of small molecules generally suffer from ultralow surface adsorption capability and stability. Here, we report Ni(OH)2 layer decorated nanoporous (NP) AuNi alloys with a three-dimensional and bimodal porous architecture, which are facilely fabricated by a combination of chemical dealloying and in situ surface segregation, for the enhanced electrocatalytic performance in biosensors. As a result of the self-grown Ni(OH)2 on the AuNi alloys with a coherent interface, which not only enhances adsorption energy of Au and electron transfer of AuNi/Ni(OH)2 but also prohibits the surface diffusion of Au atoms, the NP composites are enlisted to exhibit significant enhancement in both electrocatalytic activity and stability toward glucose electrooxidation. The highly reliable glucose biosensing with exceptional reproducibility and selectivity as well as quick response makes it a promising candidate as electrode materials for the application in nonenzymatic glucose biosensors.

Nanoporous (Pt1−xFex)3Al intermetallic compounds for greatly enhanced oxygen electroreduction catalysis

Considerable demand for the widespread commercialization of proton exchange membrane (PEM) fuel cells has stimulated intensive research into the development of oxygen electroreduction catalysts that are more efficient than carbon-supported Pt nanoparticles. Here we report a dealloyed ternary intermetallic compound of PtFeAl with a nanoporous structure composed of a (Pt1−xFex)3Al (x = 0.167) core with Pt skin [NP (Pt1−xFex)3Al/Pt]. As an oxygen reduction reaction catalyst, NP (Pt1−xFex)3Al/Pt exhibits exceptional durability in long-term electrochemical cycling, with specific and mass activities of 3.97 mA cmPt−2 and 1.94 A mgPt−1, respectively (∼10.2- and ∼14.9-fold higher than those of commercially available Pt/C). This is due to strong Pt–Al and Fe–Al bonds, which not only weaken the adsorption energy of the Pt skin but also inhibit the evolution of Pt, Fe and Al atoms. The outstanding performance makes this a promising candidate as a cathode catalyst in PEM fuel cells as well as in other electrochemical energy conversion and storage devices, such as metal–air batteries.