Session Chair: Hong-Jun Gao, Institute of Physics, Chinese Academy of Sciences Session Chair: Lain-Jong (Lance) Li, King Abdullah University of Science and Technology
4:00pm - 4:30pm Invited
Recent Progress on 2D Materials for Electrochemistry
Rutgers University, United States
Over the past few years we have shown that chemically exfoliated 2D transition metal dichalcogenides (TMDs) are excellent for electrochemical applications such as energy storage and catalysis. For example, electrodes from restacked TMDs exhibit excellent volumetric capacitance along with high energy and power densities in energy storage devices. In this presentation, we will show that the high capacitance can be used for realizing ultra-strong electrochemical actuators. In addition to energy storage and actuation, our work has demonstrated that the strained metallic 1T phase of MoS2 can lower the free energy for the HER limiting reaction so that the basal plane can be made catalytically active. In addition, we have recently demonstrated that the activity of the 2H basal planes of monolayered MoS2 nanosheets can be made comparable to state-of-the-art catalytic properties of metallic edges and the 1T phase by improving electrical coupling between the substrate and the catalyst so that electron injection from the electrode and transport to the catalyst active site is facilitated. I will summarize the recent developments in 2D materials for HER, including our recent work on using reduced graphene oxide for oxygen reduction reaction, and discuss some challenges.
4:30pm - 5:00pm Invited
Exploring Two-Dimensional Transition Metal Dichalcogenides for Monolayer Optoelectronic Devices
Nanyang Technological University, Singapore
Transitional-metal-dichalcogenide (TMD) monolayers, as the rising two-dimensional (2D) semiconductors, have attracted great interest owing to the underlying many body physics and the appealing optoelectronic applications such as light-emitting diodes, photodetectors and lasing devices. In particular, circularly polarized electroluminescence and photocurrent from such monolayers are highly demanded for the new generation valleytronic applications. Furthermore, considering practical applications, a strategy which can provide mass-product and high compatibility to the complementary metal–oxide–semiconductor processes, is necessary. Here, we report fundamental studies of strong excitonic emission of TMD monolayers and their optoelectronic device applications with the manipulation of the valley degree. Wealthy excitonic emission states of TMD monolayers have been investigated under electrical, optical, chemical and magnetic manipulation. The binding energies of diverse excitonic states and the Zeeman-like valley splitting of magnetoluminescence have been extracted. Electrically tunable valley-polarized electroluminescence and the selective spin–valley-coupled photocurrent based on monolayer WS2 and MoS2 grown by chemical vapour deposition (CVD) have been demonstrated, which exhibit large electroluminescence and photocurrent dichroisms of 81% and 60%, respectively. The mechanisms of controllable valley polarization of the electroluminescence and the helicity-dependent photocurrent have been proposed. Moreover, by incorporating 2D semiconductors with photonic architectures, the dramatically enhanced excitonic emission has been obtained, which is beneficial to develop monolayer lasing applications. Overall, our works reveal the fundamental light emission properties of semiconducting TMD monolayers and move an important step towards developing the practical optoelectronic and valleytronic devices by employing scalable CVD-grown 2D semiconductors.
5:00pm - 5:15pm Oral
Effect of Dimensionality on Thermoelectric Powerfactor of Molybdenum Disulfide
Hong Kuan NG, Dongzhi CHI, Kedar HIPPALGAONKAR
Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore
We present that two-dimensional (2D) bilayer molybdenum disulfide (MoS2) exhibits an enhanced Seebeck coefficient over its three-dimensional (3D) counterpart arising from dimensionality confinement. It has been predicted that quantum confinement enhances thermoelectric performance but no studies have focused on a single material to present a theoretical and experimental comparison, which would illustrate the enhancement of thermoelectric performance. Layered MoS2 provides an opportunity to verify this hypothesis and in this work we extensively study the Seebeck coefficient, S, the electrical conductivity, σ, and the thermoelectric powerfactor, S2σ of 2D monolayer and bilayer MoS2 using theoretical Boltzmann Transport Equation calculations and compare the results to well-characterized experimental data. We conclude that dimensional confinement indeed enhances the Seebeck coefficient by up to ~ 50% in 2D bilayer MoS2 over 3D MoS2 under similar doping concentrations because of the discretization of density of states. We also consider electrical conductivity with various energy-dependent scattering rates considering charged-impurities and phonons and comment on a theoretical comparison of the powerfactor to the best-case scenario for 3D MoS2.
5:15pm - 5:30pm Oral
Interface Confined Hydrogen Evolution Reaction in Zero Valent Metal Nanoparticles-Intercalated Molybdenum Disulfide
Zhongxin CHEN, Kai LENG, Kian Ping LOH
National University of Singapore, Singapore
Interface confined reactions, which can modulate the bonding of reactants with catalytic centers and influence the rate of the mass transport from bulk solution, have emerged as a viable strategy for achieving highly stable and selective catalysis. Herein, we demonstrate that 1T′-enriched lithiated molybdenum disulfide (MoS2) is a highly powerful reducing agent, and can be exploited for the in-situ reduction of metal ions within the inner planes of lithiated MoS2 to form a zero valent metal-intercalated MoS2. The confinement of platinum (Pt) nanoparticles within the MoS2 layered structure leads to enhanced hydrogen evolution reaction activity and stability compared to catalysts dispersed on carbon support (Pt/C). In particular, the inner Pt surface is accessible to charged species like proton and metal ions, while blocking poisoning by larger sized pollutants or neutral molecules. This points a way forward for using bulk intercalated compounds for energy related applications.