Interface-Controlled Synthesis of Au-BINOL Hybrid Nanostructures and Mechanism Study.

The combined functionality of components in organic-inorganic hybrid nanomaterials render them efficient nanoreactors. However, the development in this field is limited due to a lack of synthetic avenues and systematic control of the growth kinetics of hybrid structures. In this work, we take advantage of an ionic switch for regio-control of Au-BINOL(1,1'-Bi-2-naphthol) hybrid nanostructures. Aromatic BINOL molecules assemble into nanospheres, concomitant with the growth of the Au nanocrystals. The morphological evolution of Au nanocrystals is solely controlled by the presence of halides in the synthetic system. Here we show that quaternary ammonium surfactants (CTAB or CTAC), not only bridging Au and BINOL, but also contributing to the formation of concentric or eccentric structures when their concentrations are tuned to the range of 10-5 to 10-3 M. This facile strategy offers the potential advantage of scalable production, with diverse functional organic-inorganic hybrid nanocomposites being produced based on the specific archetype of Au-BINOL hybrid nanocomposites.

Bifunctional Monolayer WSe2/Graphene Self-Stitching Heterojunction Microreactors for Efficient Overall Water Splitting in Neutral Medium.

Developing efficient bifunctional electrocatalysts in neutral media to avoid the deterioration of electrodes or catalysts under harsh environments has become the ultimate goal in electrochemical water splitting. This work demonstrates the fabrication of an on-chip bifunctional two-dimensional (2D) monolayer (ML) WSe2/graphene heterojunction microreactor for efficient overall water splitting in a neutral medium (pH = 7). Through the synergistic atomic growth of the metallic Cr dopant and graphene stitching contact on the 2D ML WSe2, the bifunctional WSe2/graphene heterojunction microreactor consisting of a full-cell configuration demonstrates excellent performance for overall water splitting in a neutral medium. Atomic doping of metallic Cr atoms onto the 2D ML WSe2 effectively facilitates the charge transfer at the solid-liquid interface. In addition, the direct growth of the self-stitching graphene contact with the 2D WSe2 catalyst largely reduces the contact resistance of the microreactor and further improves the overall water splitting efficiency. A significant reduction of the overpotential of nearly 1000 mV at 10 mA cm-2 at the Cr-doped WSe2/graphene heterojunction microreactor compared to the ML pristine WSe2 counterpart is achieved. The bifunctional WSe2/graphene self-stitching heterojunction microreactor is an ideal platform to investigate the fundamental mechanism of emerging bifunctional 2D catalysts for overall water splitting in a neutral medium.

Using Exciton/Trion Dynamics to Spatially Monitor the Catalytic Activities of MoS2 during the Hydrogen Evolution Reaction.

The adsorption and desorption of electrolyte ions strongly modulates the carrier density or carrier type on the surface of monolayer-MoS2 catalyst during the hydrogen evolution reaction (HER). The buildup of electrolyte ions onto the surface of monolayer MoS2 during the HER may also result in the formation of excitons and trions, similar to those observed in gate-controlled field-effect transistor devices. Using the distinct carrier relaxation dynamics of excitons and trions of monolayer MoS2 as sensitive descriptors, an in situ microcell-based scanning time-resolved liquid cell microscope is set up to simultaneously measure the bias-dependent exciton/trion dynamics and spatially map the catalytic activity of monolayer MoS2 during the HER. This operando probing technique used to monitor the interplay between exciton/trion dynamics and electrocatalytic activity for two-dimensional transition metal dichalcogenides provides an excellent platform to investigate the local carrier behaviors at the atomic layer/liquid electrolyte interfaces during electrocatalytic reaction.

Enhancement of NH3 Production in Electrochemical N2 Reduction by the Cu-Rich Inner Surfaces of Beveled CuAu Nanoboxes.

The global ammonia yield is critical to the fertilizer industry as the global food demand is highly dependent on it, whereas, NH3 is also a key chemical for pharmaceutical, textile, plastic, explosive, and dye-making industries. At present, the demand for NH3 is fulfilled by the Haber-Bosch method, which consumes 1-3% of global energy and causes 0.5-1% CO2 emission every year. To reduce emissions and improve energy efficiency, the electrochemical nitrogen gas reduction reaction (N2RR) has received much attention and support after the funding announcement by the U.S. Department of Energy. In this work, we have created hollow CuAu nanoboxes with Cu-rich inner walls to improve the NH3 Faradaic efficiency in N2RR. These beveled nanoboxes are produced in different degrees of corner and edge etching, which produces both polyhedral and concave structures. In N2RR, the binary CuAu nanoboxes enhanced NH3 production compared to individual Au and Cu nanocubes. The results of DFT calculations suggest the Cu-rich inner walls in the hollow beveled CuAu nanoboxes play a major role in their performance by reducing the free energy ΔG*NNH for the potential-determining step to form *NNH (* + N2(g) + H+ + e- → *NNH). Meanwhile, the results in 10-cycle and solar-illuminated N2RR indicate the beveled CuAu nanoboxes are not only robust electrocatalysts but show promise in photocatalysis as well.

The manufacturing of a metallic nano-cluster at a tip apex for field-sensitive microscopy applications.

Using a conductive atomic force microscopic setup, a metallic nano-cluster at a tip apex was successfully manufactured by an electrochemical redox process from an anodic aluminum oxide template. The diameter of the metallic nano-clusters ranged from 15 nm to 200 nm. The diameters of the nano-clusters could be well-controlled by adjusting the pore size of the templates. The formation of a variety of metallic nano-clusters at the tip apex was accomplished by preparing the electrolyte solution from different metallic salts. The formation mechanism for the nano-cluster is outlined and discussed. Moreover, we were able to enhance the performance of the nano-cluster tips for field-sensitive scanning probe microscopy, including electrostatic force microscopy and scanning Kelvin probe microscopy by laser annealing. Our experimental results indicated that for applications in field-sensitive scanning probe microscopy the stray field effect was significantly suppressed by the nano-cluster tip and hence the spatial resolution was improved.