Electrochemistry-assisted selective butadiene hydrogenation with water.

Alkene feedstocks are used to produce polymers with a market expected to reach 128.4 million metric tons by 2027. Butadiene is one of the impurities poisoning alkene polymerization catalysts and is usually removed by thermocatalytic selective hydrogenation. Excessive use of H2, poor alkene selectivity and high operating temperature (e.g. up to 350 °C) remain the most significant drawbacks of the thermocatalytic process, calling for innovative alternatives. Here we report a room-temperature (25~30 °C) electrochemistry-assisted selective hydrogenation process in a gas-fed fixed bed reactor, using water as the hydrogen source. Using a palladium membrane as the catalyst, this process offers a robust catalytic performance for selective butadiene hydrogenation, with alkene selectivity staying around 92% at a butadiene conversion above 97% for over 360 h of time on stream. The overall energy consumption of this process is 0.003 Wh/mLbutadiene, which is thousands of times lower than that of the thermocatalytic route. This study proposes an alternative electrochemical technology for industrial hydrogenation without the need for elevated temperature and hydrogen gas.

Giant Nonlinear Optical Response via Coherent Stacking of In-Plane Ferroelectric Layers.

Thin ferroelectric materials hold great promise for compact nonvolatile memory and nonlinear optical and optoelectronic devices. Herein, an ultrathin in-plane ferroelectric material that exhibits a giant nonlinear optical effect, group-IV monochalcogenide SnSe, is reported. Nanometer-scale ferroelectric domains with ≈90°/270° twin boundaries or ≈180° domain walls are revealed in physical-vapor-deposited SnSe by lateral piezoresponse force microscopy. Atomic structure characterization reveals both parallel and antiparallel stacking of neighboring van der Waals ferroelectric layers, leading to ferroelectric or antiferroelectric ordering. Ferroelectric domains exhibit giant nonlinear optical activity due to coherent enhancement of second-harmonic fields and the as-resulted second-harmonic generation was observed to be 100 times more intense than monolayer WS2 . This work demonstrates in-plane ferroelectric ordering and giant nonlinear optical activity in SnSe, which paves the way for applications in on-chip nonlinear optical components and nonvolatile memory devices.

NANOELECTRONICS. Epitaxial growth of a monolayer WSe2-MoS2 lateral p-n junction with an atomically sharp interface.

Two-dimensional transition metal dichalcogenides (TMDCs) such as molybdenum sulfide MoS2 and tungsten sulfide WSe2 have potential applications in electronics because they exhibit high on-off current ratios and distinctive electro-optical properties. Spatially connected TMDC lateral heterojunctions are key components for constructing monolayer p-n rectifying diodes, light-emitting diodes, photovoltaic devices, and bipolar junction transistors. However, such structures are not readily prepared via the layer-stacking techniques, and direct growth favors the thermodynamically preferred TMDC alloys. We report the two-step epitaxial growth of lateral WSe2-MoS2 heterojunction, where the edge of WSe2 induces the epitaxial MoS2 growth despite a large lattice mismatch. The epitaxial growth process offers a controllable method to obtain lateral heterojunction with an atomically sharp interface.