Effect of Intrinsic Ferroelectric Phase Transition on Hydrogen Evolution Electrocatalysis.

Heterogeneous electrocatalysis closely relies on the electronic structure of the catalytic materials. The ferroelectric-to-paraelectric phase transition of the materials also involves a change in the state of electrons that could impact the electrocatalytic activity, but such correlation remains unexplored. Here, we demonstrate experimentally and theoretically that the intrinsic electrocatalytic activity could be regulated as exampled by hydrogen evolution reaction catalysis over two-dimensional ferroelectric CuInP2S6. The obvious discontinuity in the overpotential and apparent activation energy values for CuInP2S6 electrode are illustrated during the ferroelectric-to-paraelectric phase transition caused by copper displacement around Tc point (318 K), revealing the ferroelectro-catalytic effect on thermodynamics and kinetics of electrocatalysis. When loading Pt single atom on the CuInP2S6, the paraelectric phase one showed an improved hydrogen evolution activity with smaller apparent activation energy over the ferroelectric phase counterpart. This is attributed to the copper hopping between two sulfur planes, which alternate between strong and weak H adsorption at the Pt sites to simultaneously promote H+ reactant adsorption and H2 product desorption.

Tunable Room-Temperature Ferromagnetism in Two-Dimensional Cr2Te3.

The manipulation of magnetism provides a unique opportunity for the development of data storage and spintronic applications. Until now, electrical control, pressure tuning, stacking structure dependence, and nanoscale engineering have been realized. However, as the dimensions are decreased, the decrease of the ferromagnetism phase transition temperature (Tc) is a universal trend in ferromagnets. Here, we make a breakthrough to realize the synthesis of 1 and 2 unit cell (UC) Cr2Te3 and discover a room-temperature ferromagnetism in two-dimensional Cr2Te3. The newly observed Tc increases strongly from 160 K in the thick flake (40.3 nm) to 280 K in 6 UC Cr2Te3 (7.1 nm). The magnetization and anomalous Hall effect measurements provided unambiguous evidence for the existence of spontaneous magnetization at room temperature. The theoretical model revealed that the reconstruction of Cr2Te3 could result in anomalous thickness-dependent Tc. This dimension tuning method opens up a new avenue for manipulation of ferromagnetism.

Gapless van der Waals Heterostructures for Infrared Optoelectronic Devices.

Mixed-dimensional van der Waals (vdW) heterostructures based on two-dimensional (2D) materials exhibit immense potential in infrared optoelectronic applications. However, the weak vdW coupling results in limiting performance of infrared optoelectronic device. Here, we exploit a gapless heterostructure that S dangling bonds of nonlayered PbS are connected to the bonding sites of MoS2 (with factitious S vacancies) via strong orbital hybridization. The strong interface coupling leads to ultrahigh responsivity and photogain (G) exceeding 105, and the detectivity (D*) is greater than 1014 Jones. More importantly, the gapless heterostructure shows fast rise and decay times about 47 and 49 µs, respectively, which is 5 orders of magnitude faster than that of transferred vdW heterostructures. Furthermore, an ultrahigh photon-triggered on/off ratio of 1.6 × 106 is achieved, which is 4 orders of magnitude higher than that of transferred vdW heterostructures. This architecture can offer an effective approach for advanced infrared optoelectronic devices.