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Flexoelectricity and photoelectricity with their coupled effect (the so-called flexo-photoelectronic effect) is of increasing interests for electronics and optoelectronics in van der Waals layered semiconductors. However, the related device design...

Despite the growing interest in halide perovskite-based NH3 sensors, the NH3 sensing mechanism is still not well understood. Here, we report an anomalous behavior of resistance enhancement in CH3NH3PbI3(MAPbI3) perovskite films upon exposure to NH3 gas, which is contrary to a resistance drop trend in previously reported perovskites. We propose a NH3 sensing mechanism in which the anomalous resistance enhancement is dominated by grain boundaries of perovskites. It is demonstrated that NH3 molecules can substitute MA+ cations of MAPbI3 to form the insulating NH4PbI3·MA intermediate layers onto the surface of crystal grains, thereby resulting in an increase of resistance. Additionally, we construct the MAPbI3-based sensor, and achieve a gas response of 472% toward 30 ppm of NH3. This study suggests the potential of the perovskite-based NH3 sensors, and also provides guidance for developing high-performance sensing perovskite materials.

Single-atom Pt-based catalysts display a promising strategy to enhance the atomic utilization of noble metals while attaining desirable electrocatalytic properties. Moreover, rationally selecting the substrate helps optimize the water dissociation energy as well as promote H* conversion. Herein, we dispersed monoatomic Pt with ultralow content onto porous nickel nanosheets to accelerate the reaction kinetics of the hydrogen evolution reaction in an alkaline medium. Density functional theory calculations reveal that the synergistic effects between Ni−Ni and Ni−Pt sites are jointly responsible for the highly efficient hydrogen evolution reaction (HER) catalysis. Besides, ultrathin nanosheets with a porous structure of Ni substantially provide further enhancement. Consequently, the obtained NiPt alloy catalyst displays exceptional alkaline HER activity with a low overpotential of 18 mV at the specific current density of 10 mA cm −2 and a Tafel slope of 45 mV dec −1 , which significantly outperform the commercial Pt/C. This work provides valuable guidelines for the proper design and construction of single-atom alloy catalysts.