Outstanding magnetic properties are highly desired for two-dimensional ultrathin semiconductor nanosheets. Here, we propose a phase incorporation strategy to induce robust room-temperature ferromagnetism in a nonmagnetic MoS2 semiconductor. A two-step hydrothermal method was used to intentionally introduce sulfur vacancies in a 2H-MoS2 ultrathin nanosheet host, which prompts the transformation of the surrounding 2H-MoS2 local lattice into a trigonal (1T-MoS2) phase. 25% 1T-MoS2 phase incorporation in 2H-MoS2 nanosheets can enhance the electron carrier concentration by an order, introduce a Mo(4+) 4d energy state within the bandgap, and create a robust intrinsic ferromagnetic response of 0.25 μB/Mo by the exchange interactions between sulfur vacancy and the Mo(4+) 4d bandgap state at room temperature. This design opens up new possibility for effective manipulation of exchange interactions in two-dimensional nanostructures.

Realizing high-efficiency hydrogen evolution in cost-effective and longlasting electrocatalysts is critical for global production of clean and sustainable chemical fuels. Here, via modulating the metallic 1T phase in 2H MoS 2 nanosheets, we greatly improved the conductivity and effective active sites for highly efficient electrocatalytic hydrogen evolution. The as-synthesized 1T-2H MoS 2 electrocatalyst with a high 1Tphase content of 50% can significantly increase the charge concentration by an order of magnitude and triple the effective active surface sites, successfully boosting the hydrogen evolution reaction (HER) at a quite low overpotential of 126 mV at 10 mA/cm 2 and a small Tafel slope of 35 mV/dec. Ultraviolet photoelectron spectroscopy and electrochemical characterization reveal that the valence band edges of 1T-2H MoS 2 are upshifted by 0.15−0.36 eV, which obviously enhances the charge transfer ability of the surface active sites in the basal plane of MoS 2 for high HER performance.

Iridium-based perovskites show promising catalytic activity for oxygen evolution reaction (OER) in acid media, but the iridium mass activity remains low and the active-layer structures have not been identified. Here, we report highly active 1 nm IrO x particles anchored on 9R-BaIrO3 (IrO x /9R-BaIrO3) that are directly synthesized by solution calcination followed by strong acid treatment for the first time. The developed IrO x /9R-BaIrO3 catalyst delivers a high iridium mass activity (168 A gIr –1), about 16 times higher than that of the benchmark acidic OER electrocatalyst IrO2 (10 A gIr –1), and only requires a low overpotential of 230 mV to reach a catalytic current density of 10 mA cm–2 geo. Careful scanning transmission electron microscopy, synchrotron radiation-based X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy analyses reveal that, during the electrocatalytic process, the initial 1 nm IrO x nanoparticles/9R-BaIrO3 evolve into amorphous Ir4+O x H y /IrO6 octahedrons and then to amorphous Ir5+O x /IrO6 octahedrons on the surface. Such high relative content of amorphous Ir5+O x species derived from trimers of face-sharing IrO6 octahedrons in 9R-BaIrO3 and the enhanced metallic conductivity of the Ir5+O x /9R-BaIrO3 catalyst are responsible for the excellent acidic OER activity. Our results provide new insights into the surface active-layer structure evolution in perovskite electrocatalysts and demonstrate new approaches for engineering highly active acidic OER nanocatalysts.