Ultrathin two-dimensional materials for photo- and electrocatalytic hydrogen evolution

Sustainable hydrogen production via photocatalytic, electrocatalytic, and synergetic photoelectrocatalytic processes has been regarded as an effective strategy to address both energy and environmental crises. Due to their unique structures and properties, emerging ultrathin two-dimensional (2D) materials can bring about promising opportunities to realize high-efficiency hydrogen evolution. This review presents a critical appraisal of advantages and advancements for ultrathin 2D materials in catalytic hydrogen evolution, with an emphasis on structure–activity relationship. Furthermore, strategies for tailoring the microstructure, electronic structure, and local atomic arrangement, so as to further boost the hydrogen evolution activity, are discussed. Finally, we also present the existing challenges and future research directions regarding this promising field.     

Ferroelectric Localized Field–Enhanced ZnO Nanosheet Ultraviolet Photodetector with High Sensitivity and Low Dark Current

Zinc oxide (ZnO) nanosheets have demonstrated outstanding electrical and optical properties, which are well suited for ultraviolet (UV) photodetectors. However, they have a high density of intrinsically unfilled traps, and it is difficult to achieve p‐type doping, leading to the poor performance for low light level switching ratio and a high dark current that limit practical applications in UV photodetection. Here, UV photodetectors based on ZnO nanosheets are demonstrated, whose performance is significantly improved by using a ferroelectric localized field. Specifically, the photodetectors have achieved a responsivity of up to 3.8 × 10⁵ A W^?1, a detectivity of 4.4 × 10¹⁵ Jones, and a photocurrent gain up to 1.24 × 10⁶. These device figures of merit are far beyond those of traditional ZnO ultraviolet photodetectors. In addition, the devices' initial dark current can be easily restored after continuous photocurrent measurement by using a positive gate voltage pulse. This study establishes a new approach to produce high‐sensitivity and low‐dark‐current ultraviolet photodetectors and presents a crucial step for further practical applications.     

High‐Temperature Particulate Matter Filtration with Resilient Yttria‐Stabilized ZrO2 Nanofiber Sponge

Particulate matter (PM) is a major air pollutant in many regions, jeopardizing ecosystems and public health. Filtration at pollutant source is one of the most important ways to protect the environment, however, considering the high‐temperature exhaust gas emissions, effective removal of PM and related pollutants from their sources remains a major challenge. In this study, a resilient, heat‐resisting, and high‐efficiency PM filter based on yttria‐stabilized ZrO₂ (YSZ) nanofiber sponge produced with a scalable solution blow spinning process is reported. The porous 3D sponge composed of YSZ nanofibers is lightweight (density of 20 mg cm^?3) and resilient at both room temperature and high temperatures. At room‐temperature conditions, the YSZ nanofiber sponge exhibits 99.4% filtration efficiency for aerosol particles with size in the range of 20–600 nm, associated with a low pressure drop of only 57 Pa under an airflow velocity of 4.8 cm s^?1. At a high temperature of 750 °C, the ceramic sponge maintains a high filtration efficiency of 99.97% for PM_0.3–2.5 under a high airflow velocity of 10 cm s^?1. A practical vehicle exhaust filter to capture particles with filtration efficiency of >98.3% is also assembled. Hence, the YSZ nanofiber sponge has enormous potential to be applied in industry.     

Crystal structure of Cr4AlB4: A new MAB phase compound discovered in Cr-Al-B system

In this communication, the crystal structure of Cr_4AlB_4, a new MAB phase compound(where M is a transition metal, A is Al or Si, B is boron) discovered in Cr-Al-B system is reported. This new MAB phase was synthesized from a mixture of CrB and Al powders at 1000?C and its crystal structure was determined by a combination of X-ray diffraction, first-principles calculations and energy dispersive X-ray spectroscopy(EDS). Cr_4AlB_4 crystallizes in an orthorhombic structure with Immm space group. The lattice constants are a = 2.9343(6) ?, b = 18.8911(0) ?, c = 2.9733(7) ?, and the atomic positions are Cr1 at 4 g(0, 0.2936(5),0), Cr2 at 4 h(0.5, 0.5859(7), 0), Al at 2 b(0, 0.5, 0.5), B1 at 4 h(0, 0.3839(8), 0.5) and B2 at 4 g(0.5, 0.6646(2),0.5).     

Low-valence ion addition induced more compact passive films on nickel-copper nano-coatings

Ni-Cu nano-coatings were prepared by pulsed electroplating technique in the baths containing various amount of boric acid. Their microstructure, morphologies and corrosion resistance were characterized in detail. The addition of boric acid strongly influences on the microstructure of the Ni-Cu coatings. The coating with a grain size of 130 nm, obtained from the bath containing 35 g L⁻¹ boric acid, shows the highest corrosion resistance. This is attributed to the low-valence Cu ion (Cu⁺) additions in nickel oxide, which could significantly decrease the oxygen ion vacancy density in the passive film to form a more compact passive film. The higher Cu⁺ additions and the lower diffusivity of point defects (D₀) are responsible for the formation of more compact passive film on the coating obtained from the bath with 35 g L⁻¹ boric acid.