Crystalline–amorphous phase boundary engineering can be an effective strategy to develop cost-effective and high-performance electrocatalysts for water splitting.

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As bifunctional oxygen evolution/reduction electrocatalysts, transition-metal-based single-atom-doped nitrogen–carbon (NC) matrices are promising successors of the corresponding noble-metal-based catalysts, offering the advantages of ultrahigh atom utilization efficiency and surface active energy. However, the fabrication of such matrices (e.g., well-dispersed single-atom-doped M-N4/NCs) often requires numerous steps and tedious processes. Herein, ultrasonic plasma engineering allows direct carbonization in a precursor solution containing metal phthalocyanine and aniline. When combining with the dispersion effect of ultrasonic waves, we successfully fabricated uniform single-atom M-N4 (M = Fe, Co) carbon catalysts with a production rate as high as 10 mg min−1. The Co-N4/NC presented a bifunctional potential drop of ΔE = 0.79 V, outperforming the benchmark Pt/C-Ru/C catalyst (ΔE = 0.88 V) at the same catalyst loading. Theoretical calculations revealed that Co-N4 was the major active site with superior O2 adsorption–desorption mechanisms. In a practical Zn–air battery test, the air electrode coated with Co-N4/NC exhibited a specific capacity (762.8 mAh g−1) and power density (101.62 mW cm−2), exceeding those of Pt/C-Ru/C (700.8 mAh g−1 and 89.16 mW cm−2, respectively) at the same catalyst loading. Moreover, for Co-N4/NC, the potential difference increased from 1.16 to 1.47 V after 100 charge–discharge cycles. The proposed innovative and scalable strategy was concluded to be well suited for the fabrication of single-atom-doped carbons as promising bifunctional oxygen evolution/reduction electrocatalysts for metal–air batteries.

Benefiting from a large density of layer edges exposed on the surface, vertically aligned two-dimensional (2D) molybdenum disulfide (MoS2) layers have recently harvested excellent performances in the field of electrochemical catalysis and chemical sensing. With their increasing versatility for high-temperature, demanding applications, it is vital to identify their thermally driven structural and chemical stability, as well as to clarify its underlying principle. Despite various ex situ and in situ characterizations on horizontally aligned 2D MoS2 layers, the direct in situ heating of vertically aligned 2D MoS2 layers and the real-time observation of their near-atomic-scale dynamics have never been approached, leaving their thermal stability poorly understood. Moreover, the geometrical advantage of the surface-exposed vertically aligned 2D MoS2 layers is anticipated to unveil the structural dynamics of interlayer van der Waals (vdW) gaps and its correlation with thermal energy, unattainable with 2D MoS2 layers in any other geometry. Herein, we report a comprehensive in situ heating TEM study on cleanly transferred, vertically aligned 2D MoS2 layers up to 1000 °C. Several striking phenomena were newly observed in the course of heating: (1) formation and propagation of voids between the domains of vertical 2D MoS2 layers with distinct grain orientations starting at ∼875 °C; (2) subsequent decompositions of the 2D MoS2 layers accompanying a formation of Mo nanoparticles at ∼950 °C, a temperature much lower than the melting temperature of their bulk counterpart; and (3) initiation of decomposition from the surface-exposed 2D layer vertical edge sites, congruently supported by molecular dynamics (MD) simulation. These new findings will offer critical insights into better understanding the thermodynamic principle that governs the structural stability of general vdW 2D crystals as well as providing useful technological guidance for materials design and optimization in their potential high-temperature applications.

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A versatile use of a sulfur self-doped biochar derived from Camellia japonica (camellia) flowers is demonstrated as a multifunctional catalyst for overall water splitting and a supercapacitor. The native sulfur content in the camellia flower facilitates in situ self-doping of sulfur, which highly activates the camellia-driven biochar (SA-Came) as a multifunctional catalyst with the enhanced electron-transfer ability and long-term durability. For water splitting, an SA-Came-based electrode is highly stable and shows reaction activities in both hydrogen and oxygen evolution reactions, with overpotentials of 154 and 362 mV at 10 mA cm −2 , respectively. For supercapacitors, SA-Came achieves a specific capacitance of 125.42 F g −1 at 2 A g −1 and high cyclic stability in a three-electrode system in a 1 M KOH electrolyte. It demonstrated a high energy density of 34.54 Wh kg −1 at a power density of 1600 W kg −1 as a symmetric hybrid supercapacitor device with a wide working potential range of 0-1.6 V.

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