X. Ke

Defective molybdenum sulfide quantum dots as highly active hydrogen evolution electrocatalysts

Molybdenum disulfide (MoS2), a promising non-precious electrocatalyst for the hydrogen evolution reaction with two-dimensional layered structure, has received increasing attention in recent years. Its electrocatalytic performance has been limited by the low active site content and poor conductivity. Herein, we report a facile and general ultrafast laser ablation method to synthesize MoS2 quantum dots (MS-QDs) for electrocatalytic HER with fully exposed active sites and highly enhanced conductivity. The MS-QDs were prepared by ultrafast laser ablation of the corresponding bulk material in aqueous solution, during which they were partially oxidized and formed defective structures. The as-prepared MS-QDs demonstrated high activity and stability in the electrocatalytic HER, owing to their very large surface area, defective structure, abundance of active sites, and high conductivity. The present MS-QDs can also find application in optics, sensing, energy storage, and conversion technologies.

Two-in-one solution using insect wings to produce graphene-graphite films for efficient electrocatalysis

Natural organisms contain rich elements and naturally optimized smart structures, both of which have inspired various innovative concepts and designs in human society. In particular, several natural organisms have been used as element sources to synthesize low-cost and environmentally friendly electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells and metal–air batteries, which are clean energy devices. However, to date, no naturally optimized smart structures have been employed in the synthesis of ORR catalysts, including graphene-based materials. Here, we demonstrate a novel strategy to synthesize graphene–graphite films (GGFs) by heating butterfly wings coated with FeCl3 in N2, in which the full power of natural organisms is utilized. The wings work not only as an element source for GGF generation but also as a porous supporting structure for effective nitrogen doping, two-dimensional spreading, and double-face exposure of the GGFs. These GGFs exhibit a half-wave potential of 0.942 V and a H2O2 yield of < 0.07% for ORR electrocatalysis; these values are comparable to those for the best commercial Pt/C and all previously reported ORR catalysts in alkaline media. This two-in-one strategy is also successful with cicada and dragonfly wings, indicating that it is a universal, green, and cost-effective method for developing high-performance graphene-based materials.

Defective MoS2 electrocatalyst for highly efficient hydrogen evolution through a simple ball-milling method

Molybdenum disulfide (MoS2) has attracted extensive attention as an alternative to replace noble electrocatalysts in the hydrogen evolution reaction (HER). Here, we highlight an efficient and straightforward ball milling method, using nanoscale Cu powders as reductant to reduce MoS2 engineering S-vacancies into MoS2 surfaces, to fabricate a defectrich MoS2 material (DR-MoS2). The micron-sized DR-MoS2 catalysts exhibit significantly enhanced catalytic activity for HER with an overpotential (at 10 mA cm−2) of 176 mV in acidic media and 189 mV in basic media, surpassing most of Mo-based catalysts previously reported, especially in basic solution. Meanwhile stability tests confirm the outstanding durability of DR-MoS2 catalysts in both acid and basic electrolytes. This work not only opens a new pathway to implant defects to MoS2, but also provides low-cost alternative for efficient electrocatalytic production of hydrogen in both alkaline and acidic environments.摘要通过电催化将水分解可大量制备高纯度氢气, 这一过程需要高效能低成本的电催化剂材料. 二硫化钼价格低廉、 资源丰富, 且具有类似贵金属铂的氢吸附自由能, 是一种潜在的高效制氢电催化剂. 然而其仍面临着析氢过电位偏高、 稳定性差、 难以批量制备、 在碱性环境下催化析氢活性较低等问题, 限制了其实际应用. 目前, 大量文献证实制造缺陷是一种有效的优化二硫化钼电催化活性的方法. 本文通过球磨还原法制备了一种富含缺陷的二硫化钼析氢反应电催化剂. 这种新型的富缺陷二硫化钼催化剂在酸碱性条件下都显示出较高的催化活性, 在酸性条件下, 过电位为176 mV时其电流密度可达10 mA cm−2; 在碱性条件下, 过电位为189 mV时其电流密度可达10 mA cm−2, 超过了大部分报道的析氢反应电催化剂. 此外, 富缺陷二硫化钼材料显示出较小的塔菲尔斜率和良好的电化学稳定性, 进一步证实了析氢反应催化活性的增强. 这种通过球磨还原制造缺陷的思路为未来催化剂的设计与性能优化开辟了一条新的道路, 且该方法简单, 适于大规模的工业生产.

Strain accommodation through facet matching in La

Scanning nano-focused X-ray diffraction and high-angle annular dark-field scanning transmission electron microscopy are used to investigate the crystal structure of ramp-edge junctions between superconducting electron-doped Nd1.85Ce0.15CuO4 and superconducting hole-doped La1.85Sr0.15CuO4 thin films, the latter being the top layer. On the ramp, a new growth mode of La1.85Sr0.15CuO4 with a 3.3° tilt of the c-axis is found. We explain the tilt by developing a strain accommodation model that relies on facet matching, dictated by the ramp angle, indicating that a coherent domain boundary is formed at the interface. The possible implications of this growth mode for the creation of artificial domains in morphotropic materials are discussed.

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Scanning nano-focused X-ray diffraction and high-angle annular dark-field scanning transmission electron microscopy are used to investigate the crystal structure of ramp-edge junctions between superconducting electron-doped Nd1.85Ce0.15CuO4 and superconducting hole-doped La1.85Sr0.15CuO4 thin films, the latter being the top layer. On the ramp, a new growth mode of La1.85Sr0.15CuO4 with a 3.3° tilt of the c-axis is found. We explain the tilt by developing a strain accommodation model that relies on facet matching, dictated by the ramp angle, indicating that a coherent domain boundary is formed at the interface. The possible implications of this growth mode for the creation of artificial domains in morphotropic materials are discussed.