Electrochemical Injection Oxygen Vacancies in Layered Ca2Mn3O8 for Boosting Zinc-Ion Storage.

Manganese-based compounds have emerged as attractive cathode materials for zinc-ion batteries owing to their high operating voltage, large specific capacity, and no pollution. However, the structural collapse and sluggish kinetics of manganese-based compounds are major obstacles that hinder their practical applications. Here, a kind of novel layered Ca2Mn3O8 with a low ion diffusion barrier and high structural stability has been achieved through an electrochemical charging process with in situ injecting oxygen vacancies. This greatly increases the electrochemical active area and improves the Zn ions diffusion coefficient by 2 orders of magnitude, which significantly enhances the reaction kinetics, pseudocapacitance properties, and capacity. As a result, the cathode containing oxygen vacancies present an impressive reversible capacity of 368 mAh g-1, an unprecedented energy density of 512 Wh kg-1, and superior capacity retention of 92.3% at a high current density of 5 A g-1 after 3000 cycles. This work unveils an effective method for vacancy regulation of electrode materials, paving a new way to improve the electrochemical performance of zinc-ion batteries.

Interface Engineering with Ultralow Ruthenium Loading for Efficient Water Splitting.

Developing high-performance and cost-effective bifunctional electrocatalysts for water splitting is the key to large-scale hydrogen production. How to achieve higher performance with a lower amount of noble metal is still a major challenge. Herein, using a facile wet-chemistry strategy, we report the ultralow amount loading of ruthenium (Ru) on porous nickel foam (NF) as a highly efficient bifunctional electrocatalyst for water splitting. Theoretical simulations reveal that the coupling effect of Ru and Ni can significantly reduce the d-band center of the composite. The Ru-modified NF exhibits a very high level of HER activity with only 0.3 wt% of Ru, far surpassing commercial Pt/C. It only requires an extremely low overpotential (η10) of 10 mV to achieve a current density of 10 mA cm-2 in alkaline solution and a quite low Tafel slope of 34 mV dec-1. This catalyst also shows remarkable performance for overall water splitting with a low voltage of 1.56 V at 10 mA cm-2. These findings indicate the potential of this material in water-alkali electrolyzers, providing a new approach for fabrication of low-cost advanced electrocatalysts.

FIB-Patterned Nano-Supercapacitors: Minimized Size with Ultrahigh Performances.

Advances in microelectronic system technology have necessitated the development and miniaturization of energy storage devices. Supercapacitors are an important complement to batteries in microelectronic systems; and further reduction of the size of micro-supercapacitors is challenging. Here, a novel strategy is demonstrated to break through the resolution limit of micro-supercapacitors by preparing nano-supercapacitors (NSCs) with interdigital nanosized electrodes using focused ion beam technology. The minimization of the size of the NSCs leads to a large increase in capacitance, with a high areal capacitance of 9.52 mF cm-2 and a volumetric capacitance of 18 700 F cm-3 , far superior to those of other reported works. Size reduction and the narrowing of the physical separation between nanoelectrodes are proved to be the most crucial factors in the enhancement of capacitive performances. New charge-storage mechanisms are discovered with a remarkable nonfaradaic double-layer capacitance that exists due to the considerable inner electric field force at the nanoscale. The developed strategy and the first set of data provided here shed light on the design and fabrication of flexible interdigitated NSCs that rival state-of-the-art supercapacitors in performance.

Precursor-Transformation Strategy Preparation of CuPx Nanodots-Decorated CoP3 Nanowires Hybrid Catalysts for Boosting pH-Universal Electrocatalytic Hydrogen Evolution.

The development of earth-abundant, low cost, and versatile electrocatalysts for producing hydrogen from water electrolysis is still challenging. Herein, based on high hydrogen evolution reaction (HER) activity of transition metal phosphides, a CoP3 nanowire decorated with copper phosphides (denoted as CuPx ) nanodots structures synthesized through a simple and easily scalable precursor-transformation strategy is reported as a highly efficient HER catalyst. By decorating with CuPx nanodots, the optimized CoP3 nanowires electrode exhibits excellent catalytic activity and long-term durability for HER in alkaline conditions, achieving a low overpotential of 49.5 mV at a geometrical catalytic current density of 10 mA cm-2 with a small Tafel slope of 58.0 mV dec-1 , while also performing quite well in neutral and acidic media. Moreover, its overall performance exceeds most of the reported state-of-the-art catalysts, especially under high current density of 100 mA cm-2 , demonstrating its potential as a promising versatile pH universal electrocatalyst for efficient water electrolysis. These results indicate that the incorporation of earth-abundant stable element copper can significantly enhance catalytic activity, which widens the application range of copper and provides a new path for design and selection of HER catalysts.

Amorphous Sn/Crystalline SnS2 Nanosheets via In Situ Electrochemical Reduction Methodology for Highly Efficient Ambient N2 Fixation.

Electrochemical nitrogen reduction reaction (NRR) as a new strategy for synthesizing ammonia has attracted ever-growing attention, due to its renewability, flexibility, and sustainability. However, the lack of efficient electrocatalysts has hampered the development of such reactions. Herein, a series of amorphous Sn/crystalline SnS2 (Sn/SnS2 ) nanosheets by an L-cysteine-based hydrothermal process, followed by in situ electrochemical reduction, are synthesized. The amount of reduced amorphous Sn can be adjusted by selecting electrolytes with different pH values. The optimized Sn/SnS2 catalyst can achieve a high ammonia yield of 23.8 µg h-1 mg-1 , outperforming most reported noble-metal NRR electrocatalysts. According to the electrochemical tests, the conversion of SnS2 to an amorphous Sn phase leads to the substantial increase of its catalytic activity, while the amorphous Sn is identified as the active phase. These results provide a guideline for a rational design of low-cost and highly active Sn-based catalysts thus paving a wider path for NRR.

Phase, Conductivity, and Surface Coordination Environment in Two-Dimensional Electrochemistry.

The booming frontier of electrochemistry is radically transforming the landscape of global chemical and energy industry. Most recent advancements in electrocatalysts have been built on trial and error, lacking model experiments to illuminate the fundamental factors hidden behind, such as phase, conductivity, and surface coordination environment. Here, we use phase-controllable, highly oriented two-dimensional MoTe2 as the model catalysts. The 2H phase MoTe2's conductivity can be engineered both extrinsically and intrinsically by single-layer graphene and lithiation, bringing down the sheet resistance from 0.95 MΩ/□ to 0.8 kΩ/□ and 0.6 kΩ/□. The corresponding electrocatalytic performance was unlocked from a silent state, catching up to its 1T' counterpart, with a parallel Tafel slope of 141 mV/dec. A focused ion beam further exposed the edge atoms, which exhibited a hydrogen evolution turnover frequency 104 times superior to that of basal plane atoms.

Nesting Co3Mo Binary Alloy Nanoparticles onto Molybdenum Oxide Nanosheet Arrays for Superior Hydrogen Evolution Reaction.

Transition-metal alloys have attracted a great deal of attention as an alternative to Pt-based catalysts for hydrogen evolution reaction (HER) in alkaline. Herein, a facile and convenient strategy to fabricate Co3Mo binary alloy nanoparticles nesting onto molybdenum oxide nanosheet arrays on nickel foam is developed. By modulating the annealing time and temperature, the Co3Mo alloy catalyst displays a superior HER performance. Owing to substantial active sites of nanoparticles on nanosheets as well as the intrinsic HER activity of Co3Mo alloy and no use of binders, the obtained catalyst requires an extremely low overpotential of only 68 mV at 10 mA cm-2 in alkaline, with a corresponding Tafel slope of 61 mV dec-1. At the same time, the catalyst demonstrates excellent stability during the long-term measurements. The density functional theory calculation provides a deeper insight into the HER mechanism, unveiling that the active sites on the Co3Mo-based catalyst are Mo atoms. This strategy of combining catalytic active species with hierarchical nanoscale materials can be extended to other applications and provides a candidate of nonnoble metal catalysts for practical electrochemical water splitting.

A general strategy for the functionalization of two-dimensional metal chalcogenides.

Two-dimensional (2D) metal chalcogenides (MC) such as MoS2 have been recognized as promising materials for near future applications. However, general strategies to functionalize them are still scarce, while the nature of functionalization still remains unclear. Herein, we demonstrate a simple and universal functionalization route through complexation reaction between the amino-containing organic agents and MCs. Degrees of functionalization are tunable by adjusting the organic group types and ratios. No further defects are introduced and the functionalized 2D MCs are dispersible in corresponding typical solvents. Both experimental results and geometry optimization calculations indicate that the grafting of functional groups through the coordination effect truly exist, while the surface properties and resulting photoelectric properties of 2D MCs are greatly altered. More intriguingly, our proposed functionalization process is demonstrated to be universal and can be applied to different MCs, thus opening new avenues for the application of 2D MCs.

One-pot hydrothermal synthesis of magnetically recoverable palladium/reduced graphene oxide nanocomposites and its catalytic applications in cross-coupling reactions.

A facile, green, economical approach was designed to deposit palladium nanoparticles on magnetic reduced graphene oxide nanosheets (Pd-Fe3O4/rGO) via a one-pot hydrothermal synthesis method. The prepared Pd-Fe3O4/rGO nanocomposites were thoroughly characterized by Transmission electron microscopy, Scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and Raman spectroscopy. Importantly, the highly efficient catalytic property of the as-obtained Pd-Fe3O4/rGO catalyst was demonstrated for the Suzuki-Miyaura coupling reaction and Mizoroki-Heck coupling reaction. Significantly, the Suzuki-Miyaura coupling reactions could be efficiently performed in an environmentally friendly aqueous solution with no need for further additives. Besides, the nanocomposites could be conveniently separated from reaction system with an external permanent magnet for recycling and the inherent catalytic activity of the nanocomposites did not exacerbate after six repeated applications.