Yun Kuang

Ternary NiCoP nanosheet arrays: An excellent bifunctional catalyst for alkaline overall water splitting

Exploring bifunctional catalysts for the hydrogen and oxygen evolution reactions (HER and OER) with high efficiency, low cost, and easy integration is extremely crucial for future renewable energy systems. Herein, ternary NiCoP nanosheet arrays (NSAs) were fabricated on 3D Ni foam by a facile hydrothermal method followed by phosphorization. These arrays serve as bifunctional alkaline catalysts, exhibiting excellent electrocatalytic performance and good working stability for both the HER and OER. The overpotentials of the NiCoP NSA electrode required to drive a current density of 50 mA/cm2 for the HER and OER are as low as 133 and 308 mV, respectively, which is ascribed to excellent intrinsic electrocatalytic activity, fast electron transport, and a unique superaerophobic structure. When NiCoP was integrated as both anodic and cathodic material, the electrolyzer required a potential as low as ~1.77 V to drive a current density of 50 mA/cm2 for overall water splitting, which is much smaller than a reported electrolyzer using the same kind of phosphide-based material and is even better than the combination of Pt/C and Ir/C, the best known noble metal-based electrodes. Combining satisfactory working stability and high activity, this NiCoP electrode paves the way for exploring overall water splitting catalysts.

Ultrathin branched PtFe and PtRuFe nanodendrites with enhanced electrocatalytic activity

PtFe and PtRuFe nanodendrites with highly branched structure were obtained through a facile one-pot strategy. Time dependent experiments revealed that the kinetic control of the reduction process of the metal precursors played a key role in the formation of such open porous structure. Owing to its ultrathin branches, open porous but interconnected structure and synergetic effect of multicomponents, the PtRuFe nanodendrite turned out to be a high-performance electrocatalyst for methanol oxidation. It has been demonstrated that PtRuFe nanodendrites had a methanol oxidation mass activity of 1.14 A mg−1 Pt and a specific activity of 2.03 mA cm−2, which were far better than those of PtFe and commercial Pt/C catalyst.

Experimental and mathematical modeling studies of the separation of zinc blende and wurtzite phases of CdS nanorods by density gradient ultracentrifugation.

Identifying the phase purity of CdS nanorods (NRs) is complicated by the serious overlap between the X-ray diffraction peaks of zinc blende and wurtzite phases as well as anisotropic growth, which might hide a mixed phase. Here we show that the density gradient ultracentrifugation rate separation method can be used to sort CdS NRs synthesized under nitrogen according to differences in particle size and morphology. Furthermore, it was found that the different sized NRs formed in a single batch synthesis had different phases: the thinner ones (<3.5 nm in diameter) were predominantly wurtzite phase, while the thicker ones (>5 nm in diameter) were mainly zinc blende phase. Dark-field transmission electron microscopy (TEM) and high-resolution TEM images indicated the presence of numerous stacking faults in the thick zinc blende rods, while the wurtzite thin rods were exclusively single crystals. As a result of the differences in phase and stacking faults, the NRs showed different photoluminescent properties. The development of an effective way of separating such NRs thus leads to further insight into the differences in phase, structure, and optical properties between individual colloidal particles synthesized in a single batch. A preliminary mathematical model of the separation process has been proposed.

Phosphorus oxoanion-intercalated layered double hydroxides for high-performance oxygen evolution

Rational design and controlled fabrication of efficient and cost-effective electrodes for the oxygen evolution reaction (OER) are critical for addressing the unprecedented energy crisis. Nickel–iron layered double hydroxides (NiFe-LDHs) with specific interlayer anions (i.e. phosphate, phosphite, and hypophosphite) were fabricated by a co-precipitation method and investigated as oxygen evolution electrocatalysts. Intercalation of the phosphorus oxoanion enhanced the OER activity in an alkaline solution; the optimal performance (i.e., a low onset potential of 215 mV, a small Tafel slope of 37.7 mV/dec, and stable electrochemical behavior) was achieved with the hypophosphite-intercalated NiFe-LDH catalyst, demonstrating dramatic enhancement over the traditional carbonate-intercalated NiFe-LDH in terms of activity and durability. This enhanced performance is attributed to the interaction between the intercalated phosphorous oxoanions and the edge-sharing MO6 (M = Ni, Fe) layers, which modifies the surface electronic structure of the Ni sites. This concept should be inspiring for the design of more effective LDH-based oxygen evolution electrocatalysts.

High‐Performance Water Electrolysis System with Double Nanostructured Superaerophobic Electrodes

Catalysts screening and structural optimization are both essential for pursuing a high-efficient water electrolysis system (WES) with reduced energy supply. This study demonstrates an advanced WES with double superaerophobic electrodes, which are achieved by constructing a nanostructured NiMo alloy and NiFe layered double hydroxide (NiFe-LDH) films for hydrogen evolution and oxygen evolution reactions, respectively. The superaerophobic property gives rise to significantly reduced adhesion forces to gas bubbles and thereby accelerates the hydrogen and oxygen bubble releasing behaviors. Benefited from these metrics and the high intrinsic activities of catalysts, this WES affords an early onset potential (≈1.5 V) for water splitting and ultrafast catalytic current density increase (≈0.83 mA mV(-1) ), resulting in ≈2.69 times higher performance compared to the commercial Pt/C and IrO2 /C catalysts based counterpart under 1.9 V. Moreover, enhanced performance at high temperature as well as prominent stability further demonstrate the practical application of this WES.

Three-dimensional porous superaerophobic nickel nanoflower electrodes for high-performance hydrazine oxidation

Finding inexpensive electrodes with high activity and stability is key to realize the practical application of fuel cells. Here, we report the fabrication of three-dimensional (3D) porous nickel nanoflower (3D-PNNF) electrodes via an in situ reduction method. The 3D-PNNF electrodes have a high surface area, show tight binding to the electroconductive substrate, and most importantly, have superaerophobic (bubble repellent) surfaces. Therefore, the electrocatalytic hydrazine oxidation performance of the 3D-PNNF electrodes was much higher than that of commercial Pt/C catalysts because of its ultra-weak gas-bubble adhesion and ultra-fast gas-bubble release. Furthermore, the 3D-PNNF electrodes showed ultra-high stability even under a high current density (260 mA/cm2), which makes it promising for practical applications. In addition, the construction of superaerophobic nanostructures could also be beneficial for other gas evolution processes (e.g., hydrogen evolution reaction).

Development of hydrophilicity gradient ultracentrifugation method for photoluminescence investigation of separated non-sedimental carbon dots

Carbon nanodots (CDs) formed by hydrothermal dehydration occur as mixtures of differently sized nanoparticles with different degrees of carbonization. Common ultracentrifugation has failed in sorting them, owing to their extremely high colloidal stability. Here, we introduce an ultracentrifugation method using a hydrophilicity gradient to sort such non-sedimental CDs. CDs, synthesized from citric acid and ethylenediamine, were pre-treated by acetone to form clusters. Such clusters “de-clustered” as they were forced to sediment through media comprising gradients of ethanol and water with varied volume ratios. Primary CDs with varied sizes and degrees of carbonization detached from the clusters to become well dispersed in the corresponding gradient layers. Their settling level was highly dependent on the varied hydrophilicity and solubility of the environmental media. Thus, the proposed hydrophilicity-triggered sorting strategy could be used for other nanoparticles with extremely high colloidalstability, which further widens the range of sortable nanoparticles. Furthermore, according to careful analysis of the changes in size, composition, quantum yield, and transient fluorescence of typical CDs in the post-separation fractions, it was concluded that the photoluminescence of the as-prepared hydrothermal carbonized CDs mainly arose from the particles’ surface molecular state rather than their sizes.

Amorphous Co–Mo–S ultrathin films with low-temperature sulfurization as high-performance electrocatalysts for the hydrogen evolution reaction

Making defects, structuring and incorporating transition-metal elements have all been demonstrated as effective strategies to enhance intrinsic activity toward the hydrogen evolution reaction (HER), but how to integrate all these merits into one system is still a challenge. An amorphous Co–Mo–S ultrathin film fabricated via low-temperature sulfurization, with rich defects, hierarchical structuring and transition metal doping, shows excellent HER performance and good working stability in acidic media. Therefore, the low-temperature sulfurizing method and hierarchical nanoarrays are extremely important to construct highly active and stable electrocatalytic gas-evolution electrodes.

Synthesis mechanism study of layered double hydroxides based on nanoseparation.

Colloidal layered double hydroxides (LDH) nanosheets were sorted by their lateral sizes using a density gradient ultracentrifuge separation technique. Composition investigations on these size-sorted nanosheets indicated that larger sheets had higher Mg:Al ratio than the smaller ones. Experiments using different Mg:Al feed ratios confirmed that high Mg:Al ratio induced fast sheet growth speed. Tracking the source of the Mg:Al spatial distribution difference in one batch of synthesis at the nucleation process revealed the coprecipitation-redissolution of Mg(2+). Thus the discriminative separation of these nanosheets led to a new insight into the structure-composition relationship of LDH nanomaterials and more understanding on their formation mechanism.

Single Crystalline Ultrathin Nickel–Cobalt Alloy Nanosheets Array for Direct Hydrazine Fuel Cells

Ultrathin 2D metal alloy nanomaterials have great potential applications but their controlled syntheses are limited to few noble metal based systems. Herein NixCo1− x alloy nanosheets with ultrathin (sub‐3 nm) single‐crystalline 2D structure are synthesized through a topochemical reduction method. Moreover, the optimized composition Ni0.6Co0.4 alloy nanosheets array exhibits excellent performances for hydrazine oxidation reaction and direct hydrazine fuel cells.