Boron modification promoting electrochemical surface reconstruction of NiFe-LDH for efficient and stable freshwater/seawater oxidation catalysis.

Transition metal-based electrocatalysts generally take place surface reconstruction in alkaline conditions, but little is known about how to improve the reconstruction to a highly active oxyhydroxide surface for an efficient and stable oxygen evolution reaction (OER). Herein, we develop a strategy to accelerate surface reconstruction by combining boron modification and cyclic voltammetry (CV) activation. Density functional theory calculations and in-situ/ex-situ characterizations indicate that both B-doping and electrochemical activation can reduce the energy barrier and contribute to the surface evolution into highly active oxyhydroxides. The formed oxyhydroxide active phase can tune the electronic configuration and boost the OER process. The reconstructed catalyst of CV-B-NiFe-LDH displays excellent alkaline OER performance in freshwater, simulated seawater, and natural seawater with low overpotentials at 100 mA cm-2 (η100: 219, 236, and 255 mV, respectively) and good durability. This catalyst also presents outstanding Cl- corrosion resistance in alkalized seawater electrolytes. The CV-B-NiFe-LDH||Pt/C electrolyzer reveals prominent performance for alkalized freshwater/seawater splitting. This study provides a guideline for developing advanced OER electrocatalysts by promoting surface reconstruction.

Unraveling the crucial contribution of additive chromate to efficient and stable alkaline seawater oxidation on Ni-based layered double hydroxides.

Seawater electrolysis to generate hydrogen offers a clean, green, and sustainable solution for new energy. However, the catalytic activity and durability of anodic catalysts are plagued by the corrosion and competitive oxidation reactions of chloride in high concentrations. In this study, we find that the additive CrO42- anions in the electrolyte can not only promote the formation and stabilization of the metal oxyhydroxide active phase but also greatly mitigate the adverse effect of Cl- on the anode. Linear sweep voltammetry, accelerated corrosion experiments, corrosion polarization curves, and charge transfer resistance results indicate that the addition of CrO42- distinctly improves oxygen evolution reaction (OER) kinetics and corrosion resistance in alkaline seawater electrolytes. Especially, the introduction of CrO42- even in the highly concentrated NaCl (2.5 M) electrolyte prolongs the durability of NiFe-LDH to almost five times the case without CrO42-. Density functional theory calculations also reveal that the adsorption of CrO42- can tune the electronic configuration of active sites of metal oxyhydroxides, enhance conductivity, and optimize the intermediate adsorption energies. This anionic additive strategy can give a better enlightenment for the development of efficient and stable oxygen evolution reactions for seawater electrolysis.

MnOx Film-Coated NiFe-LDH Nanosheets on Ni Foam as Selective Oxygen Evolution Electrocatalysts for Alkaline Seawater Oxidation.

Compared to freshwater electrolysis, seawater electrolysis to produce hydrogen is preferable and more promising, but this technology is plagued by the electrode's corrosion and oxidative reactions of the competitive Cl- ion on the anode. To develop efficient oxygen evolution reaction (OER) catalysts for seawater electrolysis, the ultrathin MnOx film-covered NiFe-layered double-hydroxide nanosheet array is directly assembled on Ni foam (MnOx/NiFe-LDH/NF) by hydrothermal and electrodeposition in turn. This catalyst demonstrates excellent OER-selective activity in alkaline saline electrolytes. In 1 M KOH/0.5 M NaCl and 1 M KOH/seawater electrolytes, MnOx/NiFe-LDH/NF exhibits lower overpotentials at 100 mA cm-2 (η100 values of 265 and 276 mV, respectively) and Tafel slopes (73 and 77 mV decade-1, respectively) than does the NiFe-LDH/NF electrode (η100 values of 298 and 327 mV and Tafel slopes of 91 and 140 mV decade-1, respectively). In alkaline saline solutions, the stability and durability of the former are also better than those of the latter. The good OER selectivity and catalytic performance are attributed to the MnOx overlayer that selectively blocks Cl- anions from approaching catalytic centers, and the good conductivity, fast kinetics, more oxygen vacancies, and abundant active sites of MnOx/NiFe-LDH/NF. The robust stability is due to the enhanced resistance for Cl- corrosion stemming from the MnOx protective film. Hence, MnOx/NiFe-LDH/NF can act as a promising OER electrocatalyst for alkalized natural seawater electrolysis.

PEO-PPO-PEO induced holey NiFe-LDH nanosheets on Ni foam for efficient overall water-splitting and urea electrolysis.

Exploring the transition-metal-based bifunctional electrocatalysts with high performance for efficient water-splitting and urea electrolysis is significant but challenging. This work presents the in situ preparation of holey NiFe-LDH nanosheets on Ni foam (H-NiFe-LDH/NF) via a one-step hydrothermal method in the presence of PEO-PPO-PEO as the soft template. The holey NiFe-LDH nanosheets provide a high electrochemical surface area, more edge catalytic sites, and abundant oxygen vacancies. Consequently, H-NiFe-LDH/NF exhibits excellent catalytic activity to oxygen evolution, urea oxidation, and hydrogen evolution reactions (OER, UOR, and HER) with good stability in alkaline electrolytes. This electrode requires an overpotential of 261 mV for the OER, a potential of 1.480 V for the UOR to achieve a current density of 100 mA cm-2 in alkaline solutions. By employing the self-supported electrode as both the anode and cathode, this electrolysis cell (H-NiFe-LDH/NF||H-NiFe-LDH/NF) gains current densities of 10 and 100 mA cm-2 at low cell voltages of 1.575 and 1.933 V in the 1.0 M KOH solution. After adding 0.33 M urea, the voltages to deliver 10 and 100 mA cm-2 respectively decrease to 1.418 and 1.691 V. The H-NiFe-LDH/NF electrode also shows excellent stability for water-splitting and urea electrolysis. This work not only contributes to developing a low-cost, high-efficiency, bifunctional electrocatalyst but also provides a practically feasible approach for urea-rich wastewater electrolysis.

Electrodeposition of NiFe-layered double hydroxide layer on sulfur-modified nickel molybdate nanorods for highly efficient seawater splitting.

Developing high-efficiency and earth-abundant electrocatalysts for electrochemical seawater-splitting is of great significance but remains a grand challenge due to the presence of high-concentration chloride. This work presents the synthesis of a three-dimensional core-shell nanostructure with an amorphous and crystalline NiFe-layered double hydroxide (NiFe-LDH) layer on sulfur-modified nickel molybdate nanorods supported by porous Ni foam (S-NiMoO4@NiFe-LDH/NF) through hydrothermal and electrodeposition. Benefiting from high intrinsic activity, plentiful active sites, and accelerated electron transfer, S-NiMoO4@NiFe-LDH/NF displays an outstanding bifunctional catalytic activity toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in both simulated alkaline seawater and natural seawater electrolytes. To reach a current density of 100 mA cm-2, this catalyst only requires overpotentials of 273 and 315 mV for OER and 170 and 220 mV for HER in 1 M KOH + 0.5 M NaCl freshwater and 1 M KOH + seawater electrolytes, respectively. Using S-NiMoO4@NiFe-LDH as both anode and cathode, the electrolyzer shows superb overall seawater-splitting activity, and respectively needs low voltages of 1.68 and 1.73 V to achieve a current density of 100 mA cm-2 in simulated alkaline seawater and alkaline natural seawater electrolytes with good Cl- resistance and satisfactory durability. The electrolyzer outperforms the benchmark IrO2||Pt/C pair and many other reported bifunctional catalysts and exhibits great potential for realistic seawater electrolysis.

Cu2Se nanowires shelled with NiFe layered double hydroxide nanosheets for overall water-splitting.

It is imperative but challenging to develop non-noble metal-based bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Our work reports a core-shell nanostructure that is constructed by the electrodeposition of ultrathin NiFe-LDH nanosheets (NiFe-LDHNS) on Cu2Se nanowires, which are obtained by selenizing Cu(OH)2 nanowires in situ grown on Cu foam. The obtained Cu2Se@NiFe-LDHNS electrocatalyst provides more exposed edges and catalytic active sites, thus exhibiting excellent OER and HER electrocatalytic performance in alkaline electrolytes. This catalyst needs only an overpotential of 197 mV for OER at 50 mA cm-2 and 195 mV for HER at 10 mA cm-2. Besides, when employed as a bifunctional catalyst for overall water-splitting, it requires a cell voltage of 1.67 V to reach 10 mA cm-2 in alkaline media. Furthermore, the corresponding water electrolyzer demonstrates robust durability for at least 40 h. The excellent performance of Cu2Se@NiFe-LDHNS might be ascribed to the synergistic effect from the ultrathin NiFe-LDHNS, the Cu2Se nanowires anchored on the Cu foam, and the formed core-shell nanostructure, which offers large surface area, ample active sites, and sufficient channels for gas and electrolyte diffusion. This work provides an efficient strategy for the fabrication of self-supported electrocatalysts for efficient overall water-splitting.

A highly-sensitive "turn on" probe based on coumarin ß-diketone for hydrazine detection in PBS and living cells.

Herein, a new "turn on" fluorescent probe C-1 is developed to specifically detect hydrazine using coumarin nucleus as the fluorophore and ß-diketone as the recognition group. The probe shows high selectivity towards hydrazine over other common ions and amine-containing species, as well as good water solubility and quantitative detectability of hydrazine in concentration range of 1-200 µM. The detection limit is as low as 1.89 ppb, which is lower than the threshold set by EPA (10 ppb). Probe-coated filter papers are confirmed to detect gaseous hydrazine successfully through obvious fluorescence color changes. In addition, the probe has been verified to detect hydrazine in actual water environment and living cells.

NiFe-coordinated zeolitic imidazolate framework derived trifunctional electrocatalyst for overall water-splitting and zinc-air batteries.

Developing high-efficient non-noble metal electrocatalysts toward oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), water-splitting, and the zinc-air battery is essential but challenging. Zeolitic imidazole frameworks (ZIFs) are generally employed as ideal platforms for the design and fabrication of energy-related catalysts by exploiting their porous structure with high surface area and flexibility. This work presents the preparation of NiFe-bimetallic species decorated N-doped porous carbon composite (NiFe@NPC) through pyrolyzing the NiFe-coordinated ZIF precursor. The obtained NiFe@NPC shows a larger surface area and porous nanostructure comprising the active bimetallic species evenly distributed in the conductive carbon matrix. The nanocomposite demonstrates excellent trifunctional catalytic activity toward ORR, OER, and HER. For ORR, NiFe@NPC offers a half-wave potential value of 0.87 V, which is positively shifted by 30 mV relative to that of Pt/C in 1 M KOH. NiFe@NPC exhibits OER activity with superior overpotential, reaction kinetics, and durability to those of IrO2. It also demonstrates the desirable HER activity with a low overpotential of 150 mV at 10 mA/cm2 and excellent durability in an acidic electrolyte. Additionally, the water-splitting configuration and zinc-air battery assembled with NiFe@NPC catalyst reveal superior performance to noble-metal catalysts. Such excellent electrocatalytic performance can be attributed to the distinct chemical composition of evenly distributed bimetallic active sites on highly conductive carbon sheets, and the porous nanostructure with large surface area and fast mass transfer.

In situ growth of ZIF-67 on ultrathin CoAl layered double hydroxide nanosheets for electrochemical sensing toward naphthol isomers.

Zeolitic imidazole frameworks (ZIF) and ultrathin layered double hydroxide nanosheets (LDHNS) have drawn growing attention in the electrocatalysis field. Combining the merits and maximizing the electrocatalytic activity of each building block in the corresponding composite is imperative but challenging. This work thus proposes a simple strategy for the in situ growth of ZIF-67 on ultrathin CoAl-LDHNS (LDHNS@ZIF-67) without an additional Co2+ source. Thanks to the ultrathin nature, CoAl-LDHNS provide more Co reactive sites for the ordered growth of ZIF-67 nanocrystals on this 2D matrix via coordination interactions between Co2+ and 2-methylimidazole. The obtained LDHNS@ZIF-67 provides more convenient pathways to rapid electron transportation between the basal electrode and analytes. Hence, the modified electrode can be applied for the truly simultaneous detection of naphthol isomers by differential pulse voltammetry. α-naphthol and ß-naphthol exhibit irreversible oxidation peaks at 0.327 and 0.487 V vs. saturated calomel electrode, respectively, making their simultaneous detection feasible. The voltammetric responses of both isomers are linear in concentrations ranging from 0.3 to 150 µM with limits of detection of 62 and 94 nM, respectively. The sensor exhibits advantages including good reproducibility, stability, selectivity, and practicability for the simultaneous detection of naphthol isomers in real water samples.

Reductive Bis-addition of Aromatic Aldehydes to α,ß-Unsaturated Esters via the Use of Sm/Cu(I) in Air: A Route to the Construction of Furofuran Lignans.

The novel bis-addition of benzaldehydes to acrylates or maleates was achieved by the direct use of samarium metal with the assistance of CuI under mild conditions under dry air, and the useful 2-hydroxylalkyl-γ-butyrolactons and lignan derivatives were thus constructed with high efficiency. The key factors that influence the reaction efficiency were investigated. The use of potassium iodide and molecular sieves as additives can improve the reaction efficiency remarkably.

Synthesis, characterization and electrochemiluminescent properties of cyclometalated platinum(II) complexes with substituted 2-phenylpyridine ligands.

Two neutral cyclometalated platinum(II) complexes, Pt(DPP)(acac) and Pt(BPP)(acac) (DPP = 2,4-diphenylpyridine, BPP = 2-(4-tert-butylphenyl)-4-phenylpyridine, acac = acetylacetone), have been synthesized and characterized by (1)H NMR spectroscopy, mass spectrometry, elemental analyses and by X-ray crystallography for Pt(DPP)(acac). Electrogenerated chemiluminescence (ECL) of the two complexes in the absence or presence of coreactant tri-n-propylamine (TPrA) in different solvents (CH(3)CN, CH(2)Cl(2), DMF, CH(3)CN/H(2)O (V, 50 : 50)) has been studied. The ECL spectra are identical to their own PL spectra, indicating that ECL processes lead to the same metal-to-ligand charge-transfer ((3)MLCT) excited state that is generated by light excitation. The ECL potentials of Pt(DPP)(acac) and Pt(BPP)(acac)/TPrA in CH(3)CN and CH(3)CN/H(2)O solution were at ~0.75 V vs. SCE, and significantly negatively shifted by about 0.6 V compared to that of the Ru(bpy)(3)(2+)/TPrA system. The ECL quantum efficiencies of the complexes are comparable to that of the Ru(bpy)(3)(2+)/TPrA system. The significant increase of the ECL signal in the coreactant system is due to the formation of the strongly reducing intermediate TPrA˙. It is noteworthy that the ECL efficiencies of the synthesized compounds are much higher than that of the tridentate polypyridyl ligands.

2-[(Quinolin-8-yl-oxy)meth-yl]-1H-benzimid-a-zole monohydrate.

In the title hydrate, C17H13N3O·H2O, the dihedral angle between the quinoline and benzimidazole ring systems is 6.22 (7)°. The water mol-ecule is linked to the main mol-ecule by N-H⋯O and O-H⋯N hydrogen bonds. Further O-H⋯N hydrogen bonds link the organic molecules into C(6) chains running parallel to the b axis.

1,4-Bis(3-methyl-phen-yl)piperazine-2,5-dione.

The asymmetric unit of the title compound, C(18)H(18)N(2)O(2), consists of two independent mol-ecules, each of which is located about a center of inversion. The mol-ecules are not planar, showing dihedral angles of 55.84 (9) and 54.10 (8)° between the piperazinedione and the aromatic rings. The piperazine N atoms exhibit a planar configuration. The crystal packing is stabilized by inter-molecular C-H⋯O hydrogen bonds.

N,N-Bis(quinolin-8-yl)-2,2'-[(1,3,4-thia-diazole-2,5-di-yl)bis-(sulfanedi-yl)]diacetamide monohydrate.

In the title compound, C(24)H(18)N(6)O(2)S(3)·H(2)O, the thia-diazole ring makes dihedral angles of 78.00 (13) and 77.27 (13)° with the quinoline ring systems. In the crystal, mol-ecules are linked into a two-dimensional network by O-H⋯O and C-H⋯O hydrogen bonds.

N,N'-Dibenzyl-2,2'-(3,6-dioxaoctane-1,8-diyldi-oxy)dibenzamide.

The title compound, C(34)H(36)N(2)O(6), located on a center of inversion, crystallizes with one half-mol-ecule in the asymmetric unit. The dihedral angle between the benzene rings is 86.19 (2)°. An intra-molecular N-H⋯O hydrogen bond forms a six-membered ring; it affects the conformation of the mol-ecule which adopts a folded rather than open conformation. The crystal packing is stabilized by inter-molecular C-H⋯O inter-actions.

2-[(5,7-Dibromo-quinolin-8-yl)-oxy]-N-(2-meth-oxy-phen-yl)acetamide.

In the title compound, C(18)H(14)Br(2)N(2)O(3), an intra-molecular N-H⋯N hydrogen bond forms an eight-membered ring. The dihedral angle between the planes of the quinoline system and the benzene ring is 41.69 (1)°. The crystal packing is stabilized by inter-molecular C-H⋯O hydrogen bonds and short Br⋯O inter-actions [3.0079 (19) Å].

3-[2-(1,3-Benzothia-zol-2-ylsulfan-yl)eth-yl]-1,3-oxazolidin-2-one.

The title compound, C(12)H(12)N(2)S(2)O(2), consists of a benzothia-zole group and a oxazolidin-1-one linked via a flexible ethane-1,2-diyl spacer. The benzothiazole group and the oxazolidine ring are each almost planar [with maximum deviations of 0.007 (2) and 0.044 (3) Å, respectively] and make a dihedral angle of 9.35 (10)°. In the crystal structure, adjacent mol-ecules were connected through C-H⋯O and C-H⋯N hydrogen bonds, and further extended into a three-dimensional network structure through inter-molecular aromatic π-π stacking inter-actions in which the centroid-centroid distance is 3.590 (1) Å.

Design and coordination behavior of the first selective recognition ligand of 147Pm(III).

A new amide tripodal ligand, 6-[2-(2-diethylamino-2-oxoethoxy)ethyl]-N,N,12-triethyl-11-oxo-3,9-dioxa-6,12-diazatetradecanamide (4) has been designed and synthesized for the recognition of rare earth ions. Three representative complexes of trivalent lighter (La), middle (Gd), and heavier (Er) rare earth ions with 4 were synthesized and characterized by X-ray crystallography. In the complex, the heptadentate forms a cup-like coordination cavity encapsulating the central ion. Different supramolecular complex dimers are constructed by pi-pi interaction and van der Waals forces in accordance with the lanthanide contraction. The differences of the cavity and dimer structures were investigated further by assessing the separation efficiency of in multitrace solvent extraction of rare earth ions from picrate acid solution and the ligand has the best separation factor for 147Pm(III).