Constructing FeNiPt@C Trifunctional Catalyst by High Spin-Induced Water Oxidation Activity for Zn-Air Battery and Anion Exchange Membrane Water Electrolyzer.

Developing cost-efficient trifunctional catalysts capable of facilitating hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) activity is essential for the progression of energy devices. Engineering these catalysts to optimize their active sites and integrate them into a cohesive system presents a significant challenge. This study introduces a nanoflower (NFs)-like carbon-encapsulated FeNiPt nanoalloy catalyst (FeNiPt@C NFs), synthesized by substituting Co2+ ions with high-spin Fe2+ ions in Hofmann-type metal-organic framework, followed by carbonization and pickling processes. The FeNiPt@C NFs catalyst, characterized by its nitrogen-doped carbon-encapsulated metal alloy structure and phase-segregated FeNiPt alloy with slight surface oxidization, exhibits excellent trifunctional catalytic performance. This is evidenced by its activities in HER (-25 mV at 10 mA cm-2), ORR (half-wave potential of 0.93 V), and OER (294 mV at 10 mA cm-2), with the enhanced water oxidation activity attributed to the high-spin state of the Fe element. Consequently, the Zn-air battery and anion exchange membrane water electrolyzer assembled by FeNiPt@C NFs catalyst demonstrate remarkable power density (168 mW cm-2) and industrial-scale current density (698 mA cm-2 at 1.85 V), respectively. This innovative integration of multifunctional catalytic sites paves the way for the advancement of sustainable energy systems.

Constructing Nitrogen-Doped Carbon Hierarchy Structure Derived from Metal-Organic Framework as High-Performance ORR Cathode Material for Zn-Air Battery.

The development of efficient and low-cost catalysts for cathodic oxygen reduction reaction (ORR) in Zn-air battery (ZAB) is a key factor in reducing costs and achieving industrialization. Here, a novel segregated CoNiPt alloy embedded in N-doped porous carbon with a nanoflowers (NFs)-like hierarchy structure is synthesized through pyrolyzing Hofmann-type metal-organic frameworks (MOFs). The unique hierarchical NFs structure exposes more active sites and facilitates the transportation of reaction intermediates, thus accelerating the reaction kinetics. Impressively, the resulting 15% CoNiPt@C NFs catalyst exhibits outstanding alkaline ORR activity with a half-wave potential of 0.93 V, and its mass activity is 7.5 times higher than that of commercial Pt/C catalyst, surpassing state-of-the-art noble metal-based catalysts. Furthermore, the assembled CoNiPt@C+RuO2 ZAB demonstrates a maximum power density of 172 mW cm-2 , which is superior to that of commercial Pt/C+RuO2 ZAB. Experimental results reveal that the intrinsic ORR mass activity is attributed to the synergistic interaction between oxygen defects and pyrrolic/graphitic N species, which optimizes the adsorption energy of the intermediate species in the ORR process and greatly enhances catalytic activity. This work provides a practical and feasible strategy for synthesizing cost-effective alkaline ORR catalysts by optimizing the electronic structure of MOF-derived catalysts.

Reconstruction of Thiospinel to Active Sites and Spin Channels for Water Oxidation.

Water electrolysis is a promising technique for carbon neutral hydrogen production. A great challenge remains at developing robust and low-cost anode catalysts. Many pre-catalysts are found to undergo surface reconstruction to give high intrinsic activity in the oxygen evolution reaction (OER). The reconstructed oxyhydroxides on the surface are active species and most of them outperform directly synthesized oxyhydroxides. The reason for the high intrinsic activity remains to be explored. Here, a study is reported to showcase the unique reconstruction behaviors of a pre-catalyst, thiospinel CoFe2 S4 , and its reconstruction chemistry for a high OER activity. The reconstruction of CoFe2 S4 gives a mixture with both Fe-S component and active oxyhydroxide (Co(Fe)Ox Hy ) because Co is more inclined to reconstruct as oxyhydroxide, while the Fe is more stable in Fe-S component in a major form of Fe3 S4 . The interface spin channel is demonstrated in the reconstructed CoFe2 S4 , which optimizes the energetics of OER steps on Co(Fe)Ox Hy species and facilitates the spin sensitive electron transfer to reduce the kinetic barrier of O-O coupling. The advantage is also demonstrated in a membrane electrode assembly (MEA) electrolyzer. This work introduces the feasibility of engineering the reconstruction chemistry of the precatalyst for high performance and durable MEA electrolyzers.

Pillared-MOF@NiV-LDH Composite as a Remarkable Electrocatalyst for Water Oxidation.

Oxygen evolution reaction (OER) represents a highly important electrochemical transformation in energy storage and conversion technologies. Considering the low rate of this four-electron half-reaction, there is a demand for efficient, stable, and noble-metal-free electrocatalysts to improve the kinetic and economical parameters. In this work, a new pillared-MOF@NiV-LDH nanocomposite based on a CoII metal-organic framework (pillared-MOF) and heterometallic Ni/V-layered double hydroxide (NiV-LDH) was assembled via a simple protocol, characterized, and explored as an electrocatalyst in OER. A remarkable electrocatalytic efficiency of pillared-MOF@NiV-LDH in 1 M KOH is evidenced by a low overpotential (238 mV at 10 mA cm-2 current density) and a small value of the Tafel slope (62 mV dec-1). These parameters are very close to those of the reference IrO2 electrocatalyst and are superior to the majority of the LDH- and MOF-based systems previously applied for OER. Excellent stability of pillared-MOF@NiV-LDH was confirmed by the chronopotentiometry tests for 70 h and linear-sweep voltammetry after 7000 cycles. Features such as rich electroactive sites, porous structure, high surface area, and synergic effect between pillared-MOF and NiV-LDH are likely responsible for the remarkable electrocatalytic efficiency of this electrocatalyst in OER. Despite prior reports on the application of NiV-LDH in OER, the present study describes the first example where this type of LDH is blended with MOF to generate a nanocomposite material. The interface between the two components of the composite can improve the electronic structure and, in turn, the electrocatalytic behavior. The introduction of this composite paves the way toward the synthesis of other multicomponent materials with potential applications in different energy fields.

Postsynthetic Modification of NU-1000 for Designing a Polyoxometalate-Containing Nanocomposite with Enhanced Third-Order Nonlinear Optical Performance.

For the advancement of laser technologies and optical engineering, various types of new inorganic and organic materials are emerging. Metal-organic frameworks (MOFs) reveal a promising use in nonlinear optics, given the presence of organic linkers, metal cluster nodes, and possible delocalization of π-electron systems. These properties can be further enhanced by the inclusion of solely inorganic materials such as polyoxometalates as prospective low-cost electron-acceptor species. In this study, a novel hybrid nanocomposite, namely, SiW12@NU-1000 composed of SiW12 (H4SiW12O40) and Zr-based MOF (NU-1000), was assembled, completely characterized, and thoroughly investigated in terms of its nonlinear optical (NLO) performance. The third-order NLO behavior of the developed system was assessed by Z-scan measurements using a 532 nm laser. The effect of two-photon absorption and self-focusing was significant in both NU-1000 and SiW12@NU-1000. Experimental studies suggested a much superior NLO performance of SiW12@NU-1000 if compared to that of NU-1000, which can be assigned to the charge-energy transfer between SiW12 and NU-1000. Negligible light scattering, good stability, and facile postsynthetic fabrication method can promote the applicability of the SiW12@NU-1000 nanocomposite for various optoelectronic purposes. This research may thus open new horizons to improve and enhance the NLO performance of MOF-based materials through π-electron delocalization and compositing metal-organic networks with inorganic molecules as electron acceptors, paving the way for the generation of novel types of hybrid materials for prospective NLO applications.

Dinuclear Lanthanide Complexes Based on a Schiff-base Ligand: Free Lattice Solvent Inducing the Single Molecule Magnet Behavior of Dy2 Compound.

Syntheses, crystal structures and magnetic properties are described for a series of seven-coordinate dinuclear lanthanide complexes of compositions Dy2 L2 (1) (H3 L=2-{[bis(2-hydroxy-3-ethoxybenzyl)(aminoethyl)amino]methyl}phenol) and Ln2 L2 ⋅MeCN (Ln=Dy (2), Sm (3), Eu (4), Gd (5), Tb (6), Ho (7)). The reaction of Dy(NO3 )3 ⋅6 H2 O with one equivalent of H3 L at 70 °C in DMF/EtOH under autogenous pressure gave compound 1. Complexes 2-7 were prepared by means of the same method as that used for 1, except DMF was replaced by MeCN as the reaction solvent and Dy(NO3 )3 ⋅6 H2 O was changed to the corresponding lanthanide salts. Complexes 1-7 possess the similar Ln2 cores bridged by µ2 -phenoxyl oxygen atoms. The slight difference between 1 and 2-7 arises from the existence of free MeCN molecule in 2-7. The purposeful introduction of solvent MeCN molecule changes the crystal system from triclinic for 1 to monoclinic for 2 and alters the Dy-O-Dy angles and Dy⋅⋅⋅Dy distances, consequentially resulting into dramatic influences on the magnetic properties of 1 and 2. Complex 1 shows no SMM character, while compound 2 with free MeCN molecule exhibits a field-induced slow magnetization relaxation behavior. Complete active space self-consistent field (CASSCF) calculations were performed on two Dy2 compounds to rationalize the observed difference in the magnetic behavior. Theoretical calculations reveal that the energy gap between the lowest two Kramers doublets of individual DyIII fragment for 2 is higher than those of 1 (1_a and 1_b). This conlusion is consistant with the experimental result that complex 2 exhibits better magnetic properties. This work proposes an ingenious strategy for inducing the SMM behavior in the Dy2 compounds.

Two Series of Homodinuclear Lanthanide Complexes: Greatly Enhancing Energy Barriers through Tuning Terminal Solvent Ligands in Dy2 Single-Molecule Magnets.

The utilization of 2-ethoxy-6-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}phenol (H2 L) as a chelating ligand, in combination with the employment of alcohols (EtOH and MeOH) as auxiliary ligands, in 4 f-metal chemistry afforded two series of dinuclear lanthanide complexes of compositions [Ln2 L2 (NO3 )2 (EtOH)2 ] (Ln=Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7)) and [Ln2 L2 (NO3 )2 (MeOH)2 ] (Ln=Sm (8), Eu (9), Gd (10), Tb (11), Dy (12), Ho (13), Er (14)). The structures of 1-14 were determined by single-crystal X-ray crystallography. Complexes 1-7 are isomorphous. The two lanthanide(III) ions in 1-7 are doubly bridged by two deprotonated aminophenoxide oxygen atoms of two µ2 :η0 :η1 :η2 :η1 :η1 :η0 -L2- ligands. One nitrogen atom, two oxygen atoms of the NO3- anion, two methoxide oxygen atoms of two ligand sets, and one oxygen atom of the terminally coordinated EtOH molecule complete the distorted dodecahedron geometry of each lanthanide(III) ion. Compounds 8-14 are isomorphous and their structures are similar to those of 1-7. The slight difference between 1-7 and 8-14 stems from purposefully replacing the EtOH ligands in 1-7 with MeOH in 8-14. Direct-current magnetic susceptibility studies in the 2-300 K range reveal weak antiferromagnetic interactions for 3, 4, 7, 10, 11, and 14, and ferromagnetic interactions at low temperature for 5, 6, 12, and 13. Complexes 5 and 12 exhibit single-molecule magnet (SMM) behavior with energy barriers of 131.3 K for 5 and 198.8 K for 12. The energy barrier is significantly enhanced by dexterously regulating the terminal ligands. To rationalize the observed difference in the magnetic behavior, complete-active-space self-consistent field (CASSCF) calculations were performed on two Dy2 complexes. Subtle variation in the angle between the magnetic axes and the vector connecting two dysprosium(III) ions results in a weaker influence on the tunneling gap of individual dysprosium(III) ions by the dipolar field in 12. This work proposes an efficient strategy for synthesizing Dy2 SMMs with high energy barriers.