Solid-state magnetic switching triggered by proton-coupled electron-transfer assisted by long-distance proton-alkali cation transport

Rapid Construction of Double Crystalline Prussian Blue Analogue Hetero-Superstructure

The controllable construction of complex metal-organic coordination polymers (CPs) merits untold scientific and technological potential, yet remains a grand challenge of one-step construction and modulating simultaneously valence states of metals and topological morphology. Here, a thiocyanuric acid (TCA)-triggered strategy is presented to one-step rapid synthesis a double-crystalline Prussian blue analogue hetero-superstructure (PBA-hs) that comprises a Co3[Fe(CN)6]2 cube overcoated with a KCo[Fe(CN)6] shell, followed by eight self-assembled small cubes on vertices. Unlike common directing surfactants, TCA not only acts as a trigger for the fast growth of KCo[Fe(CN)6] on the Co3[Fe(CN)6]2 phase resulting in a PBA-on-PBA hetero-superstructure, but also serves as a flange-like bridge between them. By combining experiments with simulations, a deprotonation-induced electron transfer (DIET) mechanism is proposed for formation of second phase in PBA-hs, differing from thermally and photo-induced electron transfer processes. To prove utility, the calcined PBA-hs exhibits enhanced oxygen evolution reaction performance. This work provides a new method to design of novel CPs for enriching chemistry and material science. This work offers a practical approach to design novel CPs for enriching chemistry and material science.

Emerging Pristine MOF-Based Heterostructured Nanoarchitectures: Advances in Structure Evolution, Controlled Synthesis, and Future Perspectives

Metal-organic frameworks (MOFs) can be customized through modular assembly to achieve a wide range of potential applications, based on their desired functionality. However, most of the initially reported MOFs are limited to microporous systems and are not sufficiently stable, which restricts their popularization. Heterogeneity is introduced into a simple MOF framework to create MOF-based heterostructures with fascinating properties and interesting functions. Heterogeneity can be introduced into the MOFs via postsynthetic/ligand exchange. Although the ligand exchange has shown potential, it is difficult to precisely control the degree of exchange or position. Among the various synthesis strategies, hierarchical assembly is particularly attractive for constructing MOF-based heterostructures, as it can achieve precise regulation of MOF-based heterostructured nanostructures. The hierarchical assembly significantly expands the compositional diversity of MOF-based heterostructures, which has high elasticity for lattice matching during the epitaxial growth of MOFs. This review focuses on the synthetic evolution mechanism of hierarchical assemblies of MOF-based nanoarchitectures. Subsequently, the precise control of pore structure, pore size, and morphology of MOF-based nanoarchitectures by hierarchical assembly is emphasized. Finally, possible solutions to address the challenges associated with heterogeneous interfaces are presented, and potential opportunities for innovative applications are proposed.

The Inducement and "Rejuvenation" of Li Dendrites by Space Confinement and Positive Fe/Co-Sites

The high reactivity of Li metal and the inhomogeneous Li deposition leads to the formation of Li dendrites and "dead" Li, which impedes the performance of Li metal batteries (LMBs) with high energy density. The regulating and guiding the Li dendrite nucleation is a desirable tactic to realize concentrated distribution of Li dendrites instead of completely inhibiting dendrite formation. Here, a Fe-Co-based Prussian blue analog with hollow and open framework (H-PBA) is employed to modify the commercial polypropylene separator (PP@H-PBA). This functional PP@H-PBA can guide the lithium dendrite growth to form uniform lithium deposition and activate the inactive Li. In details, the H-PBA with macroporous structure and open framework can induce the growth of lithium dendrites via space confinement, while the positive Fe/Co-sites lowered by polar cyanide (-CN) of PBA can reactivate the inactive Li. Thus, the Li|PP@H-PBA|Li symmetric cells exhibit long-term stability at 1 mA cm^-2 for 1 mAh cm^-2 over 500 h. And the Li-S batteries with PP@H-PBA deliver favorable cycling performance at 500 mA g^-1 for 200 cycles.

Oriented Assembled Prussian Blue Analogue Framework for Confined Catalytic Decomposition of Ammonium Perchlorate

The design of highly dispersed active sites of hollow materials and unique contact behavior with the components to be catalyzed provide infinite possibilities for exploring the limits of catalyst capacity. In this study, the synthesis strategy of highly open 3-dimensional frame structure Prussian blue analogues (CoFe-PBA) was explored through structure self-transformation, which was jointly guided by template mediated epitaxial growth, restricted assembly and directional assembly. Additionally, good application prospect of CoFe-PBA as combustion catalyst was discussed. The results show that unexpected thermal decomposition behavior can be achieved by limiting AP(ammonium perchlorate) to the framework of CoFe-PBA. The high temperature decomposition stage of AP can be advanced to 283.6 °C and the weight loss rate can reach 390.03% min^-1 . In-situ monitoring shows that CoFe-PBA can accelerate the formation of NO and NO₂ . The calculation of reaction kinetics proved that catalytic process was realized by increasing the nucleation factor. On this basis, the catalytic mechanism of CoFe-PBA on the thermal decomposition of AP was discussed, and the possible interaction process between AP and CoFe-PBA during heating was proposed. At the same time, another interesting functional behavior to prevent AP from caking was discussed.

Electrochemical Proton Storage: From Fundamental Understanding to Materials to Devices

Simultaneously improving the energy density and power density of electrochemical energy storage systems is the ultimate goal of electrochemical energy storage technology. An effective strategy to achieve this goal is to take advantage of the high capacity and rapid kinetics of electrochemical proton storage to break through the power limit of batteries and the energy limit of capacitors. This article aims to review the research progress on the physicochemical properties, electrochemical performance, and reaction mechanisms of electrode materials for electrochemical proton storage. According to the different charge storage mechanisms, the surface redox, intercalation, and conversion materials are classified and introduced in detail, where the influence of crystal water and other nanostructures on the migration kinetics of protons is clarified. Several reported advanced full cell devices are summarized to promote the commercialization of electrochemical proton storage. Finally, this review provides a framework for research directions of charge storage mechanism, basic principles of material structure design, construction strategies of full cell device, and goals of practical application for electrochemical proton storage.

Magnetic Hysteresis in a Monolayer of Oriented 6 nm CsNiCr Prussian Blue Analogue Nanocrystals

Prussian blue analogue nanocrystals of the Cs^INi^II[Cr^III(CN)₆] cubic network with 6 nm size were assembled as a single monolayer on highly organized pyrolytic graphite (HOPG). X-ray magnetic circular dichroism (XMCD) studies, at the Ni and Cr L_2,3 edges, reveal the presence of an easy plane of magnetization evidenced by an opening of the magnetic hysteresis loop (coercive field of ≈200 Oe) when the magnetic field, B, is at 60° relative to the normal to the substrate. The angular dependence of the X-ray natural linear dichroism (XNLD) reveals both an orientation of the nanocrystals on the substrate and an anisotropy of the electronic cloud of the Ni^II and Cr^III coordination sphere species belonging to the nanocrystals' surface. Ligand field multiplet (LFM) calculations that reproduce the experimental data are consistent with an elongated tetragonal distortion of surface Ni^II coordination sphere responsible for the magnetic behavior of monolayer.

Proton switching molecular magnetoelectricity

The convergence of proton conduction and multiferroics is generating a compelling opportunity to achieve strong magnetoelectric coupling and magneto-ionics, offering a versatile platform to realize molecular magnetoelectrics. Here we describe machine learning coupled with additive manufacturing to accelerate the design strategy for hydrogen-bonded multiferroic macromolecules accompanied by strong proton dependence of magnetic properties. The proton switching magnetoelectricity occurs in three-dimensional molecular heterogeneous solids. It consists of a molecular magnet network as proton reservoir to modulate ferroelectric polarization, while molecular ferroelectrics charging proton transfer to reversibly manipulate magnetism. The magnetoelectric coupling induces a reversible 29% magnetization control at ferroelectric phase transition with a broad thermal hysteresis width of 160 K (192 K to 352 K), while a room-temperature reversible magnetic modulation is realized at a low electric field stimulus of 1 kV cm⁻¹. The findings of electrostatic proton transfer provide a pathway of proton mediated magnetization control in hierarchical molecular multiferroics.

Compared to inorganic materials, the magnetoelectric coupling in macromolecules is still hidden. Here, the authors describe machine learning coupled with additive manufacturing to accelerate the discovery of multiferroic macromolecules with a proton-mediated magnetoelectric coupling effect.

Ordered colloidal clusters constructed by nanocrystals with valence for efficient CO2 photoreduction

The ability to construct discrete colloidal clusters (CCs) as complex as molecular clusters is limited due to the lack of available colloidal building blocks and specific directional bonds. Here, we explore a strategy to organize anisotropic Prussian blue analog nanocrystals (NCs) toward CCs with open and highly ordered structures, experimentally realizing colloidal analogs to zeolitic clathrate structures. The directional interactions are derived from either crystallographic or morphological anisotropy of the NCs and achieved by the interplay of epitaxial growth, oriented attachment, and local packing. We attribute these interparticle interactions to enthalpic and entropic valences that imitate hybridized atomic orbitals of sp 3 d 2 octahedron and sp 3 d 3 f cube. Benefiting from the ordered multilevel porous structures, the obtained CCs exhibit greatly enhanced catalytic activity for CO2 photoreduction. Our work offers some fundamental insights into directional bonding among NCs and opens an avenue that promises access to unique CCs with unprecedented structures and applications.

Boosting the activity of Prussian-blue analogue as efficient electrocatalyst for water and urea oxidation

The design and fabrication of intricate hollow architectures as cost-effective and dual-function electrocatalyst for water and urea electrolysis is of vital importance to the energy and environment issues. Herein, a facile solvothermal strategy for construction of Prussian-blue analogue (PBA) hollow cages with an open framework was developed. The as-obtained CoFe and NiFe hollow cages (CFHC and NFHC) can be directly utilized as electrocatalysts towards oxygen evolution reaction (OER) and urea oxidation reaction (UOR) with superior catalytic performance (lower electrolysis potential, faster reaction kinetics and long-term durability) compared to their parent solid precursors (CFC and NFC) and even the commercial noble metal-based catalyst. Impressively, to drive a current density of 10 mA cm-2 in alkaline solution, the CFHC catalyst required an overpotential of merely 330 mV, 21.99% lower than that of the solid CFC precursor (423 mV) at the same condition. Meanwhile, the NFHC catalyst could deliver a current density as high as 100 mA cm-2 for the urea oxidation electrolysis at a potential of only 1.40 V, 24.32% lower than that of the solid NFC precursor (1.85 V). This work provides a new platform to construct intricate hollow structures as promising nano-materials for the application in energy conversion and storage.

Hollow Structures Based on Prussian Blue and Its Analogs for Electrochemical Energy Storage and Conversion

Due to their special structural characteristics, hollow structures grant fascinating physicochemical properties and widespread applications, especially in electrochemical energy storage and conversion. Recently, the research of Prussian blue (PB) and its analog (PBA) related nanomaterials has emerged and has drawn considerable attention because of their low cost, facile preparation, intrinsic open framework, and tunable composition. Here, the recent progress in the study of PB- and PBA-based hollow structures for electrochemical energy storage and conversion are summarized and discussed. First, some remarkable examples in the synthesis of hollow structures from PB- and PBA-based materials are illustrated in terms of the structural architectures, i.e., closed single-shelled hollow structures, open hollow structures, and complex hollow structures. Thereafter, their applications as potential electrode materials for lithium-/sodium-ion batteries, hybrid supercapacitors, and electrocatalysis are demonstrated. Finally, the current achievements in this field together with the limits and urgent challenges are summarized. Some perspectives on the potential solutions and possible future trends are also provided.

Two-electron redox-active tricyano iron(ii) complex with 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine as a building block for coordination polymers

A new tricyano iron(ii) building unit, [{K(H2O)4}{FeII(CN)3(L)}]·3H2O (1), was synthesized by the reaction of Moor's salts with 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (L) as a capping ligand. X-ray structural analysis reveals that the mononuclear iron(ii) tricyano complex consists of one ligand and three cyanide groups, with K+ ions coordinated between neighboring units to form a one-dimensional chain network structure. 1 shows two reversible redox waves at +0.713 and -0.849 V vs. SCE, which are assigned as Fe(ii)/Fe(iii) and L/L˙- processes, respectively. One-dimensional 4,2-ribbon chain type coordination polymers, [MII(H2O)2{FeII(CN)3(L)}2]·6H2O (M = Fe (2) and Mn (3)), were synthesized by using 1 as a building unit. Cryomagnetic studies reveals that 2 and 3 show paramagnetic behaviour of S = 2 and 5/2, respectively. On the other hand, reaction of 1 and Gd(NO3)3·6H2O forms another one-dimensional chain, [GdIII(NO3)2(H2O)3{FeII(CN)3(L)}]·0.5H2O·2CH3OH (4), showing S = 7/2 paramagnetic behaviour.

Oriented assembly of anisotropic nanoparticles into frame-like superstructures

It is fascinating but challenging for nanoscientists to organize nanoparticles (NPs) into ordered architectures just as it is for chemists to manipulate atoms and molecules to form functional molecules and supramolecules. We explore a strategy to assemble anisotropic NPs into open frame-like superstructures via oriented attachment (OA), experimentally realizing a nanoscale analog to the bonding behavior in M₈L₁₂-type supramolecular cubes. We highlight the role of NP shape in the OA-involved assembly for constructing predictable superstructures. In addition, the frame-like superstructures can retain their basic structure when undergoing postcrystallization of the building blocks as well as annealing for conversion toward functional electrocatalytic materials. Our work enables fundamental insights into directional "bonding" among NPs and adds to the growing body of knowledge for bottom-up assembly of anisotropic NPs into sophisticated functional materials.

Enforcing Multifunctionality: A Pressure-Induced Spin-Crossover Photomagnet

Photomagnetic compounds are usually achieved by assembling preorganized individual molecules into rationally designed molecular architectures via the bottom-up approach. Here we show that a magnetic response to light can also be enforced in a nonphotomagnetic compound by applying mechanical stress. The nonphotomagnetic cyano-bridged Fe(II)-Nb(IV) coordination polymer {[Fe(II)(pyrazole)4]2[Nb(IV)(CN)8]·4H2O}n (FeNb) has been subjected to high-pressure structural, magnetic and photomagnetic studies at low temperature, which revealed a wide spectrum of pressure-related functionalities including the light-induced magnetization. The multifunctionality of FeNb is compared with a simple structural and magnetic pressure response of its analog {[Mn(II)(pyrazole)4]2[Nb(IV)(CN)8]·4H2O}n (MnNb). The FeNb coordination polymer is the first pressure-induced spin-crossover photomagnet.

Anatase-driven charge transfer involving a spin transition in cobalt iron cyanide nanostructures

A charge transfer between Fe and Co in cobalt hexacyanoferrate takes place with concomitant spin transition at the Co site.