Layered Hydroxides Research Articles

Cinnamate-Intercalated Layered Yttrium Hydroxide: UV Light-Responsive Switchable Material.

In recent years, there has been an increasing interest in stimuli-responsive host-guest materials due to the high potential for their application in switchable devices. Light is the most convenient stimulus for operating these materials; a light-responsive guest affects the host structure and the functional characteristics of the entire material. UV-transparent layered rare earth hydroxides intercalated with UV-switchable anions are promising candidates as stimuli-responsive host-guest materials. The interlayer distance in the layered rare earth hydroxides depends on the size of the intercalated anions, which could be changed in situ, e.g., via anion isomerisation. Nevertheless, for layered rare earth hydroxides, the possibility of such changes has not been reported yet. A good candidate anion that is capable of intercalating into the interlayer space is the cinnamate anion, which undergoes UV-assisted irreversible trans-cis isomerisation. In this work, both trans- and cis-cinnamate anions were intercalated in layered yttrium hydroxide (LYH). Upon UV-irradiation, the interlayer distance of trans-cinnamate-intercalated layered yttrium hydroxide suspended in isopropanol changed from 21.9 to 20.6 Å. For the first time, the results obtained demonstrate the possibility of using layered rare earth hydroxides as stimuli-responsive materials.

Specificity of the Thermal Stability and Reactivity of Two-Dimensional Layered Cu-Fe Sulfide-Mg-Based Hydroxide Compounds (Valleriites).

We recently synthesized prospective new materials composed of alternating quasi-atomic sheets of brucite-type hydroxide (Mg, Fe)(OH)2 and CuFe1-xS2 sulfide (valleriites). Herein, their thermal behavior important for many potential applications has been studied in inert (Ar) and oxidative (20% O2) atmospheres using thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses and characterization with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). In the Ar media, the processes are determined by the dehydroxylation of the hydroxide layers forming MgO, with the temperature of the major endothermic maximum of the mass loss at 413 °C. Sulfide sheets start to degrade below 500 °C and melt at nearly 800 °C, with bornite, chalcopyrite, and troilite specified as the final products. In the oxidative atmosphere, the exothermic reactions with the mass increase peaked at 345 and 495 °C, corresponding to the partial and major oxidations of Cu-Fe sulfide layers. Sulfur oxides captured in magnesium hydroxide layers to form MgSO4 compromised the layer integrity and promoted the oxidation of the sulfide entities. The final products also contained minor MgO, Cu2MgO3, Fe3O4, and MgFe2O4 phases. Samples doped with Al, which decreases the content of Fe in hydroxide layers, show notably impeded decay of valleriite in argon but facilitated the oxidation of Cu-Fe sulfides, while the impact of Li (it slightly increases the number of the Fe-OH sites) was less expressed. The mutual stabilization of the two-dimensional (2D) hydroxide and sulfide layers upon heating in an inert atmosphere but not in oxygen as compared with bulk brucite and chalcopyrite was suggested to explain high thermal resistance across the stacked incommensurate sheets, which slows down the endothermic reactions and accelerates the exothermic oxidation; the high number of Fe atoms in the hydroxide sheets are expected to promote the phonon exchange and heat transfer between the layers.

Rapid degradation and detoxification of metronidazole using calcium sulfite activated by CoCu two-dimensional layered bimetallic hydroxides: Performance, mechanism, and degradation pathway

In this study, cobalt copper-layered double hydroxides (CoCu-LDHs) were prepared by coprecipitation as catalysts to activate CaSO3 for metronidazole (MNZ) degradation. This is the first report on layered double hydroxides activating sulfite for the degradation of organic pollutants. Meanwhile, to address the issue of self-quenching reactions readily occurring in conventional sulfite advanced oxidation systems and resulting in low oxidant efficiency, CaSO3 with slightly soluble in water was used instead of commonly used Na2SO3, to improve the limitations of traditional systems. The results showed that in the CoCu-LDHs/CaSO3 system, the degradation rate of MNZ reached 98.7% within 5 min, representing a 23.0% increase compared to the CoCu-LDHs/Na2SO3 system. Owing to the excellent catalytic performance exhibited by CoCu-LDHs, characterizations including XRD, FTIR, SEM, TEM, BET and XPS were carried out to investigate this further. The results confirmed the successful synthesis of CoCu-LDH, and the activation mechanism study revealed that Co and Cu were considered to the main elements in activating CaSO3, demonstrating good synergistic effects. In addition, the oxygen vacancies on the catalyst surface also played a positive role in generating radicals and promoting electron transfer. Subsequently, the effects of Co/Cu ratio, catalyst dosage, oxidant concentration, pollutant concentration, pH and coexisting substances on MNZ degradation were investigated. Additionally, based on the LC-MS analysis of degradation products and toxicity tests, MNZ was transformed into different intermediates with low toxicity through four pathways, eventually mineralizing into inorganic small molecules. After six cycles, the MNZ degradation rate still reached 82.1%, exhibiting excellent stability and recyclability. In general, this study provides new ideas for activating sulfite, while providing theoretical support for subsequent research on sulfite advanced oxidation system.

Upscaling the urea method synthesis of CoAl layered double hydroxides.

Research on two-dimensional materials is one of the most relevant fields in materials science. Layered double hydroxides (LDHs), a versatile class of anionic clays, exhibit great potential in photocatalysis, energy storage and conversion, and environmental applications. However, its implementation in real-life devices requires the development of efficient and reproducible large-scale synthesis processes. Unfortunately, reliable methods that allow for the production of large quantities of two-dimensional LDHs with well-defined morphologies and high crystallinity are very scarce. In this work, we carry out a scale-up of the urea-based CoAl-LDH synthesis method. We thoroughly study the effects of the mass scale-up (25-fold: up to 375 mM) and the volumetric scale-up (20-fold: up to 2 L). For this, we use a combination of several structural (XRD, TGA, and N2 and CO2 isotherms), microscopic (SEM, TEM, and AFM), magnetic (SQUID), and spectroscopic techniques (ATR-FTIR, UV-vis, XPS, ICP-MS, and XANES-EXAFS). In the case of the volumetric scale-up, a reduction of 45% in the lateral dimensions of the crystals (from 3.7 to 2.0 µm) is observed as the reaction volume increases. This fact is related to modified heating processes affecting the alkalinization rates and, concomitantly, the precipitation, even under recrystallization at high temperatures. In contrast, for the tenfold mass scale-up, similar morphological features were observed and assigned to changes in nucleation and growth. However, at higher concentrations, simonkolleite-like Co-based layered hydroxide impurities are formed, indicating a phase competition during the precipitation related to the thermodynamic stability of the growing phases. Overall, this work demonstrates that it is possible to upscale the synthesis of high-quality hexagonal CoAl-LDH in a reproducible manner. It highlights the most critical synthesis aspects that must be controlled and provides various fingerprints to trace the quality of these materials. These results will contribute to bringing the use of these 2D layered materials closer to reality in different applications of interest.

Development, Analytical Characterization, and Bioactivity Evaluation of Boswellia serrata Extract-Layered Double Hydroxide Hybrid Composites.

Boswellia serrata Roxb. extract (BSE), rich in boswellic acids, is well known as a potent anti-inflammatory natural drug. However, due to its limited aqueous solubility, BSE inclusion into an appropriate carrier, capable of improving its release in the biological target, would be highly desirable. Starting with this requirement, new hybrid composites based on the inclusion of BSE in a lamellar solid layered double hydroxide (LDH), i.e., magnesium aluminum carbonate, were developed and characterized in the present work. The adopted LDH exhibited a layered crystal structure, comprising positively charged hydroxide layers and interlayers composed of carbonate anions and water molecules; thus, it was expected to embed negatively charged boswellic acids. In the present case, a calcination process was also adopted on the LDH to increase organic acid loading, based on the replacement of the original inorganic anions. An accurate investigation was carried out by TGA, PXRD, FT-IR/ATR, XPS, SEM, and LC-MS to ascertain the nature, interaction, and quantification of the active molecules of the vegetal extract loaded in the developed hybrid materials. As a result, the significant disruption of the original layered structure was observed in the LDH subjected to calcination (LDHc), and this material was able to include a higher amount of organic acids when its composite with BSE was prepared. However, in vitro tests on the composites' bioactivity, expressed in terms of antimicrobial and anti-inflammatory activity, evidenced LDH-BSE as a better material compared to BSE and to LDHc-BSE, thus suggesting that, although the embedded organic acid amount was lower, they could be more available since they were not firmly bound to the clay. The composite was able to significantly decrease the number of viable pathogens such as Escherichia coli and Staphylococcus aureus, as well as the internalization of toxic active species into human cells imposing oxidative stress, in comparison to the BSE.

Zinc Layered Hydroxide 2-methyl-4-chlorophenoxyacetate: Synthesis via ZnO, Characterization and Effect on Seed Germination

2-methyl-4-chlorophenoxyacetic acid (MCPA) was successfully intercalated into zinc layered hydroxide (ZLH) by anion exchange technique followed by hydrothermal treatment, resulting in the formation of nanoherbicide, zinc-layered hydroxide-2-methyl-4-chlorophenoxyacetic acid (ZMCPA). Fourier-transform infrared spectroscopy (FTIR) and Powder X-ray diffraction (PXRD) was used to confirm the intercalation of herbicide into ZLH, while Ultraviolet-visible spectroscopy (UV-vis) was employed to assess the plant’s protein content and amino acid composition before and after 1 h treatment with ZnO, MCPA and ZMCPA via the foliar technique and direct soil application. The basal spacing of ZMCPA in this study is 21.6 Å at 4.0815°, revealing the triumphant incorporation of MCPA into the ZLH host. The zinc oxide (ZnO) fingerprint from 30° to 60° that certainly vanished in the ZMCPA diffractogram indicates that all ZnO has successfully converted to ZLH matrices. The FTIR spectrum of ZMCPA shows the similarity of most MCPA spectra, but with the COO– peaks at 1610 and 1700 cm–1 replacing the intense C=O band at 1742.21 cm–1, implying that the herbicide has assimilated into the host. The protein level of the plant treated with ZMCPA was discovered to be more significant, which signifies that ZLH has effectively acted as a herbicide carrier. This study has depicted the potential of ZMCPA as a more unassailable agrochemical agent in increasing crop productivity while minimizing environmental consequences. HIGHLIGHTS Successful Intercalation of MCPA into Zinc Layered Hydroxide (ZLH) Enhanced Plant Protein Levels with nanocomposite, ZMCPA Treatment ZMCPA as a potentially more effective and environmentally friendly agrochemical agent compared to the traditional agrochemical GRAPHICAL ABSTRACT

Revealing the potential of hierarchical heterostructure of tri-metallic selenide and MOFs etched layered hydroxide dodecahedron laminated with rGO-Ni foam for a hybrid supercapacitor applications

Inaugurating the multistage hierarchical hybrid structure with ample surface area and synergistic contribution from polymetallic selenide and layered hydroxide in a conductive 3D substrate has been supposed to be appealing and highly-rated electrode material to enhance the general electrochemical parameters of supercapacitors (SCs), thanks to exclusive structural features, immense electronic states and relatively paramount electrical conductivity of the final product. In this work, hydrothermal assisted zinc‑nickel‑cobalt-selenide (ZNC-Se) nanosheets have been uniformly prepared onto the conductive rGO decorated Ni foam substrate, chased by uniform decoration of metal organic frameworks (MOFs) templated nickel‑cobalt-layered double hydroxide (NC-LDH) onto tri-metallic (ZNC-Se) nanosheets to achieve the hierarchical hybrid structure of [email protected]@rGO-NF. The as-prepared hierarchical [email protected]@rGO-NF delivers remarkable specific capacity value along with outstanding cycle stability. The proposed [email protected]@rGO-NF and MOFs derived open and hollow carbon structure (MDOHCS)-based hybrid device disclosed remarkable cyclic life and an energy/power density of 80.3 W h kg−1/15970.9 W kg−1.

Immuno-Nanozymes Mediated Synergistic Chemodynamic/Immuno-Therapy with Potentiated Anti-Tumor Efficacy.

Nanozymes mediated chemodynamic therapy (CDT) is a newly developed therapeutic modality with high specificity. The efficacy of CDT, however, still confronts challenges from the immune inhibitory tumor microenvironment (TME). It is thus of great significance to synergize CDT with immunotherapeutic interventions. Herein, this work reports the design and preparation of CpG loaded, Cu2+ doped double layered hydroxides nanosheets (CpG/Cu-LDHs) as immuno-nanozymes to potentiate overall anti-tumor efficacy by synergizing CDT with immunogenic cell death (ICD)-activated local and systemic immune responses. Such cooperative CDT-immuno effect together with immunosuppressive TME remodeling capacity conferred by CpG/Cu-LDHs led to effective suppression of both treated primary tumor and untreated distant tumor on a mouse tumor model. Thereby, synergizing CDT with ICD-driven, in situ vaccine-like immunotherapy by immuno-nanozymes provides a novel and generalized paradigm for devising highly efficient and specific anti-tumor strategy without the use of external stimulations.

Intercalation of silsesquioxane surfactant in layered double hydroxide for silicone rubber composites: Enhancing interfacial interactions toward improvement of mechanical, thermal, and gas barrier properties

AbstractThe incorporation of two‐dimensional layered metal hydroxides (LDHs) into nonpolar silicone rubber (SR) is not yet universal, mainly because of their originally hydrophilic surface and limited interlamellar galleries that make nanoparticle dispersion and intercalation of polymer segments more difficult. In this work, we develop a modified Ca‐Mg‐Al LDH form by conjugating the ternary Ca‐Mg‐Al LDH with silsesquioxane (SQ) surfactants containing benzoic acid moieties and polyethylene glycol chains via an in‐situ intercalation process. The bulky anions conjugation to the hydroxide layers dictated both the surface hydrophobicity and interlayer spacing of the modified Ca‐Mg‐Al LDH, enabling strong inter‐constituent interactions within the nanocomposites as well as extensive polymer penetration after incorporation into the SR matrix. The SR/modified LDH nanocomposites show excellent thermal stability and satisfactory mechanical properties due to the homogeneous dispersion and good compatibility of modified Ca‐Mg‐Al LDH. Moreover, we have observed that the shear‐induced orientation of the nano‐layered particles upon application of stress imparts a more notably decreased SR/LDH‐SQ‐40 gas transmission rate (reduced by 55% with respect to that in the unstretched composite films). This result also corroborates the better interfacial bonding and highly efficient load transfer between silsesquioxane‐modified LDH and polymer in melt extrusion mixing of such composites.Highlights Modified Ca‐Mg‐Al LDH with increased layer spacing and reduced hydrophilicity. Modifier enhanced the interfacial adhesion between Ca‐Mg‐Al LDH and SR matrix. SR/modified LDH showed excellent thermal stability and mechanical properties. Orientation and exfoliation enhanced gas barrier properties of SR/modified LDH.

Combination of layered-based materials as an innovative strategy for improving active corrosion protection of carbon steel

Layered hydroxide salt and layered double hydroxide intercalated respectively with molybdate (LHS-M) and gluconate (LDH-G) were used together for corrosion protection of carbon steel for the first time. Essays revealed that inhibitor release from LHS-M and LDH-G occurred in presence of chloride anions, within different timescales. Electrochemical studies performed for inhibitors, directly in solution and intercalated into the nanocontainers, showed that the protection of carbon steel can be tuned using the right ratio of inhibitors and nanocontainers. Coatings loaded with a mixture of the nanocontainers were applied on carbon steel plates and found to improve the anticorrosion performance, attributed to the inhibitors' action and chloride anions trapping.

Tuning the Structure of Layered Hydroxides for Boosting Energy Application Performance

We are currently on a race against the clock to protect our planet from greenhouse gas emissions. The solution could be inspired from mother nature talking about renewable energies or so-called green energies including wind, solar, hydraulic, biomass and so on, which allows us to reduce the fossil fuels consumption. However, these kinds of energy devices should be coupled to an energy storage system such as batteries and supercapacitors to compensate the absence of wind and sun. For this purpose, we are looking forward to developing strong energy and power application systems by focusing on the development of novel electrode materials.Among 2D materials, layered hydroxides emerge as one of the most attractive electrode materials based on earth-abundant metals, at the same time inside of this family, three type can distinguish: the first one is the Brucite-like structure1 (β-structure) where the metal is arranged in the octahedral position and the interlayer space is defined by Van-Der-Waals interaction. The second one is the Hydrotalcite-like structure also called Layered Double Hydroxide (LDH) recognized by the following formula MII 1-x MIII x (OH)2 Ax. xH2O. The LDH regroups in the same layer a divalent and trivalent metals and are both arranged in the octahedral position2. The Simonkolleite-like structure3 (α-structure) with M1-x Oh Mx Td (OH)2-x Ax. yH2O as formula, is the third type which only contains divalent metals arranged in tetrahedral (Td) and octahedral (Oh) position.Layer double hydroxides are explored materials in the energy field. Multiple studies have been reported on the behaviour of the layered hydroxides materials in energy storage4 and conversion5. This material is very appealing for researchers worldwide due to their good electrochemical behaviour, chemical versatility, electrochemical stability, and their low cost as well6. For instance, LDHs based on earth-abundant elements are good candidates for electrode materials for oxygen evolution reaction (OER) in alkaline condition, as well as for supercapacitors. However, one of the major drawback of these materials is their low electrical conductivity, which represents a limitation in the optimization of the electrochemical performance and the assemble of devices.Among the different approximation to overcome this issue, we are intensively working on the modulation of the electronic properties of LHs. In this line, Co-based α-layered hydroxides, exhibiting simonkolleite-like structure, can be an interesting case of study since the covalent bond between the hydroxylated layer and the anion (figure 1). Indeed, we have recently demonstrated that the electrical properties can be modulated by halide substitution6, where the band gap can be reduced by ligand to metal charge transfer as demonstrated by DFT+U simulations. Considering these previous results, we decided to analyse the role of these chemical modifications in terms of the electrochemical properties.Interestingly, our results evidence a better electrochemical activity of Co-based α-LHs in comparison with the typical β-LHs or LDHs analogues, in both OER and specific capacitance performance7. Moreover, in the case of α-LHs the values can be further enhanced by tuning the nature of the anion: for instance, structures containing iodide overpass in more than 40% those ones containing chloride, as mentioned by DFT+U simulation (figure 2).Hence, this work positions α-CoII hydroxides as key phases among the layered hydroxides family as electrode materials for energy storage and conversion, where the conductivity can be improved by anion substitution8. 1 Brindley, G. W.; Kao, C.-C. Structural and IR Relations among Brucite-like Divalent Metal Hydroxides. Phys. Chem. Miner. 1984, 10 (4), 187–191. 2 Du, Y.; O’Hare, D. Synthesis, Morphology, Structure, and Magnetic Characterization of Layered Cobalt Hydroxyisocyanates. Inorg. Chem. 2008, 47 (8), 3234–3242. 3 Oestreicher, V.; Dolle, C.; Hunt, D.; Fickert, M.; Abellán, G. Room Temperature Synthesis of Two-Dimensional Multilayer Magnets Based on α-CoII Layered Hydroxides. Nano Mater. Sci. 2022, 4 (1), 36–43. 4 Zhang, D.; Cao, J.; Zhang, X.; Zeng, Z.; Insin, N.; Qin, J.; Huang, Y. Modification Strategies of Layered Double Hydroxides for Superior Supercapacitors. Adv. Energy Sustain. Res. 2022, 3 (3), 2100183. 5 Wang, Y.; Yan, D.; El Hankari, S.; Zou, Y.; Wang, S. Recent Progress on Layered Double Hydroxides and Their Derivatives for Electrocatalytic Water Splitting. Adv. Sci. 2018, 5 (8), 1800064. 6 Oestreicher, V.; Hunt, D.; Torres-Cavanillas, R.; Abellán, G.; Scherlis, D. A.; Jobbágy, M. Halide-Mediated Modification of Magnetism and Electronic Structure of α-Co(II) Hydroxides: Synthesis, Characterization, and DFT+U Simulations. Inorg. Chem. 2019, 58 (14), 9414–9424. 7 R. Sanchis-Gual, V. Oestreicher, G. Abellan et al. Submitted. 8 Y. Diouane, V.Oestreicher, G. Abellan et al, manuscript in preparation Figure 1

An in-Situ Study of the Transformation of Hybrid Layered Hydroxides into Metallic Nanocomposites with Interest in Energy Storage Systems

The high increase of energy demand in recent decade and the necessity of reduce the fossil fuel consumption have triggered the interest of the scientific community in the search of 'green' alternatives. Due to the characteristic intermittence of solar and wind technologies, there is a huge effort on the development energy storage systems. Among them hybrid capacitors (HCs) are promising systems due its high energy and power density values, in comparison with Li-ion batteries, that make them ideal for industrial and automobile applications. Battery-like materials such as nanocomposites (NCs) based on metallic nanoparticles (working as pseudo-capacitor based in redox reactions) with a carbon matrix (working as electric double layer capacitors) are key HCs systems itself. These NCs exhibits a notorious enhancement on their electrochemical performance by applying an external magnetic field. [1] Typically, NCs are obtained by the thermal decomposition of hybrid materials under inert atmosphere, as it has been demonstrated for the case of layered double hydroxides (LDHs), layered hydroxides (α-LHs) and metal organic frameworks (MOFs). [1-3] However, there is a lack of information in terms how the thermal transformation takes places.In this work, we present for the first-time an in-situ study about the transformation of hybrid layered hydroxides into NCs. For that, synchrotron measurements of X-ray absorption spectroscopy (XAS) and powder X-ray diffraction (PXRD) are performed for different hybrid layered hydroxides to follow the transformation in terms of oxidation state and crystallinity. These hybrid layered hydroxides will variate on: (i) the layered hydroxide structure and the anion-layer interactions (LDHs vs α-LHs + electrostatic vs covalent), (ii) the cation nature, and (iii) the identity of the organic linkers, to name a few. For instance, in the case of α-LHs, while the LHs structure defines the thermal decomposition, and the organic molecule length controls the quality and quantity of the final carbon matrix at the NCs.[4] Interestingly, in function of the amount of carbon present on the organic molecule, the oxidation state and the formation of the carbon matrix on the final material are conditioned, which imply that there is a minimum amount of carbon to obtain the NCs. In the other hand, for the previous NCs obtained, the electrochemical characterization is performed in pouch cells, applying an external magnetic field throughout the galvanostatic cycles. This assembly prevents the loss of material along the time and during the process, where it is evidenced how the magnetic field improves the electrochemical performance with an increase in the specific capacity of the NCs. In overall, this work introduces fundamental knowledge on the rational design of hybrid layered hydroxides and the subsequent nanocomposites and its performance in energy storage systems.

Fundamental Insights into Reaction Centers and Catalytic Mechanisms of Ni- and Co-Based Layered Oxyhydroxides for the Oxygen Evolution Reaction

Water splitting to generate green H2 fuel and O2 is essential for global CO2 reductions toward net-zero emissions. In this process, however, O2 generation at the anode through the oxygen evolution reaction (OER) is inherently slower by orders of magnitude than H2 generation at the cathode. Thus, improving OER efficiency has been a major effort in electrolysis. Ni-based and Co-based layered hydroxides are among the most active and studied non-previous catalysts in alkaline electrolytes. Although tremendous advances have been made toward improving the activity and the stability of the catalysts over the past decade, there is still a lack of fundamental insights into active sites and reaction mechanisms, which has hindered the establishment of structure-property relationships.This talk will first provide fundamental insights into reaction centers and catalytic mechanisms of classic Ni oxyhydroxides and Co oxyhydroxides with and without ligand intercalation. We will further discuss the multiple-site synergy in Ni- and Co-based layered double hydroxides (LDH) and ternary hydroxides. We will show that the OER proceeds via a Mars van Krevelen mechanism, starting with the oxidation of bridge OH at the reaction centers with dual metal sites, i.e., M1-OH-M2. We will demonstrate that, to approach the minimum overpotential dictated by a specific OH-OOH scaling relationship, the key is to break the OH-O scaling relationship. A possible route is to form binary metal oxyhydroxides with dual metal sites at the reaction centers or introduce a third element into NiFe LDH or CoFe LDH. If time permits, We will further discuss the role of the non-covalent interaction and polaron-like electronic states in promoting OER at M1-OH-M2 centers.

Nanocomposite Anion Exchange Membranes for Aems Electrolyzers: Ion Transport and Carbonation Studies

Anion-exchange membranes (AEMs) have received increased interest in recent years as the electrolyte separator in different electrochemical energy conversion and storage (EECS) devices. [1] AEM fuel cells and electrolyzers devices can reach the performance level required by applications with electrocatalysts that do not require a high loading of platinum-group metals (PGMs) due to the alkaline environment at the electrodes. However, the AEM based EECS development and implementation is significantly hindered by the anion exchange membrane (AEM) stability during cell operation, their low OH- conductivity and the low kinetics of the electrocatalysts. In fact, the electrolytic anion-exchange membrane (AEM) is a crucial component which should allow good charge and water transport, i.e. high ionic conductivity, but should also guarantee good chemical, thermal and mechanical stability and high durability. [2]In this work, nanocomposite AEMs based on Polysulfone ionomer (PSU) and two different nanoadditives, Layered Double Hydroxide (LDH) and Nanoscale Ionic Materials (NIM), have been developed and studied. [3] LDHs are mineral anionic clays with elevated ion exchange capacity (IEC). They consist of the positively charged metal hydroxide layers with anions located in the interlayer space. This allows strong hydration of the material together with a large number of hydroxyls on the host layers forming a dense network of hydrogen bonds along the two-dimensional surface, therefore facilitating OH- ion conduction by diffusion mechanism. NIMs have a nanostructure consisting of a spherical silica core functionalized with an ionic oligomeric corona. Due to the extremely high number of functional groups present, these materials are able to significantly increase the ionic conduction capacity of the resulting electrolyte. [4]PSU is a thermoplastic polymer with high thermal stability, good chemical resistance and mechanical properties. However, since it has two activated positions per repetition unit for electrophilic aromatic substitution, it can undergo high degrees of functionalisation, which reduce the mechanical properties. We developed a two steps procedure, with allow a functionalization degree between 60 and 80%, preserving its stability.Nanocomposites AEMs were investigated in both OH- and HCO3 - forms, comparing swelling capacity, ionic conductivity and water diffusion. The latter was studied by NMR spectroscopy, measuring the self-diffusion coefficient by the Pulse Field Gradient (PFG) NMR techniques. The nanocomposite membranes are able to maintain good hydration at high temperatures, and to create an adequate nanostructure with the polymer chains, which favour the Grotthuss diffusion mechanism for the OH- ions. Such feature is reflected in the ionic conductivity and in the alkali stability, where they demonstrated the highest conductivity and a reduced membrane degradation rate. Finally, electrolysis cell tests were conducted on MEAs based on these hybrid membranes, and preliminary results showed very promising performance.

Fe3+ induced etching of NiCo-MOF derived transformations into layered ternary hydroxides as efficient oxygen evolution catalyst

Hydrogen energy is the only new energy that meets the requirements of resources, environment and sustainable development due to its advantages such as rich resources, diverse sources, storable, renewable, high calorific value, clean and pollution-free. Electrochemical water splitting technology can achieve large-scale hydrogen production commercially, but the slow kinetics of OER process seriously hinders the development of electrochemical water splitting technology, therefore, high-efficiency and low-cost OER electrocatalyst is urgently needed. Here, we synthesized a layered ternary hydroxide NiCoFe-LTH@NiCo-MOF/NF-30 electrocatalyst with NiCo-MOF as the sacrificial template on conductive substrate nickel foam by a two-step solvothermal method, which requires only low overpotentials of 207 mV and 283 mV to achieve current densities of 10 mA cm−2 and 100 mA cm−2, respectively. Tafel slope is as low as 78.44 mV dec−1, and favorable electrochemical stability can be maintained for at least 50 h. The strategy may provide valuable references for future researchers to prepare better MOF-based electrocatalysts.

Different metal precursor based rapid synthesis of α-Ni(OH)2-type Ni-Co-Mn layered double hydroxides and its use as electrodes for high performance energy storage devices

Improvement in the specific capacity of battery type electrode material is vital for creating hybrid devices with superior electrochemical performance. To accomplish this, mixed metal hydroxides, Ni0.7Co0.2Mn0.1(OH)2, are synthesized via a simple co-precipitation method by rapid pH switching using chloride, nitrate, acetate and sulphate salts of Ni, Co and Mn. P-XRD analysis confirmed the formation of pure and highly crystalline materials stabilized in the α-Ni(OH)2 structure. Finely divided particle type microstructure with sub 100 nm size and homogenous distribution of elements are confirmed by FESEM and EDX analysis, respectively. Among the studied samples, the layered hydroxide synthesized using chloride salts (Ni0.7Co0.2Mn0.1 LDH-Cl) shows the highest specific surface area of 58.8 m2 g−1 and pore volume of 0.083 cc g−1. The compound exhibited a high specific capacity of 978 C g−1 at 1 A g−1. The observed capacity is much higher than all other double hydroxides studied here and those we have come across in the literature reports on similar metal hydroxides. The diffusion dominance (b = 0.55) and quantitative separation of diffusion and capacitive capacity at different scan rates for Ni0.7Co0.2Mn0.1 LDH-Cl is also studied by CV analysis. Nyquist plot equivalent circuit fitting shows low charge transfer resistance (Rct = 17.6 Ω) and Warburg impedance (Zw = 35 Ω) for Ni0.7Co0.2Mn0.1 LDH-Cl. The high-capacity retention of 90 % for 5000 CV cycles at 100 mV sec−1 and 99 % for 1000 GCD cycles at 5 A g−1 for Ni0.7Co0.2Mn0.1 LDH-Cl confirm its potential for use as a battery type electrode material for practical applications.

Phase-Engineering of Layered Nickel Hydroxide for Synthesizing High-Quality NiOx Nanocrystals for Efficient Inverted Flexible Perovskite Solar Cells.

Nickel oxide (NiOx) nanocrystals have been widely used in inverted (p-i-n) flexible perovskite solar cells (fPSCs) due to their remarkable advantages of low cost and outstanding stability. However, anion and cation impurities such as NO3- widely exist in the NiOx nanocrystals obtained from calcinated nickel hydroxide (Ni(OH)2). The impurities impair the photovoltaic performance of fPSCs. In this work, we report a facile but effective way to reduce the impurities within the NiOx nanocrystals by regulating the Ni(OH)2 crystal phase. We add different alkalis, such as organic ammonium hydroxide and alkali metal hydroxides, to nickel nitrate solutions to precipitate layered Ni(OH)2 with different crystalline phase compositions (α and β mixtures). Especially, Ni(OH)2 with a high β-phase content (such as from KOH) has a narrower crystal plane spacing, resulting in fewer residual impurity ions. Thus, the NiOx nanocrystals, by calcinating the Ni(OH)x with excess β phase from KOH, show improved performance in inverted fPSCs. A champion power conversion efficiency (PCE) of 20.42% has been achieved, which is among the state-of-art inverted fPSCs based on the NiOx hole transport material. Moreover, the reduced impurities are beneficial for enhancing the fPSCs' stability. This work provides an essential but facile strategy for developing high-performance inverted fPSCs.

Investigation of the properties influencing the deactivation of iron electrodes in iron-air batteries

Iron-air batteries hold the potential to be a key technology for energy storage, thanks to their energy density, low cost, safety and abundance of their materials. In order to scale the technology up and optimize the cell formulations, it is key to obtain a clear understanding of how the physical-chemical properties of the electrode influence their electrochemical behaviour, in particular, the capacity loss. In this work, we propose for the first time mathematical correlations between textural and crystallographic properties of iron electrodes and their electrochemical stability. By adjusting synthesis parameters, we were able to tune pore size and volume, surface area and crystal size of iron oxides, and found that stability is highly correlated to both surface area and pore size. Large surface area and small average pore size provide electrodes with enhanced stability. We hypothesize that the cause for deactivation is the passivation of the electrodes ascribed to the formation of a non-conductive, non-reactive iron (II) hydroxide layer during discharge, which then cannot be reduced to iron again. We validate this hypothesis with electrochemical impedance spectroscopy studies, which show that, in the more stable electrodes, the charge transfer resistance in the Fe(OH)2 to Fe reduction does not significantly change after cycling, contrary to the behaviour of the less stable electrodes, corroborating our hypothesis. Furthermore, the electrode with the best properties was cycled 100 times, retaining almost 75% of its initial capacity at the end of the 100 cycles. These results are highly relevant for the future design and operation of iron-air batteries.

Coupling silsesquioxane nanocages into Fe-Mg-Al layered metal hydroxide for enhanced flame retardancy and surface charring of silicone elastomer

Bonding of two-dimensional layered metal hydroxides (LMHs) to silicone rubber (SR) is not yet common, mainly due to the hydrophilic surface and limited layer spacing of LMHs, which make it difficult to achieve uniform distribution. In this work, we modified Fe-Mg-Al LMH nanoparticles by incorporating silsesquioxane nanocages bearing anionic benzoate groups and polyethylene glycol chains (SQ–COOH) using a co-precipitation procedure. The modification step leads to an enlarged interlayer spacing for LMHs and simultaneously transforms their intrinsic hydrophilic surfaces into hydrophobic ones, originating from the rigid and bulky nature and also the intercalation capacity of the modifiers. When melt-blended with SR, this SQ–COOH-incorporating strategy allowed an enhanced LMH dispersion via an interfacial compatibilization between the elastomer matrix and the modified nanoparticles. The resulting SR/LMH@SQ–COOH composites showed the expected improvement in mechanical properties while demonstrating outstanding thermal stability and flame retardancy performance. Most importantly, the synergistic effect of Fe-Mg-Al LMH with SQ–COOH endows this SR composite with significant surface charring ability resulting in a compact and strengthened ceramic-like layer to inhibit progressive combustion, which will find application in packing and other utility.

Crystallographic and Geometrical Dependence of Water Oxidation Activity in Co-Based Layered Hydroxides.

Cobalt-based layered hydroxides (LHs) stand out as one of the best families of electroactive materials for the alkaline oxygen evolution reaction (OER). However, fundamental aspects such as the influence of the crystalline structure and its connection with the geometry of the catalytic sites remain poorly understood. Thus, to address this topic, we have conducted a thorough experimental and in silico study on the most important divalent Co-based LHs (i.e., α-LH, β-LH, and LDH), which allows us to understand the role of the layered structure and coordination environment of divalent Co atoms on the OER performance. The α-LH, containing both octahedral and tetrahedral sites, behaves as the best OER catalyst in comparison to the other phases, pointing out the role of the chemical nature of the crystalline structure. Indeed, density functional theory (DFT) calculations confirm the experimental results, which can be explained in terms of the more favorable reconstruction into an active Co(III)-based oxyhydroxide-like phase (dehydrogenation process) as well as the significantly lower calculated overpotential across the OER mechanism for the α-LH structure (exhibiting lower Egap). Furthermore, ex situ X-ray diffraction and absorption spectroscopy reveal the permanent transformation of the α-LH phase into a highly reactive oxyhydroxide-like stable structure under ambient conditions. Hence, our findings highlight the key role of tetrahedral sites on the electronic properties of the LH structure as well as their inherent reactivity toward OER catalysis, paving the way for the rational design of more efficient and low-maintenance electrocatalysts.