Assessing Challenges of 2D-Molybdenum Ditelluride for Efficient Hydrogen Generation in a Full-Scale Proton Exchange Membrane (PEM) Water Electrolyzer.

Proton exchange membrane (PEM) water electrolyzers are critical enablers for sustainable green hydrogen production due to their high efficiency. However, nonplatinum catalysts are rarely evaluated under actual electrolyzer operating conditions, limiting knowledge of their feasibility for H2 production at scale. In this work, metallic 1T'-MoTe2 films were synthesized on carbon cloth supports via chemical vapor deposition and tested as cathodes in PEM electrolysis. Initial three-electrode tests revealed that at 100 mA cm-2, the overpotential of 1T'-MoTe2 approached that of leading 1T'-MoS2 systems, confirming its promise as a hydrogen evolution catalyst. However, when tested in a full-scale PEM electrolyzer, 1T'-MoTe2 delivered only 150 mA cm-2 at 2 V, far below expectations. Postelectrolysis analysis revealed an unexpected passivating tellurium layer, likely inhibiting catalytic sites. While initially promising, the unanticipated passivation caused 1T'-MoTe2 to underperform in practice. This highlights the critical need to evaluate emerging electrolyzer catalysts in PEM electrolyzers, revealing limitations of the idealized three-electrode configuration. Moving forward, validation of model systems in actual electrolyzers will be key to identifying robust nonplatinum catalysts for sustainable green hydrogen production.

Direct purification and immobilization of his-tagged enzymes using unmodified nickel ferrite NiFe2O4 magnetic nanoparticles.

Purification of valuable engineered proteins and enzymes can be laborious, costly, and generating large amount of chemical waste. Whilst enzyme immobilization can enhance recycling and reuse of enzymes, conventional methods for immobilizing engineered enzymes from purified samples are also inefficient with multiple-step protocols, regarding both the carrier preparation and enzyme binding. Nickel ferrite magnetic nanoparticles (NiFe2O4 MNPs) offer distinct advantages in both purification and immobilization of enzymes. In this work, we demonstrate the preparation of NiFe2O4 MNPs via a one-step solvothermal synthesis and their use in direct enzyme binding from cell lysates. These NiFe2O4 MNPs have showed an average diameter of 8.9 ± 1.7 nm from TEM analysis and a magnetization at saturation (Ms) value of 53.0 emu g-1 from SQUID measurement. The nickel binding sites of the MNP surface allow direct binding of three his-tagged enzymes, D-phenylglycine aminotransferase (D-PhgAT), Halomonas elongata ω-transaminase (HeωT), and glucose dehydrogenase from Bacillus subtilis (BsGDH). It was found that the enzymatic activities of all immobilized samples directly prepared from cell lysates were comparable to those prepared from the conventional immobilization method using purified enzymes. Remarkably, D-PhgAT supported on NiFe2O4 MNPs also showed similar activity to the purified free enzyme. By comparing on both carrier preparation and enzyme immobilization protocols, use of NiFe2O4 MNPs for direct enzyme immobilization from cell lysate can significantly reduce the number of steps, time, and use of chemicals. Therefore, NiFe2O4 MNPs can offer considerable advantages for use in both enzyme immobilization and protein purification in pharmaceutical and other chemical industries.

Gold-iron oxide (Au/Fe3O4) magnetic nanoparticles as the nanoplatform for binding of bioactive molecules through self-assembly.

Nanomedicine plays a crucial role in the development of next-generation therapies. The use of nanoparticles as drug delivery platforms has become a major area of research in nanotechnology. To be effective, these nanoparticles must interact with desired drug molecules and release them at targeted sites. The design of these "nanoplatforms" typically includes a functional core, an organic coating with functional groups for drug binding, and the drugs or bioactive molecules themselves. However, by exploiting the coordination chemistry between organic molecules and transition metal centers, the self-assembly of drugs onto the nanoplatform surfaces can bypass the need for an organic coating, simplifying the materials synthesis process. In this perspective, we use gold-iron oxide nanoplatforms as examples and outline the prospects and challenges of using self-assembly to prepare drug-nanoparticle constructs. Through a case study on the binding of insulin on Au-dotted Fe3O4 nanoparticles, we demonstrate how a self-assembly system can be developed. This method can also be adapted to other combinations of transition metals, with the potential for scaling up. Furthermore, the self-assembly method can also be considered as a greener alternative to traditional methods, reducing the use of chemicals and solvents. In light of the current climate of environmental awareness, this shift towards sustainability in the pharmaceutical industry would be welcomed.

Mechanistic insights of molecular metal polyselenides for catalytic hydrogen generation.

Molecular metal chalcogenides have attracted great attention as electrocatalysts for the hydrogen evolution reaction (HER). However, efficient utilisation of the active sites and catalytic performance modulation has been challenging. Here we explore the design of immobilized molecular molybdenum polyselenides [Mo2O2S2(Se2)(Sex)]2- that exhibit efficient hydrogen evolution at low overpotential and stability over 1000 cycles. Density functional calculations provide evidence of a unimolecular mechanism in the HER process via the exploration of viable reaction pathways. The discussed findings are of a broad interest in the development of efficient molecular electrocatalytic materials.

Effective Storage of Electrons in Water by the Formation of Highly Reduced Polyoxometalate Clusters.

Aqueous solutions of polyoxometalates (POMs) have been shown to have potential as high-capacity energy storage materials due to their potential for multi-electron redox processes, yet the mechanism of reduction and practical limits are currently unknown. Herein, we explore the mechanism of multi-electron redox processes that allow the highly reduced POM clusters of the form {MO3}y to absorb y electrons in aqueous solution, focusing mechanistically on the Wells-Dawson structure X6[P2W18O62], which comprises 18 metal centers and can uptake up to 18 electrons reversibly (y = 18) per cluster in aqueous solution when the countercations are lithium. This unconventional redox activity is rationalized by density functional theory, molecular dynamics simulations, UV-vis, electron paramagnetic resonance spectroscopy, and small-angle X-ray scattering spectra. These data point to a new phenomenon showing that cluster protonation and aggregation allow the formation of highly electron-rich meta-stable systems in aqueous solution, which produce H2 when the solution is diluted. Finally, we show that this understanding is transferrable to other salts of [P5W30O110]15- and [P8W48O184]40- anions, which can be charged to 23 and 27 electrons per cluster, respectively.

Application of a 2D Molybdenum Telluride in SERS Detection of Biorelevant Molecules.

Two-dimensional (2D) transition-metal dichalcogenides have become promising candidates for surface-enhanced Raman spectroscopy (SERS), but currently very few examples of detection of relevant molecules are available. Herein, we show the detection of the lipophilic disease marker ß-sitosterol on few-layered MoTe2 films. The chemical vapor deposition (CVD)-grown films are capable of nanomolar detection, exceeding the performance of alternative noble-metal surfaces. We confirm that the enhancement occurs through the chemical enhancement (CE) mechanism via formation of a surface-analyte complex, which leads to an enhancement factor of ≈104, as confirmed by Fourier transform infrared (FTIR), UV-vis, and cyclic voltammetry (CV) analyses and density functional theory (DFT) calculations. Low values of signal deviation over a seven-layered MoTe2 film confirms the homogeneity and reproducibility of the results in comparison to noble-metal substrate analogues. Furthermore, ß-sitosterol detection within cell culture media, a minimal loss of signal over 50 days, and the opportunity for sensor regeneration suggest that MoTe2 can become a promising new SERS platform for biosensing.

Synthesis of Conductive Carbon Aerogels Decorated with ß-Tricalcium Phosphate Nanocrystallites.

There has been substantial interest in research aimed at conductive carbon-based supports since the discovery that the electrical stimulus can have dramatic effect on cell behavior. Among these carbon-aerogels decorated with biocompatible polymers were suggested as future materials for tissue engineering. However, high reaction temperatures required for the synthesis of the aerogels tend to impair the stability of the polymeric networks. Herein, we report a synthetic route towards carbon-aerogel scaffolds decorated with biocompatible ceramic nanoparticles of tricalcium phosphate. The composites can be prepared at temperature as high as 1100 °C without significant effect on the morphology of the composite which is comparable with the original aerogel framework. Although the conductivity of the composites tends to decrease with the increasing ceramic content the measured conductivity values are similar to those previously reported on polymer-functionalized carbon-aerogels. The cell culture study revealed that the developed constructs support cell proliferation and provide good cell attachment suggesting them as potentially good candidates for tissue-engineering applications.

Localization of Coated Iron Oxide (Fe3O4) Nanoparticles on Tomato Seeds and Their Effects on Growth.

Food demand due to the growing global population has been stretching the agriculture sector to the limit. This demands the cultivation of plants in shrinking land areas which makes the search for highly effective systems for plant nutrition and pest control important. In this context, the application of nanoparticles (NPs) in agriculture can have a transformative effect on food production techniques as it can enable the delivery of bioactive agents (including growth factors, pesticides, and fungicides) directly to plants. Herein, we report the application of unfunctionalized as well as amine-functionalized and polycaprolactone-coated Fe3O4 NPs to seed treatment in tomato (Solanum lycopersicum). The study reveals that the treatment has no side effects on plant germination and development. Furthermore, the translocation of NPs in seeds and seedlings posttreatment depends on the surface functionalization of the NPs. X-ray fluorescence spectroscopy analysis of seedlings suggested that around 66% of unfunctionalized Fe3O4 NPs were translocated in the cotyledons, while only 50% of functionalized NPs (both amine and polycaprolactone) were translocated. Our results demonstrate that all particles were taken up by the seeds, thus suggesting that the functionalized NPs can act as a versatile platform for delivering of active compounds, such as fungicides and growth factor agents.

Antimicrobial Properties of Gallium(III)- and Iron(III)-Loaded Polysaccharides Affecting the Growth of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, In Vitro.

Antimicrobial resistance (AMR) has become a global concern as many bacterial species have developed resistance to commonly prescribed antibiotics, making them ineffective to treatments. One type of antibiotics, gallium(III) compounds, stands out as possible candidates due to their unique "Trojan horse" mechanism to tackle bacterial growth, by substituting iron(III) in the metabolic cycles of bacteria. In this study, we tested three polysaccharides (carboxymethyl cellulose (CMC), alginate, and pectin) as the binding and delivery agent for gallium on three bacteria (Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus) with a potential bioresponsive delivery mode. Two types of analysis on bacterial growth (minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC)) were carried out while iron(III)-loaded polysaccharide samples were also tested for comparison. The results suggested that gallium showed an improved inhibitory activity on bacterial growth, in particular gallium(III)-loaded carboxymethyl cellulose (Ga-CMC) sample showing an inhibiting effect on growth for all three tested bacteria. At the MIC for all three bacteria, Ga-CMC showed no cytotoxicity effect on human dermal neonatal fibroblasts (HDNF). Therefore, these bioresponsive gallium(III) polysaccharide compounds show significant potential to be developed as the next-generation antibacterial agents with controlled release capability.

Author Correction: The rapid electrochemical activation of MoTe2 for the hydrogen evolution reaction.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The rapid electrochemical activation of MoTe2 for the hydrogen evolution reaction.

The electrochemical generation of hydrogen is a key enabling technology for the production of sustainable fuels. Transition metal chalcogenides show considerable promise as catalysts for this reaction, but to date there are very few reports of tellurides in this context, and none of these transition metal telluride catalysts are especially active. Here, we show that the catalytic performance of metallic 1T'-MoTe2 is improved dramatically when the electrode is held at cathodic bias. As a result, the overpotential required to maintain a current density of 10 mA cm-2 decreases from 320 mV to just 178 mV. We show that this rapid and reversible activation process has its origins in adsorption of H onto Te sites on the surface of 1T'-MoTe2. This activation process highlights the importance of subtle changes in the electronic structure of an electrode material and how these can influence the subsequent electrocatalytic activity that is displayed.

Tuning and mechanistic insights of metal chalcogenide molecular catalysts for the hydrogen-evolution reaction.

The production of hydrogen through water splitting using earth-abundant metal catalysts is a promising pathway for converting solar energy into chemical fuels. However, existing approaches for fine stoichiometric control, structural and catalytic modification of materials by appropriate choice of earth abundant elements are either limited or challenging. Here we explore the tuning of redox active immobilised molecular metal-chalcoxide electrocatalysts by controlling the chalcogen or metal stoichiometry and explore critical aspects of the hydrogen evolution reaction (HER). Linear sweep voltammetry (LSV) shows that stoichiometric and structural control leads to the evolution of hydrogen at low overpotential with no catalyst degradation over 1000 cycles. Density functional calculations reveal the effect of the electronic and structural features and confer plausibility to the existence of a unimolecular mechanism in the HER process based on the tested hypotheses. We anticipate these findings to be a starting point for further exploration of molecular catalytic systems.

Thermally Stable, High Performance Transfer Doping of Diamond using Transition Metal Oxides.

We report on optimisation of the environmental stability and high temperature operation of surface transfer doping in hydrogen-terminated diamond using MoO3 and V2O5 surface acceptor layers. In-situ annealing of the hydrogenated diamond surface at 400 °C was found to be crucial to enhance long-term doping stability. High temperature sheet resistance measurements up to 300 °C were performed to examine doping thermal stability. Exposure of MoO3 and V2O5 transfer-doped hydrogen-terminated diamond samples up to a temperature of 300 °C in ambient air showed significant and irreversible loss in surface conductivity. Thermal stability was found to improve dramatically however when similar thermal treatment was performed in vacuum or in ambient air when the oxide layers were encapsulated with a protective layer of hydrogen silsesquioxane (HSQ). Inspection of the films by X-ray diffraction revealed greater crystallisation of the MoO3 layers following thermal treatment in ambient air compared to the V2O5 films which appeared to remain amorphous. These results suggest that proper encapsulation and passivation of these oxide materials as surface acceptor layers on hydrogen-terminated diamond is essential to maximise their environmental and thermal stability.

Optimized unconventional superconductivity in a molecular Jahn-Teller metal.

Understanding the relationship between the superconducting, the neighboring insulating, and the normal metallic state above T c is a major challenge for all unconventional superconductors. The molecular A3C60 fulleride superconductors have a parent antiferromagnetic insulator in common with the atom-based cuprates, but here, the C60 (3-) electronic structure controls the geometry and spin state of the structural building unit via the on-molecule Jahn-Teller effect. We identify the Jahn-Teller metal as a fluctuating microscopically heterogeneous coexistence of both localized Jahn-Teller-active and itinerant electrons that connects the insulating and superconducting states of fullerides. The balance between these molecular and extended lattice features of the electrons at the Fermi level gives a dome-shaped variation of T c with interfulleride separation, demonstrating molecular electronic structure control of superconductivity.

Synthesis of face-centred cubic Cs3C60 in THF.

A solution chemistry synthetic route yields Cs(3)C(60) with a face-centred cubic structure. The described method uses well-established Schlenk techniques and THF as a solvent. The controlled addition of an organo-metallic salt reducing agent prevents the formation of C(60)(4-) salts. The final product can be precipitated from the solution using hexane as an anti-solvent.

Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary.

The alkali fullerides, A(3)C(60) (A = alkali metal) are molecular superconductors that undergo a transition to a magnetic Mott-insulating state at large lattice parameters. However, although the size and the symmetry of the superconducting gap, Δ, are both crucial for the understanding of the pairing mechanism, they are currently unknown for superconducting fullerides close to the correlation-driven magnetic insulator. Here we report a comprehensive nuclear magnetic resonance (NMR) study of face-centred-cubic (f.c.c.) Cs(3)C(60) polymorph, which can be tuned continuously through the bandwidth-controlled Mott insulator-metal/superconductor transition by pressure. When superconductivity emerges from the insulating state at large interfullerene separations upon compression, we observe an isotropic (s-wave) Δ with a large gap-to-superconducting transition temperature ratio, 2Δ0/k(B)T(c) = 5.3(2) [Δ0 = Δ(0 K)]. 2Δ0/k(B)T(c) decreases continuously upon pressurization until it approaches a value of ~3.5, characteristic of weak-coupling BCS theory of superconductivity despite the dome-shaped dependence of Tc on interfullerene separation. The results indicate the importance of the electronic correlations for the pairing interaction as the metal/superconductor-insulator boundary is approached.

Dynamic Jahn-Teller effect in the parent insulating state of the molecular superconductor Cs3C60.

The 'expanded fulleride' Cs(3)C(60) is an antiferromagnetic insulator in its normal state and becomes a molecular superconductor with T(c) as high as 38 K under pressure. There is mounting evidence that superconductivity is not of the conventional BCS type and electron-electron interactions are essential for its explanation. Here we present evidence for the dynamic Jahn-Teller effect as the source of the dramatic change in electronic structure occurring during the transition from the metallic to the localized state. We apply infrared spectroscopy, which can detect subtle changes in the shape of the C(60)3- ion due to the Jahn-Teller distortion. The temperature dependence of the spectra in the insulating phase can be explained by the gradual transformation from two temperature-dependent solid-state conformers to a single one, typical and unique for Jahn-Teller systems. These results unequivocally establish the relevance of the dynamic Jahn-Teller effect to overcoming Hund's rule and forming a low-spin state, leading to a magnetic Mott-Jahn-Teller insulator.

Polymorphism control of superconductivity and magnetism in Cs(3)C(60) close to the Mott transition.

The crystal structure of a solid controls the interactions between the electronically active units and thus its electronic properties. In the high-temperature superconducting copper oxides, only one spatial arrangement of the electronically active Cu(2+) units-a two-dimensional square lattice-is available to study the competition between the cooperative electronic states of magnetic order and superconductivity. Crystals of the spherical molecular C(60)(3-) anion support both superconductivity and magnetism but can consist of fundamentally distinct three-dimensional arrangements of the anions. Superconductivity in the A(3)C(60) (A = alkali metal) fullerides has been exclusively associated with face-centred cubic (f.c.c.) packing of C(60)(3-) (refs 2, 3), but recently the most expanded (and thus having the highest superconducting transition temperature, T(c); ref. 4) composition Cs(3)C(60) has been isolated as a body-centred cubic (b.c.c.) packing, which supports both superconductivity and magnetic order. Here we isolate the f.c.c. polymorph of Cs(3)C(60) to show how the spatial arrangement of the electronically active units controls the competing superconducting and magnetic electronic ground states. Unlike all the other f.c.c. A(3)C(60) fullerides, f.c.c. Cs(3)C(60) is not a superconductor but a magnetic insulator at ambient pressure, and becomes superconducting under pressure. The magnetic ordering occurs at an order of magnitude lower temperature in the geometrically frustrated f.c.c. polymorph (Néel temperature T(N) = 2.2 K) than in the b.c.c.-based packing (T(N) = 46 K). The different lattice packings of C(60)(3-) change T(c) from 38 K in b.c.c. Cs(3)C(60) to 35 K in f.c.c. Cs(3)C(60) (the highest found in the f.c.c. A(3)C(60) family). The existence of two superconducting packings of the same electronically active unit reveals that T(c) scales universally in a structure-independent dome-like relationship with proximity to the Mott metal-insulator transition, which is governed by the role of electron correlations characteristic of high-temperature superconducting materials other than fullerides.

Structural phase transitions and superconductivity in Fe(1+delta)Se0.57Te0.43 at ambient and elevated pressures.

The ternary iron chalcogenide, Fe(1.03)Se(0.57)Te(0.43) is a member of the recently discovered family of Fe-based superconductors with an ambient pressure T(c) of 13.9 K and a simple structure comprising layers of edge-sharing distorted Fe(Se/Te)(4) tetrahedra separated by a van der Waals gap. Here we study the relationship between its structural and electronic responses to the application of pressure. T(c) depends sensitively on applied pressure attaining a broad maximum of 23.3 K at approximately 3 GPa. Further compression to 12 GPa leads to a metallic but nonsuperconducting ground state. High-resolution synchrotron X-ray diffraction shows that the superconducting phase is metrically orthorhombic at ambient pressure but pressurization to approximately 3 GPa leads to a structural transformation to a more distorted structure with monoclinic symmetry. The exact coincidence of the crystal symmetry crossover pressure with that at which T(c) is maximum reveals an intimate link between crystal and electronic structures of the iron chalcogenide superconductors.

The disorder-free non-BCS superconductor Cs3C60 emerges from an antiferromagnetic insulator parent state.

The body-centered cubic A15-structured cesium fulleride Cs3C60 is not superconducting at ambient pressure and is free from disorder, unlike the well-studied face-centered cubic A3C60 alkali metal fulleride superconductors. We found that in Cs3C60, where the molecular valences are precisely assigned, the superconducting state at 38 kelvin emerges directly from a localized electron antiferromagnetic insulating state with the application of pressure. This transition maintains the threefold degeneracy of the active orbitals in both competing electronic states; it is thus a purely electronic transition to a superconducting state, with a dependence of the transition temperature on pressure-induced changes of anion packing density that is not explicable by Bardeen-Cooper-Schrieffer (BCS) theory.