Immediate Formation/Precipitation of Icosahedrally Structured Iron–Molybdenum Mixed Oxides from Solutions Upon Mixing Simple Iron(III) and Molybdate Salts

Unravelling the Bi-Functional Electrocatalytic Properties of {Mo72Fe30} Polyoxometalate Nanostructures for Overall Water Splitting Using Scanning Electrochemical Microscope and Electrochemical Gating Methods

This study reports the use of Keplerate-type {Mo72Fe30} polyoxometalate (POMs) nanostructures as a bi-functional-electrocatalyst for HER and OER in an alkaline medium with a lower overpotential (135 mV for HER and 264 mV for OER), and excellent electrochemical stability. The bi-functional catalytic properties of {Mo72Fe30} POM are studied using a scanning electrochemical microscope (SECM) via current mapping using substrate generation and tip collection mode. Furthermore, the bipolar nature of the {Mo72Fe30} POM nano-electrocatalysts is studied using the electrochemical gating via simultaneous monitoring of the electrochemical (cell) and electrical ({Mo72Fe30} POM) signals. Next, a prototype water electrolyzer fabricated using {Mo72Fe30} POM electrocatalysts showed they can drive 10 mA cm-2 with a low cell voltage of 1.62 V in lab-scale test conditions. Notably, the {Mo72Fe30} POM electrolyzers' performance assessment based on recommended conditions for industrial aspects shows that they require a very low overpotential of 1.89 V to drive 500 mA cm-2, highlighting their promising candidature toward clean-hydrogen production.

Tetrahedral Keggin Core Tunes the Visible Light-Assisted Catalase-Like Activity of Icosahedral Keplerate Shell

In this work, the effect of Keggin polyoxometalates encapsulated in Keplerate {Mo₇₂Fe₃₀} shell (K shell) on the visible light-assisted catalase-like activity (H₂O₂ dismutation) of the resulting core-shell clusters PMo₁₂@K, SiMo₁₂@K, and BW₁₂@K was investigated. Superior photodismutation activity of PMo₁₂@K compared to that of K shell and two other core-shell clusters was discovered. The homogeneity of PMo₁₂@K and its improved oxidative stability, increased redox potential, and reduced band gap caused by a synergistic effect between the Keplerate shell and Keggin core seem reasonable to explain such a superiority. The light-dependent photocatalytic performance of PMo₁₂@K evaluated by action spectra revealed a maximum apparent quantum efficiency (AQY) at 400 nm, demonstrating the visible light-driven photocatalytic reaction. A first-order rate constant of 2 × 10^-4 s^-1 and activation energy of 108.8 kJ mol^-1 alongside a turnover frequency of 0.036 s^-1 and a total turnover number of up to ∼3800 approved the effective photocatalytic activity and improved the oxidative stability of PMo₁₂@K. A nonradical photocatalytic mechanism through a Fe-OOH intermediate was proposed. Thus, the structure, optical activity, and oxidative stability of a host Keplerate-type nanocluster can be tuned significantly by encapsulation of a guest, like "cluster-in-cluster" structures, which opens the scope for introducing new visible light-sensitive hierarchical nanostructures.

Molybdenum Blue Preassembly Strategy to Design Bimetallic Fe0.54Mo0.73/Mo2C@C for Tunable and Low-Frequency Electromagnetic Wave Absorption

Advanced electromagnetic wave absorption nanomaterials can play an important role in addressing the issue of increasing electromagnetic pollution in wireless communication field. Herein, a series of coralloid bimetallic Fe0.54Mo0.73/Mo2C@C (FMC)...

Nanoblackberries of {W72Fe33} and {Mo72Fe30}: Electrocatalytic Water Reduction

The reversible self-assembly of a {Mo₇₂Fe₃₀} cluster into nanoblackberries in a dilute solution of the relevant crystalline compound [Mo₇₂Fe₃₀O₂₅₂(CH₃COO)₁₂{Mo₂O₇(H₂O)}₂{H₂Mo₂O₈(H₂O)}(H₂O)₉₁]·150H₂O ({Mo₇₂Fe₃₀}_cryst) was demonstrated by Liu, Müller, and their co-workers as a landmark discovery in the area of polyoxometalate chemistry. We have described, in the present work, how these ∼2.5 nm nano-objects, {M₇₂Fe₃₀} (M = W, Mo) can be self-assembled into nanoblackberries irreversibly, leading to their solid-state isolation as the nanomaterials Fe₃[W₇₂Fe₃₀O₂₅₂(CH₃COO)₂(OH)₂₅(H₂O)₁₀₃]·180H₂O ({W₇₂Fe₃₃}_NM) and Na₂[Mo₇₂Fe₃₀O₂₅₂(CH₃COO)₄(OH)₁₆(H₂O)₁₀₈]·180H₂O ({Mo₇₂Fe₃₀}_NM), respectively (NM stands for nanomaterial). The formulations of these one-pot-synthesized nanoblackberries of {W₇₂Fe₃₃}_NM and {Mo₇₂Fe₃₀}_NM have been established by spectral analysis including Raman spectroscopy, elemental analysis including ICP metal analysis, volumetric analysis (for iron), microscopy techniques, and DLS studies. The thermal stability of the tungsten nanoblackberries {W₇₂Fe₃₃}_NM is much higher than that of its molybdenum analogue {Mo₇₂Fe₃₀}_NM. This might due to the extra three ferric (Fe³⁺) ions per {W₇₂Fe₃₀} cluster in {W₇₂Fe₃₃}_NM, which are not part of the {W₇₂Fe₃₀} cluster cage but are placed between two adjacent clusters (i.e., each cluster has six surrounding 0.5Fe³⁺) to form this self-assembly. The isolated blackberries behave like an inorganic acid, a water suspension of which shows pH values of 3.9 for {W₇₂Fe₃₃}_NM and 3.7 for {Mo₇₂Fe₃₀}_NM because of the deprotonation of the hydroxyl groups in them. We have demonstrated, for the first time, a meaningful application of these inexpensive and easily synthesized nanoblackberries by showing that they can act as electrocatalysts for the hydrogen evolution reaction (HER) by reducing water. We have performed detailed kinetic studies for the electrocatalytic water reduction catalyzed by {W₇₂Fe₃₃}_NM and {Mo₇₂Fe₃₀}_NM in a comparative study. The relevant turnover frequencies (TOFs) of {W₇₂Fe₃₃}_NM and {Mo₇₂Fe₃₀}_NM (∼0.72 and ∼0.45 s^-1, respectively), the overpotential values of {W₇₂Fe₃₃}_NM and {Mo₇₂Fe₃₀}_NM (527 and 767 mV, respectively at 1 mA cm^-2), and the relative stability issues of the catalysts indicate that {W₇₂Fe₃₃}_NM is reasonably superior to {Mo₇₂Fe₃₀}_NM. We have described a rationale of why {W₇₂Fe₃₃}_NM performs better than {Mo₇₂Fe₃₀}_NM in terms of catalytic activity and stability.

Synthesis of High Dimensionally Structured Mo-Fe Mixed Metal Oxide and Its Catalytic Activity for Selective Oxidation of Methanol

High-dimensionally structured Mo-Fe oxide (HDS-MoFeO) was synthesized through an assembly of structural units supplied from Keplerate-type polyoxometalate, {Mo₇₂Fe₃₀}, under an appropriate hydrothermal condition. HDS-MoFeO showed excellent catalytic activity for the selective oxidation of methanol with slightly lower selectivity for formaldehyde than that of a conventional Mo-Fe oxide catalyst.

Giant iron polyoxometalate that works as a catalyst for water oxidation

A polyoxometalate (POM) cluster [Mo₇₂Fe₃₀O₂₅₂(CH₃COO)₁₂{Mo₂O₇(H₂O)}₂ {H₂Mo₂O₈(H₂O)} (H₂O)₉₁]. ca. 150 H₂O (catalyst I) has been explored as a light-driven water oxidation catalyst. The catalyst is stable and could be reused/recycled several times.

A nanoscopic icosahedral {Mo72Fe30} cluster catalyzes the aerobic synthesis of benzimidazoles

In this study, the catalytic efficiency of amorphous {Mo₇₂Fe₃₀} nanocapsules as a safe Keplerate polyoxometalate in organic synthesis was exploited. The easy-made solid catalyst exhibited high efficiency using a very low dosage (0.02–0.05 mol%) in the catalyzed condensation of various aromatic 1,2-diamines and aldehydes for the aerobic synthesis of benzimidazoles with very small E-factor values (0.11–0.33). The superior catalytic activity of amorphous nanoclusters compared to that of its crystalline counterpart was demonstrated. The high activity and recyclability of heterogeneous catalysts in a green reaction media under oxygen atmosphere, make this environmentally benign organic process appropriate for our applied goals.

Catalytic activity of amorphous {Mo₇₂Fe₃₀} nanoclusters as a safe Keplerate polyoxometalate in aerobic synthesis of benzimidazoles was described.

Visible-light driven catalase-like activity of blackberry-shaped {Mo72Fe30} nanovesicles: combined kinetic and mechanistic studies

Catalase-like activity of blackberry-shaped {Mo₇₂Fe₃₀} nanovesicles was exploited in aqueous solution under visible-light irradiation.

Isolation of Blackberry-Shaped Nanoparticles of a Giant {Mo72Fe30} Cluster and Their Transformation to a Crystalline Nanoferric Molybdate

When an aqueous solution of sodium molybdate is added to an aqueous solution of ferric chloride, acidified with acetic acid, a giant {Mo₇₂Fe₃₀} cluster is instantaneously formed as the amorphous substance Na₂[Mo₇₂Fe₃₀O₂₅₂(CH₃COO)₄(OH)₁₆(H₂O)₁₀₈]·180 H₂O (1). Compound 1 consists of aggregated nanovesicles of {Mo₇₂Fe₃₀} clusters, as confirmed by field-emission scanning electron microscopy and transmission electron microscopy images of 1. An aqueous suspension of 1 upon moderate heating results in the formation of crystalline nanoferric molybdate, which gives insight into understanding the formation of a yellow coating mineral, ferrimolybdite, frequently found on the ores of molybdenum.