Fe─N─C Electrocatalyst for Enhancing Fe(II)/Fe(III) Redox Kinetics in Thermo-Electrochemical Cells

Harvesting low-grade waste heat, which constitutes 60% of the overall waste heat, is key to halting climate change. Electrochemical waste-heat harvesting has recently drawn attention to practical low-grade waste-heat harvesting. In this study, a power density maximization strategy is presented in scalable and cost-effective aqueous redox couple-based thermo-electrochemical cells (TECs). The n-type feature of the water-soluble Fe^2+/3+ redox couple is essential for constructing the TEC p–n leg device; however, it has not been investigated much so far. The modulation of the chaotropicity of counteranions enhances the absolute value of the Seebeck coefficient for the Fe^2+/3+ redox couple with an inner-sphere reaction mechanism because of the greater structural disorder in the solvation shell. Moreover, the use of a cost-effective Fe─N─C electrocatalyst shows redox kinetics and a power density comparable to those of state-of-the-art Pt electrodes, economically compensating for the sluggish charge-transfer kinetics of the inner-sphere redox mechanism. The Fe─N─C -based TEC device exhibits 1.73 W m⁻² of power density at 0.1 $ W⁻¹ of cost per power, which is 1.24% with respect to the Carnot efficiency, exceeding 0.23–0.53% compared to those reported for previous Pt-based TEC devices with the same redox chemistry.     

Enhanced Hydrogen Production by Photoreforming of Renewable Oxygenates Through Nanostructured Fe2O3 Polymorphs

Sunlight‐driven hydrogen production via photoreforming of aqueous solutions containing renewable compounds is an attractive option for sustainable energy generation with reduced carbon footprint. Nevertheless, the absence of photocatalysts combining high efficiency and stability upon solar light activation has up to date strongly hindered the development of this technology. Herein, two scarcely investigated iron(III) oxide polymorphs, β‐ and ε‐Fe₂O₃, possessing a remarkable activity in sunlight‐activated H₂ generation from aqueous solutions of renewable oxygenates (i.e., ethanol, glycerol, glucose) are reported. For β‐Fe₂O₃ and ε‐Fe₂O₃, H₂ production rates up to 225 and 125 mmol h^?1 m^?2 are obtained, with significantly superior performances with respect to the commonly investigated α‐Fe₂O₃.     

Hydrogen Selective NH2‐MIL‐53(Al) MOF Membranes with High Permeability

Hydrogen‐based energy is a promising renewable and clean resource. Thus, hydrogen selective microporous membranes with high performance and high stability are demanded. Novel NH₂‐MIL‐53(Al) membranes are evaluated for hydrogen separation for this goal. Continuous NH₂‐MIL‐53(Al) membranes have been prepared successfully on macroporous glass frit discs assisted with colloidal seeds. The gas sorption ability of NH₂‐MIL‐53(Al) materials is studied by gas adsorption measurement. The isosteric heats of adsorption in a sequence of CO₂ > N₂ > CH₄ ≈ H₂ indicates different interactions between NH₂‐MIL‐53(Al) framework and these gases. As‐prepared membranes are measured by single and binary gas permeation at different temperatures. The results of singe gas permeation show a decreasing permeance in an order of H₂ > CH₄ > N₂ > CO₂, suggesting that the diffusion and adsorption properties make significant contributions in the gas permeation through the membrane. In binary gas permeation, the NH₂‐MIL‐53(Al) membrane shows high selectivity for H₂ with separation factors of 20.7, 23.9 and 30.9 at room temperature (288 K) for H₂ over CH₄, N₂ and CO₂, respectively. In comparison to single gas permeation, a slightly higher separation factor is obtained due to the competitive adsorption effect between the gases in the porous MOF membrane. Additionally, the NH₂‐MIL‐53(Al) membrane exhibits very high permeance for H₂ in the mixtures separation (above 1.5 × 10^?6 mol m^?2 s^?1 Pa^?1) due to its large cavity, resulting in a very high separation power. The details of the temperature effect on the permeances of H₂ over other gases are investigated from 288 to 353 K. The supported NH₂‐MIL‐53(Al) membranes with high hydrogen separation power possess high stability, resistance to cracking, temperature cycling and show high reproducibility, necessary for the potential application to hydrogen recycling.     

Biodegradable Fe(III)@WS2‐PVP Nanocapsules for Redox Reaction and TME‐Enhanced Nanocatalytic,Photothermal, and Chemotherapy

In this study, biocompatible Fe(III) species‐WS₂‐polyvinylpyrrolidone (Fe(III) @ WS₂‐PVP) nanocapsules with enhanced biodegradability and doxorubicin (DOX) loading capacity are one‐pot synthesized. In this nanocapsule, there exists a redox reaction between Fe(III) species and WS₂ to form Fe²⁺ and WO₄^2?. The formed Fe²⁺ could be oxidized to Fe³⁺, which reacts with Fe(III) @ WS₂‐PVP again to continuously produce Fe²⁺ and WO₄^2?. Such a repeated endogenous redox reaction leads to an enhanced biodegradation and DOX release of DOX @ Fe(III) @ WS₂‐PVP. More strikingly, the Fe²⁺ generation and DOX release are further accelerated by the overexpressed H₂O₂ and the mild acidic tumor microenvironment (TME), since H₂O₂ and H⁺ can accelerate the oxidation of Fe²⁺. The continuously generated Fe²⁺ catalyzes a fast Fenton reaction with the innate H₂O₂ in tumor cells and produces abundant highly toxic hydroxyl radicals for nanocatalytic tumor therapy. Together with the high photothermal transforming capability, the DOX @ Fe(III) @WS₂‐PVP nanocapsules successfully achieve the endogenous redox reaction and exogenous TME‐augmented tumor photothermal therapy, chemo and nanocatalytic therapy outcome. The concept of material design can be innovatively extended to the synthesis of biodegradable Fe(III) @ MoS₂‐PVP nanocomposite, thus paving a promising novel way for the rational design of intelligent theranostic agents for highly efficient treatment of cancer.     

Fe2+-Induced In Situ Intercalation and Cation Exsolution of Co80Fe20(OH)(OCH3) with Rich Vacancies for Boosting Oxygen Evolution Reaction

The efficiency of water splitting is largely hindered by the sluggish kinetics of the oxygen evolution reaction. Cobalt-based (oxy)hydroxides are promising electrocatalysts, but their performance is still under the expected goal due to the restricted active sites and intrinsic activity. Herein, Co₈₀Fe₂₀(OH)(OCH₃) (CoFeMe) is synthesized with intercalation and rich vacancies by a cation exsolution process in a one-step solve-thermal reaction. With the help of the Fe incorporation, the specific surface area of CoFeMe increases to 101.6 m² g⁻¹, which is six times that of Co(OH)(OCH₃) (CoMe) (16.5 m² g⁻¹). Also, the induced rich vacancies are traced in the X-ray absorption spectra of CoFeMe. Because of the synergistic effect between the intercalation, Fe incorporation and vacancies, the overpotential of CoFeMe is only 240 mV to drive the current density to 10 mA cm⁻², which is reduced 110 mV compared with that of pristine CoMe (350 mV).     

Mg-Doped Na4Fe3(PO4)2(P2O7)/C Composite with Enhanced Intercalation Pseudocapacitance for Ultra-Stable and High-Rate Sodium-Ion Storage

Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP) is considered as a promising cathode material for sodium-ion batteries (SIBs) due to its low cost, non-toxicity, and high structural stability, but its electrochemical performance is limited by the poor electronic conductivity. In this study, Mg-doped NFPP/C composites are presented as cathode materials for SIBs. Benefiting from the enhanced electrochemical kinetics and intercalation pseudocapacitance resulted from the Mg doping, the optimal Mg-doped NFPP/C composite (NFPP-Mg5%) delivers high rate performance (capacity of ≈40 mAh g⁻¹ at 20 A g⁻¹) and ultra-long cycling life (14 000 cycles at 5 A g⁻¹ with capacity retention of 80.8%). Moreover, the in situ X-ray diffraction and other characterizations reveal that the sodium storage process of NFPP-Mg5% is dominated by the intercalation pseudocapacitive mechanism. In addition, the full SIB based on NFPP-Mg5% cathode and hard carbon anode exhibits the discharge capacity of ≈50 mAh g⁻¹ after 200 cycles at 500 mA g⁻¹. This study demonstrates the feasibility of improving the electrochemical performance of NFPP by doping strategy and presents a low-cost, ultra-stable, and high-rate cathode material for SIBs.     

Supercritical‐Fluid‐Assisted One‐Pot Synthesis of Biocompatible Core(γ‐Fe2O3)/Shell(SiO2) Nanoparticles as High Relaxivity T2‐Contrast Agents for Magnetic Resonance Imaging

Monodisperse iron oxide/microporous silica core/shell composite nanoparticles, core(γ‐Fe₂O₃)/shell(SiO₂), with a diameter of approximately 100 nm and a high magnetization are synthesized by combining sol–gel chemistry and supercritical fluid technology. This one‐step processing method, which is easily scalable, allows quick fabrication of materials with controlled properties and in high yield. The particles have a specific magnetic moment (per kg of iron) comparable to that of the bulk maghemite and show superparamagnetic behavior at room temperature. The nanocomposites are proven to be useful as T₂ MRI imaging agent. They also have potential to be used in NMR proximity sensing, theranostic drug delivery, and bioseparation.