Platinum (Pt) is recognized as the most active material for the hydrogen evolution reaction in acidic media; however, its catalytic activity is often underestimated in proton exchange membrane water electrolysis (PEMWE) due to poor utilization of the cathode catalyst layer. In this study, we present the synthesis, characterization, and application of Pt nanoparticles with atomic precision on a microporous-layer-coated gas diffusion layer for PEMWE. The Pt nanoparticles were synthesized via atomic layer deposition, a technique that enables precise control over loading and particle size at the atomic scale. The resulting gas diffusion electrode with an exceptionally low platinum loading (1.08–5.40 μg cm^-2) demonstrated mass activity at least one order of magnitude higher than that of benchmark Pt. Furthermore, the electrode exhibited exceptional stability at a current density of 1 A cm^-2 over 200 hours. It also showed robust performance under dynamic operation, enduring 25,000 cycles of alternating cell voltages between 1.45 V and 2 V.

The growing need for advanced materials with tunable properties has triggered an increasing interest in innovative surface modification techniques. Fluidized-bed atomic layer deposition (FB-ALD) offers a powerful solution for surface engineering and functionalization of powder-based materials for a variety of applications. By relying on its capability for controlling uniformity and conformality of the coatings precisely at the atomic scale, ALD can effectively modify surface characteristics to improve the functionality and durability of the materials. In this review, we will provide comprehensive fundamentals and strategies to improve the fluidization of nanopowders and reveal the potential of FR-ALD in two emerging applications. The first application is in energy devices, where FB-ALD is employed to develop Pt-based electrocatalysts for fuel cells and other catalytic reactions. We demonstrate that FB-ALD enables precise control of size, composition, and dispersion of Pt nanoparticles over the support surface, resulting in a strong enhancement in catalytic performance. We additionally discuss the application of FB-ALD in boosting the stability and durability of catalysts by surface engineering with ultrathin films and ultrasmall nanoparticles without compromising their activity. These capabilities open new avenues for the development of high-performance and durable catalysts for energy applications. The second application is in pharmaceutical research, where FB-ALD is employed to coat active pharmaceutical ingredients with thin films of biocompatible materials, such as Al₂O₃, ZnO, SiO₂, and TiO₂, to control their release profiles and improve their physical properties, such as wettability, dispersibility, flowability, and solubility, which are essential for enhancing therapeutic efficacy and patient compliance. The versatility and precision of FB-ALD position it as a key technology for the development of next-generation materials, addressing the critical challenges of performance, stability, and functionality of powder-based materials for different fields.

Inhaled drug delivery is a promising strategy for the rapid treatment of respiratory diseases due to its direct targeting of the pulmonary system. Nevertheless, challenges remain in optimizing deposition efficiency, particularly in reaching deeper lung generations and achieving directional control of particle transport. To achieve effective deep-lung aerosol delivery, the present proof-of-concept study proposes computational optimization of particle release strategies. Both non-invasive and invasive approaches are explored, with particular emphasis on release concentration and spatial positioning. Numerical simulations are conducted using a previously validated subject-specific mouth-to-lung model reconstructed from high-resolution Computed Tomography (CT) scans, ensuring anatomical realism and geometrical reproducibility. The results show that concentrated non-invasive release at the mouth plane improves particle penetration through the constricted laryngeal region. Meanwhile, invasive strategies involving focused delivery (such as catheter-based injection) lead to enhanced deposition in the deeper lung regions. Notably, directional control of deposition was preliminarily achieved, with particles preferentially targeting either the left or right lung lobe based on the injection position, offering new potential for site-specific therapy. It is concluded that the presented computational framework can provide detailed insights for optimizing particle transport and deposition in specific lung regions. These detailed insights could provide valuable information for developing novel clinical treatments for respiratory diseases.

The long-term operation of CO₂ electrolyzers using membrane electrode assemblies (MEAs) is limited by challenges related to water management. However, the water balance in CO₂ electrolyzer cells still has not been fully understood, and conflicting observations have been reported in the literature. In this study, a one-dimensional non-isothermal multiphysics model of an exchange MEA CO₂ electrolyzer with a Tokuyama A201 anion exchange membrane is developed to investigate the role of different physical and chemical phenomena on the water balance. The relative contributions of these processes vary with current density and membrane transport properties, which shift the dominant water transport mechanism in the cell. Our results highlight the significant contribution of homogeneous reactions, particularly OH⁻, to the water balance across the membrane. At low currents (i < 130 mA cm⁻²), homogeneous buffer reactions dominate the water balance and result in net water production near the catalyst layer. At higher currents (i > 130 mA cm⁻²), the flux is governed by electro-osmotic drag and a temperature gradient over the cathode gas diffusion electrode (GDE) with their relative contributions depending on membrane properties. Homogeneous buffering can re-emerge as the dominant mechanism at high currents if the hydroxide ion concentration in the membrane increases, for example under CO₂-limited cathode conditions, allowing hydroxide ions to react with depleted bicarbonate near the anode.

Noble metal nanoparticles (NPs), particularly platinum (Pt), are widely used in heterogeneous catalysis due to their exceptional activity. However, controlling their size and preventing sintering during synthesis remains a major challenge, especially when aiming for high dispersion and stability on supports such as graphene. Atomic layer deposition (ALD) has emerged as a promising method to address these issues, yet conventional processes often lead to broad particle size distributions (PSDs). This work introduces a new approach for the deposition of size-controlled and sintering-resistant Pt NPs on graphene by atmospheric-pressure ALD using MeCpPtMe₃and O₂. In this approach, the deposition temperature varies in a cyclic manner in accordance with the Pt precursor and the O₂exposure steps. In every ALD cycle, the MeCpPtMe₃exposure is carried out at either 150 or 200 °C, and the O₂exposure is at room temperature. The room-temperature step hinders the diffusion and coalescence of Pt NPs, resulting in significantly narrower PSDs compared to those achieved by the conventional ALD processes at 150 and 200 °C. Importantly, Pt NPs with narrower PSDs exhibit higher catalytic activity and improved stability, which are demonstrated for the propene oxidation reaction, despite having a significantly lower Pt loading. Our approach may open a new avenue toward the size-selection synthesis of noble metal NPs for catalytic applications.

Evaluation of the hydrodynamics of opaque multi-phase flows remains a challenging task, with implications for various industrial processes such as chemical processing, pharmaceutical, and mineral processing. Understanding how design and operational variables affect the complex behavior of multi-phase flow systems is essential for optimizing processing conditions and improving efficiency. Radioactive particle tracking (RPT) has been a proven measurement technique to evaluate hydrodynamics in multi-phase flow systems. However, a limitation of the classical RPT technique exists in the assumptions made in the simulation of the count rate received by the detectors in correcting for varying flow-induced fluctuations in the volume fraction of the dispersed phase, often encountered in industrial multi-phase flow systems. In this paper, we introduce a fundamentally novel experimental RPT method that directly uses detected incident photon hit locations for the reconstruction of the three-dimensional radioactive tracer particle position. We argue that this approach is inherently more robust as varying attenuation does not affect the reconstruction. The RPT setup consists of three identical γ-radiation slit collimator detectors that are placed equidistantly at 120° intervals. A subsequent calibration-experimentation procedure is established that allows reconstruction of the tracer particle position with spatial accuracy and precision in the order of 1 mm. We demonstrate the applications of this technique in evaluating hydrodynamics in multi-phase systems by characterizing the flow field of industrial-grade polypropylene reactor powder in a laboratory-scale horizontal stirred bed reactor.

Conventional fluidization of cohesive powders is challenging due to their strong interparticle forces, often requiring assistance methods. In this study, the hydrodynamics of pulsed and vibrated beds of cohesive Geldart C silica powder (Sauter mean diameter d₃₂=7.9μm) in a 19.2cm diameter column were investigated using X-ray imaging. The results show that low-frequency, moderate-amplitude gas pulsation improves fluidization by disrupting long, persistent gas channels. Higher-frequency pulsation is dampened throughout the bed, resulting in negligible improvement over unassisted systems. When coupled with mechanical vibration, gas pulsation slightly mitigates solid compaction at the bottom section, but the overall flow pattern remains largely unchanged compared to vibration alone. The findings highlight the potential of integrating gas pulsation with other assistance methods to enhance fluidization in practical applications.

Atomic layer deposition (ALD) of platinum (Pt) has gained significant interest in the recent years due to its capability of depositing various Pt nanostructures for applications in different fields, such as Pt nanoparticles (NPs) for catalytic reactions and energy devices and Pt thin films for microelectronic technology. Among various developed processes, Pt ALD using MeCpPtMe₃as the precursor has been most popularly employed owing to the high reactivity, volatility, and thermal stability of the precursor, which enable controlled deposition of Pt nanostructures in a broad range of temperatures. Typical MeCpPtMe₃-based Pt ALD processes use O₂and H₂as the coreactants. In this study, we explore atomic hydrogen as an alternative and reveal its exceptional reactivity that outperforms H₂and O₂. Specifically, atomic hydrogen enables the deposition of highly dispersed Pt NPs with narrow particle size distributions (i.e., standard deviation <0.3 nm) on various oxide surfaces, including TiO₂, SiO₂, CeO₂and V₂O₅, which is unattainable with H₂under identical experimental conditions. In addition, it facilitates the deposition of Pt NPs with improved size uniformity and accelerates the closure of Pt films compared to ALD processes using O₂as the coreactant. The results demonstrate a significant potential of atomic hydrogen as a highly effective coreactant for ALD of Pt NPs and thin films.

Nanoparticles are usually fluidized as agglomerates, which are in dynamic states of agglomeration and fragmentation. It is critical to consider the size distribution of agglomerates in modeling of the fluidization of nanoparticle agglomerates. In this article, the fluidization behavior of nanoparticle agglomerates is investigated using a two-fluid model─population balance model. The model includes the agglomeration and breakage kernel functions based on the continuum theory of cohesive particles developed by Kellogg et al. (J. Fluid Mech. 2017;832:345-382). The ratio of the critical breakage velocity to the critical agglomeration velocity is defined to represent the cohesion of nanoparticles. The predictions of bed pressure drop, bed expansion ratio, and bed collapse curves agree well with those of experiments. By changing the critical agglomeration velocity and the ratio between the critical velocities, the transition from almost defluidization to uniform fluidization is predicted. Finally, the model’s ability to simulate the fluidization of fine particles with a few micrometers is also shown. This study provides a practical tool for simulating the fluidization of nanoparticle agglomerates.

Horizontal stirred bed reactors are widely used in the commercial manufacturing of polypropylene. However, a comprehensive understanding of the particle dynamics in horizontal stirred bed reactors remains elusive, primarily due to the lack of detailed experimental data. In this work, we studied the influence of operating parameters on the particle flow dynamics in a laboratory-scale horizontal stirred bed reactor using single-photon emission radioactive particle tracking. The results show that the general solids flow behavior is strongly affected by both the agitator rotation speed and reactor fill level. Operation at low rotation speed and low fill level results in solids flow with poor radial and circumferential distribution due to internal bed circulation. On the contrary, at increased rotation speeds and fill levels, solids motion throughout the bed is continuous resulting in excellent solids distribution. The solids circulation was found to increase for both an increase in rotation speed and reactor fill level. The axial dispersion coefficient, on the other hand, shows a linear relation with the rotation speed, but no conclusive relation between the axial dispersion coefficient and the reactor fill level was found.