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This research introduces dynamic modeling and real-time control of fractal structure in particulate materials fabricated by the ball milling process, specifically addressing challenges of unavailable real-time non-destructive and non-invasive imaging measurements in the enclosed rotating vials. A description of the internal temperature dynamics in the container is established along with a thermal regulator based on external temperature feedback. The fractal dimension is introduced as a structural measure, and its dynamics is established via an analytical formulation through a lumped model, along with a full thermostructural computational model of the ball milling particulate microstructure. These models are used as real-time observers of inaccessible internal states during the process. In addition, they are used as model references in an adaptive control system, regulating the fractal structure with adaptation via external temperature measurements, available experimentally via an infrared thermocouple. The controller is designed on the basis of the dynamic models and is tested experimentally. The controller is demonstrated to command the duration of the process at steady conditions to obtain the necessary thermal exposure yielding the desired microstructure for the ball-milled particulates. Keywords: Ball milling, Adaptive control, Aluminum alloys, Fractal dimension

The current paper presents a combined ab initio and experimental study of H2 adsorption on carbon. Adsorption energetics of a H2 molecule on pristine graphene were obtained for various molecule orientations, showing that the perpendicular-to-surface orientation is energetically more preferable (Eads = −0.076eV/H2) than the parallel orientations (Eads ≈−0.071eV/H2). Subsequently, B, Co, Ni, Pd, Pt and Ru substituents of a C atom in graphene were considered, leading to the conclusion that Pt and Ru promote the H2 adsorption by ≈−0.012eV/H2. Pt promotes adsorption in all its neighbouring hexagons, while Ru impact is localised to the position directly above the dopant. Pure, Pt and Ru-doped ordered mesoporous carbon samples were evaluated experimentally for their H2 adsorption performance under a low-pressure regime (up to 1 bar) at cryogenic and room temperatures (i.e., 77 and 298 K, respectively). These experimental measurements indicated that, while the specific area of the metal-decorated carbons is lower than that of the pristine carbon material, the presence of Pt and Ru nanoparticles leads to a slight improvement of the H2 uptake performance at room temperature.

This work establishes a computationally efficient model of temperature and diffusion dynamics in ball milled bimetallic Ni-Al particulates. Mechanical contact conditions between adjacent bimetallic domains and temperature fields generated upon impact define the diffusive fluxes through the domains' interfaces. The concentration distributions are studied via Green's function methods, by defining mirror images which reflect the boundary diffusive resistance conditions. Predictions of the model are validated against experimental open-loop scanning electron micrographs and X-ray diffraction spectra at steady-state. Dynamic models of diffusion saturation and internal temperature are developed for the design of closed-loop controller via simulation. This feedback controller is implemented on a laboratory device, equipped with infrared thermometry for external vial temperature measurement, as a self-tuning regulator. The controller adapts an efficiency parameter of the model that thus serves as a real-time observer for internal temperature and diffusion saturation, which are physically inaccessible during processing. Experimental open-loop results are employed to set thresholds of diffusion penetration to avoid early exothermic reaction during fabrication. By controlling the process duration, the regulation system successfully reproduces the material composition of the open-loop reference tests, to ensure desired thermodynamic properties of the ball milled products and safety of the operation. Keywords: Ball milling, Diffusion control, Thermal dynamics, Green's function, Self-tuning regulation

This article belongs to the Special Issue Catalysis for Energy Production Multifunctional materials for energy conversion and storage could act as a key solution for growing energy needs. In this study, we synthesized nanoflower-shaped iron-nickel sulfide (FeNiS) over a nickel foam (NF) substrate using a facile hydrothermal method. The FeNiS electrode showed a high catalytic performance with a low overpotential value of 246 mV for the oxygen evolution reaction (OER) to achieve a current density of 10 mA/cm2, while it required 208 mV at 10 mA/cm2 for the hydrogen evolution reaction (HER). The synthesized electrode exhibited a durable performance of up to 2000 cycles in stability and bending tests. The electrolyzer showed a lower cell potential requirement for a FeNiS-Pt/C system (1.54 V) compared to a standard benchmark IrO2-Pt/C system (1.56 V) to achieve a current density of 10 mA/cm2. Furthermore, the FeNiS electrode demonstrated promising charge storage capabilities with a high areal capacitance of 13.2 F/cm2. Our results suggest that FeNiS could be used for multifunctional energy applications such as energy generation (OER and HER) and storage (supercapacitor).

Several crucial problems, such as rapid population growth and extended demands for food, water and fuels, could lead to a severe lack of clean water and an energy crisis in the coming decade. Therefore, low-cost and highly-efficient technologies related to filtration of alternative water supplies (e.g., purification of wastewater and water-rich liquids) and advanced energy storage (e.g., supercapacitors) could play a crucial role to overcome such challenges. A promising class of solid materials for these purposes is exfoliated graphene, and more specifically, its nanoporous forms that exhibit large specific surface areas and pore volumes. In the current work, two plasma-exfoliated graphene-based materials with distinctive morphological and porosity features, including non-porous and low-specific surface area platelets versus nanoporous and high-specific surface area flakes, were tested as filters for water purification purposes (i.e., decolourization and deacidification) and as electrodes for supercapacitors (i.e., ion electrosorption). The findings of this study suggest that a nanoporous and large specific surface area graphene-based material promotes the water purification behaviour by removing contaminants from water-based solutions as well as the energy storage performance by confining ions of aqueous electrolytes.

To contribute to solving global energy problems, a multifunctional CoFe2O4 spinel was synthesized and used as a catalyst for overall water splitting and as an electrode material for supercapacitors. The ultra-fast one-step electrodeposition of CoFe2O4 over conducting substrates provides an economic pathway to high-performance energy devices. Electrodeposited CoFe2O4 on Ni-foam showed a low overpotential of 270 mV and a Tafel slope of 31 mV/dec. The results indicated a higher conductivity for electrodeposited compared with dip-coated CoFe2O4 with enhanced device performance. Moreover, bending and chronoamperometry studies suggest excellent durability of the catalytic electrode for long-term use. The energy storage behavior of CoFe2O4 showed high specific capacitance of 768 F/g at a current density of 0.5 A/g and maintained about 80% retention after 10,000 cycles. These results demonstrate the competitiveness and multifunctional applicability of the CoFe2O4 spinel to be used for energy generation and storage devices.

Naturally short-length multi-walled Russian-doll-like carbon nanotubes derived by a catalyst-free arc-discharge method were used as nano-sized “cutters” to transform bulk graphitic sheets into thin/few-layered graphene-like nano-sized platelets (GNPs) during a jet milling procedure. A short follow-up oxygen plasma treatment in a plasma reactor further increases the number of smaller (i.e. ∼80 nm) and thinner nanoparticles (i.e. three-layered GNPs) as well as their oxygen content (i.e. up to ∼8 at.%). These oxygen-rich surface-functionalized GNPs are suitable additives for producing stable nanogels as demonstrated by the preparation of carbon ink dispersions. 146 779 784

The facile, rapid and bulk production of composite materials consisting of carbon nanostructures doped with metal-based compounds has been a significant challenge for various research areas where such types of materials can be applied, including catalysis, energy storage and water purification. In this work, a carbon foam‑aluminum fluoride composite (C-AlF3) was developed by adopting a combustion synthesis approach, which is an attractive alternative to wet chemical methods usually employed for such purposes. The flame ignition and combustion of a solid-state mixture comprising a fluoropolymer and nano-sized Al powder leads to the formation of a porous carbon foam network doped with dispersed cubic-like AlF3 nanoparticles (100 to 500 nm in size), as observed by high-resolution microscopy methods. Selective area electron diffraction and X-ray diffraction studies revealed a rhombohedral α-AlF3 crystal structure for these embedded particles, while micro-Raman spectroscopy indicated typical carbonaceous features for the foamy matrix. The C-AlF3 composite also showed a combination of micro-, meso- and macro-porous characteristics (i.e. pore sizes in the nanometer scale) based on the analysis of N2 sorption data collected at 77 K. The findings of this study provide useful insights for further research on carbon-based nanocomposite materials prepared via direct combustion synthesis routes. Keywords: Nanocomposite, Porous material, Carbon foam, Aluminum fluoride, Combustion synthesis

Significant efforts have been focused on the search of earth-abundant elements to solve growing energy issues and to provide bifunctional behavior for both hydrogen and oxygen evolution reaction. Mixed transition metals could provide promising synergistic electrochemical properties and serve as bi-catalyst for overall water splitting process. In this study, a needle grass array of nanostructured nickel cobalt sulfide (NiCo2S4) was synthesized using a hydrothermal process. The synthesized NiCo2S4 electrodes showed promising electrocatalytic activity with a low overpotential of 148 mV and 293 mV for hydrogen and oxygen evolution reactions, respectively. The electrolyzer cell consisting of two NiCo2S4 electrodes displayed excellent performance with high electrochemical stability and low overall cell potential of 1.61 V to achieve a current density of 10 mA/cm2. Our study suggests that mixed transition metal chalcogenides such as NiCo2S4 could be used as efficient and stable electrocatalyst for overall water splitting process. 354 306 312