While the Discrete Element Method (DEM) provides high-fidelity insights into granular processes like high-energy ball milling, its computational cost can become prohibitive when exploring extensive parameter spaces required for scale-up. This limitation hinders the rapid design and optimization cycles crucial for emerging applications, like mechanochemistry. Surrogate modeling offers a promising path to overcome these computational barriers, yet existing approaches often struggle to accurately represent the complex, moving boundary conditions typical of milling equipment. In this work, we leverage a Signed Distance Function Graph Neural Network (SGN) surrogate tailored to the high-energy, moving-boundary regime of the Emax mill. Trained on DEM data, the SGN jointly predicts particle kinematics for recursive roll-out and a mechanochemistry-relevant global quantity, the global dissipated energy. The model exhibits strong generalization to unseen motion trajectories and moderate jar-shape edits without retraining, while operating with a timestep over 100x larger than required by DEM. In a CPU-only comparison, it achieves a minimum of 6.6× wall-clock speedup. This approach provides a powerful and promising technique for the simulation, analysis, and design optimization of high-energy ball milling equipment.

Hydrogen carriers are attractive alternative fuels for the shipping sector. They are zero-emission, have high energy densities, and are safe, available, and easy to handle. Sodium borohydride, potassium borohydride, dibenzyltoluene, n-ethylcarbazole, and ammoniaborane are hydrogen carriers with high theoretical energy densities. The energy density is paramount to implementing hydrogen carriers as a high energy density enables compact and lightweight storage. The effective energy density depends on integrating heat and masses with energy converters. This combination defines the energy efficiency and, thus, the energy density of the system. This paper addresses the effective energy density of the hydrogen carriers, including the dehydrogenation process. Using a 0D model, we combined the five carriers with two types of fuel cells, namely proton exchange membrane (PEM) and solid oxide fuel cells (SOFC), an internal combustion engine and a gas turbine. N-ethylcarbazole and dibenzyltoluene offer medium energy densities, reaching almost 4 MJ/kg. However, the effective energy density of sodium borohydride and ammoniaborane is very high, up to 15 MJ/kg, including the energy converter. This is similar to the energy density of marine diesel oil combined with an internal combustion engine. Thus, we conclude hydrogen carriers are alternative fuels that deserve more attention because of their strong potential to make shipping zero-emission.

– Hydrogen carriers, such as liquid organic hydrogen carriers (LOHCs) and borohydrides, are promising zero-emission alternative fuels for ships. Bringing these hydrogen carriers on board, however, creates new challenges. A major challenge is their spill behaviour. Knowing the spill behaviour is paramount to avoid large-scale environmental disasters. This paper investigates the spill behaviour of four hydrogen carriers (and their conjugates): sodium borohydride, ammonia borane, dibenzyltoluene, and n-ethylcarbazole. The hydrogen carriers were all dissolved in artificial seawater to test their behaviour. Sodium borohydride reacts with seawater, as it also reacts with pure water. However, contrary to expectations, it reacts faster with seawater than regular water. The reaction mechanism behind this is unknown. Ammonia borane does not visibly react with normal water or with seawater. Dibenzyltoluene sinks and forms tiny bubbles which are easily perturbed. Unfortunately, perhydro dibenzyltoluene could not be tested due to technical problems. N-ethylcarbazole breaks up into smaller pieces and predominantly stays afloat, likely due to the surface tension of water. Perhydro n-ethylcarbazole floats but is barely visible in seawater due to its transparency. Preventive measures must be established to avoid large-scale spills if these substances are utilised on ships, as they are likely challenging to clean up.

Mechanochemical synthesis faces reproducibility and scale-up challenges due to complex parameter interactions. This study employs machine learning (ML) to predict NaBH4 regeneration yield, integrating chemical experimental data and DEM (Discrete Element Method) derived invariant mechanical descriptors (Ēn, Ēt, fcol/nball). Various algorithms were evaluated, including a two-step modeling strategy to isolate the dominant effect of milling time in our process. Results demonstrate that a two-step Gaussian Process Regression (GPR) model achieves good predictive performance (R2 = 0.83), significantly outperforming single-stage models and providing valuable uncertainty estimates. Tree-based ensembles (XGBoost, RF) also benefit from the two-step approach and can enhance interpretability. This work establishes a framework for using ML to optimize mechanochemical processes, reducing experimental cost and offering a method to link mechanical milling conditions to chemical outcomes, thereby enabling predictive mechanochemistry.

To reduce global emissions, hydrogen is increasingly considered as an energy carrier for renewable energy storage. However, traditional storage methods for hydrogen such as compression or liquefaction require high pressures, extremely low temperatures, and still result in a low volumetric energy density. As a solution, sodium borohydride (NaBH₄) is proposed as an alternative method to store hydrogen. NaBH₄ is a granular material that can be stored using ambient temperature and pressure, and has a relatively high volumetric and gravimetric energy density compared to traditional hydrogen storage. This paper explores the application of NaBH₄ as a fuel in the maritime industry, and elaborates on how the use of NaBH₄ leads to a circular bunkering (refuelling) process. By using hydrolysis to extract hydrogen from NaBH₄ during vessel operation, a so called spent fuel remains and needs to be stored on the vessel until next port call. Additionally, examples of various bunkering equipment that can be used to design the circular bunkering process of NaBH₄ are presented. Moreover, it explains how design of bunkering equipment depends on the mechanical characteristics of the fuel and spent fuel. The main finding of this work is that NaBH₄ is a promising solution for a sustainable future. Before NaBH₄ can be used as a fuel, vessels and ports need to be adapted to facilitate circular bunkering with such a novel solid-state energy carrier.

High-energy ball milling is a versatile method utilized in mechanochemical reactions and material transformations. Understanding and characterizing the relevant mechanical variables is crucial for the optimization and up-scaling of these processes. To achieve this, the present study delves into differentiating the contributions of normal and tangential interactions during high-energy collisions. Using Discrete Element Method (DEM) simulations, we characterize how operational parameters influence these energy dissipation modes, emphasizing the significance of tangential interactions. Our analysis also reveals how different operational parameters such as ball size, fill ratio, and rotational speed affect the mechanical action inside the milling jar giving rise to multiple operating zones where different modes of energy dissipation can thrive. Finally, we present master curves that generalize findings across a wide range of configurations, offering a tool for characterizing and predicting mechanochemical processes beyond the presented cases. These results provide a robust framework for improving mechanochemical reaction efficiency, and equipment design.

One of the most promising energy carriers for transport applications are hydrogen-based energy carriers. NaBH₄ is a hydrogen energy carrier and produces hydrogen bubbles when it is dissolved in water. The formation of hydrogen bubbles hinders experimental measurements of the thermodynamic and transport properties of aqueous NaBH₄ solutions at elevated temperatures. Accurate knowledge of these properties is essential for the NaBH₄ hydrolysis reactor modeling and design. Molecular dynamics (MD) simulations provide the option to study the thermodynamic and transport properties of NaBH₄ aqueous solutions without hindering hydrogen bubble formation. In this work, a new force field is developed for BH₄^-, namely, the Delft force field of BH₄^- (DFF/BH₄^-), which, combined with additional force fields, can accurately describe experimental densities and viscosities of 0 to 5 m (mol salt/kg water) NaBH₄, 0 to 3 m NaB(OH)₄, and 1 m NaOH aqueous solutions at 295 K within 1.8% and 10.8% maximum deviation, respectively. Empirical fitting correlations are created for densities, viscosities, and self-diffusivities obtained from the MD simulations of 0 to 5 m NaBH₄, 0 to 5 m NaB(OH)₄, and 0 to 1 m NaOH aqueous solutions at 295-363 K for NaBH₄ hydrolysis reactor modeling and design purposes.

Electrochemical conversion of CO₂ to hydrocarbons is limited by the low solubility and slow transport of CO₂ in aqueous systems. We demonstrate that we can reach partial current densities for CO₂-to-CO of 40 mA/cm² in fully aqueous systems, without the use of gas diffusion electrodes. We alleviate the mass transfer limitation by combining a suspension of catalytically active silver nanoparticles (Ag NPs) with a flow-through current collector. This extends the reactive area into the electrolyzer channel and improves the accessibility of dissolved CO₂ in a larger volume of electrolyte. The flow-through electrode system also outperforms a fully suspended electrode (based on carbon black particles), due to enhanced electric conductivity and smaller carbon area to minimize parasitic side-reactions. Additionally, we show that the distribution of the Ag NPs is pivotal for high CO₂ conversion rates, demonstrated by the highest CO current density obtained when a suspension of Ag NPs and SDS as surfactant is flowing through the 3D electrodes as pre-treatment. A stable CO current density can be sustained for more than 4 h. Although the conversion rate is still moderate compared to gas-fed CO₂ electrolzyers, the partial current density for flow-through electrodes is more than an order of magnitude larger than for planar flow systems. This work shows that CO₂ conversion in aqueous systems can be enhanced considerably by exploiting larger electrolyte volumes via smart electrode designs, such as a flow-through principle.

We compare the influence of tangential (shear) and normal (compressive) stress events on the mechanochemical regeneration of sodium borohydride NaBH₄ from hydrated sodium metaborate [Figure presented] and magnesium hydride MgH₂. Discrete element method (DEM) mechanical descriptors are used to design experiments that either maintain the mill at a constant rotational speed or maintain a constant total dissipation power, thereby separating stress distribution from net power input. Under constant power operation, a tangential rich regime achieves a record 94% conversion yield with 37.5% shorter milling time, 40% lower ball-to-powder ratio, and 34% reduced speed. However, this high yield requires such a substantial power consumption that the converted mass per Watt drops to only 0.090 gW⁻¹, below both balanced (0.113 gW⁻¹) and normal-bias (0.108 gW⁻¹) cases. By contrast, a tangential bias at half the power (3 W) still delivers 84% yield and peaks at 0.185 gW⁻¹, illustrating the often disregarded trade-off between absolute conversion and energetic productivity in mechanochemistry. Specific yield (conversion per Watt) likewise peaks at 0.28 W⁻¹ and declines linearly with fill ratio (R²>0.99). Mechanochemical energy leverage analysis reveals that, at most, 1.7–3.7% of input mechanical work is theoretically recoverable on an enthalpy basis, 2.1–4.4% on a Gibbs free energy basis, and 4–8.7% when considering the fuel value of all available hydrogen. Our mill-agnostic framework provides a transferable blueprint for cross-platform optimization of mechanochemical processes.

We demonstrate that pulsed electrolysis can unlock higher performance in CO2 electroreduction (CO2ER) on gas diffusion electrodes (GDEs), which we find are limited by cation-induced CO2 depletion and reduced Faradaic efficiency (FE) at high cathodic potentials. Using continuum-scale modeling, we show that pulsing strategies significantly enhance current density compared to steady-state operation at the same mean potential. Thicker catalyst layers (CLs) particularly benefit from pulsed electrolysis, achieving higher current densities near the gas/liquid interface along with overall improvements in Faradaic and cathodic efficiency compared to constant-potential systems. This is caused by the prolonged time for the cations to transport back to and block the catalytic surface, which improves CO2 accessibility. Tuning the pulse parameters, especially with unequal durations, results in a similar current density as a constant potential system, but with better Faradaic and cathodic efficiency. These findings underscore pulsed electrolysis as a scalable and effective method to enhance CO2ER performance in GDE systems, offering practical improvements for industrial applications.

In this study we investigate the mechanochemical regeneration of sodium borohydride (NaBH₄) from a system comprising hydrated sodium metaborate ( [Formula presented] ) and magnesium hydride (MgH₂). We explore the individual and joint impact of key operational parameters (rotational speed, milling time, ball-to-powder ratio (BPR), and molar ratio) on the regeneration yield. Furthermore, a method for quantifying chemical conversion is introduced relying only on water and thus, offering environmental benefits. This approach additionally facilitates the production and storage of a “ready-to-use” NaBH₄ solution with minimal losses at room temperature. Notably, a yield of 90% is achieved, with a 20% reduction in rotational speed compared to prior literature. This research contributes to sustainable hydrogen storage and presents practical advancements in mechanochemical processes.

We investigated the evaporative crystallization of aqueous glycine sessile droplets on hydrophilic glass, hydrophobic Teflon surfaces, and hydrophobic Teflon surfaces, where the contact angle is manipulated dynamically with electrowetting. Microscopy experiments and analytical characterization revealed that the size, morphology, and polymorphic form (α, β, and γ) of the glycine crystals are influenced by the surface wettability as well as the amplitude and frequency of electrowetting. On a hydrophilic glass surface, a coffee-stain-shaped residue composed of a mixture of bipyramidal α and needle-like β crystals was observed. On a hydrophobic Teflon surface, the droplets evaporated with minimum contact line pinning, producing hemispherical residue shapes, and bipyramidal α crystals smaller than 100 μm were formed. On a Teflon surface with electrowetting, glycine could be manipulated to crystallize into distinct polymorphic forms (β and γ) and residue shapes not observed on hydrophilic glass and hydrophobic Teflon surfaces. The frequency and amplitude of electrowetting were optimized to produce single large crystals. We observed the highest chance of producing single-millimeter-scale crystals at a frequency of 1 kHz and a voltage amplitude of 80 Vrms. We attribute this observation to a combination of nucleation at lower bulk supersaturation compared to the experiment on Teflon surfaces and electrowetting-induced mixing most prominent at 1 kHz. Our results highlight the opportunities arising from the dynamic manipulation of surface wettability

Electrochemical reactors, such as water electrolyzers, CO₂ electrolyzers, fuel cells, and flow batteries, will be essential in electrifying industry as part of the global transition towards a defossilized and sustainable economy. These technologies require further optimization to enhance efficiency and reduce costs for widespread adoption. Hydrodynamics and mass transfer at electrode–electrolyte interfaces significantly affect electrochemical conversion reactions by influencing the reactant availability and pH in the local reaction environment. 3D electrodes, such as flow-through foams and suspension electrodes, hold a great advantage over 2D electrodes as they moderate pH changes and reactant depletion by spreading the current over a larger electrode area and electrolyte volume. We study the diffusion boundary layer in operando around a single mm-sized particle, representing an element of a 3D electrode. We visualize the local and transient pH with Fluorescence Lifetime Imaging Microscopy (FLIM) during H₂O reduction at various current densities and electrolyte flow velocities at a resolution down to 9 μm and 2 Hz. In addition, we apply an intermittent current to investigate how long the capacitive electric double layer of a suspension electrode particle can maintain an electrochemical reaction during their time of non-contact with a current collector, mimicking applications with Faradaic charge transfer (i.e. flow batteries, microbial fuel cells, capacitance-based electrolyzers). We demonstrate that the diffusion boundary layer is not symmetrical, but depend on the direction of the electric field, the current density and the flow conditions. The substantial pH gradients and boundary layer formation at the scale of hundreds of micrometers underline the importance of controlling flow in or around electrodes, making 3D electrodes an important asset for creating suitable reaction conditions in mass transport-limited electrochemical conversions.

Sodium borohydride (NaBH4) is increasingly considered as an alternative fuel for maritime vessels due to its relatively high energy density. When stored in dry solid form, it is a granular material, similar to coal, starch, and iron ore. As NaBH4 is historically used in the chemical industry in aqueous solutions, virtually no details regarding its behaviour as a solid granular material are known. Therefore, after determining particle properties such as size, shape, and density, this study characterises granular NaBH4 in three flow regimes using three experimental setups. Ring shear tests are used for the quasi-static regime, ledge tests for the dense flow regime, and rotating drum tests characterise both dense and gaseous flow, depending on the rotational speed. Various operational conditions, including temperature, humidity, time consolidation, and handling stresses, are taken into account. Experimental results demonstrate that above a threshold temperature and humidity, NaBH4 readily absorbs moisture from ambient air but remains free-flowing for most scenarios. However, time consolidation can transform this free-flowing material into a very cohesive substance. While this cohesiveness is reversible, requiring minimal agitation, the transformation from free-flowing to cohesive is accelerated by elevated moisture contents and a reduced particle size. Additionally, handling stresses were found to have minimal effect on the flow behaviour and characteristics of NaBH4. These findings are ultimately used to derive implications for the design of handling and storage equipment for NaBH4, enabling its use as an alternative fuel for maritime vessels.

The local conditions inside a gas diffusion electrode (GDE) pore, especially in the electrical double layer (EDL) region, influence the charge transfer reactions and the selectivity of desired CO₂ER products. Most GDE computational models ignore the EDL or are limited in their applicability at high potentials. In this work, we present a continuum model to describe the local environment inside a catalytic pore at varying potentials, electrolyte concentrations and pore diameters. The systems studied in this work are based on an Ag catalyst in contact with KHCO₃ solution. Our study shows that steric effects dominate the local environment at high cathodic potentials (≪−25 mV vs pzc at the OHP), leading to a radial drop of CO₂ concentration. We also observe a drop in pH value within 1 nm of the reaction plane due to electrostatic repulsion and attraction of OH⁻ and H⁺ ions, respectively. We studied the influence of pore radii (1-10 nm) on electric field and concentrations. Pores with a radius smaller than 5 nm show a higher mean potential, which lowers the mean CO₂ concentration. Pores with a favourable local environment can be designed by regulating the ratio between the pore radius and Debye length.

New alternative maritime fuels are required to reduce or eliminate the use of fossil fuels in shipping. This need extends across all shipping industry sectors, including the Navy. However, Navy vessels comply with unique requirements compared to vessels within the general shipping industry. Increased safety is one of these and alternative fuels like ammonia may not meet these safety standards. Other alternative fuels, such as methanol, require additional mitigating measures like cofferdams. However, solid hydrogen carriers, such as ammonia borane and sodium borohydride, will most likely not require further safety measures and could even increase safety. These solid hydrogen carriers have a powder-like nature, high flashpoint, and high energy density, of about half that of MDO. They could be suitable not only as an alternative fuel but also as a damper to reduce impact consequences. This research aims to explore whether these two alternative fuels can mitigate the impact and what the consequences of this impact will be on the survivability of a ship. Both impact with and without heat will be taken into account. Ship collisions happen to civilian ships and naval ships alike, so heatless impact remains a vital topic of study. Additionally, the current geopolitical state of affairs may also require civilian ships to sail through more hostile waters than before, possibly even experiencing impacts where heat is generated. The research will follow a conceptual approach based on chemistry and chemical reactions. This approach allows for the evaluation of alternative fuels for various ship types.

Greenhouse gas emissions drive global warming, posing significant risks to ecosystems and human society. The maritime sector contributes approximately 3% of global emissions, leading the International Maritime Organization (IMO) to target a 40% reduction in emissions by 2030 and 70% by 2050, compared to 2008 levels. This reduction can be achieved by improving vessel efficiency or adopting alternative fuels such as hydrogen. Traditionally, hydrogen is stored as a gas, liquid, or cryocompressed, but these methods have drawbacks, including high pressure and energy demands. A promising alternative is sodium borohydride (NaBH4), a solid hydrogen carrier that offers high volumetric energy density and safe storage at ambient conditions. When used in maritime vessels, NaBH4 reacts with water to produce hydrogen and a byproduct, which is stored and later regenerated onshore. Both NaBH4 and its spent fuel are granular materials, requiring specific handling equipment. This paper aims to identify the mechanical characteristics of NaBH4 and its spent fuel to design appropriate storage and handling systems using the Discrete Element Method (DEM).