Steady-state Conditions Research Articles

Significance of nanoparticle aggregation for thermal transport over magnetized sensor surface

Abstract This article explores the dynamics of nanofluids consisting of copper (TiO2) nanoparticles suspended in water, as they interact with sensor surfaces between two parallel squeezing plates with porous characteristics. This research specifically targets applications involving enhanced heat transfer and magnetohydrodynamic (MHD) control in nanofluid systems. The primary aim is to analyze the effects of nanoparticle aggregation and non-aggregation on sensor surfaces, considering MHD formations and heat transfer in the energy and momentum equations. The research adopts a steady-state fluid condition and utilizes similarity transformations to convert partial differential equations into more manageable ordinary differential equations. The methodology involves shooting methods for solving these nonlinear ordinary differential equations and employs graphical analyses to study the impacts of various parameters such as permeability, magnetic influence, squeeze flow, and radiation on the temperature and velocity profiles of the nanofluid. The results reveal significant dependencies of temperature and velocity profiles on the studied parameters, illustrating varied behaviors in scenarios of both aggregation and non-aggregation of nanoparticles. The findings emphasize how each parameter distinctively influences the heat and flow characteristics of the nanofluid, offering insights into optimizing conditions for better performance and control in practical applications. Future research could focus on extending the model to include transient fluid states and exploring the effects of other nanoparticle materials and shapes. There is also potential to investigate the interactions under different environmental conditions and to incorporate more complex boundary conditions to simulate real-world applications more accurately. Further experimental validation of the theoretical predictions would be beneficial to enhance the reliability and applicability of the findings.

Chromium removal from concentrated ammonium-nitrate solution: Electrocoagulation with iron in a plug-flow reactor

Highly concentrated ammonium nitrate (AN) solutions are characteristic of explosives manufacturing wastewaters and liquid fertilizer commodities, but chromium (Cr) contamination from corroding metal infrastructure or source impurities can pose problems. Technologies are needed to decontaminate AN from Cr without chemical alterations if AN is to be recovered as a resource. Iron-based electrocoagulation is a proven way to produce Fe(II) for reducing dissolved Cr(VI) to the less soluble and less toxic form of Cr(III), but is an untested technology for AN brines. This work examined Cr removal from synthetic wastewater with high concentrations of AN (400 g/L) by electrocoagulation in a flow-through reactor, where the effects of time, solution flow rate, applied current, and coexisting ions were analyzed. This method not only reduces Cr(VI) to Cr(III) using the produced Fe(II), but also promotes complete Cr removal from solution with the formation of insoluble Fe-Cr precipitates. A slower flow rate and higher applied current increased the removal efficiency of the reactor; furthermore, the reactor took up to one hour to reach steady state conditions, depending on the flow rate. Cr concentrations along the anode length were modeled using a simplified advection–dispersion-reaction model, providing reaction rate coefficients for various flow rates and currents. Overall, the results of this work showed that electrocoagulation with iron can be used for treatment of AN solution contaminated with Cr(VI). This work also provides design guidelines with a corresponding model for field applications in future work.

A Comprehensive Method for Computing Non-Linear Elastokinematic Properties of Passenger Car Suspension Systems: Double Wishbone Case Study

Abstract Suspension and steering design play a major role in ensuring the correct dynamic behavior of road vehicles. Passenger cars are especially demanding from this point of view: NVH and ride comfort requirements often collide with active safety-related requirements such as road holding in steady-state conditions and stability in transients. Driving pleasure is also important for market success, therefore accurate steering feedback and predictable handling properties are additional priorities. Since flexible bushings are used as interface between the suspension arms and the chassis, extra degrees-of-freedom make the design process a complex task. While the use of a multibody software is common practice in the industry, a dedicated computational tool can be more practical and straightforward, especially when undertaking the design of a new suspension concept ground-up. The paper presents a computational methodology for the design of an independent suspension with the associated kinematic and compliance attributes. Typical elastokinematic properties like toe, camber, wheelbase, and track variations versus tyre forces and moments can be computed by means of a dedicated software tool. A sort of validation was performed either by means of a comparison with a MathWorks Simscape® Multibody based model. Finally, a sensitivity analysis is given as an example. Computationally, the method proposed is intuitively based on the equilibrium equations. The nonlinear equations are then solved with Newton–Raphson algorithm. The method can be also optimized for computational efficiency and is thoroughly described so that the reader can easily replicate it in the desired programing environment.

Photovoltaic panel cooling with new composite of phase change materials and hierarchical nanoparticles

In this research, the use of a new type of phase change materials (PCM) and hierarchical nanoparticles is discussed to improve the electrical and thermal efficiency of PV panels. TiO2/CuO hierarchical nanoparticles are synthesized by hydrothermal method, and PCMs containing nanoparticles (2.5–10%wt) are prepared, and then experiments are performed in indoor conditions under solar simulator light. The PV panel with a maximum nominal power of 30W is used. The new PCM is made from a mixture of lauryl alcohol and beeswax (LABW). A spiral heat exchanger is placed in the PCM container, in which the flow rate of cool water is variable (m˙ = 0.002–0.01 kg s−1). Firstly, the temperature and voltage-current changes of the PV panel with time are investigated without using PCMs as a reference case, and in steady-state conditions, the temperature and output power values are 67.34 °C and 22.33W. The use of LABW compared to pure beeswax leads to a significant decrease in the PV panel temperature and as a result, an increase in its electrical and thermal efficiency. Also, adding nanoparticles to PCMs from 2.5 % to 7.5 %wt due to the improvement of their thermal conductivity and increasing the heat storage rate of the PV panel leads to an increase in its electrical and thermal efficiency. There is no significant change to decrease the temperature and increase the production capacity of PV panels by increasing the percentage of nanoparticles from 7.5 % to 10%wt. The maximum production power, electrical and thermal efficiency of the PV panel at a flow rate of 0.01 kg s−1, 10%wt of nanoparticles, and a radiation intensity of 1000 W m−2 are 28.92 W, 12.55 %, and 76.67 %, respectively.

Optimizing thermal performance in tube-in-tube heat exchangers with metal foam inserts: experimental and RSM analysis

ABSTRACT This study investigates tube-in-tube heat exchanger performance under steady-state conditions, examining co-current and counter-current flows. It explores various configurations, including metal foam enhancements, to optimize heat transfer efficiency and minimize pressure drop. Driven by the potential of metal foam to enhance heat transfer, the study aims to demonstrate significant improvements in thermal performance compared to conventional designs. Experimental methods involve testing four configurations with Nickel foam (10 PPI, 0.90 porosity) inserts, evaluating temperatures and pressure drops across flow rates of 25 to 50 LPH. Hot water at 65°C flows in the annulus, while normal water at 31°C flows in the outer annulus. Results show metal foam’s substantial enhancement in heat transfer, with counter-current metal foam configurations achieving up to 3.71 times greater efficiency than parallel flow setups. Moreover, comprehensive performance evaluation reveals that the counter-flow heat exchanger with metal foam is 2.03 times more efficient than the conventional co-current flow without metal foam. Conclusions highlight metal foam’s effectiveness in improving heat transfer performance and optimizing thermal systems through systematic parameter optimization using response surface methodology.

Analysis of an anaerobically digested animal waste-based microturbine driven-biogas energy system

The paper designs a biogas power plant that runs on anaerobically digested (AD) animal waste and integrated with a micro turbine and permanent magnet synchronous generator to generate renewable power. Cow dung, poultry manure, and swine have been explored as potential feedstocks for AD, and the various subprocesses are investigated at discrete temperature intervals that cover both the mesophilic and thermophilic temperature ranges (30 °C–50 °C). The biodegradability of animal wastes, retention time, loading rate, and the size of the reactor influence the overall biogas yield. Methane production from cow dung increased from 131.4 L/d at 30 °C to 171.12 L/d at 50 °C in 15 days. Whereas the methane output from poultry manure, and swine at 50 °C were 278.4 L/d and 284.5 L/d respectively. Moreover, a methane recovery efficiency of 75 % and a purge efficiency of 97 % were attained through pressure swing adsorption (PSA). Furthermore, the system is maintained at 25 kW at steady-state conditions, attaining saturation for a torque value of 7.77 p.u. In a dynamic setting, the load is varied for a range of 25 kW–40 kW, and stable sinusoidal waveforms are generated as outputs that indicate the system's ability to withstand load variations.

Links between soil pore structure, water flow and solute transport in the topsoil of an arable field: Does soil organic carbon matter?

An improved understanding of preferential solute transport in soil macropores would enable more reliable predictions of the fate of agrochemicals and the protection of water quality in agricultural landscapes. The objective of this study was to investigate how soil organic carbon (SOC) and soil texture shape soil pore structure and thereby determine the susceptibility to preferential transport under steady-state near-saturated flow conditions. To do so, we took intact topsoil samples from an arable field that has large variations in SOC content (1.1–2.7%) and clay content (8–42%). Soil pore structure was quantified by X-ray tomography and soil water retention measurements. Non-reactive solute transport experiments under steady-state near-saturated conditions were carried out at irrigation rates of 2 and 5 mm h−1 to quantify the degree of preferential transport. Near-saturated hydraulic conductivities at pressure heads of −1.3 and −6 cm were also measured using a tension disc infiltrometer. The results showed that larger abundances of small macropores (240–720 µm diameter) and mesopores (5–100 µm diameter) resulted in weaker preferential transport, due to larger hydraulic conductivities in the soil matrix that prevented the activation of water flow and solute transport in large macropores. In particular, the degree of preferential transport was most strongly and negatively correlated with the mesoporosity in the 30–100 µm diameter class. In contrast, the degree of preferential transport was not correlated with connectivity measures (e.g. the percolating fraction and critical pore diameter for the macropore network), probably because i.) the pore space of almost all samples was highly connected, being dominated by one percolating cluster, and ii.) only a part of this percolating macroporosity was active under the near-saturated conditions of the experiment. We also found that the degree of preferential transport was strongly and negatively correlated with clay content, whilst the effects of SOC were not significant. Nevertheless, macroporosity in the 240–720 µm diameter class and mesoporosity were positively correlated with SOC content in our soils and in some previous studies. Therefore, SOC sequestration in arable soils may potentially reduce the risk of preferential transport under near-saturated flow conditions through better developed networks of small macropores and mesopores.

Evaluating hydrogen ion mobilization during hemodialysis using only predialysis and postdialysis blood bicarbonate concentrations.

The hydrogen ion (H+) mobilization model has been previously shown to provide a quantitative description of intradialytic changes in blood bicarbonate (HCO3) concentration during hemodialysis (HD). The current study evaluated the accuracy of different methods for estimating the H+ mobilization parameter (Hm) from this model. The study compared estimates of the H+ mobilization parameter using predialysis, hourly during the HD treatment, and postdialysis blood HCO3 concentrations (Hm-full2) with those determined using only predialysis and postdialysis blood HCO3 concentrations assuming steady state conditions (Hm-SS2) during the midweek treatment in 24 chronic HD patients treated thrice weekly. Estimated Hm-full2 values (0.163 ± 0.079 L/min [mean ± standard deviation]) were higher than, but not statistically different (p = 0.067) from, those of Hm-SS2 (0.152 ± 0.065 L/min); the values of Hm-full2 and Hm-SS2 were highly correlated with a correlation coefficient of 0.948 and a mean difference that was small (0.011 L/min). Further, the H+ mobilization parameter values calculated using only predialysis and postdialysis blood HCO3 concentrations during the first and third HD treatments of the week were not different from those calculated during the midweek treatment. The H+ mobilization model can be used to provide estimates of the H+ mobilization parameter without the need to measure hourly intradialytic blood HCO3 concentrations.

Study on non-uniform circumferential temperature distribution of annular fuel in the tight lattice configuration of a lead-bismuth cooled fast reactor

To guarantee the safe operation of nuclear reactors and protect fuel elements from being damaged under long-term thermal stress, analyzing the circumferential temperature distribution of the outer cladding of nuclear fuel rods in reactors with tight lattice structures is crucial. In this work, a mathematical and physical model was established through theoretical analysis to calculate the circumferential temperature distribution of the outer cladding of an annular fuel rod. The proposed model provides an analytical expression for the circumferential temperature distribution, and the key factors influencing this distribution are determined. The results of the mathematical-physical model and numerical simulation are then combined through numerical fitting. Consequently, a numerical fitting equation is obtained under the steady-state condition of the lead-bismuth reactor using annular fuel and compared with the numerical simulation data acquired via computational fluid dynamics. The results demonstrate that the proposed numerical fitting equation has high accuracy and can serve as a valuable computational tool for analyzing the circumferential temperature of fuel claddings during the operation of lead-bismuth reactors with annular fuels.

Helminth infection driven gastrointestinal hypermotility is independent of eosinophils and mediated by alterations in smooth muscle instead of enteric neurons.

Intestinal helminth infection triggers a type 2 immune response that promotes a 'weep-and sweep' response characterised by increased mucus secretion and intestinal hypermotility, which function to dislodge the worm from its intestinal habitat. Recent studies have discovered that several other pathogens cause intestinal dysmotility through major alterations to the immune and enteric nervous systems (ENS), and their interactions, within the gastrointestinal tract. However, the involvement of these systems has not been investigated for helminth infections. Eosinophils represent a key cell type recruited by the type 2 immune response and alter intestinal motility under steady-state conditions. Our study aimed to investigate whether altered intestinal motility driven by the murine hookworm, Nippostrongylus brasiliensis, infection involves eosinophils and how the ENS and smooth muscles of the gut are impacted. Eosinophil deficiency did not influence helminth-induced intestinal hypermotility and hypermotility did not involve gross structural or functional changes to the ENS. Hypermotility was instead associated with a dramatic increase in smooth muscle thickness and contractility, an observation that extended to another rodent nematode, Heligmosomoides polygyrus. In summary our data indicate that, in contrast to other pathogens, helminth-induced intestinal hypermotility is driven by largely by myogenic, rather than neurogenic, alterations with such changes occurring independently of eosinophils. (<300 words).

Multiple-dose pharmacokinetics of cenerimod and the effect of charcoal on its elimination.

Cenerimod is a sphingosine-1-phosphate receptor 1 modulator that reduces tissue availability of circulating lymphocytes. The compound is in Phase3 development for the treatment of systemic lupus erythematosus. Its pharmacokinetic properties are characterized by slow absorption and multiphasic elimination with a long terminal half-life (t½), potentially caused by enterohepatic circulation (EHC). In this trial in healthy participants, oral cenerimod 0.5 and 4mg once daily was administered for 50 days, followed by oral administration of activated charcoal (ie, 50 mg every 12 h for 11 days, starting 24 h after the last cenerimod dose), to investigate the potential EHC of cenerimod and assess whether elimination of cenerimod can be accelerated. The multiple-dose pharmacokinetics, pharmacodynamics, safety, and tolerability of cenerimod were also evaluated. For both doses, peak plasma concentrations were reached 6 and 7h after dosing. Cenerimod accumulated approximately eightfold and (near) steady-state conditions were reached after 50 doses, resembling clinically meaningful exposure to cenerimod. The t½ following 0.5 and 4 mg of cenerimod was 767and 799 h (ie, 32 and 33 days) and 720 and 780h (ie, 30 and 33 days) with or without administration of charcoal, respectively, indicating no statistically significant difference. Therefore, charcoal did not accelerate cenerimod elimination suggesting that there is no EHC of cenerimod. A reversible, dose-dependent decrease in total lymphocyte count was observed. No safety concerns were identified; administration of charcoal was well tolerated.

Friction and Wear Behavior of 3D-Printed Inconel 718 Alloy under Dry Sliding Conditions

Tailor-made materials used for advanced applications are nowadays of great research interest in various industrial and technological fields, ranging from aerospace and automotive applications to consumer goods and biomedical components. In the present research, Inconel 718 superalloy specimens were fabricated by the selective laser melting (SLM) technique. Structural characterization of the 3D-printed samples showed that they consisted of γ solid solution along with spherical carbide particles. To explore the applicability of these materials in abrasive tribological applications, reciprocating sliding tests were performed under dry conditions versus an Al2O3 counter-body. A 3D representation (triboscopy) of the tangential force during each sliding cycle was carried out in order to obtain better insight on the evolution of friction and to visualize localized tribological phenomena. Quantification of wear was performed with confocal microscopy and the wear mechanisms were analyzed with SEM and EDS techniques. Furthermore, the effect of surface finishing (as-printed and polished) on friction and wear were also investigated, and a comparison with other industrial materials is also included to evaluate the applicability of these alloys. The results indicated that surface finishing had an effect on friction during the run-in stage, whereas in steady-state conditions, no significant differences were observed between the as-printed and polished specimens. In all cases, the main wear mechanisms observed were a mixture of two-body and three-body abrasion, along with oxidative wear (indicated by the formation of an oxide-based tribo-layer).

Dynamics of liquid bridges between patterned surfaces

We have simulated the motion of a single vertical, two-dimensional liquid bridge spanning the gap between two flat, horizontal solid substrates consisting of alternating hydrophilic and hydrophobic stripes, using a multicomponent pseudopotential lattice Boltzmann method. This extends our earlier work where the substrates were uniformly hydrophilic or hydrophobic. In steady-state conditions, we calculate the following, as functions of pattern wavelength: (i) the velocity fields of moving bridges, in particular their (time-averaged) terminal velocities; (ii) the deformation of moving bridges, as measured by the deviation of bridge contact angles from their equilibrium values; (iii) the minimum applied force that breaks a moving bridge. In addition, we found that a bridge moving between patterned substrates cannot be mapped onto a bridge moving between uniform substrates endowed with some effective contact angle, even in the limit of very small pattern wavelength compared to bridge width.

Self-stabilizing economic nonlinear model predictive control applied to modular systems

Recent advances have been made in self-stabilizing Economic Nonlinear Model Predictive Control (eNMPC) formulation without pre-calculated setpoints, which leverages norm-based steady-state optimality conditions to enhance system robustness. To enable practical implementation, a generalized time-domain formulation is proposed, accommodating the discrete-time nature of control instrumentation and the continuous-time nature of first-principles models. A case study involving a modular membrane reactor illustrates the applicability of self-stabilizing eNMPC in real-world industrial scenarios.

Radon and water geochemistry at the active Campi Flegrei volcano (Italy): The role of pore-water phenomena

This study provides new 222Rn measurements performed by RAD7 on 31 thermal waters from the Campi Flegrei caldera, the active volcanic-geothermal field close to Naples (Southern Italy). Waters sampled between 2021 and 2023 are characterized for physical parameters, major ions geochemistry and radium content. Rn contents from Somma-Vesuvius, Ischia and Vulcano volcanoes, together with the river plain north to the Campi Flegrei, were obtained for comparison. The Campi Flegrei caldera reaches the highest Rn concentrations respect to the other sites, varying from 0.03 ± 0.02 to ca. 1887 ± 13 Bq/L, although mostly are below 60 Bq/L. We detect a steady-state condition of constant temperature, facies and radon activity that characterizes most sites, with only minor impacts from seasonalilty and Weigel's effects. Just a small fraction of 222Rn derives from its 226Ra parent in solution, while radon activity in local waters is mainly due to emanation from the radium-containing rock reservoir. Our dataset proofs that radon couples with temperature, sulfate and CO2 in relations to rock-leaching and pore-water phenomena that proceed in the reservoir as it warms up and degasses. Rn and CO2 are decoupled in deeply and timely equilibrated geothermal fluids.Two main end-members, i.e., a low radioactive cold diluted and the Rn-richest hypersaline water from the deep geothermal reservoir are recognized; seawater contamination and heating over 70 °C play a major role in radon decrease.Related radium contents, physical parameters and major ions geochemistry are also presented for a comparison with published data.

Emergence of lobed wakes during the sedimentation of spheres in viscoelastic fluids

The motion of rigid particles in complex fluids is ubiquitous in natural and industrial processes. The most popular toy model for understanding the physics of such systems is the settling of a solid sphere in a viscoelastic fluid. There is general agreement that an elastic wake develops downstream of the sphere, causing the breakage of fore-and-aft symmetry, while the flow remains axisymmetric, independent of fluid viscoelasticity and flow conditions. Using a continuum mechanics model, we reveal that axisymmetry holds only for weak viscoelastic flows. Beyond a critical value of the settling velocity, steady, non-axisymmetric disturbances develop peripherally of the rear pole of the sphere, giving rise to a four-lobed fingering instability. The transition from axisymmetric to non-axisymmetric flow fields is characterized by a regular bifurcation and depends solely on the interplay between shear and extensional properties of the viscoelastic fluid under different flow regimes. At higher settling velocities, each lobe tip is split into two new lobes, resembling fractal fingering in interfacial flows. For the first time, we capture an elastic fingering instability under steady-state conditions, and provide the missing information for understanding and predicting such instabilities in the response of viscoelastic fluids and soft media.

Electrochemical CO2 Reduction on Silver – a Perspective through Electrochemical Impedance Spectroscopy

Anthropogenic carbon rise in the earth's atmosphere is the leading cause towards global warming. Electrochemical CO2 reduction (eCO2RR) is one of the most promising sustainable pathways for the utilization and recycling of anthropogenic carbon. The current challenge in eCO2RR is to make the process more energy efficient and to drive the selectivity toward the desired products. eCO2RR normally takes place in parallel with hydrogen evolution reaction (HER). Additionally, dependent on catalyst material and potential different C-products can be obtained. The mechanistic understanding of the interplay between different reactions is still limited, since the involved reactions are characterized by faster kinetics and/or different adsorbed species as well as mass transfer dependences than the other ones. Moreover, we have recently shown that under dynamic conditions eCO2RR product selectivity towards CO can be tuned1. In that study, we developed a simple model and identified key kinetic parameters which govern product selectivity under dynamic conditions. The model included only the electrochemical kinetics of two parallel reactions without consideration of adsorbed species or mass transport limitations. Therefore, some of the experimental observations could not be completely explained. In such complicated cases involving different physicochemical phenomena acting in parallel at different time scales, the use of electrochemical impedance spectroscopy (EIS) to analyse the system could shed light on the understanding of the process.In this contribution, we have developed a mathematical model which couples micro-kinetics with continuum transport. At first, the model was validated under steady-state conditions. The experiments have been performed under different conditions (mass transport and buffer concentrations) on silver rotating disk electrodes and the product distribution (H2 and CO) has been determined with the help of online gas chromatography. This model was then used to calculate EIS. Based on this approach, we present here a detailed interpretation of the EIS spectrum during eCO2RR and the features obtained at different applied electric potentials. Key insights are drawn about the role of charge and mass transport as well as adsorbed intermediates on the observed features.

Enhancing Efficiency and Selectivity of Electrochemical Regeneration of NADH By Dynamic Operation

The demand for the reduced nicotinamide adenine dinucleotide (1,4-NADH) and reduced nicotinamide adenine dinucleotide phosphate 1,4-NAD(P)H in industrial processes, particularly in the pharmaceutical sector, necessitates their continuous regeneration to mitigate cost implications [1]. In this respect, direct electrochemical cofactor regeneration is a promising alternative, but challenges in achieving optimal selectivity have hindered its widespread industrial integration.This study focuses on advancing the efficiency and selectivity of electrochemical NADH regeneration through dynamic potential inputs, inspired by recent findings demonstrating improved selectivity using dynamic potential inputs instead of steady-state conditions [2]. Various dynamic, pulsed potential profiles are tested and compared with steady-state conditions, revealing distinct advantages in selectivity. Nicotinamide adenine dinucleotide reduction reaction is then coupled with the enzymatic conversion of a substrate (cyclohexenone) to a product (cyclohexanone). In this electroenzymatic biotransformation, 1,4-NADH formed electrochemically is utilized as a second substrate of enzyme enoate reductase. The success of this coupling is evident in the observed formation of the desired product. This research not only contributes to the fundamental understanding of electrochemical co-factor regeneration but also demonstrates its practical application. By combining the advantages of electrochemical and enzymatic reactions, we pave the way for more sustainable and economically viable industrial processes. The presented results mark a significant step towards harnessing the full potential of electrochemical regeneration in facilitating enzymatic transformations with enhanced efficiency and selectivity through a pulsed dynamic operation.

Simulation Studies of Interfacial Kinetics of Dye-Sensitized Solar Cells Photoanodes in Scanning Electrochemical Microscopy

Approach curves in the feedback mode of scanning electrochemical microscopy (SECM) were simulated for photoanodes in dye-sensitized solar cells by finite element simulation using COMSOL Multiphysics and compared to experimental data for the sample set with varying the photoanode film thickness (ZnO, cobalt mediator, organic dye). This reveals quantitatively the effect of the mass transport limitation of the mediator diffusion and organic dye regeneration kinetics in the mesoporous photoanode. The simulation of the mesoporous material was made with a pseudo-homogeneous approach in two space dimensions.The simulation allows to extract the maximum information content from the experimental data. The light adsorption was treated as exponential decay of intensity within the photoanode (Lambert-Beer law), electron injection in the conduction band of ZnO photoanode and loss mechanism was explicitly considered. The light illumination is homogeneous over the entire simulation domain of 1 mm in diameter. Just like in the experiment, the built geometry used for the simulation has a conducting blocking layer (0.6 µm in thickness) to prevent the recombination of electrons with the back contact. The porous dye-sensitized layer has a porosity of 50 - 60% and a thickness of 1- 10 µm. The inner surface holds the dye for absorbing light. The mediator diffuses in the pore of the photoanode (internal solution) and in the bulk of the electrolyte (external diffusion). The transparent conducting glass makes the boundary of the simulation domain. The electrolyte-platinum contact is not modelled. The selected boundary conditions are equivalent to the short-circuit operation of the cell.Interestingly, the simulation suggests that built meshes which had earlier been used for porous electrode simulation could not adequately describe the electron concentration profile for thinner electrodes despite providing a correct ME electrode current for limiting cases. The mesh convergence analysis studies were made to optimize the mesh to reduce computation time and memory size. The electrons in the conduction band were quantitatively determined because transport in the semiconducting photoanode is primarily driven by a thermally activated trapping-untrapping mechanism that can be described by transport equations similar to Fick's laws.The unknown parameters (dye absorption coefficient and recombination rate constant) were adjusted to ensure various light intensities in the simulation correspond to the experiment. An accurate description of the electrons within the semiconductor is critical for explaining the time-dependent behavior of the dye-sensitized photoanode in SECM approach curves. After obtaining agreement with experimental approach curves under steady-state conditions, the same parameters are used to study the current transient obtained under intermittent illumination.

(Invited) Novel Design of Low-Loaded Membrane Electrode Assemblies for Advanced Low-Temperature Water Electrolyzers

Development of advanced low-temperature (LT) water electrolyzers (WEs) is of crucial importance for implementation of the Hydrogen Economy. This future green economy will eliminate the greenhouse gas emissions and stop the imminent global warming and climate change. “Green” hydrogen can be produced at large scale by integration of WEs with renewable energy sources. Currently, the low-temperature proton exchange membrane (PEM) and anion exchange membrane (AEM) WEs are considered to be the most advanced WEs that can be integrated with solar panels and wind turbines to produce large quantities of green H2. The main challenges that the state-of-the-art membrane electrode assemblies (MEAs) for LTWEs are currently facing are: (i) high cost because of the high platinum group metals (PGM) loadings in their catalysts layers; (ii) limited durability caused by the instability of the catalysts and the other cell components, and (iii) safety concerns associated with the hydrogen gas crossover and the absence of technologies that can effectively keep it below the safety level of the lower flammability limit (LFL) [1, 2, 3].This work is aimed on designing of novel MEAs for LTWEs with dramatically reduced catalysts loadings, enhanced durability, and improved H2 crossover capabilities. Reactive Spray Deposition Technology (RSDT) is used as an innovative methodology for designing of advanced catalysts, catalyst and recombination layers, and MEAs for LTWEs. The RSDT is a flame assisted method [4, 5] that combines the catalysts synthesis and deposition directly on the membrane in one-step, which results in fast and facile fabrication of large scale (up to 1000 cm2) MEAs for application in LT fuel cells and water electrolyzers [5, 6]. As fabricated MEAs with ultra-low PGM catalysts loadings are tested at operating conditions typical for industrial PEM hydrogen production systems, and performance of 1.8 V at 3 A/cm2 is achieved. The MEAs of interest are tested for over 1000 hrs at steady-state conditions at 3 A/cm2. Comprehensive post-test characterization is performed by using high-resolution TEM, STEM, EDS, SEM, ICP, XRF, XCT, and digital optical microscopy and the governing degradation mechanisms are identified and discussed in detail. The impact of the design of low-loaded MEAs for LTWEs on their performance and durability is discussed in detail and their potential to meet and surpass the DOE 2030 targets is demonstrated.References https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_myrdd_fuel_cells.pdf https://www.energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdfKlose, P. Trinke, T. Böhm, B. Bensmann, S. Vierrath, R. Hanke-Rauschenbach, and S. Thiele, J. Electrochem. Soc., 165, F1271–F1277 (2018).Kim, S., Myles, Maric, R., et al. Electrochimica Acta, 177, 190-200 (2015).Yu, H., Baricci, A., Bisello, A., Bonville, L., Maric, R., et al. Electrochimica Acta, 247, 1155-1168 (2017).Mirshekari, G., Ouimet, R., Zeng, Z, Yu, H., Bliznakov, S., Bonville, L., Niedzwiecki, A., Errico, S., Capuano, C., Mani, P., Ayers, K., Maric, R. International Journal for Hydrogen Energy, 46(2), 2021, pp. 1526-1539 (2021).