Anode Gas Research Articles

Investigation of an Ammonia-Fueled SOFC-mGT Hybrid System: Performances Analysis and Comparison With Natural Gas-Based System

Abstract Hybrid systems (HS) are highly attractive in power generation due to their potential for higher power outputs and efficiencies by integrating different technologies. Among solid oxide fuel cell (SOFC) plants, the SOFC-Micro-Gas Turbine (mGT) system is particularly innovative. In this setup, the SOFC replaces the mGT combustion chamber, with an afterburner completing fuel combustion before the expander. Various configurations and control systems have been explored over the years, and prototypes have demonstrated satisfactory efficiency. However, these systems have predominantly used NG and Biogas, which do not achieve zero carbon emissions. The growing global demand for carbon-free energy production is increasing, highlighting the importance of alternative fuels in the power generation sector: among them, thanks to its chemical and physical properties, ammonia is gaining more and more interest. This work investigates an innovative ammonia-to-power system based on an SOFC-mGT HS, focusing on thermodynamic parameters, system features, and technical and environmental challenges. A MATLAB/Simulink model, built on a validated HS model fueled by NG, was developed to analyze the new system configuration. This configuration replaces the SOFC prereformer with an ammonia cracker, allowing for the exploration of anode gas recirculation effects and optimal system design. Key operating parameters such as anodic recirculation factor, fuel utilization, performance, and gas turbine characteristics are discussed. Finally, a comparison is made between hybrid systems and mGTs powered by methane, biogas, and ammonia.

Real-time analysis of anodic mixed gas generated on carbon electrodes during TiO reduction in a LiCl-based salt at 650 °C

The anode gas components produced during the electrolytic reduction of TiO was analyzed in this study in real time using a carbon anode in LiCl containing various Li2O and Li2CO3 concentrations under high-potential operation at 650 °C. A molten salt with 0.3 wt% Li2O under 6 V cell voltage predominantly generated CO2 until depletion of the initial oxygen ion source, after which Cl2 gas began to form. A molten salt containing 0.2 and 1.3 wt% Li2O and 1.3 wt% Li2CO3, respectively, also generated CO2 as the main anode gas, followed by CO, O2, and Cl2 gas generation. In contrast, a molten salt with 0.8 and 0.5 wt% Li2O and Li2CO3, respectively, initially generated CO, leading to carbonate accumulation, which gradually decreased as the concentration of generated CO2 increased and it became the dominant gas, while that of O2 remained constant (6–9%). Cl2 was predominantly generated upon depletion of the oxygen ion source in the salt. Cl2 reacted with carbonate ions in the salt, thus releasing CO2 gas and preventing carbonate accumulation in the salt. This study revealed that anode gas composition during electrolytic reduction with carbon anodes is critically influenced by the oxygen ion source concentration of the salt.

Reducing CO[formula omitted] emissions, energy consumption, and decarbonization costs in manganese production by integrating fuel-assisted solid oxide electrolysis cells in two-stage oxide reduction

Manganese is one of the most consumed metals due to its use in iron and steel making, which generates between 7%–9% of all CO2 emissions produced globally per annum. For the first time, this work explores the potential of a novel process concept to reduce CO2 emissions, energy consumption, and decarbonization costs in manganese production, which involves integrating fuel-assisted solid oxide electrolysis cells (FASOECs) in a two-stage scheme for the reduction of raw manganese ores. In this scheme, higher oxides that are present in raw manganese ores (MnO2, Mn2O3, Mn3O4) are pre-reduced using CO, yielding manganese monoxide (MnO) that is further reduced to Mn in a submerged arc furnace (SAF) using coke and electricity. In the proposed FASOEC integration concept, off-gas from the manganese ores after pre-reduction (a mixture of H2, CO, and CO2) is supplied to the FASOECs’ anode as fuel, in order to produce high-purity H2 in the cathode that is directed to the first stage of manganese reduction. H2 has enhanced reaction kinetics for reducing higher manganese oxides in comparison to CO; therefore, integrating FASOECs can improve manganese oxide conversion rates during pre-reduction, resulting in lower consumption rates of coke and energy in the SAF. The off-gas supplied to the FASOECs’ anode also lowers the amount of energy required for H2 production in the cathode (can also generate electricity, simultaneously) and produces anode exhaust gas containing only CO2 and steam. Since steam can be easily condensed from this stream, the integration of FASOECs also enables efficient decarbonization of the manganese production process, thus eliminating the need for a designated CO2 capture system. The techno-economic analysis performed herein demonstrates that directing the full supply of off-gas produced by the SAF to the FASOECs’ anode at 800 °C reduces the overall energy consumption of manganese production by up to 18% in comparison to conventional processes. This results in decarbonization cost reductions by as much as 3%–15% and a corresponding decarbonization price range of $4-32 per ton of manganese product for plant capacities of 50 and 200 kt, respectively.

Modeling and experimental research on adjustable ejector in fuel cell gas circulation system

Fuel cells can be made to operate under a variety of conditions by implementing adjustable ejectors in their anode gas circulation systems. Based on a quasi-two-dimensional model and considering factors such as friction and variable area effects, a theoretical model of ejectors with needles was established to predict their primary and secondary flow rates. Theoretical calculations were used to analyze the variations in internal parameters and flow losses along the ejector, explain the reasons and laws behind the effect of needle position on ejector performance, and explore the control mechanism of different needle shapes on ejector flow rates. Finally, flow control experiments were conducted on three types of adjustable needle shapes–oblique straight, quadratic, and parabolic–to validate the precision of the adjustable ejector theoretical model and the controls of different shapes on the ejector flow rates. The research indicates that the relative errors of the quasi-two-dimensional model in predicting primary and secondary flow rates are within ± 5 % and + 20 % to −5%, respectively. Both the primary and secondary flow rates were impacted by the needle position variation, though the impact on the secondary flow was weaker. The parabolic shape was optimal for the linear control of primary flow rates, followed by the oblique straight shape. The quadratic shape was the weakest, although the quadratic-shaped needle had a wider range of flow rate control. Modeling and experimental research on the adjustable ejector contributes to understanding the influence of the needle on the ejector performance under different working conditions, broadening the application range of the ejector, and providing a basis for flow control in the fuel cell system.

Dynamic performance analysis of proton exchange membrane fuel cell in marine applications

To investigate the dynamic characteristics of proton exchange membrane fuel cells (PEMFCs) on maritime vessels, a lumped-parameter model for the PEMFC systems was developed based on a hybrid vessel propulsion systems model. Simulations and analyses of the dynamic characteristics of PEMFCs were conducted under typical sailing conditions. The results reveal a noticeable hysteresis in the operating temperature of PEMFC stacks during vessel voyages, with a delay of about 25 s, leading to significant overvoltage in activation, ohmic, and concentration differences. Significant variations in vessel loads can cause large fluctuations in the component gas pressures in the cathode and anode flow paths within 16.6–19.8 kPa and 78.57–93.06 kPa, respectively. A comparison of different humidification levels for cathode and anode gases demonstrates that, at the same moment, as the humidification of cathode and anode gases increases from 20 % to 100 %, the water content in the proton membrane increases from 2.29 to 13.47, the ohmic impedance decreases from 1.35 mΩ/cm2 to 0.174 mΩ/cm2, and the overshoot of the fuel cell voltage decreases. The output delay decreases from 25 s to 8 s, enhancing overall fuel cell performance. These findings are significant for optimizing the design, performance, and real-time control of marine PEMFC systems.

Hydrogen evolution coupled with microplastic upcycling in seawater via solvent-free plasma F-functionalized CoNi alloy catalysts

The deleterious impacts of marine polyethylene terephthalate (PET) microplastic pollution on aquatic organisms have garnered global concern. Crafting a more cost-effective method to derive high value-added products from these microplastics is a pivotal challenge in marine resource reuse. This study introduces a strategy for electrooxidation of PET microplastics coupled with seawater electrolysis for green hydrogen production, resulting in value-added chemical formic acid at the anode and hydrogen gas at the cathode. Specifically, a catalyst composed of carbon nanotube-interconnected CoNi alloy-loaded carbon nanocages was fabricated, and F were doped onto the catalyst surface via solvent-free CF4 plasma treatment. Owing to its unique hollow 1D/3D interconnected structure, the synergistic effect of the CoNi alloy, and the ease of reconstruction of metal-F bonds in an alkaline environment, the prepared electrocatalyst exhibited excellent performance in the hydrogen evolution reaction and oxygen evolution reaction, the current density of 10 mA cm−2 was obtained at the overpotential of 187 mV and 315 mV, respectively. Furthermore, the proposed coupling strategy achieved a potential saving of 165 mV at a current density of 10 mA cm−2. This research offers promising prospects for the development of “marine hydrogen mining” and the management of ocean microplastics.

Influence factors and improvement scheme on the breakdown behavior of pseudospark switch

Abstract High-power pulse generators are widely used in civil and military fields. The main switch directly determines the output characteristics of the high-power pulse generators, such as the voltage front time (tf). Pseudospark switches (PSS) show a promising future for middle voltage, high repetitive frequency pulse power applications. However, how to further improve the breakdown behavior without reducing its advantages is a challenging task. In this paper, the influence of operating parameters (anode voltage UA and gas pressure p) and structural parameter (number of cathode holes) on the breakdown behavior are investigated, the related mechanism are explained, and specific improvement schemes are proposed. It is found that the tf of the single channel PSS (SCPSS) decreased significantly with increasing p, but hardly varied with UA under moderate p. However, it is not a sound solution to increase the p excessively to reduce tf. Besides, increasing the number of cathode holes can obtain a shorter tf at low pressures (which implies superior repetition frequency performance). However, at 25 Pa, the jitter (which is defined as the standard deviation of tf in multiple tests) of the 2-channel PSS is larger than that of the SCPSS. And the jitter of the 4-channel and 8-channel PSS is also greater than 6 ns and 2 ns, respectively. Through experimental and simulation analyses, it can be explained as the stepwise penetration of the virtual anode and the non-simultaneous ignition of the channels. A scheme to increase the trigger energy (ε) has been adopted to improve the simultaneous ignition probability, while shortening tf and reducing jitter. After optimization, the good ignition probability of the 4-channel PSS has been improved to 82% and the jitter has been reduced to less than 1 ns at 25 Pa and 14.7 mJ.

Asymmetric gas diffusion layers for improved water management in PGM-free electrodes

Proton-exchange-membrane fuel cells (PEMFCs) offer a long-term, carbon-emission free solution to the energy needs of the transportation sector. However, high cost continues to limit PEMFC commercialization. Replacing expensive platinum group metal (PGM) catalysts with PGM-free catalysts could reduce cost, but the low active site density of PGM-free catalysts necessitates the use of thick electrodes that suffer from substantial mass transport losses. In these thick PGM-free electrodes, effective water management and oxygen transport are crucial to achieve high performance. In this work, we investigate the role of anode and cathode gas diffusion layer (GDL) configurations in controlling water management. Asymmetric GDL configurations, in which the anode GDL exhibits higher permeability than the cathode GDL, showed higher performance compared to conventional symmetric configurations. Computational modeling showed that the improved performance is mainly due to improved water management, resulting in lower liquid water saturation and faster oxygen transport in the cathode.

(Invited) Electron Microscopy Investigation of PEM Electrolyzer Degradation at Low Iridium Loadings

The employment of hydrogen as an energy carrier provides a promising solution toward zero carbon emission and battling climate change. To meet the DOE’s Hydrogen Shot goal of $1 per kilogram of hydrogen by 2031, proton exchange membrane (PEM) water electrolysis is a key technology of hydrogen production from renewable energy sources. Successful deployment of PEM electrolyzers requires reducing cost while simultaneously improving performance and lifetime. While cost reduction is expected from a variety of strategies including scaling up, operation optimization, and advanced manufacturing, it remains vital to reduce the use of noble-metal catalyst due to its scarcity and vulnerable supply chain subject to market disturbance. [1]Reducing the loading of iridium catalyst on the anode while maintaining electrolyzer performance and durability is of great challenge. In this talk, we discuss issues in PEM electrolyzer component development and advanced manufacturing of electrode layers related to catalyst loading reduction with an emphasize on analytical electron microscopy which provides valuable insight on materials morphology, crystalline structure, and chemical compositions. The batch-to-batch variance of catalyst morphology and elemental composition/distribution from commercial suppliers will be examined for catalyst down-selection. We then analyze the effect of reducing Ir loading on the electrode layer structure and ionomer distribution. These results are correlated with electrochemical measurements in the electrolyzer cell, which help elucidate the effect of low catalyst loading on electrolyzer performance. Morphologies of degraded low-loading anode catalyst layer and gas recombination layers will be investigated, and the dissolution and migration of iridium will be studied. We will also examine impact of different roll-to-roll manufacturing strategies for low-loading catalyst layers and on electrolyzer durability. Last but not least, we analyze MEAs subject to cation contamination and recovery procedure with electron microscopy. [2]References[1] Alia, S.M., Current Opinion in Chemical Engineering 2021, 33:100703.[2] Funding for this work was provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office through the H2NEW Consortium. Electron microscopy research conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.

A Green Slurry Electrolysis to Recover Valuable Metals from Waste Printed Circuit Board (WPCB) in Recyclable pH-Neutral Ethylene Glycol

The continuous growth of e-waste necessitates an efficient method to recover their metal contents to improve their recycling rate. The successful recovery of the metallic component from Waste Electrical and Electronic Equipment (WEEE) can generate great economic benefits to incentivize the industrial recycling effort. In this study, we report the use of slurry electrolysis (SE) in pH-neutral ethylene glycol (EG) electrolyte to extract and recover the metallic component from waste printed circuit broad (WPCB) powder. The system operates at room temperature and atmospheric pressure, and the electrolyte can be recycled multiple times with no signs of chemical degradation. The EG electrolyte system can oxidize the metallic component without triggering anodic gas evolution, which allowed us to incorporate a reticulated vitreous carbon (RVC) foam anode to maximize the capture and oxidation of the metal content. The system demonstrated up to 99.1% Faraday efficiency for the cathodic metal deposition and could recover Cu from the WPCB powder in a selective manner of 59.7% in the presence of 12 other metals. The SE reaction system was also scalable and displayed no compromises on the Cu recovery selectivity. With the ability to leach and recover metallic content from WPCB in a mild and chemically benign condition, the SE system displayed much promise to be adapted for industrial-scale metal recovery from WPCB. Reference Liu, K., Lam, JCH. et al. "A green slurry electrolysis to recover valuable metals from waste printed circuit board (WPCB) in recyclable pH-neutral ethylene glycol." J. Hazard. Mater. 2022433: 128702.Liu, K., Lam, JCH. et al. "Teaching Electrometallurgical Recycling of Metals from Waste Printed Circuit Boards via Slurry Electrolysis Using Benign Chemicals." J. Chem. Educ. 2023 100(2): 782-790. Figure 1

Effectiveness of Gas Recombination Catalyst Layers in Mitigating H2 Crossover in PEM Water Electrolyzers Operating at High Differential Pressure

Gigawatt-scale deployment of proton exchange membrane water electrolyzers (PEMWE) to produce green hydrogen at $1/kg of H2, the US department of energy’s (DOE) ultimate cost target, requires the use of thinner membranes to reduce ohmic losses at high current densities as well as differential pressure operation to improve the overall system efficiency.1 High differential pressure operation results in significant hydrogen crossover through PEMs leading to safety concerns due to the formation of a flammable gas mixtures at anode (> 4% H2 in O2).2 Therefore, the successful deployment of PEMWEs at scale relies on successful implementation strategies to reduce the hydrogen concentration at anode to enable safe operation at high efficiency. These strategies include incorporating gas recombination catalyst (GRC) in the membrane, PTL or downstream in the anode gas outlet. However, the impact of GRC layers on PEMWE performance and hydrogen crossover rates at high differential pressure is not well understood.In this work, we employ in-operando gas chromatography coupled with thermal conductivity detector along with PEMWEs operating at differential pressures (up to 30 bar) to quantify hydrogen crossover rates through PEM at differential pressure. Using this setup, we evaluate the effectiveness of gas recombination layers incorporated in PEMWE membrane electrode assemblies (MEA) in mitigating the risk of formation of the flammable gas mixture. Further, we will also discuss implications of high differential pressure operation on PEMWE performance, durability, and operational safety.

Enhancing PEMEC Efficiency: A synergistic approach using CFD analysis and Machine learning for performance optimization

The proton exchange membrane electrolytic cell (PEMEC) is a clean, pollution-free, and promising device for producing hydrogen from water electrolysis. This paper enhances the electrochemical performance of the PEMEC by developing a comprehensive three-dimensional two-phase non-isothermal heat and mass transfer cell model. An analysis was conducted to study the influence of various operating parameters on the temperature safety and efficiency of the cell. The performance of the latter was optimized by adopting the machine learning technology, which aimed at identifying optimal conditions for improved performance. The obtained results showed that, when the inlet water flow rate and membrane thickness were increased, the average temperature of the anode catalyst layer (A-CL) was decreased by 1.4 K and 2.31 K, respectively. This allowed to improve the safety of the electrolytic cell. However, it would reduce the hydrogen and oxygen mole fraction in the electrolyzer. On the contrary, enhancing the porosity or thickness of the anode gas diffusion layer can increase the average A-CL temperature and decrease the oxygen and hydrogen mole fraction. Therefore, the backpropagation neural network and non-dominated sorting genetic algorithm were used to predict and optimize the performance of the electrolyzer, in order to maximize its temperature safety, electrochemical reaction rate, and hydrogen evolution efficiency as much as possible. The results of this study provide a theoretical foundation for the selection of suitable cell models according to different conditions in engineering applications. It also has an application value in energy saving and sustainable development.

Analysis of the technology of electrochemical production of hafnium

The paper analyzes promising industrial processes for obtaining electrolytic hafnium powder. It is shown that extraction and iodide refining are the main processes used to purify hafnium from impurities, achieving both reactor-grade and high purity. The conducted studies have demonstrated the possibility of creating an alternative, more economical, and environmentally safe technology for hafnium recovery, compared to the current magnesium-thermal method. Production of reactor hafnium by electrolysis from molten electrolyte K2HfF6–KCl–KF is possible due to obtaining hafnium oxynitrate salt of nuclear purity and the creation of a hermetic electrolyzer. It is shown that the process of electrolysis leads to the accumulation of potassium fluoride in the electrolyte and requires its periodic draining with deterioration of technological indicators associated with increased recycling of the electrolyte. It was found that along with hafnium, metallic potassium is released on the cathode, which additionally worsens the technical and economic indicators of production. Sealing the electrolyzer makes it possible to create an overpressure of anode gas and determine its quantitative and chemical composition. Processing hafnium cathode sludge with potassium carbonate solution preserves the potassium cycle in the system and eliminates the effluents generated by ammonium carbonate.

Study of Mass Transport in the Anode of a Proton Exchange Membrane Fuel Cell with a New Hydrogen Flow‐Rate Modulation Technique

AbstractHydrogen transport in the anode of a proton‐exchange membrane fuel cell (PEMFC) has been studied with a modulation technique relating the hydrogen flow‐rate ( ) and the faradaic current ( ), called Current‐modulated Hydrogen flow‐rate Spectroscopy (CH2S). A simple analytical expression for the transfer function, H(jω)=n F / , is provided, showing a skewed semicircle in Nyquist representation (−H'' vs. H'), extending from H’=0 to H’=1, and with the maximum frequency at ωmax=2.33(DH2 /Li2), where DH2 is the effective hydrogen diffusivity and Li the thickness of the anode gas diffusion layer (GDL). The expression for CH2S is also calculated with an existing reversible chemical reaction in the GDL. Experimental results under different operation conditions show two transport processes limiting the anode reaction, one attributed to molecular diffusion through the partially saturated GDL, and the other to the microporous layer (MPL), or its interfaces with GDL or with the catalyst layer (CL). CH2S provides the hydrogen diffusivities (DH2,i) associated to each process under the different conditions. Current density decreases slightly the diffusivity of the GDL, while it becomes activated in the MPL; using two GDLs in the anode improves both GDL and MPL diffusivities; humidification decreases the diffusivity in both, GDL and MPL; finally, a superhydrophobic anodic CL prepared by electrospray improves hydrogen diffusivity in GDL and MPL.

In-situ electrochemical impedance analysis of a commercial SOFC stack fueled by real wood gas

The combination of solid oxide fuel cells (SOFCs) and wood gasification has the potential to significantly increase renewable electricity production and decrease emissions. Depending on the quality of the wood gas, degradation processes have a significant impact on the reliability and lifetime of the SOFC. Using electrochemical impedance spectroscopy (EIS) and subsequent distribution of relaxation times (DRT) analysis, the impact on the degradation of coupling wood gasification with a commercial SOFC stack is determined in this study. The thermal behavior of the SOFC stack under various operating conditions, as well as various synthetic wood gas mixtures classified by their hydrogen-to-carbon (H/C) ratio, was assessed. The decrease in the H/C ratio from 8 to 1, observed during syngas and real wood gas operation, leads to a rightward shift in the Nyquist plots, suggesting an increase in the SOFC stack's impedance. Correlations between variations in the H/C ratio and their effects on anodic electrooxidation, ionic conduction, gas transport, and diffusion were identified using DRT analysis to interpret the EIS results. By incorporating an upstream desulfurization system and ensuring an H/C ratio greater than 2, the coupling of biomass gasification with the SOFC stack was stable to degradation issues.

Preparation and properties of self‐humidifying anodic gas diffusion layer with hydrophilic polymer material

AbstractIn this paper, an anodic gas diffusion layer (GDL) with a gradient hydrophobic structured microporous layer (MPL) was prepared using a spraying method. The hydrophobicity of the MPL was changed by adding polyvinylpyrrolidone to the MPL close to the catalyst layer side to obtain a bilayer MPL with a gradient hydrophobic structure. By performing the above operation, we designed a double‐layer MPL structure with different hydrophobic gradients. In this study, we analyzed the effect of the gradient hydrophobic structure of bilayer MPL on the electrochemical performance of proton exchange membrane fuel cell by characterizing the physical properties, such as water contact angle, of anode self‐humidified GDL prepared in the laboratory. The study compared the limiting power density of the laboratory‐prepared GDL sample 10% with that of the commercial GDL29BC. The limiting power density of the sample 10% is 1.59, 1.5, and 1.49 W/cm2 under three humidity conditions of 40%, 60%, and 100%, respectively, which improve the performance by 19.5%, 17.2%, and 23.1% over that of the commercial GDL29BC. The anode GDL samples prepared in the laboratory showed good self‐wetting effect, which play a positive role in the improvement of fuel cell performance.

Comparative analysis of degradation mechanisms in HT-PEM fuel cells under start–stop and load cycling with hydrogen and nitrogen-diluted feeds

The integration of reformers into high-temperature polymer electrolyte membrane (HT-PEM) fuel cells presents a significant opportunity to improve fuel flexibility and cost-effectiveness. To understand their degradation, we applied two start–stop cycling procedures: one with pure H2 and another with an 80 vol % H2 and 20 vol % N2 mix to simulate reformate gas. We also performed a load cycling test with H2 as anode gas. The results indicated that degradation rate of pure H2 start–stop cycling showed 306 μV h−1, while load cycling demonstrated a degradation rate of 19.7 μV h−1 for the current density of 0.2 A cm−2, and 88.2 μV h−1 for the current density of 0.4 A cm−2. Start–stop cycling with diluted gas resulted in a constant voltage drop with a degradation rate of 3.129 mV h−1. Electrochemical impedance spectroscopy (EIS) indicated an increased ohmic resistance during start–stop cycling and higher charge transfer (high-frequency) and mass transport (low-frequency) resistance with nitrogen introduction. Scanning electron microscope results confirmed MEA degradation. In conclusion, start–stop cycling and anode gas dilution are stressors that accelerate HT-PEM fuel cell degradation, reducing its lifetime.

State of the Art of Modelling and Design Approaches for Ejectors in Proton Exchange Membrane Fuel Cell

Proton exchange membrane fuel cell (PEMFC) has a promising future in the power generation and transportation fields. Recirculation of unused anodic gases is fundamental to achieve a high-performance energy system, and this is usually attained employing ejectors or pumps. With respect to the latter, ejectors present no moving parts, thus resulting in both higher overall efficiency of the system and lower maintenance cost. Their main drawback is represented by the narrow optimal operative range: the entrainment ratio (ER) greatly depends on primary pressure, working pressure, and operative condition in general. In the last decade, numerous authors focused their efforts on fully comprehending and correctly simulating their working principles and analyzing how geometrical parameters influence ER and design different geometries to enlarge the operative range. The aim of this paper is to present in an ordered and clear manner the state of the art of ejector design, both from simulative (turbulence model, single or multiphase stream, etc.) and empirical (commonly used “rule of thumb”) points of view.

Unveiling ionic structure in the LiF-NdF3 molten salt system as determined by Raman spectroscopy and quantum chemical calculations

Understanding the structural intricacies of LiF–NdF3 molten salts is of paramount importance for advancing the neodymium electrolysis technology. In this study, the vibrational structure of a LiF–NdF3 molten salt with a LiF/NdF3 molar ratio of 1 was analyzed through in situ Raman spectroscopy, coupled with an in-depth analysis of the ionic structure using molecular simulation techniques. This investigation revealed the presence of various species, including NdF63−, NdF52−, NdF4−, and Nd2F7−, in the molten salt. The primary bands corresponding to these ions were unambiguously identified at wavenumbers of 400, 443, and 491 cm−1, with an intriguing overlapping band at 491 cm−1 corresponding to Nd2F7− and NdF4−. Notably, the results revealed a network of interconversion pathways among these species within the LiF–NdF3 molten salt. Remarkably, Nd2F7− exhibited D3d and D3h group symmetry structures, with a small single-point energy difference of only 0.43 kcal/mol, highlighting their uniform coexistence and stability within the molten salt matrix. Moreover, anodic perfluorocarbon gas was formed by the electrochemical reactions between the F atoms in NdF63−, NdF52−, NdF4−, and Nd2F7− species that were most prone to undergo electrophilic reactions and anodic carbon during the neodymium electrolysis process. By focusing on the complexities of the ionic structure, this study provides insights into the behavior of the LiF–NdF3 molten salt, highlighting its role in the development of neodymium electrolysis technologies.

Improved control-oriented polarization characteristic modeling for proton exchange membrane water electrolyzer with adaptive hunting game based metaheuristic optimization

The proton exchange membrane water electrolyzer has garnered increasing attention for the large-scale consumption of intermittent renewable energy to produce high purity “green hydrogen”, contributing to the realization of futural carbon neutrality goals. The necessity of control-oriented polarization characteristic modeling with accurate parameter identification remains a significant challenge for the performance evaluation of this type of water electrolyzer. In this paper, an improved control-oriented polarization characteristic modeling for proton exchange membrane water electrolyzer with adaptive hunting game based metaheuristic optimization is proposed to foster collaborative performance enhancement between model improvement and optimizer investigation. The inspiration behind model improvement lies in the nonlinear mechanism linkage between partial pressures of liquid water supplying and anode gas separator. Then, an adaptive hunting game based metaheuristic optimizer is proposed to address the inherent local multi-extremum distribution problem in the established model. Experimental data from a commercial water electrolyzer system is used to validate the effectiveness and practicability of the proposed model-optimizer pair. Detailed comparisons reveal that the improved model development, with its consideration of critical mechanisms, ensures enhanced metaheuristic efficiency in the designed optimizer, both in terms of robust intensity evaluation and efficient quasi-Newton based local search. Statistically, the collaboration performance enhancement reaches up to 7.33% when compared with the other model-optimizer.