Electrolysis Process Research Articles

Biomass-to-Green Hydrogen: A Review of Techno-Economic-Enviro Assessment of Various Production Methods

H2 is considered a practical substitute for fossil fuels, especially for transportation by road and air, created either from fossil fuels or through the process of electrolysis of water. Research questions were included based on numerous research and the analysis of articles. The cost analysis of H2 processes, techno-economic hurdles in commercialization, and the economic comparison of various H2-production methods were the basis for the study of papers. The current research examines the different methods of thermochemical, biological, and electrochemical processes utilized in converting biomass into hydrogen. The benefits, constraints, and significant enhancements of every procedure are outlined. The examination assesses the cost of production, the level of technology readiness, and the potential for scalability. Thermochemical techniques, such as gasification and steam reforming, are effective at producing hydrogen. Steam gasification is perfect for moist and dry biomass in the absence of an oxidizing agent. Dark fermentation is more efficient for biological conversion because it requires less energy. Moreover, the electrochemical procedure is viable for biomass. Thermochemical treatment is significantly more advanced than biological or electrochemical treatment when it comes to scaling opportunities based on comparisons of current processes. The results of this research show that biomass–hydrogen processes have the potential for increasing H2 production, but further enhancements are needed to produce larger quantities for competitiveness.

Evaluation of fluoride emissions and pollution from an electrolytic aluminum plant located in Yunnan province

The monitoring and evaluation of fluoride pollution are essentially important to make sure that concentrations do not exceed threshold limit, especially for surrounding atmosphere and soil, which are located close to the emission source. This study aimed to describe the atmospheric HF and edaphic fluoride distribution from an electrolytic aluminum plant located in Yunnan province, on which the effects of meteorological conditions, time, and topography were explored. Meanwhile, six types of solid waste genereted from different electrolytic aluminum process nodes were characterized to analyze the fluoride content and formation characteristics. The results showed that fluoride in solid waste mainly existed in the form of Na3AlF6, AlF3, CaF2, and SiF4. Spent electrolytes, carbon residue, and workshop dust are critical contributors to fluoride emissions in the primary aluminum production process, and the fluorine content is 17.14 %, 33.30 %, and 31.34 %, respectively. Unorganized emissions from electrolytic aluminum plants and solid waste generation are the primary sources of fluoride in the environment, among which the edaphic fluoride content increases most at the sampling sites S1 and S7. In addition, the atmospheric HF concentration showed significant correlations with wind speed, varying wildly from March to September, with daily average and hourly maximum HF concentrations of 4.32 μg/m3 and 9.0 μg/m3, respectively. The results of the study are crucial for mitigating fluorine pollution in the electrolytic aluminum industry.

Neodymium oxide concentration state recognition model in neodymium molten salt electrolysis process based on flame image features

Accurate recognition of the concentration state of neodymium-oxide (Nd2O3) in the neodymium (Nd) molten salt electrolysis process provides crucial feedback information for online adjustment of process parameters during Nd metal batch production. This paper proposes a Nd2O3 concentration state recognition model based on flame image features. The model employs the lightweight flame segmentation algorithm (FEC-Net) to accurately segment the flame regions in the collected Nd electrolysis cell flame images. Then, using image processing techniques, geometric and color features of the flame regions are extracted. Finally, a Support Vector Machine (SVM) is used to establish a nonlinear mapping model between the flame features and Nd2O3 concentration states. This model classifies the collected flame image dataset to verify the Nd2O3 concentration state during a certain period of Nd molten salt electrolysis. Experiments demonstrate that the recognition accuracy of SVM reaches 96.09%, meeting the monitoring requirements of the Nd molten salt electrolysis process.

H2S-Responsive NIR-II Fluorescent Nanozyme that Regulates Tumor Microenvironment for Activatable Synergistic CO Therapy/Catalytic Therapy/Immunotherapy.

Nanozyme catalytic therapy triggered by the tumor microenvironment (TME)-responsive enzyme-like catalytic activities is an emerging approach for tumor treatment. However, the poor catalytic efficiency of nanozymes in tumors and the toxic side effects on normal tissues limit their further development, primarily due to the limited uptake and penetration depth of nanozyme in tumor tissues. Here, a tumor-targeting TME and electric field stimuli-responsive nanozyme (AgPt@CaCO3-FA) is developed, which is capable of catalyzing the generation of ROS to induce cell death and releasing carbon monoxide (CO) specifically in tumor tissues for on-demand CO therapy and immunotherapy. Benefiting from the endogenous H2S activated NIR-II fluorescence (FL) imaging guidance, AgPt@CaCO3-FA can be delivered into the deeper site of tumor tissues resulted from the TME regulation via generated CO during the electrolysis process to improve the catalytic efficiency of nanozymes in tumors. Moreover, CO effectively relieve immunosuppression TME via reeducating tumor-supportive M2-like macrophages to tumoricidal M1-like macrophages and induce mitochondrial dysfunction by reducing mitochondrial membrane potential, triggering tumor cells apoptosis. The enzyme-like activities combined with CO therapy arouse distinct immunogenic cell death (ICD) effect. Therefore, AgPt@CaCO3-FA permits synergistic CO gas, catalytic therapy and immunotherapy, effectively eradicating orthotopic breast tumors and preventing tumor metastasis and recurrence.

Insights into Ir-Based Trimetallic Nano-Catalyst for Acidic Water Electrolysis

In the pursuit of a sustainable and environmentally friendly energy future, water electrolyzers emerge as indispensable players in the landscape of renewable energy storage. At the core of their significance lies the ability to convert surplus renewable energy, such as solar or wind power, into hydrogen - a clean and versatile energy carrier. Through the process of electrolysis, water molecules are split into hydrogen (via Hydrogen evolution reaction, HER) and oxygen (via Oxygen evolution reaction, OER) using electricity, typically derived from renewable sources. However, current hydrogen production is still heavily relying on fossil fuels, with natural gas reforming as the primary source. Despite its high cost, iridium oxide (IrO2) is the most commonly used catalyst for the sluggish OER. Combining Ir with other non-noble metals is one strategy to reduce Ir loading, while maintaining and even increasing catalyst activity. Bimetallic alloying of Iridium-based nanomaterials has the potential to enhance its intrinsic catalytic properties towards acidic OER than that of the single element doped catalyst. The mechanisms include providing more reaction active sites, tuning the electronic structure of the matrix, and synergistic effects that promote the catalytic reaction by facilitating the formation and stabilization of active oxygen intermediates. Although many transition metals, such as Ni, Co, Fe, Mn, W, Sn, Nb, and Ti, have been doped into Ir to from bimetallic and trimetallic catalyst structures, no studies have explored the fundamental relationship between dopant and catalyst activity. This work systematically investigates the effect of doping Iridium-Cobalt matrix with a third, fourth-period transition metals including Mn, Cr, Fe, Co, Ni and Cu, towards acidic OER activity. A facile one pot chemical reduction synthesis is used to synthesize the trimetallic nanomaterials. Half-cell measurements are conducted to evaluate the electrochemical performance and stability of the catalysts. Lastly, physio-chemical methods are used to characterize the composition and structure of the catalysts. At the ECS meeting, we will share our results to provide new insight into structure-function relationships of our bimetallic-doped Ir catalysts.

Membrane Electrode Assembly Development for Industrial CO2 Electrolysis

Membrane electrode assemblies (MEAs) are the key components of zero-gap CO2 electrolyzers, having various functions in the electrolysis process. The catalyst layers serve as the reaction interface, the porous transport layers ensure reactant and product transport to and from the catalysts, while the membrane is responsible for the ion transport between the two half cells. Thus, the structure of the MEA has a determining role on the electrolyzer operation. Industrial application requires large surface area electrolyzers and / or assembly of stacks. The scale-up, however, imposes different challenges on MEA preparation and on electrolyzer operation, therefore the optimal operating conditions can not necessarily be translated from small-scale (< 10 cm2) experiments.With the aim to scale-up the CO2 electrolysis to an industrially relevant level (>2500 cm2 active area), we thoroughly study the MEA components in a test electrolyzer cell having 100 cm2 active area. Currently we focus mainly on the optimization of the catalyst layers and the porous transport layers. The used electrolyzer size is already large enough that we can draw relevant conclusions for the operation of the large-scale electrolyzer, however, still offers possibility to screen a wide range of parameters.I will present selected results on how the improvement of the quality of the catalyst layers - through the optimization of the catalyst ink and the coating process- results in enhanced CO2 reduction performance. We also focus on the screening of different porous transport layers on the anode side with the long-term goal to reduce the precious metal consumption of the CO2 electrolysis. In the second part of my presentation, I will show how the operational parameters (e.g. cell temperature, humidity) affect the stability of the electrolysis. We have thoroughly investigated one of the biggest issues of the anion exchange membrane CO2 electrolysis: the carbonate precipitate formation and the related flooding phenomenon. We identified the pressure drop at the cathode side as a key test output parameter, which can serve as an early warning for the start of the undesired precipitation. When it is recognized in time, and the adequate preventive measures are applied, the lifetime of the electrolyzers can be greatly improved.

(Invited) Novel Polymer and Membrane Development Strategies for Water Electrolysis

Water electrolysis processes play a crucial role in transitioning to a climate-friendly society. They facilitate the integration of renewable energy, offer a clean and versatile energy carrier, decarbonize industries, improve energy storage and grid stability, and support the development of sustainable transportation solutions. As technology advances and economies of scale are realized, electrolysis is expected to play an increasingly significant role in the clean energy landscape, contributing to a more sustainable and resilient future.Various water-splitting electrolysis processes currently exist, including alkaline, solid oxide, proton exchange membrane (PEM), anion exchange (AEM), acidic-alkaline amphoteric, microbial, and photoelectrochemical methods [1]. In our research group, we are actively involved in membrane development for both PEM and AEM water electrolysis.In PEM electrolysis membrane development, our group explores several approaches, such as (a) aromatic main-chain block copolymers[2],(b) acid-base blend membranes using sulfonated and partially fluorinated aromatic polyether, polybenzimidazole, and a PSU-derived basic polymer[2], (c) poly(fluorene)-based sulfonated ionomers, (d) sulfonated and phosphonated poly(pentafluorostyrene) polymers with flexible side groups, and (d) nanophase-separated block copolymers based on phosphonated[3] or sulfonated pentafluorostyrene and octylstyrene. Additionally, we investigate (e) H+-conductive fiber-mat reinforced perfluorosulfonic acid (PFSA) polymers[4].The development of anion exchange membranes in our research group includes (a) polystyrene-based side chain anion exchange polymers and their blends with polybenzimidazole[5], (b) polynorbornene-based optionally ionically and covalently crosslinked anion exchange polymers and membranes, (c) side chain anion exchange polymers and membranes prepared by polyhydroxyalkylation[6], and (d) anion exchange blend membranes made from polydiallyldimethylammonium salts and polybenzimidazole.This contribution highlights the application of two polymer types in PEM and AEM membrane water electrolysis, respectively:(A) PEM Water Electrolysis (PEMWE): Membranes from PEM types (a) and (b) demonstrated good performance. PEM (a) achieved 2.2 V@6 A/cm2, and PEM (b) reached 2.26 V@6 A/cm2 (compared to Nafion212: 2.26 V@6 A/cm2)[2]. These performances were accomplished with non-optimized membrane-electrode assemblies using Nafion as the electrode ionomer. Further performance improvements are expected with optimized electrodes containing the same ionomers as used in the membrane.(B) AEM Water Electrolysis (AEMWE): Blend membranes from AEM type (a) exhibited excellent alkali stability (no conductivity decrease after 1000 hrs of storage in 1M KOH@85°C) and good AEMWE performance (CuCo anode catalyst, 1M KOH, 70°C, 2 V@3 A/cm2)[5]. Type (c) AEMs were applied to a seawater electrolysis cell at 60°C, achieving a performance of 2 V@1 A/cm2 using completely noble metal-free catalysts in both the anode and cathode[6].[1] M. F. Ahmad Kamaroddin, N. Sabli, T. A. Tuan Abdullah, S. I. Siajam, L. C. Abdullah, A. Abdul Jalil, A. Ahmad, Membranes 2021, 11.[2] J. Bender, B. Mayerhöfer, P. Trinke, B. Bensmann, R. Hanke-Rauschenbach, K. Krajinovic, S. Thiele, J. Kerres, Polymers 2021, 13.[3] S. Auffarth, M. Wagner, A. Krieger, B. Fritsch, L. Hager, A. Hutzler, T. Böhm, S. Thiele, J. Kerres, ACS Materials Lett. 2023, 5, 2039.[4] M. S. Mu'min, M. Komma, D. Abbas, M. Wagner, A. Krieger, S. Thiele, T. Böhm, J. Kerres, Journal of Membrane Science 2023, 685, 121915.[5] L. Hager, M. Hegelheimer, J. Stonawski, A. T. S. Freiberg, C. Jaramillo-Hernández, G. Abellán, A. Hutzler, T. Böhm, S. Thiele, J. Kerres, J. Mater. Chem. A 2023.[6] M. L. Frisch, T. N. Thanh, A. Arinchtein, L. Hager, J. Schmidt, S. Brückner, J. Kerres, P. Strasser, ACS Energy Lett. 2023, 8, 2387.

Carbonate Electrolysis for Energy Efficient Direct Air Capture of CO2

Yearly global energy related CO2 emissions continue to increase, reaching a record breaking 37 billion metric tons in 2022. As a major greenhouse gas, CO2 levels need to be reduced by 10s of gigatons to prevent the worst of climate change, something that is no longer feasible with net-zero emissions alone. Removing atmospheric CO2 is therefore of critical importance for the future of our planet. While major improvements have been made in CO2 capture from large point sources, a significant portion of CO2 emitted each year from the United States comes from distributed sources such as cars and smaller factories. Due to the dilute concentrations of CO2 in ambient air, Direct Air Capture (DAC) needs to be highly selective to preferentially absorb CO2 to collect useable amounts. These challenges have made current DAC systems quite costly, both energetically and economically, and require vastly different strategies than carbon capture from concentrated sources.At Giner, we are developing a novel process for the capture and regeneration of CO2 from air into a purified, concentrated CO2 stream that can be redirected as a feedstock for a wide range of applications, including chemical manufacturing and syngas formation. This process involves the capture of CO2 in a concentrated KOH solution using a high-surface area air contactor to form potassium carbonate. The potassium carbonate is then efficiently electrolyzed in a hydrogen-assisted process to regenerate the CO2 at a low operating potential, increasing the electrical efficiency of the process while producing concentrated and purified CO2. In addition, water, hydrogen, and KOH are also regenerated as byproducts that can be recycled back into the CO2 capture and electrolysis processes, reducing both overall energy and chemical consumption.Giner has developed a unique 3-compartment carbonate electrolysis flow cell. Using our electrolyzer, we have seen operating voltage as low as 1.2 V at 100 mA/cm2 in a 5 cm2 cell for potassium carbonate conversion to CO2 with H2 assisted electrolysis. Significant improvements in operating voltage have come from optimization of gas-diffusion layers (GDLs), cell geometry, and membrane selection. Furthermore, we have achieved >97% pure CO2 formation in the internal flow-through compartment. Currently, scale-up is in progress to apply these developments to approach comparable conditions in a 50 cm2 multi-cell stack. Further developments will enable pairing with an in-house, carbonate based, air contactor allowing for capture and regeneration of over 1 ton CO2 per year. Acknowledgement: The project is financially supported by the Department of Energy's ARPA-E Office under the Grant DE-AR0001495

Recycling of Waste Secondary Battery Materials to Recovery of Lithium Carbonate By Using Eco-Friendly Pyro-Metallurgical Electrolysis Process

Recently, many types of vehicles that has been used fossil fuels energy are being replaced with EVs (Electric Vehicles) uses electrical energy. Since secondary batteries that use as the main power device of electric vehicles have a constant lifespan of 7 to 8 years, accordingly, many operating countries are constructing various plans and policies to handle with this issue. Various valuable rare metals such as nickel, cobalt, lithium, and manganese that all has limited resource, are contained in the wasted cathode material, and it could be used as a useful high-quality source if those materials can be recovered in recycle process. Thus, in this study, recover existing resources from waste cathode materials through the eco-friendly Molten Carbonate Electrolysis (MCE) process was performed. Through the process, the lithium, the main recovery target element could be recovered in the form of a compound as lithium carbonate while valuable metals such as nickel and manganese were separated and precipitated. Even though this process does not require any of acidic or organic solvent, it showed high recovery results with more environmentally friendly than the commercial hydrometallurgical recovery method while the sequence was also relatively simple. Various analysis was performed in Xray diffraction, X-ray fluorescence and FE-SEM to confirming characteristics status in recovered lithium carbonate and other precipitated powder, and thermodynamical calculation was accompanied by HSC chemistry to estimate the proper process conditions and electrode materials. In addition, through electrochemical analysis such as chronoamperometry (CA) and cyclic-voltammetry (CV), the correlation between electrode reaction tendency and lithium compound recovery rate was identified.

(Henry Linford Award) Overcoming Challenges in Teaching Electrochemical Engineering

Electrochemical engineering is a highly interdisciplinary topic, requiring some preliminary knowledge of chemistry, material science, transport, kinetics, and process design. The major challenge in teaching the topic is that unlike most classes, where all students are ‘in-step’ in terms of their preparation, electrochemical engineering courses typically draw students from different disciplines (e.g., chemical engineering, chemistry, material science, biomedical engineering) with different background and preparation. This problem is further exacerbated in teaching electrochemical engineering short courses, which are typically attended by practicing engineers having quite different backgrounds, experience levels, and interests.When first encountering these issues, I thought that the best approach is to start from the basics, and obtain, through detailed mathematical derivations, very convincingly, the relevant equations. I could not be more wrong: students quickly lost interest, and the practical significance was often missed. I found out, that it is much more effective to first describe the issues and relevancy of the topic, and then, while still emphasizing the fundamentals, only outline the detailed derivations and skip to the final results, explaining the assumptions and limitations, while focusing on the applications and use. The students were still given class notes detailing the derivations and were directed to appropriate book chapters and publications for further reading.In terms of course content, I followed my admired and memorable teacher, Charles Tobias, who first introduced me, and so many others, to electrochemical engineering. Starting with ionic conduction and transport, and moving on to electrochemical thermodynamics, overpotentials, current distributions, multi-components and alloy deposition, transient effects, and scaling. Each topic was accompanied by relevant examples and homework problems which were later reviewed in class. I found out that it was not an effective use of class time to provide detailed discussion of specific electrochemical process technologies, which the students could read about in textbooks. Consequently, just one class period was devoted for brief discussion of each of the following: batteries and fuel-cells, electroplating, electrowinning and electrorefining, electrolytic processes, and corrosion. Emphasis was placed on discussing the fundamentals, issues, and major challenges for each. Students had the opportunity for in-depth study of additional specific applications by preparing and presenting in class a term-paper. To minimize direct reproduction from the literature, students had to indicate and discuss relevancy to fundamentals studied in class. Students could select their own topics and thereby relate the class material to their own disciplinary interests.To foster critical thinking and discussion, and to integrate the material taught, comprehensive case studies were presented and discussed in class. These case studies included among others, topics related to my own research, including scaling analysis, roughness evolution and dendritic growth, bottom-up plating of semi-conductor interconnects, and periodic reverse plating. These will be discussed in the oral presentation in more detail.I would like to conclude by thanking all my former students, who enriched my life so much, and whom I treasure as my ‘academic family’. Lastly and very importantly, I thank my dear friends and colleagues at Case Western Reserve University who made my teaching and research there most enjoyable, through stimulating discussions and close friendships.

Drivers of Membrane Fouling in the Non-Aqueous Vanadium Acetylacetonate Redox Flow Battery

Due to their unique advantages in terms of long cycle life and modular design, redox flow batteries (RFBs) are being developed to load-level and peak shave energy from intermittent sources such as wind and sunlight. RFBs have yet to meet the stringent cost requirements needed to achieve broad market penetration, however. The second largest cost associated with state-of-the art RFBs after the electrolyte itself is the ion-exchange membrane, which accounts for 30% of the total cell cost [1]. Porous separators provide a pathway to substantially decrease the cost of RFBs, but long-term performance has been difficult to assess due to the coupling of electrolyte degradation, self-discharge, and membrane fouling. This study applies an adaptive observer model to estimate crossover from the open-circuit voltage relaxation of RFB cells, providing detailed information that can be used to decouple membrane fouling from electrolyte degradation by side reactions.For this study the nonaqueous V(acac)3 (vanadium acetylacetonate) electrolyte chemistry [2] is used. Because the RFB cell reaction is based on an electrochemical disproportionation of the neutral V(acac)3 complex, crossover of the active species in this system only results in reversible self-discharge.A novel set of 'canary cell' experiments unequivocally point to membrane fouling as the predominant factor that drives permanent cell degradation. An adaptive observer [3] is used to monitor the crossover rate, which is a proxy for membrane porosity, during self-discharge experiments where the cell is fully charged and the voltage is monitored during an open-circuit relaxation. Figure 1 shows that the porous Daramic separator starts off with ideal Fickian behavior because crossover is a linear function of the state of charge. Over time, however, the cell deviates, with active-species crossover becoming non-Fickian as the membrane fouls. The mass transfer coefficient (determined by the slope of the curve) decreases with exposure to current. It is hypothesized that pore clogging is responsible for this decreasing mass transfer coefficient, and in turn the diminution of cell performance. Deconvoluting membrane and electrolyte processes is a crucial step to determine the stability and long-term viability of RFB electrolyte systems.

(Battery Student Slam 8 Award Winner) Enable Processing of Sulfide Solid Electrolytes in Humid Ambient Air

Sulfide solid-state electrolytes (SSEs) are promising candidates to realize all solid-state batteries (ASSBs) due to their superior ionic conductivity and excellent ductility. However, their hypersensitivity to moisture requires processing environments that are not compatible with today’s lithium-ion battery manufacturing infrastructure. Herein, we present a modification strategy that enables the processability of sulfide SSEs under humid ambient air. We demonstrate that compatible modification with the electrolyte with negligible impact on its ion conductivity. Importantly, the modification extends the amount of time that the sulfide SSE can be exposed to air with limited degradation of its structure while retaining the conductivity for days, a more than 100x improvement in protection time over competing approaches. Experimental and computational results reveal the interaction between modification to the SSE. The modified SSE maintains its function after exposure to ambient humidity when implemented in a Li0.5In/LiNi0.8Co0.1Mn0.1O2 ASSB. The proposed protection strategy represents a major step forward towards cost-competitive and energy-efficient sulfide SSE manufacturing for ASSB applications.

(Invited) Achieving Circularity in the Battery Industry through Salt Splitting Electrolysis

In an era focused on sustainability, Aepnus Technology introduces a transformative approach in electrochemical engineering that enables circularity in the manufacturing of battery chemicals. Aepnus’ innovation centers on advanced gas diffusion electrodes (GDEs), engineered to significantly boost efficiency and lower the costs of electrolytic salt splitting processes. GDEs offer a cost-effective alternative to traditional planar electrodes, and open new reaction pathways for versatile product generation. For example, GDE’s can improve on the incumbent technologies capable of converting sodium sulfate waste into useful chemicals such as sodium hydroxide and sulfuric acid. Aepnus’ GDEs are poised to revolutionize the recycling of sodium sulfate, the largest waste product of the lithium battery supply chain.The application of these GDE’s can extend into the synthesis of various metal hydroxides and other essential commodity chemicals. Aligning with the principles of circular economy and eco-manufacturing, our project addresses challenges in electrolyzer design, catalyst advancement, and reactor optimization. We underscore the translation from academic research to scalable solutions, integrating our technology seamlessly into existing industrial processes.This presentation will delve into the environmental and operational advantages of Aepnus GDEs, their role in reducing the ecological footprint of chemical manufacturing for the battery industry, and our journey to manufacture chemicals in ways that are circular and carbon neutral. Additionally, we will provide insights into the setbacks of existing electrochemical technologies such as membrane electrolysis and bi-polar electrodialysis (BPED), while demonstrating the real-world applicability of our technology through performance data at lab and pilot-scales.

Nickel-Based Metal-Organic Framework Materials with Mixed Ferrocene-Based Ligands As Anodic Catalysts for Water Electrolysis and Urea Electrolysis

Water electrolysis is a highly promising technology for hydrogen production, generating green hydrogen with no greenhouse gas emissions. The water electrolysis reaction involves two half-reactions: hydrogen evolution and oxygen evolution. While oxygen evolution in water electrolysis involves a four-electron transfer requiring higher overpotential and thus leading to energy consumption. Urea electrolysis offers lower theoretical energy consumption than water electrolysis, making them a key technology in future electrolytic hydrogen production processes. Conventional anodic catalysts, such as Ir and Ru, exhibit good performance in oxygen evolution, but being precious metals, they face limitations due to high cost and limited abundance. Its is crucial to find an active, durable and cost-effective anode catalyst for realistic application.Metal-organic framework (MOF) materials, due to their high porosity, large surface area, and unique structural features, have emerged as promising materials for water electrolysis. However, their relatively poor stability is a drawback that needs to be overcome. In herein, we design the mixed ligand strategy for synthesizing the MOF materials. Ferrocene-based ligands, ferrocenedicarboxylic acid (Fd), combing with terephthalic acid (H2BDC) as the mixed ligands for this study. The MOF catalysts, namely Ni-BDC and Ni-BDC-Fd, was synthesized using a simple one-step hydrothermal method with ferrocenedicarboxylic acid and terephthalic acid.Raman spectra revealed the presence of Fe-O, originating from the iron in Fd, demonstrating a structural transformation during the hydrothermal process. XRD analysis also confirmed the existence of FeO. The SEM images showed nanosheets and nanoneedles morphologies for Ni-BDC, while a dense nanofiber structure for Ni-BDC-Fd demonstrating the effect of 2nd ligand on the MOF structure.Electrochemical tests were conducted in 1 M KOH electrolyte and 1 M KOH + 0.5 M urea electrolyte, including oxygen evolution reaction (OER), urea oxidation reaction (UOR). The overall reaction comprising the same catalysts for the anode and the cathode side is performed to examine the real electrolysis performance.Results showed that the addition of Fd enhanced OER and UOR activity in alkaline and urea electrolytes. Ni-BDC-Fd achieved 1.483 V vs. RHE and 1.386 V vs. RHE at 65 mA/cm-2 driving potential for OER and UOR, respectively, requiring a smaller potential than Ni-BDC to achieve the same current density. To verify that the performance improvement was not solely due to iron, NiFe-BDC was synthesized by adding iron nitrate, showing inferior UOR performance compared to Ni-BDC-Fd but superior OER performance to NiFe-BDC. This indicated that the performance improvement resulted from structural changes rather than just the presence of iron atoms. Ni-BDC-Fd exhibited the lowest Tafel slope in OER, indicating a faster reaction rate due to the increased active surface area during OER. After continuous catalysis for 80 hours in the alkaline water electrolysis cell and urea electrolysis cell, a significant improvement in the loss of potential was observed.These results suggest that the addition of ferrocene dicarboxylic acid altered the structure of Ni-BDC, maintaining an appropriate interlayer distance. This not only enhanced its catalytic performance but also improved its catalytic stability, demonstrating a promising strategy for preparing metal-organic framework materials for electrocatalysis applications. Figure 1

Low-Temperature Water Electrolysis Under a Sustained pH-Gradient for the Electrochemically-Induced Decarbonation of Limestone into Hydrated Lime

Conventional low-temperature water electrolysis processes operate either at high or low pH to enhance conductivity, minimizing electrical resistance. Neutral water electrolysis in a buffer solution is considered non-competitive due to higher energy consumption. Nevertheless, interest in water electrolysis using a salt-based electrolyte has grown due to its ability to generate a pH gradient inside the cell. Electrolysis using a neutral salt-based electrolyte has higher operating costs due to its higher standard equilibrium potential (due to the pH gradient) and lower conductivity. Although this approach incurs higher operating costs, it presents a unique advantage: the production of additional valuable elements thanks to the pH gradient generated.In 2019, Ellis & al. [1] highlighted the possibility to use this pH gradient to electrify the production of hydrated lime (calcium hydroxide). Lime has applications in different areas such as the removal of impurities during steel production and aqueous or gaseous effluent treatments. It can also be used as a precursor of cement. Cement production is accounting for 8% of global CO2 emissions. The acidity generated by water oxidation at the anode dissolves the calcium carbonate inserted. Carbon dioxide from the dissolution is recovered with the oxygen generated. The calcium cations migrate through the cationic membrane towards the cathodic compartment to react with the hydroxide ions generated by water reduction at the cathode. Calcium hydroxide is finally collected after precipitation. Figure 1 compares the conventional process with the electrochemical way and describes more precisely the steps involved in Figure 1. More recently, another way of exploiting this gradient has been proposed by Ni & al. [2] for the recycling of spent Li-ion batteries. With the growing interest in process electrification, other applications may emerge.In this paper, this hybrid electrochemical system for the simultaneous production of hydrogen, oxygen and calcium hydroxide has been intensively studied. Water electrolysis has been performed in a two-compartment cell at different applied currents. Calcium concentration and pH measurement enabled the study of the sub-step efficiencies and equilibria in anodic and cathodic chambers. Perfect faradic efficiencies were obtained with perchlorate salt electrolytes and platinum-free electrodes. The establishment of the pH gradient has been proven and correlated with the transport number of protons through the cationic membrane. Finally, the kinetics of calcium ion migration and calcium hydroxide precipitation have been investigated as well. Continuous addition of calcium carbonate as opposed to a single excess addition was shown to be able to tune the working pH in the anodic compartment and thereby reducing the risk of precipitation on the membrane. Our experimental results lead to the formulation of practical recommendations for achieving optimal reaction stoichiometry in each stage. These findings pave the way for scaling up a promising new sustainable process for lime and cement production.[1] L. D. Ellis, A. F. Badel and M. L. Chiang, "Toward electrochemical synthesis of cement," PNAS, vol. 117, no. 23, pp. 12584-12591, 2019.[2] N. Jihong, Z. Jiayin, B. Jinhong and G. Xiaofei, "Recycling the cathode materials of spent Li-ion batteries in a H-Shaped neutral water electrolysis cell," Separation and Putification Technology , vol. 278, p. 119485, 2022. Figure 1 - Conventional and electrochemical production route of Ca(OH)2 and a simplified scheme of the hybrid electrolyzer used in this work, with the reactions involved. Figure 1

Distinguishing Electrochemical Processes in PEM Electrolysis By Impedance Modeling – Distribution of Relaxation Times

Proton exchange membrane (PEM) water electrolysis is a key technology in hydrogen production to provide capacity and flexibility for renewable energy power sources. Various research topics for electrolyzer development focus on cost reduction, performance optimization and lifetime extension with minimum platinum group metal (PGM) loading required [1]. Understanding degradation mechanisms in PEM electrolysis cells becomes necessary for developing mitigation strategies in dynamic durability tests, which facilitates the importance of advanced electrochemical characterization methods.Electrochemical impedance spectroscopy (EIS) is a commonly used diagnostic technique in electrochemical systems. For impedance interpretation, equivalent circuit model (ECM) can be an option with prior knowledge about the system and appropriate circuit elements to prevent overfitting. Alternatively, distribution of relaxation times (DRT) provides a model-free pathway to address electrochemical mechanisms with different time constants and it has been applied to fuel cells, batteries and capacitors in the past years [2, 3]. Impedance deconvolution by DRT, however, has not been well adapted for PEMECs. In this study, electrochemical processes are successfully identified from the DRT profile by varying membrane electrode assembly (MEA) compositions and different operational conditions. In a single cell testing, four main peaks in DRT results associated with (1) mass transport losses (2) reaction kinetic (3) ionic conductivity within the catalyst layer and (4) ohmic properties at the interface of membrane and catalyst layers can be separated and quantified. Examination of electron microscopy provides further explanation of different MEA characteristics in performance analysis. This study verifies DRT is a promising tool to better understand PEM electrolysis processes and will be applied to degradation mitigation in the future.

Finding the Fingerprint of an PEMWE Electrolyzer Using Applied Machine Learning Techniques

The energy transition is picking up pace and renewable energy sources are playing an increasing role in our energy supply. The use of green hydrogen is considered an important energy carrier, to store renewable energy and allow many industries to decarbonize. There are different ways to produce hydrogen, whereas low-temperature proton exchange membrane water electrolysis (PEMWE) is one of the more mature electrolysis technologies. The benefits of proton exchange membrane water electrolysis (PEMWE) include the ability to deliver pressurized hydrogen and/or oxygen, operate using intermittent and renewable power sources, and have a reduced footprint. To evaluate the characteristic performance of PEMWE, the voltage/current relation is an important metric. The voltage/current relation is commonly represented in jV-curves. jV-curves contain relevant information, and any issues or out-of-specification performance can be observed immediately. The shape of the curve, and indicated values allow to interpret the performance of the PEWME cell. Nevertheless, proper interpretation of jV-curves and understanding of the source leading to the out-of-specification performance requires expertise.This study aims to evaluate jV-curves and identify faults by applying machine learning (ML) techniques. A conventional approach has been used to create the model. In the model the Nernst voltage, activation voltage on the anode, and the voltage losses due to ohmic resistance are modeled. Implementation of optimization algorithms allow to fit measured jV-curve to the model. Literature has shown relevant techniques to apply these kinds of ML techniques to electrolysis data, for example Particle Swarm Optimization and a modified Honer Badger algorithm. The application of ML to electrolysis data enables the opportunity to develop online monitoring and automated interpretation of data. In this study particle Swarm Optimization (PSO) has been implemented to fit the model to the jV-curve and find the unknown parameters. Those parameters are unique, depending on the performance of the electrochemical cell, and can be interpreted at the fingerprint thereof.The data shown in the figure has been measured on a single-cell material screener using Nafion 117 CCMs. Although both CCMs have been produced in the same batch, a difference between the measurements can be observed. The jV-curve of sample 1 shows performance as expected. This expected performance is characterized by its linear behavior above 0.5 A/cm2. Observing sample 2 shows an increase in voltage at increasing current densities compared to sample 1. This increase in voltage results in increased energy consumption and therefore a less efficient electrolysis process. Both CCMs are measured under comparable conditions. The anode and cathode pressure were during the both tests close to atmospheric, and the average cell temperature was kept constant at 333.15 K.Despite high volume production processes for coating and manufacturing, the origin of the difference in performance remains unknown. The application of automated data analysis allows for the immediate evaluation of the parameters at fault. The preliminary results show a discrepancy in the modeling parameters relevant to the sub-model describing ohmic losses. Furthermore, ML allows for the creation of data sets that contain experiences from the past. This can help to develop faster performance evaluation protocols by reducing testing activities. For future work, alternative algorithms have to be considered as well. Utilizing ML can enable the opportunity for online monitoring, predictive maintenance, and optimizing control strategies. Figure 1

A Sustainable Process for Rare Earth Electrowinning in Chloride Based Molten Salts

Neodymium production has become increasingly important due to use of neodymium–iron–boron (NdFeB) magnets in green energy, consumer technology and defense applications. The state-of-the-art practice features a neodymium fluoride and lithium fluoride molten salt with a consumable carbon anode converting dissolved neodymium oxide and carbon to neodymium metal and CO2.1-2 The anode effect results in PFCs and CO emissions, which make the current neodymium electrowinning process unsustainable.3-4 Some attempts have been made to electrolyze the chloride salt of neodymium to produce chlorine at the anode. Chlorine is a value-added product which neither consumes the anode nor produces other deleterious GHGs. Additionally, the chloride of neodymium can be non-carbothermically produced through a spontaneous reaction with hydrochloric acid, producing only water as a side product. However, a common problem in chloride rare earth electrowinning is the low Coulombic efficiency (10-50%) obtained in lab-scale and pilot-scale efforts.5 The neodymium chloride electrolysis process notoriously encounters a two-step reduction producing an intermediate divalent (Nd2+) oxidation state which is stable in the chloride media.6-7 The intermediate neodymium species diffuses away from the cathode leading to Coulombic efficiency loss. Additionally, the kinetics of the chlorine evolution reaction (CER) in chloride molten salts are known to be relatively sluggish, causing significant anodic overpotentials which elevate the specific energy consumption during electrowinning. Furthermore, electrowinning from molten salts often produces spongy or dendritic deposits of metal requiring energy-intensive purification. In this talk, we will address all aforementioned technical hurdles and report on our efforts achieving high Coulombic efficiency (~85%), and compact deposits with superior as-electrowon neodymium metal purity (>99 wt.%). Furthermore, we will report the development of a new anode which catalyzes chlorine evolution, lowering the anodic overpotential considerably during electrolysis at high current densities of practical interest for electrowinning. Specific energy consumption is calculated for some example cases and found to be between 2.1 and 3.5 kWh/kg representing a significant improvement over the conventional oxyfluoride process. Figure 1

(Invited) Cost Reduction Strategies in Low Temperature Water Electrolysis with Improved Catalytic Activity

Proton exchange membrane water electrolysis (PEMWE) technology is especially advantageous for green H2 production as a clean energy vector. During the water electrolysis process, the oxygen evolution reaction (OER) requires a large amount of iridium (2-3 mgIr cm−2) as catalyst. This material is scarce and expensive, representing a major bottleneck for large-scale deployment of electrolyzers. Recently, Retuerto et al. have synthesized different Ir double perovskites (Sr2CaIrO6) with the Ir atoms in a high oxidation state (Ir6+/5+) 1 and their catalytic activity was extensively investigated. Specifically, a Ca-based double perovskite (Sr2CaIrO6) has showed the highest OER activity similar to those of Ir or Ir oxides-based catalysts while being stable for the OER in half cell measurements. We report the development of a membrane electrode assembly taking advantage of the high activity of the Sr2CaIrO6 catalyst that has only 0.2 mgIr cm−2, around 10 times lower compared to what it is used in the anodes of commercial PEMWE, showing superior performance and stability. The morphology/structure of the developed anode and Sr2CaIrO6 catalyst, before and after operation in PEMWE, were extensively characterized by X-ray diffraction (XRD, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption near edge structure (XANES). We discuss in this contribution how the finding of this work can provide a strategy to lower the Ir content in commercial PEMWE.Anion exchange membrane water electrolysis (AEMWE) combines the advantages of proton exchange membrane water electrolysis (PEMWE), i.e., high current density while maintaining high efficiency and fast dynamic response with the advantages of alkaline water electrolysis (AWE), i.e., low-cost materials. However, AEMWE technology is still depends on a supporting electrolyte and its durability is low. In this regard, the German Aerospace Center (DLR) is developing novel approaches and cell components. Raney-nickel electrodes were developed via vacuum plasma spraying, reaching performance and stability comparable to SoA MW size PEMWE. The electrodes were further refined, switching to lower cost atmospheric plasma spraying while maintaining high performance. Studying the effect of supporting electrolyte concentration it was found, that lowering the ohmic resistance is by far the largest challenge for high performance AEMWE, especially at low KOH concentrations and electrode kinetics are less impactful. Moreover, a 17% efficiency uplift was achieved by applying a carefully tuned, thermally sprayed, nickel-based macro porous layer (MPL) onto a traditional mesh porous transport layer. Both ohmic and mass transport resistances were found to be lowered by the MPL. FIB-SEM and µCT analysis revealed an ideal structure, i.e., 30-40% porosity, almost exclusively open pores, and a broad pore size distribution2. In a fundamental study3, the mechanism of the OER activity was investigated as well as the effect of trace amounts of iron in Ni(OH)2. X-ray diffraction (XRD) and Thermogravimetric analysis (TGA) TGA analysis lead to the conclusion, that iron stabilized the α-Ni(OH)2which is the most active. CV analysis showed that an important redox switching step is also accelerated by Fe-doping. M. Retuerto, L. Pascual, J. Torrero, M. A. Salam, Á. Tolosana-Moranchel, D. Gianolio, P. Ferrer, P. Kayser, V. Wilke, S. Stiber, V. Celorrio, M. Mokthar, A. S. Gago, K. A. Friedrich, M. A. Peña, J. A. Alonso, D. G. Sanchez, S. Rojas, Highly Active and Stable OER Electrocatalysts Derived from Sr2MIrO6 for Proton Exchange Membrane Water Electrolyzers. Nat. Commun. 2022, 13, 7935. Razmjooei, F.; Morawietz, T.; Taghizadeh, E.; Hadjixenophontos, E.; Mues, L.; Gerle, M.; Wood, B. D.; Harms, C.; Gago, A. S.; Ansar, S. A.; Friedrich, K. A., Increasing the performance of an anion-exchange membrane electrolyzer operating in pure water with a nickel-based microporous layer. Joule 2021, 5 (7), 1776-1799. Wang, L.; Saveleva, V. A.; Eslamibidgoli, M. J.; Antipin, D.; Bouillet, C.; Biswas, I.; Gago, A. S.; Hosseiny, S. S.; Gazdzicki, P.; Eikerling, M. H.; Savinova, E. R.; Friedrich, K. A., Deciphering the Exceptional Performance of NiFe Hydroxide for the Oxygen Evolution Reaction in an Anion Exchange Membrane Electrolyzer. ACS Applied Energy Materials 2022, 5 (2), 2221-2230.

Multiphysics Modeling of Electrode Dissolution Under Hydrodynamic Conditions in Low Conductivity Water

Efficient plug-flow electrochemical reactors are characterized by their ability to effectively convert species with significant ionic strength and/or with the assistance of a well-behaved electrolyte. Because of the classic electroconductivity requirement, electrochemical reactors are not particularly attractive options for applications with low-conductivity conditions, especially for low-pressure feeds. However, these reactors can still find application in dedicated processes such as ultra-clean water conditioning and biological-coupled separation systems. Consequently, a multi-physics model was developed using COMSOL Multiphysics to characterize different reactor-design conditions based on the Tertiary Current Distribution which accounts for the effects of expected variations in electrolyte composition and ionic strength on the electrochemical process, as well as solution resistance and electrode kinetics. The modelling framework presented here employs single-phase laminar fluid flow, the Nernst-Planck equation, the water-based electroneutrality condition, and concentration-dependent overpotentials. This investigation particularly explores the electrolysis process of “anodic dissolution,” in which elemental species dissociate from the solid matrix of the electrode and enter the liquid phase of the electrolyte as soluble ions. The reactor configuration of interest has a rectangular parallel-electrode design and is operated galvanostatically. A series of parametric studies are carried out to inspect the response of the system when hydrodynamic, kinetic, and geometric conditions are changed. The parametric sweep resulted in variable effluent concentrations and system voltage, which reveal underlaying optimization patterns for electrode dissolution in low conductivity water.