bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural Analysis of Stainless Steel Support/Ni-YSZ Anode Interface in Metal-Supported SOFCs
Authors: Ishiguro Hikaru , Muroyama Hiroki , Matsui Toshiaki
Published: December 2024

Solid oxide fuel cells (SOFCs) have attracted attention due to their high energy conversion efficiency and fuel flexibility. However, conventional anode-supported SOFCs composed solely of ceramics are susceptible to thermal stress such as rapid temperature rises and drops, which can cause cell cracks. Therefore, metal-supported SOFCs (MS-SOFCs) have been devised that use a stainless steel with excellent heat resistance as a support. In MS-SOFCs, elemental diffusion from the metal support during the cell manufacturing process causes microstructural changes in electrodes, leading to a reduction in cell performance [1, 2]. Although the microstructure and diffusion state of elements at the support layer/anode interface are different from those of conventional anode-supported cells, the phenomena as well as the chemical and physical states that occur at the interface have not been sufficiently studied. In this study, then, the microstructural characteristics of the stainless steel support/anode interface were quantitatively analyzed to understand the phenomena occurring and to develop methods to suppress the diffusion of metallic elements.

Gd-doped CeO2 (GDC) was coated as a diffusion barrier layer (DBL) on a SUS430 stainless steel substrate by magnetron sputtering, followed by the NiO-YSZ (8 mol% Y2O3-ZrO2) slurry coating. The composition of SUS430 is given in Table 1. Samples without DBL were also fabricated. These samples were sintered at 1250 ºC for 10 hours in 50% H2-50% Ar. Three-dimensional reconstruction of the microstructures of these samples was performed using a focused ion beam-scanning electron microscope (FIB-SEM), and microstructural parameters were calculated. In addition, elemental diffusion at the interface was analyzed using an energy dispersive X-ray spectroscopy (EDS) analysis.

When the sample was sintered at 1250 °C in a reducing atmosphere, the diffusion of Fe was significantly suppressed by the insertion of DBL. Therefore, it was confirmed that the GDC layer is effective to suppress the Fe diffusion as well as to prevent the formation of solid solution with Ni. However, no significant difference in Cr diffusion was observed. Furthermore, SEM observation revealed that the Ni surface was partially covered with Mn-Cr oxides. The formation of such a characteristic structure had a negative effect to reduce the effective triple phase boundary (TPB) length of the anode. Thus, it was concluded that the insertion of GDC layer suppressed the formation of Ni-Fe solid solution, while the patrial coverage of the Ni surface with Mn-Cr oxides reduced the effective TPB length.

Acknowledgements

This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

[1] M.C. Tucker, J. Power Sources, 195, 15 (2010).

[2] T. Franco, et al., ECS Transactions, 7, 771, (2007).

Figure 1
Influence of Heterogeneous Composite Cathode on La(Sr)Ga(Mg)O3-Based Solid Oxide Fuel Cells
Authors: Ju YoungWan , Shin Tae Ho
Published: December 2024

Solid oxide fuel cells (SOFCs) are promising energy conversion systems because of their high energy efficiency and fuel flexibility. The field of these SOFCs primarily focuses on the catalytic activity of the electrodes. Particularly, the development of high-performance cathodes is essential in SOFCs due to the sluggish electrochemical reaction occurring at the cathode. To overcome this, extensive research is focused on the development of cathodes with superior ORR properties for SOFCs. In this study, a fibrous composite cathode composed of Sm0.5Sr0.5CoO3−δ (SSC) and Sm0.2Ce0.8O2−δ (SDC) is fabricated via electrospinning. Composite fiber cathodes prepared at specific ratios exhibit ORR properties and oxygen-ion conductivity, which are attributed to the growth of small SSC particles in the fibrous electrode and nanolattice strain of SSC at the SSC and SDC interface. As such, the enhanced cathode performance contributes to an improvement in the power-generation characteristics of SOFCs (1.33 W cm−2 at 1073 K using 300 μm thick La(Sr)Ga(Mg)O3 electrolyte). This structural engineering of dual-phase fiber is a promising design that promotes cathodic ORR performance.
Development of Nano-Composite Structured Electrode for High Performance Metal-Supported Solid Oxide Cells
Authors: Park Dayoung , Kim Yo Han , Won Bo-Ram , Jeong Hyeongwon , Myung Jaeha
Published: December 2024

Solid oxide cells can reversibly operate with high conversion efficiency and fuel flexibility. Metal-supported SOCs (MS-SOCs) have attracted attention for their exceptional thermomechanical stability and cost-effectiveness. In this study, we present a precisely controlled metal-supported structure and Ni/YSZ-YSZ dual-nanocomposite catalyst to achieve high performance in various conditions. Controlling the Ni/Fe ratio allows for precise tailoring to the thermal behavior of NiFe, a crucial factor in its interconnectivity with the metal-ceramic interface. Nanocomposite electrodes, with a maximized density of triple-phase boundaries (TPBs), enhance cell performance in both the oxidation and reduction reactions of various fuels compared to micro-sized electrodes. The optimal cells with NiFe support (150 μm)|Ni/YSZ-YSZ electrode (20 μm)|ScSZ electrolyte (10 μm)|LSM-ScSZ electrode (20 μm) exhibited maximum power densities of 1.1 and 1.0 W cm-2 in fuel-cell mode and current densities of -0.61 and -0.5 A cm-2 in electrolysis-cell mode (1.3 V) at 650 °C under H2O/H2 and CO2/CO fuel systems, respectively. Our study suggests fundamental techniques for improving the structural stability and activity to operate in diverse fuel systems.
Optimization of the Parameters for Developing the Buffer Layer By Reactive Magnetron Sputtering in Order to Increase the Performance of a SOFC
Authors: Guesnet Laura , Laurencin Jérôme , Vulliet Julien , Briois Pascal
Published: December 2024

Solid oxide cells (SOCs) are electrochemical devices operating at high temperature. This technology can directly convert fuel into electricity (fuel cell mode – SOFC) or electricity into fuel (electrolysis mode – SOEC). In recent years, the interest on SOCs has grown significantly thanks to the need of massive and low-cost production of H2, and their capability of reversible operation.

The main objectives still remaining for these electrochemical cells are to enhance their initial performances and to increase their durability. The key parameters are obviously the choice of the materials chosen for the functional electrodes, the electrolyte or the barrier layer, but also the microstructures of each layers. It’s well know that the performances could be improved by decreasing the thickness layers, in particular for the electrolyte and the barrier layer which induce additionnal resistances or by increasing their quality (density for instance). The reference cell, used for this study, consists of Ni-YSZ for the hydrogen electrode, YSZ for the electrolyte, GDC for the barrier layer and LSCF for the oxygen electrode. This cell is produced by screen printing and tape casting;

During this work, the production of the GDC barrier layer by physical deposition and more particularly by magnetron cathode sputtering in reactive conditions was studied. The GDC thin film was produced from a metallic target of cerium with 10 atomic % of gadolinium; This layer must have many qualities such as good adhesion, resistant in the conditions of synthesis of the other layers of the cell as well as in the conditions of use, covering, and thin to limit its resistance.The influence of the operating conditions in PVC on the quality of the GDC barrier layer will be discussed such as the bias voltage of the sample holder, the regulation system, the working pressure, etc. for all the synthesis conditions of the SEM observations of raw samples and after heat treatments will be presented; Then, the selected synthesis protocol will be carried out on a reference half-cell (Ni-YSZ/YSZ) and a reference electrode will be deposited using the same method as the reference cell; Electrochemical performance in electrolysis configuration over a temperature range of 700 to 800°C with different flow rate ranges.
Advances in Solid Oxide Electrolysis Cell (SOEC) Technology for Sustainable, Efficient, and Durable Hydrogen Production
Authors: Kim Sun-Dong , Choi Yoonseok , Park Hoonmin
Published: December 2024

The global transition towards sustainable energy sources has significantly heightened interest in efficient hydrogen production technologies. Among these, solid oxide electrolysis cells (SOECs) have emerged as a standout method for their efficient conversion of electrical and thermal energy into hydrogen through water electrolysis. This study presents recent developments in SOEC technology at the Korea Institute of Energy Research, emphasizing crucial innovations in cell and stack designs that enhance both performance and durability under high-temperature electrolysis conditions.

Our research demonstrates significant improvements in SOECs, aiming to meet the increasing demand for sustainable and efficient hydrogen production. Innovations include the introduction of cells with thicknesses ranging from 250 to 300 microns and enhanced support porosity of over 40%, transitioning from 8YSZ to 3YSZ for support and subsequently to 9.5YSZ for the electrolyte. These materials achieve higher mechanical strengths and reduced area-specific resistance. These advancements have resulted in a 20-25% reduction in power consumption compared to conventional lower-temperature electrolysis methods such as alkaline, PEM, or AEM, which is crucial for scaling hydrogen production.

In stack development, optimized bipolar plate designs and surface treatments have been introduced to ensure efficient steam distribution and effective thermal management. Strategic operational control has maintained stack voltage within optimal ranges (12.8V at 700°C and 14V at 650°C) under a current of 100A, demonstrating robust performance over prolonged periods with minimal degradation—validated by long-term testing showing less than -0.7% degradation per 1000 hours under these specified conditions. Testing and evaluation within the specified range confirmed that there was no observed degradation, considering the reduction in power consumption.

These improvements not only showcase our commitment to advancing SOEC technology but also pave the way for its broader application and commercialization. This aligns with global efforts to utilize renewable and nuclear energy resources for environmentally friendly hydrogen production, addressing technical challenges associated with high-temperature electrolysis, and contributing to the low-carbon solution in the global energy transition.

Figure 1
Deconvoluting Soecs – One Cell at a Timeinsights from Single-Cell Analysis of Solid Oxide Electrolysis Cells at Topsoe
Authors: Padinjarethil Aiswarya , Sala Elena Marzia , Pirou Steven , Brodersen Karen , Blennow Peter Gustav , Despesse Elise , Sune Thyden Karl Tor , Tiruvalam Ramchandra , Lundegaard Lars F. , Rasmussen Søren B , Hauch Anne
Published: December 2024

The escalating need for sustainable energy solutions has intensified research into Solid Oxide Electrolysis Cells (SOECs), a cornerstone technology in the green transition facilitating the conversion of electricity into green fuels. Topsoe has made significant strides in the field of green technologies, aiming to revolutionize the production of zero-emission fuels and chemicals, thereby contributing to global carbon emission reduction efforts.

Topsoe's commitment to leading the carbon emission reduction technologies by 2024 is demonstrated through the development of its advanced SOEC technology. This technology is central to future Power-to-X plants, providing a highly efficient electrolysis solution that complements downstream processes. The upcoming SOEC manufacturing facility in Denmark, anticipated to commence operations in 2025, epitomizes this commitment. The facility is poised to produce electrolysis cells, stacks and modules, aiming for an annual production capacity of 500 MW, with scalability prospects. Topsoe's comprehensive expertise from electrolyzers to various downstream processes enables the transformation of renewable resources into zero-emission products such as green hydrogen, green ammonia, e-Methanol, and eFuels, marking a significant step towards a sustainable future1.

The core of the work presented here entails the in-depth analysis facilitated by single-cell studies, both within Topsoe as well in close co-operation with different research institutions. Historical and ongoing research into single-cell testing, dating back several decades, has provided substantial insights into optimizing cell setup and operational parameters. These studies allow for a detailed understanding of individual cell resistance contributions, crucial for deconvoluting the impact of raw materials and manufacturing steps on the full cell performance and durability. The methodological approach includes a spectrum of techniques from in-situ characterization, such as Electrochemical Impedance Spectroscopy (EIS) and current-voltage (IV) curves, to pre- and post-mortem analyses using Scanning Electron Microscopy (SEM), Transmission Electron microscopy (TEM), Raman spectroscopy, and Energy Dispersive X-ray Spectroscopy (EDS) etc.

Such detailed single-cell level studies are pivotal in addressing the mechanical and electrochemical performance requirements of SOECs, aiming to map them to stack and system performance. Furthermore, the studies delve into the challenges of scaling up these technologies, emphasizing the importance of stress tests and impurity evaluations to enhance system lifetime and efficiency.

1.www.topsoe.com/hubfs/Investor%20Images/Annual%20Reports/Annual%20report%202023/Topsoe_AR_2023_FINAL.pdf?hsLang=en
Unveiling the Significant Influence of Metal Oxide Infiltration on Surface Oxygen Exchange Activity in Perovskite Oxides
Authors: Kim Hyunseung , Seo Han Gil , Ahn Sejong , Tuller Harry L. , Jung WooChul
Published: December 2024

Enhancing the oxygen reduction activity of mixed electronic-ionic conducting oxides is crucial for various energy and fuel conversion technologies. One effective approach involves modulating the surface oxygen kinetics on fluorite-type oxides by leveraging the acidity of infiltrated binary oxides. Extending this strategy to complex perovskite-oxide-based electrocatalysts, we investigated the influence of surface infiltration of basic CaO or acidic Al2O3 on the oxygen exchange kinetics of SrTi1-xFexO3-δ (STFx) mixed conductors. Through systematic evaluation of the (de)activation induced by infiltration on STFx as a function of iron concentration x, we confirmed the applicability of the acid-base approach to perovskite oxides. Intriguingly, despite uninfiltrated specimens showing a surface oxygen exchange rate diverging by over an order of magnitude with variations in x, it tended to converge to a specific value following CaO or Al2O3 infiltration. This underscores the benefits of utilizing infiltrated STFx with low iron content, providing improved mechanical, thermal, and chemical stability.
Stabilizing the LSCF Oxygen Electrode of Solid Oxide Electrolysis Cell via Adjustment in Stoichiometry: Doping in a-Site with Ca and B-Site with Larger Cations
Authors: Karki Surendra B , Springer Renaldo , Seymour Lorraine , Le Long , Liu Tian , Ryo Sangbong , Marina Olga A
Published: December 2024

Lanthanum strontium cobalt iron oxide (LSCF) is considered as a superior state-of-the-art oxygen electrode material for SOEC because of its high mixed ionic and electronic conductivity, superior oxygen evolution activity, compatible thermal expansion coefficient (TEC) to ceria compatible, lower reaction activation energy, and suitable sintering temperature (1000). However, LSCF suffers in performance during the long-term SOEC operation due to issues related to undesired reactivity and Sr migration. Such issues are detrimental to the electrochemical performance as they trigger the formation of multiple oxide phases, including insulating phases and electrode or barrier layer delamination. Therefore, stabilization of LSCF phase via adjustment in stoichiometry is one of the crucial strategies to develop highly stable electrodes.

In this work, several LSCF-based compositions have been synthesized by doping with size matching cation in A-site (La/Ca/Sr ratio adjustment), and doping B-site with larger cations such as Nb5+, Zr4+, and Ga3, attempting to enhance the chemical stability of LSCF and stabilize the perovskite structure. Electrical and chemical properties of these electrodes were studied using multiple characterization techniques. Electrocatalytic activity of these electrodes was evaluated in symmetric cells and in Ni-YSZ electrode-supported button cells. Structural and performance trends will be discussed in details.
Co-Electrolysis of H2O and CO2 at Intermediate Temperatures with Protonic Ceramic Cell Reactors
Authors: Li Nannan , Marousiadou Eirini , Kyriakou Vasileios
Published: December 2024

Co-electrolysis of H2O and CO2 in protonic ceramic membrane reactors (PCMRs) is considered a promising approach to convert CO2 into value-added products, but also a way to in-situ store green hydrogen from intermediate temperature (400-600 oC) H2O electrolysis in the form of chemicals or fuels.1 In such PCMRs, steam is split (oxygen evolution reaction-OER) over the anodic electrode (positrode) while the protons created are subsequently transported through the ceramic electrolyte to the cathodic electrode (negatrode) where they react with CO2. This system exhibits significant challenges regarding the choice of the electrocatalysts’ components at both sides of the ceramic membrane. For instance, the highly oxidizing environment of the anodic steam electrolysis rules out the state-of-art Ni-based ceramometallic (cermet) electrodes, whereas the CO2 electrocatalyst environment should be appropriately tuned to achieve high selectivity to the desired products.2

Herein, we have synthesized, characterized and evaluated the performance of promising mixed ionic-(protons, oxygen ions) electronic conducting oxides (perovskites and misfit layered oxides) for use as anodes for OER. The as synthesized electrode systems were firstly characterized with several physicochemical methods (XRD, TPR, TGA, XPS) and then deposited on Ni-cermet supported half-cells for the electrocatalytic studies (EIS, LSV, CP). The results have shown that several candidate materials could allow > 80% faradaic efficiencies, while a significant number of protons reacted with CO2 towards primarily CO and less towards CH4. Interestingly, the distribution of the products showed a strong dependence on the operation temperature and current density with methane selectivity to be improved at lower operation temperatures and high current densities. The latter is practically results in higher ratios of H2/CO2 which is expected to enhance methane yields.

References

Vøllestad, R. Strandbakke, M. Tarach, D. Catalán-Martínez, M.-L. Fontaine, D. Beeaff, D. R. Clark, J. M. Serra, T. Norby;Mixed proton and electron conducting double perovskite anodes for stable and efficient tubular proton ceramic electrolysers; Nature Materials 2019, 18, 752-759.

Duan, R. Kee, H. Zhu, N. Sullivan, L. Zhu, L. Bian, D. Jennings, R. O’Hayre,“Highly efficient reversible protonic ceramic electrochemical cells for power generation and fuel production”, Nature Energy 2019, 4, 230-240.J. Martin, ChemCatChem.
Organic-Inorganic Composite Membrane Containing Low-Cost Functionalized Organosilane (FOSi) Polymer for Vanadium Redox Flow Batteries
Authors: Ajeya Kanalli Vinayak , Kim Baek Ahm , Park Sung Chul , Jung Ho-Young
Published: December 2024

Even though the perfluorinated polymer membranes show the promising performance in various type of energy device, they are suffered from their high cost, high permeability, and difficulty in synthesis. Composite membranes prepared by adding either organic polymer or inorganic materials can reduce the amount of perfluorosulfonic acid (PFSA) and its permeability without compromising conductivity.

A new composite membrane containing low-cost and unique functionalized organosilane (FOSi) with various PFSA (long & short side chain PFSA) as a hybrid organic-inorganic composite membrane (OICM) in large-scale production has shown in this study. The OICM solution is fabricated by varying the amount of PFSA and FOSi using Roll to Roll (R2R) film casting machine. The OICM’s proton conductivity and performance are comparable to the Nafion membrane, owing to the additional hydrophilic functionalized group in the membrane. The OICM possesses high proton conductivity in the range of 0.10 to 0.135 S/cm and an ion exchange capacity in the range of 1.00 -1.45 meq/g, even though the water uptake has been lowered than the PFSA owing to better dispersion of FOSi. The prepared OICM has been used for vanadium redox flow battery (VRFB) and showed a low vanadium permeability and remarkable selectivity, which is a significant benefit. Consequently, the OICM performs comparably to Nafion in energy efficiency combined with coulombic and voltage efficiency. The unit cell with OICM has a normalized coulombic efficiency due to low permeability than PFSA and high voltage efficiency due to high proton conductivity.
Constructing Membrane-Free Faradaic Deionization Systems with High Capacity and High Rate of Salt Removal/Recovery
Authors: Hu Chi-Chang , Tu Yi-Heng , Yang Yu-Hsiang , Huang Hung-Yi
Published: December 2024

Electrochemical deionization (ECDI) systems are attractive desalination devices that can achieve high salt adsorption capacity (SAC) with acceptable energy consumption, which can be employed as a promising complement or alternative method to other desalination techniques. The deionization mechanisms of the ECDI system can be divided into two distinct categories [1]: (1) formation of the electric double-layer (EDL) on the electrode surface to capture ions and (2) Faradaic materials via redox reactions using the charge compensation, ion intercalation, and compound formation, etc. The Faradaic materials including the pseudocapacitive materials and battery materials, based on the redox mechanisms, generally exhibit a high SAC because of the large charges involving the redox couples within the electroactive materials. Accordingly, the ECDI systems utilizing the pseudocapacitive//pseudocapacitive, battery//battery, and hybrid pseudocapacitive//battery combinations are considered to be the next generation ECDI systems, not only their high SACs but also the high salt-removal rate, especially when the electrochemical reversibility of redox couples within the active materials is high. Furthermore, the Faradaic materials are able to exhibit the unique “memory effect” [2] which can be used to concentrate the high-value ions for resource recovery and circular economy without employing any membranes (i.e., membrane-free ECDIs), which are very attractive to the practical applications. Here, we will provide the design guidelines for constructing the electrochemical deionization systems with high capacity and high rate of salt removal but without any membranes. The examples will include MnO2//PPy (PPy: polypyrrol) [1,2], CuHCF@CNT//PPy (CuHCF: copper hexacyanoferrate@carbon nanotube) [3], and PPy-p-TS//PPy-ClO4 (PPy-p-TS: 4-methylbenzene-sulfonic acid-doped PPy) systems [4].

References:

C.-C. Hu, et al., “A highly efficient faradaic desalination system utilizing MnO2 and polypyrrole-coated titanium electrodes”, Desalination 498 (2021) 114807.

C.-C. Hu, et al., “Construction of an inverted-capacitive deionization system utilizing pseudocapacitive materials”, Electrochemistry Communications 104 (2019) 106486.

C.-C. Hu, et al., “A high-capacity hybrid desalination system using battery type and pseudocapacitive type electrodes”, Desalination 545 (2023) 116160.

C.-C. Hu, et al., "Dopant-designed conducting polymers for constructing a high-performance, electrochemical deionization system achieving low energy consumption and long cycle life”, Chemical Engineering Journal 457 (2023) 141373.
In-Situ Desalination-Coupled Electrolysis with a Membrane Stack System Producing Value-Added Chemicals
Authors: Kim Byeong-ju , Park Hyunwoong
Published: December 2024

An efficient multi-functional electrolyzer with an electrodeposited Ni- and Fe-layered double hydroxide (NiFe-LDH) anode and an electrodeposited NiMo cathode is designed for overall water splitting coupled with the desalination of saline water and production of acid and base solution. NiFe-LDH is characterized by abundant active sites for OH adsorption and an optimal binding energy for M-OH. Meanwhile, loading bimetallic NiMo on an active electrode for the HER has been known to improve the electrocatalytic activity and durability owing to its high surface area. The NiFe-LDH and NiMo pairs separated by a bipolar membrane (BPM) show overpotentials as low as those of noble metal catalysts for oxygen and hydrogen evolution reactions in 1 M KOH and 1 M H2SO4 solutions, respectively. Thereafter, the electrode pair with an array of anion- and cation-exchange membranes (AEMs and CEMs) in alternatively stacking manner showed the desalination of brackish water and seawater at specific energy consumption of 1.8 kW h m−3, with concurrent production of HCl and NaOH. The Faradaic efficiencies of the device for O2 and H2 production are >95% at J = 100 mA cm−2 over 20 h, while the initial pH values of the anolyte and catholyte remain unchanged. The proposed multi-functional electrolyzer is highly promising for converting electrical energy into hydrogen energy, simultaneously desalinating saline water, and producing value-added chemicals. Subsequently, we compared electrodialytic performance over unit cell thickness, types of ion exchange membranes, and number of stacks in the device.

This work is financially supported by Korea Water Cluster (KWC) as Korea Water Cluster ProjectLab. This work was supported by the Technology Innovation Program (or Industrial Strategic Technology Development Program-Alchemist Project) (NTIS-1415187362, 20025773, Development of building-Integrated Carbon Control Technologies) funded By the Ministry of Trade, Industry & Energy(MOTIE, Korea).
Solar Desalination Charger for Water Treatment and Value-Added Chemical Production
Authors: Kim Seonghun , Park Hyunwoong
Published: December 2024

This study presents a photoelectrocatalytic desalination charger for remediation of aquatic pollutants and production of value-added chemicals. Under 1 sun irradiation, a Co-WBVO (BiVO4 doped with W and deposited with CoOOH) photoelectrode and aqueous NaxC electrode (Na on carbon felt, NaxC) pair efficiently desalinates brackish water (0.171 M NaCl) through ion-exchange membranes at an ion transport efficiency of ~100%. The desalted chloride is partially oxidized by photogenerated holes into reactive chlorine species (RCSs) at a Faradaic efficiency (FE) of >90%. The in-situ generated RCSs are actively involved in the sequential oxidation of As(III) and NH4
+. Meanwhile, the desalted Na+ are rapidly inserted into NaxC without any accumulation. Upon coupling with the charged NaxC, electrocatalytic production of H2O2 via O2 reduction with carbon nanotubes, H2 via H2O reduction with NiMoS, and HCOOH via CO2 reduction with porous Bi are achieved at FEs of >80%. The as-designed PEC hybrid of the proof-of-concept can be applied to various purposes, including desalination, seawater electrolysis, production of value-added chemicals, and energy storage.

Acknowledgements

This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(2022R1C1C2011712). This work is financially supported by Korea Water Cluster (KWC) as Korea Water Cluster ProjectLab
Triggering Catalyst-Mediated Electron Transfer for Enhanced Ion Separation in Redox-Flow Battery Desalination System
Authors: Chen Tsai-Hsuan , Tsai Shih-Kuan , Hou Chia-Hung
Published: December 2024

Redox-flow battery desalination (FBD), an emerging electro-membrane separation technology, has garnered considerable attention due to its advantages such as continuous operation, low energy consumption, and relatively high average salt removal rate. FBD systems consist of current collectors, redox-flow electrolyte, and ion-exchange membranes (IEM) arranged in a 4-chamber structure. During operation, electron currents from the current collectors are converted into ion currents via the redox reaction of redox-active couples, such as Fe(CN)6
3− and Fe(CN)6
4−. Consequently, the ion current transported through the IEM leads to the production of diluted stream and concentrated stream in the dilute chamber and concentrate chamber, respectively.

To optimize the performance of the FBD system, enhancing the efficiency of the redox reaction is crucial. The reaction mechanism involves three steps. Taking oxidation as an example, the first step entails the transfer of Fe(CN)6
4− from the bulk solution to the surface of the current collector. Subsequently, Fe(CN)6
4− undergoes electron transfer to the electrode, forming Fe(CN)6
3−. The third step is the diffusion of Fe(CN)6
3− into the bulk solution. To shorten the path of redox couple and enhance the transportation of electron current, studies have attempted to use conductive electrode in FBD system, such as graphite felt and electrospun carbon fiber. However, limited attention has been given to the electrochemical reaction kinetics between redox couples. Hence, there is an opportunity to focus on catalyzing the redox reaction within FBD systems.

In this study, the FBD system performance were enhanced by incorporating an electrocatalyst. Nickel oxide (NiO) was chosen as the electrocatalyst and coated onto the graphite felt electrode (GF) through a hydrothermal method, resulting in the formation of the NiO-GF electrode. Electrochemical characterization conducted in Fe(CN)6
3−/4− electrolyte revealed that the NiO-GF electrode exhibited a smaller semicircle in EIS spectra and higher corresponding current in the CV loop, compared to the GF electrode. These results suggest that the NiO-GF electrode can effectively serve as a catalyst-mediated electrode in FBD process. Further investigations will be conducted to assess its performance in the FBD process, with a focus on its potential applications in high water recovery.

Figure 1
(Invited) Electrochemical Stripping for Ammonia Recovery: Mechanisms and Impacts of Chlorine Evolution
Authors: Ma Jinxing , He Jiazhou
Published: December 2024

Electrochemical stripping is an attractive alternative to converting NH4
+ to NH3(g) via the OH− produced by the hydrogen evolution reaction at the cathode. However, conventional electrochemical systems suffer from relatively low ammonia recovery (<80%) and need of external acid solution to absorb ammonia. To address the limitations, this work has developed a novel stacked system that uses anodic oxygen evolution reaction (OER) to in−situ produce acid and achieve chemical free ammonia recovery. To solve the issue of ammonia escape caused by constant current charging in conventional electrochemical systems, pulsed electric field (PEF) has been applied to regulate side reactions and interfacial mass transfer, weakening the sweeping effect of hydrogen gas produced by the cathodic hydrogen evolution reaction on ammonia gas. With an ammonia removal rate of 35.1 g−N m−2 h−1 and an electrical energy consumption of 28.9 kWh kg−N−1, our chemical−free system in PEF mode has achieved significantly higher ammonia recovery (>90%) from high-strength streams.

With regard to a high concentration of chloride, high potentials during electrolysis may lead to the generation of strong active chlorine. The non−specific oxidation of ammonia by active chlorine results in lower ammonia recovery. This study therefore combined in−situ Raman spectroscopy to explore the effects of chloride ion concentration and pH on ammonia speciation and recovery. Under strong acidic conditions, active chlorine mainly escaped in the form of Cl2(g), thus having a negligible effect on ammonia recovery. The proposed system maintained good stability after 390 h continuous operation. While the effect of active chlorine on ammonia oxidation was negligible, the reaction of chlorine with dissolved organic matter (DOM) can form more toxic by-products. This work further realized the effective control of by-products through the integration with activated carbon adsorption process.

Overall, the total cost to recover 1 kg of NH3–N using the electrochemical system from real waste stream is $15.9, which includes $11.1 for capital expenses (CapEx) and $4.8 for operating expenses (OpEx). This highlights the great potential for realizing high ammonia recovery in practical applications, and provides insights to innovations in treatment and resource recovery.
Enhancing Charge-Transfer Performance of Titanium Electrodes through Surface Coatings for Improved Electrochemical Systems
Authors: Krall Eric , Overland Alexandra E. L. , Rivera Jesus , Ceron Maira Raquel , Hawks Steven A.
Published: December 2024

Flow-electrode capacitive deionization (FCDI) is a promising new desalination technology. However, the commercialization of this technology faces hurdles, one of which is the lack of suitable electrode materials. Electrodes made of graphite for FCDI, while boasting excellent charge-transfer properties, are plagued by issues such as anodic oxidation, brittleness, and poor machinability. On the other hand, titanium electrodes exhibit superior durability, but suffer from poor charge-transfer performance due to self-passivation tendencies. To address this, our study aims to explore various surface coatings tailored to enhance the charge-transfer capabilities of titanium electrodes while preserving their corrosion resistance in a flow-electrode electrochemical system.

Our findings highlight the significant improvement achievable solely through surface coatings, enhancing the charge-transfer kinetics and stability of titanium electrodes. This advancement paves the way for the development of sophisticated electrochemical systems, characterized by practically ideal current collection capabilities.
Cell Design and Optimization for Efficient Hydrogen Production through Ammonia Electrolysis
Authors: Long Haowei , Paliwal Akhil , Gewirth Andrew A. , Kenis Paul J.A
Published: December 2024

Hydrogen, pivotal for a carbon-neutral energy framework, faces hurdles in storage and transport, leading to the consideration of ammonia as a viable hydrogen carrier. Compared to hydrogen, ammonia can be liquefied at moderate temperatures and has higher energy volumetric density. Despite ammonia's potential, presently an energy-intense thermal cracking process is necessary to convert it back to hydrogen. This prompted us to explore ammonia electrolysis as a less energy intense, more sustainable alternative for ammonia-to-hydrogen process. This method promises lower theoretical energy consumption and could in principle be driven by renewable energy sources. The number of research efforts focusing on ammonia electrolysis (ammonia electro-oxidation) is limited and most frequently focuses on catalyst development to minimize poisoning and overpotentials. Studies pursuing electrolysis cell designs for ammonia oxidation are even scarcer. Our study delves into design strategies for an ammonia electrolyzer, pairing ammonia oxidation with hydrogen evolution, aiming to optimize the entire process to enhance the prospects of ammonia as a hydrogen carrier.

This presentation will compare three different designs for ammonia electrolysis: batch, flow, and membrane electrolyte assembly (MEA) cell configurations. Each cell is characterized with respect to durability and product selectivity. Ultimately, we studied multiple factors, including flow rate, ammonia concentration, pH, and different operation protocols for MEA cells. The results provide guidance toward optimal cell design and operational protocols for a high-performing ammonia electrolyzer.
Designing Ni Single Atom Catalysts Mimicking the Ni SOD Enzyme for Efficient H2O2 Electrosynthesis
Authors: Lim June Sung , Kim Jinjong , Joo Sang Hoon
Published: December 2024

Hydrogen peroxide (H2O2) is one of essential commodity chemicals that is extensively used in various applications such as pulp & paper bleaching, wastewater treatment, and chemical synthesis. The electrochemical H2O2 production via oxygen reduction (2e− ORR) has emerged a promising method of H2O2 production, as it allows clean, continuous, and on-site H2O2 production. We have extensively explored the preparative chemistry of Ni single atom catalysts (Ni SACs) for H2O2 electrosynthesis, inspired by an H2O2-producing metalloenzyme, nickel superoxide dismutase (Ni SOD) with cofactor structures, which consists of a distorted square planar Ni2+ site, phenol group in tyrosine, and amine group in cysteine. We found that the formation of distorted square planar Ni2+–N
x
sites with an appropriate degree of distortion is crucial for boosting H2O2 electrosynthesis activity. The optimized Ni SAC exhibited the best H2O2 electrosynthesis mass activity among the reported non-precious metal SACs and carbon-based catalysts. By subjecting the optimized Ni SAC to post-synthetic heat treatments, different types of heteroatom functionality were formed with almost similar Ni2+–N
x
coordination structure. The catalyst possessing edge amine and phenol groups with distorted square planar Ni2+–N
x
sites exhibited further enhanced catalytic activity. The Ni TOF calculation revealed a synergistic effect between the Ni2+–N
x
sites and heteroatom groups.
BiVO4-Based Chloride Oxidation for Hypochlorous Acid (HOCl) Production, and Analysis of the Causes of Saturation Phenomenon
Authors: Kim Inho , Park Hyunwoong
Published: December 2024

Hypochlorous acid (HOCl) is commonly used in antibacterial and disinfection treatments due to its strong oxidizing properties in aqueous solutions. Chlor-alkali process, an electrolysis method based on sodium chloride (NaCl), is the primary method for producing HOCl in industry. However, this process incurs significant energy costs, approximately 150 TWh annually, and presents dangers of environmental pollution. To address these issues and achieve environmental and economic benefits, reducing energy consumption in HOCl production using renewable energy sources such as solar power is proposed as a viable solution. Various metal oxides like TiO2, WO3, and BiVO4 have been utilized in photocatalytic systems. Among these, BiVO4 photocathodes, with a bandgap energy of around 2.4 eV, efficiently absorb a significant portion of visible light spectrum, enabling effective oxygen generation from water. However, the low value of generated oxygen (O2) prompts the development of novel photocatalytic systems from a product value perspective. Chloride oxidation reactions, instead of water oxidation, present another promising avenue in photocatalytic systems.

In this study, we easily fabricate BiVO4 electrodes via spin-coating method. We investigate the synthesis of high-value chemicals by using the oxidation of Cl- to hypochlorous acid at the anode in electrolytes containing Cl-, such as sodium chloride (NaCl) solution. Furthermore, saturation phenomena were observed during the oxidation of sodium chloride to hypochlorous acid; when the oxidation reaction persisted for over an hour, the production of hypochlorous acid reached saturation, indicating no further increase. We aim to identify and analyze the fundamental causes of this phenomenon to understand the limiting factors in this process.

Acknowledgements

This work was supported by the Technology Innovation Program (or Industrial Strategic Technology Development Program-Alchemist Project) (NTIS-1415187362, 20025773, Development of building-Integrated Carbon Control Technologies) funded By the Ministry of Trade, Industry & Energy(MOTIE, Korea)

This work is financially supported by Korea Water Cluster (KWC) as Korea Water Cluster ProjectLab
Development of Highly Active, Selective, and Durable Non-Precious Electrocatalysts for Advanced Membrane Electrode Assemblies for Direct Seawater Electrolyzers
Authors: Bliznakov Stoyan , Bonville Leonard J. , Maric Radenka
Published: December 2024

Direct seawater electrolysis faces fundamental electrochemical challenges, such as suppression of chlorine adsorption and/or evolution reactions that poison the current state-of-the-art anode catalysts and accelerate the degradation processes in the anion exchange membrane (AEM). The technically favored solution path for addressing these issues includes development of novel selective catalysts and implementation of limited operating conditions. Therefore, development of highly active, selective, cost-effective, and stable seawater-splitting catalysts is required for a successful commercialization of the AEM water electrolyzers (AEMWEs). In this paper, we report on the development of selective and durable non-precious electrocatalysts for the OER, and demonstrate a durableperformance for over 1000 hours of advanced AEMWEs, operating directly with seawater. To fabricate the membrane electrode assemblies (MEAs), catalyst coated electrodes (CCEs) are assembled with Sustainion® X37-50 grade T anion exchange membranes. The anode CCEs are fabricated by spraying an ink prepared from nanostructured layered double hydroxide (LDH) catalysts that are synthesized by the solvothermal method and deposited directly onto platinum coated titanium porous transport layers (PTLs). The cathode CCEs are prepared by spraying an ink prepared from Renay-Nickel catalyst onto a nickel fiber felt. As prepared AEM electrolyzer cells operated with seawater and demonstrated durable performance for over 1000 hours.
Cathodic Protection System Against a Reverse-Current after Shut-Down in Zero-Gap Alkaline Water Electrolysis
Authors: Lim Young Jin , Jung Sang-Mun , Kim Yoona , Kim Yong-Tae
Published: December 2024

Growing the hydrogen economy requires improving the stability, efficiency, and economic value of water-splitting technology, which uses an intermittent power supply from renewable energy sources. Alkaline water electrolysis systems face a daunting challenge in terms of stabilizing hydrogen production under the condition of transient start-up/shut-down operation. Herein, we present a simple but effective solution for the electrode degradation problem induced by the reverse-current under transient power condition based on a fundamental understanding of the degradation mechanism of nickel (Ni). It was clearly demonstrated that the Ni cathode was irreversibly oxidized to either the β-Ni(OH)2 or NiO phases by the reverse-current flow after shut-down, resulting in severe electrode degradation. It was also determined that the potential of the Ni electrode should be maintained below 0.6 VRHE under the transient condition to keep a reversible nickel phase and an activity for the hydrogen evolution reaction. We suggest a cathodic protection approach in which the potential of the Ni electrode is maintained below 0.6 VRHE by the dissolution of a sacrificial metal to satisfy the above requirement; irreversible oxidization of the cathode is prevented by connecting a sacrificial anode to the Ni cathode. In the accelerated durability test under a simulated reverse-current condition, lead was found to be the most promising candidate for the sacrificial metal, as it is cost effective and demonstrates chemical stability in the alkaline media. A newly defined metric, a reverse-current stability factor, highlights that our system for protecting the cathode against the reverse-current is an efficient strategy for stable and cost effective alkaline hydrogen production.
Hydrogen Terminal Braunschweig – a Research Demonstration Facility Along the Hydrogen Value Chain
Authors: Hasché Frédéric , Sauss David , Oezaslan Mehtap
Published: December 2024

Two of the greatest challenges in the energy transition are still the transportation and storage of renewable energy. For a green hydrogen economy, electrochemistry will play a major role. This project will show a comprehensive integration of various hydrogen technologies to an integrated physical network at megawatt scale. Our demonstration facility, namely Hydrogen Terminal Braunschweig, is located in Lower Saxony, Germany and was established in Summer 2024 [1].

In the Hydrogen Terminal Braunschweig, the green hydrogen (H2) is generated by the world's first commercially available 1 MW electrolyzer prototype of anion exchange membrane (AEM) technology [2]. The produced H2 from the renewable energy will be stored and used for a heavy-duty truck refilling station (350 bar) as well as transported to internal and external fuel cell test benches via pipelines. In addition to the H2 supply, one of the external consumption points is also fed with electrolysis “waste” heat. The waste heat from the 1 MW electrolyzer is collected, processed in a high-temperature heat pump and supplied via a local heating network. Moreover, the technical interplay and conjunction between electrolyzers and fuel cells with a large battery storage system (1.1 MWh storage capacity) and photovoltaic systems to stabilize the electrical grid will be investigated in detail. Here, a medium-voltage switchgear enables off-grid island operation as well as partial load and full load scenarios of all connected electrical components via switch positions. Last but not least, we will develop an education and training program for various target groups in the field of hydrogen technologies and energy transition in the near future.

References

[1] https://magazin.tu-braunschweig.de/en/pi-post/opening-and-open-day-of-the-hydrogen-terminal-braunschweig/, press releases, 21. June 2024

[2] https://www.enapter.com/aem-electrolysers/aem-nexus/, Aug 2024