KOH Solution Research Articles

Devolopment of Co-doped Fe2O3 Nanoparticles for Electrochemical Supercapacitor

Co-doped Fe2O3 nanoparticles were synthesized by the co-precipitation method. These crystalline nanostructures were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The electrochemical characteristics include charge–discharge cycling, which improves the conductivity and capacitance for the high-performance supercapacitor. The CV analysis of the pure Fe2O3 and Co-doped Fe2O3 electrode was distinctive in the 1 M KOH solution case. The nanoparticle size electrode reveals enhanced specific capacitance compared to Co-doped Fe2O3 and Fe2O3 to the electrode has a specific capacitance of about 33.50 F×g-1 and 13.74 F×g-1 with a scan rate 5 mV×s-1. Keywords: Supercapacitor, Co-precipitation method, Electrochemical, Energy storage

Designing Switchable Transition Metal Nitrides/Carbides from High-Entropy PBA Derivative As Bifunctional Oxygen Electrocatalyst for Rechargeable Zinc-Air Batteries

In response to the growing energy and environmental challenges, considerable endeavors have been directed towards the development of sustainable and eco-friendly energy technologies as alternatives to fossil fuels. Moreover, rechargeable zinc-air batteries (RZABs) stand out due to their high energy density and environmental friendliness, although the sluggish cathode oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics restrict RZABs performance. Prussian blue analogues (PBAs), owing to their highly porous structure and tunable morphology, are often utilized as the precursors of the materials. Particularly, high-entropy PBAs (HEPBAs), formed by blending five or more metals in a random lattice, have achieved enhanced thermal and chemical stability via a robust structure with multiple transition metal ions. Meanwhile, transition metal carbides (TMCs) were investigated for ZAB applications due to their higher catalytic activity. Herein, we introduced CNT into HEPBA nanoparticles, followed by calcination processes, resulting in the synthesis of high-entropy metal carbides on CNT (HE-TMCs/CNT) which are effective for the bifunctional OER and ORR performance. HE-TMCs/CNT demonstrate superior activity towards the ORR (E1/2 = 0.77 V) in a 0.1 M KOH solution and OER (η = 330 mV @10 mA cm−2) in a 1 M KOH solution. The ZAB with HE-TMCs/CNT as the cathode demonstrated an open-circuit voltage of 1.39 V, providing a high energy density of 71 mW cm-2 under a current density of 102 mA cm-2. It exhibited the ability to be charged and discharged in cycles for up to 40 hours, revealing good stability under an applied current density of 5 mA cm-2. These results offer a straightforward pathway for the development of efficient bifunctional electrocatalysts for high-performance RZABs. Figure 1

Changing the Linking Functionality in a Triblock Co-Polymer for Electrolyzer or Fuel Cell Membrane or Ionomer for Chemical Stability Improvements and Potentially Other Consequences.

We have developed a versatile scalable triblock polymer system for anion exchange membrane (AEM) based electrochemical energy conversion devices. This system is uniquely suited to solving both the membrane and ionomer challenges for the commercialization of AEM water electrolysis or fuel cells. Using our advanced fundamental understanding of AEMs based on our work which began in 2010, we can design systems from first principles to match the needs of the device. A triblock ABA polymer is readily fabricated that has both chemical and mechanical stability. The synthesis of these systems is robust, high yield and amenable to high volume production. It utilizes a novel dual chain transfer agent to mediate the chain-transfer ring-opening metathesis polymerization (ROMP) of cyclooctene (COE) or the polymerization of isoprene (IP) to give the hydrophobic B block of the polymer. This is followed by the reversible addition-fragmentation chain transfer radial polymerization of chloromethylstyrene (CMS). The polyCMS (pCMS) blocks are then quaternized with an amine to give the cationic hydrophilic A block. Before quaternization the B block is hydrogenated to give either semi-crystalline polyethylene (pE) or amorphous polymethylbutylene (pMB) from pCOE and pIP respectively. The obvious achilles heal in this system from a chemical durability standpoint is the linking ether functionality between the hydrophobic and hydrophilic blocks. The material we have synthesized to date have exceptional chemical and mechanical stability. It performs very well in ex-situ testing with KOH solutions and in device testing we have demonstrated >500 h at 50°C in water electrolysis in 5 cm2 cells in 1M carbonate electrolyte at 0.5 A cm-2. We attribute the chemical stability to the fact that we post quaternize the membrane to give methylpipiridinium cations and we assume that this reaction does not fully penetrate down the hydrophilic chain. This leaves a hydrophobic un-quaternized region close to the hydrophobic block that does not allow access to the ether linkage by the hydrated hydroxide anion. Recently a new approach to the telehelic mid block pCOE has been reported that has no ether linkages and allows the hydrophobic outer blocks to be linked by a methylene linker. This gives use an opportunity to directly contrast the chemical stability of two identical triblock co-polymers one with an ether linkage and one with a methylene linkage between blocks. In this presentation we will show the results from ex-situ chemical stability test one at low temperatures and higher hydroxide concentration and one at higher temperature and lower hydroxide concentration. There are many examples in polymer electrolyte chemistry where a simple change leads to unintended consequences. The geometry of the ether linkage versus the methylene linkage will change the way that the polymer chains will organize and entangle in ways that are not currently predictable. To probe the mechanical, chemical and morphological difference between these two polymers we will fully characterize and contrast both polymers physical chemical properties including water uptake, ionic conductivity, DSC, TGA, tensile strength and morphology through SAXS, WAXS and HRTEM. Data for the two polymer membranes will also be contrasted and compared in small laboratory 5 cm2 single cells for both electrolysis in dilute carbonate and H2/O2 fuel cells using conventional catalysts.

Boron Modified Nife-MOF-74 Catalyst for Application in Advanced Anion Exchange Membrane Water Electrolyzers

Despite the promising potential of non-platinum group metal electrocatalysts for anion exchange membrane (AEM) electrolysis, their practical application remains a challenge.1 Metal–organic frameworks (MOFs) and their derivatives have gained significant attention due to their high surface area, 3D periodic porous structure, large porosities, diverse composition, and well-defined metal centers as potential OER electrocatalysts in AEM electrolysis.2 However, there is a limited research report that MOFs could be used in the membrane electrode assembly (MEA) test due to the inherent limitations, such as poor stability in water, especially under basic/acidic conditions and low electrical conductivities.3,4 To address these challenges, we present a novel approach involving the introduction of boron atoms into an aromatic carbon framework. In this study, we have successfully fabricated micro-nano flower-like bimetallic NiFe-MOF-74 doped with boron. These innovative materials exhibit exceptional catalytic activity, boasting an impressively low overpotential of 318 mV for OER at a laboratory-grade current density ranging from 10 to 100 mA/cm2. Moreover, they demonstrate rapid reaction kinetics, as evidenced by a small Tafel slope of 89 mV dec-1 in 1.0 M KOH solution. In addition, our research highlights the outstanding performance of boron-modified NiFe-MOF-74 as a robust anode material for AEM water electrolysis. This significant development paves the way for a promising electrocatalyst in the realm of anion exchange membrane water electrolysis. Our findings hold great potential for advancing the field and overcoming the existing challenges associated with non-platinum group metal electrocatalysts in AEM electrolysis.Reference:(1) Song, W.; Peng, K.; Xu, W.; Liu, X.; Zhang, H.; Liang, X.; Ye, B.; Zhang, H.; Yang, Z.; Wu, L.; Ge, X.; Xu, T. Upscaled Production of an Ultramicroporous Anion-Exchange Membrane Enables Long-Term Operation in Electrochemical Energy Devices. Nat Commun 2023, 14 (1), 2732. https://doi.org/10.1038/s41467-023-38350-7.(2) He, F.; Zheng, Q.; Yang, X.; Wang, L.; Zhao, Z.; Xu, Y.; Hu, L.; Kuang, Y.; Yang, B.; Li, Z.; Lei, L.; Qiu, M.; Lu, J.; Hou, Y. Spin-State Modulation on Metal–Organic Frameworks for Electrocatalytic Oxygen Evolution. Advanced Materials 2023, 35 (41), 2304022. https://doi.org/10.1002/adma.202304022.(3) Meena, A.; Thangavel, P.; Jeong, D. S.; Singh, A. N.; Jana, A.; Im, H.; Nguyen, D. A.; Kim, K. S. Crystalline-Amorphous Interface of Mesoporous Ni2P @ FePOxHy for Oxygen Evolution at High Current Density in Alkaline-Anion-Exchange-Membrane Water-Electrolyzer. Applied Catalysis B: Environmental 2022, 306, 121127. https://doi.org/10.1016/j.apcatb.2022.121127.(4) Zhang, B.; Zheng, Y.; Ma, T.; Yang, C.; Peng, Y.; Zhou, Z.; Zhou, M.; Li, S.; Wang, Y.; Cheng, C. Designing MOF Nanoarchitectures for Electrochemical Water Splitting. Advanced Materials 2021, 33 (17), 2006042. https://doi.org/10.1002/adma.202006042.

Unlocking the potential: strategic synthesis of a previously predicted pyrazolate-based stable MOF with unique clusters and high catalytic activity.

The metal-organic framework (MOF) constructed from [Co4Pz8] clusters (Pz = pyrazolate) and 1,3,5-tris(pyrazolate-4-yl) benzene (BTP3-) ligands was structurally predicted many years ago, and expected to be a promising candidate for various applications owing to its unique clusters and highly open 3D framework structure. However, this MOF has not been experimentally prepared yet, despite extensive efforts were made. In this work, we present the successful construction of this MOF, hereinafter referred to as BUT-124(Co), by adopting a two-step synthesis strategy, involving the initial construction of a template framework (BUT-124(Cd)) followed by a post-synthetic metal metathesis process. The effects of various cobalt sources and solvents were systematically investigated, and an innovative stepwise metathesis strategy was employed to optimize the exchange rates and the porosity of the material. BUT-124(Co) demonstrates high catalytic activity in the oxygen evolution reaction (OER), achieving a competitive performance with an overpotential of 393 mV at a current density of 10 mA cm-2, and also affords remarkable long-term stability during potentiostatic electrolysis in 1 M KOH solution, surpassing the durability of many benchmark catalysts. This work not only introduces a novel MOF material with promising properties but also exemplifies a strategic synthesis approach for pyrazolate-based MOFs, paving the way for advancements in diverse application fields.

Kinetics of Oxygen Catalyst Based on Pyrochlore Oxide Nano-Particles for Low Temperature Water Electrolysis

Alkaline water electrolysis is carried out at 60 to 80 oC using nickel-based electrode materials and highly concentrated KOH solutions, which make highly corrosive environment against the electrodes, the separator, the current collector, and the others of the cell. Reduction in operating temperature would be preferable to suppress corrosion, although it would also make the catalytic activity for OER and HER down, making the cell voltage up. Since oxygen evolution is known as a high overpotential reaction which is more than 400 mV with nickel-based oxides at 60 oC or more, and alternative materials with lower overpotential and higher stability for OER in AWE have been needed. This paper presents a novel oxygen catalyst nano-particles based on bismuth ruthenium oxide, in which ruthenium at the B site in the pyrochlore structure is partly replaced with manganese1).Mn-doped bismuth ruthenium oxide (MBRO) was prepared by precipitation of metal hydroxide precursor, which had been obtained by addition of NaOH solution into the metal salt solution containing Bi(III) and Ru(III) with Mn(II), followed by calcination at 600 oC. XRD, EDX, EXAFS, ICP-AES, and RBS were used for structural and compositional analyses of MBRO. The obtained oxide was added into distilled water and the solution was treated by ultrasonic vibration to make a suspension, which was then dropped on a titanium disk (4 mm diam.) and dried at RT for 24 h, resulting in oxide particles-coated titanium disk, in which no binders or ionomers were used in the process. The disk was mounted in a commercial rotating disk electrode and was used as the working electrode with a platinum counter electrode, an Hg/HgO reference electrode, and 0.1 mol/L KOH solution. Polarization curves were measured by LSV for OER, of which the results were analyzed to obtain the onset potential, Tafel slope, exchange current density. All measurements were performed at RT (25 oC).EDX and EXAFS studies of MBRO showed that Ru(IV) was replaced with Mn(IV) at the B-site of pyrochlore structure, and this doping made a single phase of pyrochlore structure oxide without sub-product up to 30 at% replacement . Linear sweep voltammetry revealed the overpotential of MBRO for OER was less than 200 mV and the Tafel slope analysis of the LSV curve gave 40 mV/dec or less. The onset potential and the Tafel slope were almost the same when Ru:Mn atomic ratio of MBRO was changed from 100:0 to 70:30 at%. Further analysis of the polarization curve indicated the exchange current density slightly decreased with increasing Mn ratio. These results suggest that Ru is the active site for OER but Mn is as well. The Tafel slope of OER catalysts reported in literatures is mostly 60 mV/dec or more, including more than 200 mV/dec of nickel-based oxides2,3). Therefore, MBRO is a hyper catalytic oxide for OER in alkaline media and can significantly reduce the overpotential of the anode in AWE even at ambient temperature.Ref.1) M. Morimitsu, Patent US.2022085387.A1.2) T. Shinagawa, A. T. Garcia-Esparza, K. Takanabe, Scientific Reports, Vol. 5, Article No.13801 (2015).3) S. Yagi, et al., Nature Communications, Vol. 6, Article No. 8249 (2015).

PFAS-Free: Robust and Chemically Stable Ion-Solvating Polymer Membrane Derived from Poly(arylene alkylene) for High-Performance Alkaline Water Electrolysis

Polymeric ion-solvating membranes1 derived from poly(arylene alkylene)s2 have emerged as promising candidates for alkaline water electrolysis, offering a PFAS-free, robust, and chemically stable alternative. This work focuses on the development of such a membrane with an emphasis on high resistance to gas crossover, addressing the challenges associated with conventional ion-exchange materials.The polymer membrane presented in this study demonstrated very good performance in alkaline water electrolysis. At 80 degrees Celsius, the membrane exhibits a specific conductivity of 36 mS/cm, underscoring its ion-solvating ability and efficiency in a 20 wt% KOH solution. The electrochemical performance is exemplified by the attainment of a 700-mA current below 2.6V with uncatalyzed nickel foam electrodes, showcasing the superior conductivity and efficiency in facilitating the electrolysis process.One of the key features of these membranes is their longevity, as evidenced by their ability to operate for more than 200 hours without any discernible voltage decay. This extended operational lifespan underscores the robustness and durability of the developed membranes, making them highly suitable for practical applications in alkaline water electrolysis.Furthermore, the membranes exhibit a high resistance to gas crossover, addressing a common challenge in electrolysis systems. This property ensures enhanced selectivity and efficiency by minimizing unwanted reactions and improving the overall electrolysis process.In conclusion, the presented work signifies a significant advancement in the development of ion-solvating polymer membranes derived from poly(arylene alkylene) for alkaline water electrolysis. The membranes not only outperform existing alternatives but also offer a sustainable and environmentally friendly solution by being PFAS-free. The demonstrated high performance, stability, and resistance to gas crossover make these membranes promising candidates for the advancement of alkaline water electrolysis technology, contributing to the development of efficient and environmentally conscious hydrogen production systems. Keywords: Alkaline; electrolysis; Poly (arylene alkylene)s; membranes; ion-solvating

Ni-Derived NiO Nanosphere Electrocatalyst for Hydrogen Evolution Reaction: The Effect of Synthesis Variables on Activity and Durability

Transition to a decarbonized society will rely on clean energy resources, in particular on "green” hydrogen—a renewable energy carrier that can be generated via water electrolysis [1]. Unlike proton exchange membrane water electrolyzers (PEMWE), anion exchange membrane water electrolyzers (AEMWEs) enable the use of earth-abundant transition metals in both the cathode and anode [2]. In addition, unlike liquid alkaline water electrolyzers, which use a highly concentrated alkaline media (6 M KOH), AEMWEs can operate with low-concentrated electrolyte, and even pure water [3]. Developing active and durable platinum group metal-free (PGM-free) electrocatalysts is crucial for the large-scale implementation of the AEMWE technology. Ni-based electrocatalysts have shown good activity towards the hydrogen evolution reaction (HER) in alkaline media [4]. Herein, carbon supported Ni-derived NiO nanosphere electrocatalysts are synthetized via a sol-gel method followed by thermal treatment under reducing atmosphere. We explored several synthesis parameters, i.e., Ni-to-carbon ratio, annealing temperature, and annealing time. We also investigated the impact of these synthesis variables on the HER activity in alkaline electrolyte. The catalysts were characterized by XRD, SEM, and EDS. The formation of Ni metal particles with a thin oxygen-rich layer on the surface was demonstrated by microscopy and crystallographic characterization. Following optimization, the HER overpotential of the best performing electrocatalyst at a current density of 10 mA cm−2 was reduced to ca. 130 mV. The catalyst durability was tested over 100 h in KOH solutions at different electrolyte concentrations using various testing protocols such as constant current hold and potential cycling. The catalyst showed higher HER activity (100 mV lower HER overpotential) and better durability behavior (0.15 mV/h lower degradation rate) compared to a commercial Ni supported Vulcan XC-72 electrocatalyst.

Integrating Electrochemical Analysis and Machine Learning for Enhanced Discovery of Conductive MOFs: A Database-Driven Approach

Metal-organic frameworks (MOFs) are highly versatile structures composed of metal ions linked by organic molecules. They offer a broad range of applications in electronics and light-based technologies due to their flexibility. However, the connection between metal ions and organic components often hinders efficient charge movement, which is essential for electrical conduction. To address this challenge, researchers have been innovatively designing MOFs to enhance their conductivity, which is typically low. This process is complex and time-consuming. To overcome these barriers, and to save both time and costs, we integrated machine learning (ML) with electrochemical testing. Our aim was to pinpoint ion and electron conductive MOFs from the Computation-Ready, Experimental Metal–Organic Framework (CoREMOF) Database, which contains over 14,000 MOFs. The ML approach predicted 84 intrinsically conductive MOFs, which were then subjected to rigorous experimental validation through synthesis and conductivity performance testing. Further experimental data confirmed that only two conductive MOFs, containing copper and pyrazole structures with carbonyl groups, exhibited both proton and electron conductivity. The differences between them lie solely in the preparation techniques and solvents used. Sample 1 was prepared using hydrothermal methods and alcohol as the solvent, and NH4@1 was prepared with an ammonium solution at room temperature. To understand deeper their intrinsic conductivity and semiconductor properties, we employed temperature-dependent conductivity and electrochemical measurements, including Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), Linear Sweep Voltammetry (I-V), and Mott-Schottky analysis. The EIS data showed a smaller semicircular arc for synthesized NH4@1, indicating its lower charge transfer resistance due to the presence of two different positive charge carriers on its surface. We investigated the effect of increasing positive charge carriers by raising the humidity up to 98% RH. EIS data showed that increasing positive charge has a significantly reduced charge transfer resistance of sample 1 compared to NH4@1. Because NH4@1 consists of ammonium and H3O+ simultaneously, causing saturation of positive charges and increasing charge transfer resistance. Mott-Schottky analysis further elucidated the electrical properties of compounds 1 and NH4@1, revealing their p-type behavior with negative slopes and flat band potentials of 0.61 V and 0.9 V, respectively. The CV analysis of pyrazole carboxylic acid in a 0.1 M KOH solution, using three reference electrodes, revealed reduction and oxidation peaks vs. Ag/AgCl. These peaks highlight the redox behavior of the linker, generating a stable carboxylate anion (-COO−) that facilitates charge hopping. This reversible redox activity is crucial for the charge transport mechanism within the MOFs. CV analyses confirmed the presence of different copper oxidation states in both compounds, with cathodic peaks indicating the reduction from Cu(II) to Cu(I), suggesting active charge transfer. Extensive electrochemical studies, encompassing both Mott-Schottky and EIS analyses, provided deeper insights into charge carriers and transfer resistance, areas not extensively explored in previous research on intrinsically conductive MOFs. Our results underscore the critical role of experimental validation of ML predictions in accelerating the discovery and characterization of conductive MOFs for potential applications in batteries.

Maximizing Quantum Hole Collection on Anatase TiO2 Thin Films with (001) Facets for Photoelectrochemical Oxigen Evolution Reaction Efficiency

Hydrogen production from water, a key element in the renewable energy portfolio, offers a solution to reduce reliance on fossil fuels. Photoelectrochemical (PEC) hydrogen production, using light-absorbing semiconductors and catalysts, offers a clean and cost-effective method for harnessing solar energy. To enhance the efficiency of PEC, this study explores the use of anatase TiO2 thin film photoelectrodes as an alternative to expensive and rare catalysts, aiming to generate hydrogen as a clean fuel with oxygen as a byproduct.Anatase titanium dioxide is a well-established functional material widely applied in the fields of environment and energy. Recognized as one of the premier materials for photocatalysis and a promising photoanode material for water splitting, titanium dioxide (TiO2) finds use in diverse applications such as dye-sensitized solar cells, perovskite-based solar cells, and cleaning devices. Its band gap of 3.2 eV, stability, strong absorption in the UV region, and energetics of the valence and conduction band edges make anatase particularly suitable for PEC water splitting, especially for the oxygen evolution reaction (OER).Our research focuses on the development of anatase thin films with strong [001] texture and (001) facets at the surface of the film. The (001) facets are known to accumulate photogenerated hole states while the [001] orientation imparts a negative flat band potential. We hypothesize that these two properties, (001) facets and [001] texture, are ideal for OER. This study combines these two structural characteristics within the semiconductor TiO2 layer to enhance PEC performance and maximize the efficiency of hole collection during water oxidation.Anatase TiO2 thin films with (001) facets and [001] orientation were hydrothermally synthesized on a fluorine-doped tin oxide (FTO) substrate and annealed at 500°C. The films exhibited [001] orientation and (001) faceting as shown by grazing incidence X-ray diffraction (GI-XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Photoelectrochemical measurements via cyclic voltammetry in a 0.1 M KOH and Na2SO3 solution demonstrated the films' hole collection efficiency under a 365 nm UV light source. The photoelectrochemical (PEC) and oxygen evolution reaction (OER) characteristics of anatase thin films were observed both under dark and light conditions. Prior to illumination, only the Ti3+/Ti4+ redox couple was observed with an onset potential of 0.01 V (RHE) and negligible OER at anodic potentials. When UV irradiated, the TiO2 thin films exhibited a photocurrent that increased through the anodic scan. The onset potential of photocurrent, measured in the presence of the hole scavenger, exhibited a negative shift ranging from -100 to -200 mV compared to the KOH onset potential. This shift is attributed to the film surface's limited efficiency in collecting holes for water oxidation at low potentials, as rapid recombination kinetics compete with water oxidation. Interestingly, the photocurrent observed with Na2SO3 electrolyte was 0.15 to 0.3 times more than what we saw with KOH electrolyte. Our preliminary results indicate a current density of ~2.0-2.5 mA cm-2 at 1.8 V and a hole collection efficiency of ~84 % at 1.23 V vs RHE, the thermodynamic water oxidation potential. In summary, we have made significant progress toward enhancing the PEC activity of anatase TiO2 thin films by optimizing the film structure for both reactivity and charge transport.

Bridging the Gap between Laboratory and Industrial Scale Electrochemical Characterisation of Raney Ni Electrodes for Alkaline Water Electrolysis

The most mature water electrolysis technology is alkaline electrolysis, where an aqueous solution of KOH is used as the electrolyte. While this technology has been used for decades, there is still a lot of potential to improve the performance of these devices. Much research is focused on the optimisation of the electrodes containing novel catalyst materials that lower the activation energy barrier of the electrolysis process. However, one of the issues described by Ehlers et al.1 is that the current academic electrolysis research is done under conditions that are far from practical (e.g. at low current densities, room temperature, and dilute electrolytes).In this study, we characterise a commercial Raney nickel electrode in various setups using a systematic series of experiments, including a typical laboratory-scale three-electrode setup, two different flow-cell setups and a 10-kW electrolysis stack of 17 cells. In addition to the cell geometry (electrode area ranging from 1 cm2 to 960 cm2), the varied measurement conditions include temperature (ranging from room temperature to 80 degrees Celsius), pressure (from atmospheric pressure to ), electrolyte concentration (from 0.1 M to 30 wt% KOH), and the level of Fe impurities in the electrolyte. The resulting electrochemical data received from different measurement setups and measurement conditions are compared, and insights about the challenges related to correlating laboratory experiments to industrial-scale experiments are provided. Figure 1. Alkaline electrolysis measurement setups with the typical measurement conditions used to study Raney nickel electrodes within this work – a typical laboratory-scale three-electrode setup (a), two different flow-cell setups (b, c) and a 10-kW electrolysis stack of 17 cells (d). Acknowledgements This work was supported by the Applied Research Program of Enterprise Estonia ("Developing and Validating Alkaline Electrolysis Stack Technology with Nanoceramic Electrodes", RE.5.04.22-0109) and by the Estonian Research Council (EAG273 "Highly active electrodes for precious metal free alkaline electrolysers" (1.09.2023−31.08.2024)). References J. C. Ehlers, A. A. Feidenhans’l, K. T. Therkildsen, and G. O. Larrazábal, ACS Energy Lett., 8, 1502–1509 (2023). Figure 1

Tetrazole-Containing Polyelectrolytes: A New Class of Ion-Solvating Membranes for Alkaline Water Electrolysis

Alkaline ion-solvating membranes, such as those based on polybenzimidazole (PBI), offer high ion conductivity and good gas barrier properties, making them promising for next-generation alkaline water electrolyzers.1 However, the stability of commonly used PBI derivatives is limited due to gradual backbone degradation. Consequently, alternative PBI chemistries and other polymer options like poly(vinyl alcohol),2 and carboxylate functionalized styrene-ethylene-butylene copolymers are being explored to address this inherent stability issue.3 In this study, we present the synthesis and characterization of a novel type of ion-solvating membranes for alkaline water electrolyzers. These membranes are based on tetrazole functionalized polymers derived from poly(styrene-co-acrylonitrile). A one-step click-type [3+2] cycloaddition reaction was utilized to introduce tetrazole pendants by converting acrylonitrile groups in poly(styrene-co-acrylonitrile). The degree of functionalization was controlled by adjusting the content of acrylonitrile units in the polymer. Subsequent treatment in aqueous KOH solution led to the formation of negatively charged tetrazolide pendants with high ionization degrees.The alkaline stability of the tetrazolides was evaluated using both DFT simulations and model compound studies, demonstrating remarkable stability with no degradation observed for over 3000 hours in 25 wt.% KOH at 80 °C. Physicochemical properties such as electrolyte uptake, swelling behavior, thermal stability, and ion conductivity were assessed for the synthesized polymers. The electrolyte-imbibed membranes exhibited high ion conductivity, reaching up to 90 mS cm-1 in 15 wt% KOH at 80 °C. Electrolysis operation using these membranes showed stable performance for 600 hours with no signs of degradation. 1 D. Aili, M. R. Kraglund, S. C. Rajappan, D. Serhiichuk, Y. Xia, V. Deimede, J. Kallitsis, C. Bae, P. Jannasch, D. Henkensmeier, J. O. Jensen, ACS Energy Letters, 2023, 1900–1910. 2 Y. Xia, S. C. Rajappan, D. Serhiichuk, M. R. Kraglund, J. O. Jensen, D. Aili, J Memb Sci 2023, 680, 121719. 3 D. Serhiichuk, D. Tian, M. R. Almind, Z. Ma, Y. Xia, M. R. Kraglund, C. Bae, J. O. Jensen, D. Aili ACS Applied Energy Materials 2024 7 (3), 1080-1091 Figure 1 Tetrazolation of poly(styrene-co-acrylonitrile) and formation of corresponding potassium tetrazolide following equilibration in aqueous KOH. Figure 1

PH Effects in the Electrochemical Reduction of CO at Cu Electrocatalysts in an MEA Cell Configuration

We explore the impact of pH and buffer on the electrochemical reduction of CO at Cu electrocatalysts in a membrane electrode assembly (MEA) cell. Anolytes included alkaline KOH solution with potassium hydrogen phosphate and potassium dihydrogen phosphate buffers with pH values ranging from 8 to 14. Results show near-neutral pH electrolytes enhance acetate selectivity. Figure 1 shows Faradaic efficiencies to acetate over 85% at a current density of 300 mA/cm². More alkaline electrolytes resulted in increasing HER along with coproduction of ethanol and n-propanol.Previous works have shown that ethylene production is enhanced at near-neutral pH values and other works have demonstrated that acetate is more favored in alkaline conditions, with ketene identified as a key intermediate. This study highlights the role of phosphate buffers in acetate selectivity at near-neutral pH. SEM, XPS, and XRD analyses show morphological and compositional changes in the Cu catalyst under different pH conditions. We propose that the phosphate buffers stabilize acetate precursors.Figure 1: Electrochemical performance measurement at different anolyte pH; Faradaic Efficiency of H2, C2H4, CH4, Ethanol, Acetate, and n-Propanol during CO electroreduction in a zero-gap MEA configuration at 300 mA*cm−2. Figure 1

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

(Invited) Overview of Ion-Conducting Polymer Membranes and Membrane Separators for Water Electrolysis

Traditional liquid alkaline electrolyzer uses a porous diaphragm to allow diffusion of hydroxide ion from a feed of concentrated KOH solution while separating anode and cathode and suppressing mixing of produced H2 and O2 gases. Although liquid alkaline electrolyzer is considered as a matured technology, recent renaissance of new electrode separators suggests there is significant potential for improvement in efficiency and cost reduction by lowering area specific resistance and increasing operation current density.Ion-conducting polymers (e.g., proton or hydroxide) are used as a key component of polymer electrolyte membranes, such as acidic proton exchange membrane (PEM) and alkaline anion exchange membrane (AEM), in electrochemical energy conversion and storage technologies including water electrolyzers. For example, the state-of-the-art PEM electrolyzers have used Nafion for a PEM and ionomer catalyst binder for decades, though it is not ideal proton-conducting membrane material for those applications. Recent pressure on perfluoroalkyl substrates (PFASs) from government and environmental activist groups due to their environmental and health hazard has attracted the development of alternative polymer electrolyte membranes based on hydrocarbon polymers within electrochemical society. Compared to perfluorosulfonated Nafion, hydrocarbon ion-conducting polymers (both PEMs and AEMs) can offer advantages of flexible synthetic tunability, lower gas permeability, and importantly lower production cost.In this tutorial, an overview of recent progress in the development of advanced porous membrane separators, PEMs and AEMs, their key membrane properties, and the state-of-the-art performance in applications of water electrolyzers will be discussed. Figure 1

Hollow-Structured Co-MoSx/Graphene Trifunctional Electrocatalyst for Self-Powered Hydrogen Production System.

Developing a single electrocatalyst that can facilitate both rechargeable aqueous metal-air batteries and water splitting has become a crucial focus in renewable-energy technologies. This necessitates addressing the three distinct electrocatalytic reactions: the electrochemical oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). Despite significant efforts, the creation of a alkaline medium based trifunctional catalyst with high activity at a low cost has proven to be a considerable challenge. Currently, Pt and its alloys have been considered as the most active catalysts for the ORR and HER, whereas noble-metal oxides such as IrO2 and RuO2 are considered as the golden standards of OER catalyst. However, noble-metals based catalyst have been suffered from their high cost, limited reserves in the Earth’s crust, and poor electrocatalytic stability. Moreover, these noble metals face challenges in simultaneously exhibiting trifunctional catalytic activity for ORR, OER, and HER. In recent study, Transiton metal sulfides(TMSs) have great attraction as trifunctional catalyts due to their eqrth abudance, tunnable band structure, and crystal structure. especially, one of widely used TMCs is MoS2 because of their Pt-like high catalytic activity for HER as well as thermodynamic electrochemical stability and rich catalytic sites in the planar nature. However, the most stable 2H (hexagonal) phase MoS2 suffers from poor electrical conductivity, low wettability, and aggregation indced reducing active catalytic sites and resulting high resistance. 2H MoS2 also shows poor activity for OER and ORR, thereby hampering its practical applications as trifunctional catalyst. To overcome this threshold, various strategies have been conducted to improve their electrochemical charateristics, such as defect engineering, heterojunction foramtion, phase transform and integrating porosity control. However, commonly considered method to synthesis requires complex multi-steps with high temperature, vaccum system, explosive gas, and toxic etchant.In this study, we successfully synthesized the homogeneous growth of a Co-based nanometer-scale metal-organic framework (MOF) on graphene oxide at room temperature. Furthermore, a facile one-pot solvothermal method was employed to synthesize Co-MoSx/Graphene, which consists of a hollow, heterogeneous bimetallic sulfide (Co3S4/MoS2 with Co-S-Mo bonding) within a sandwiched graphene/MoS2 layer, demonstrating superior trifunctional activity and stability. Incorporating a conductive graphene layer between MoS2 layers is an effective strategy for not only realizing high electrical conduction to MoS2 layers, but also increasing MoS2 interlayer spacing for high ion accessibility. Besides, a variety of techniques, including Cs-corrected scanning transmission electron microscope (Cs-STEM), X-ray diffraction(XRD), and X-ray absorption spectroscopy (XAS), are used to confirm the atomic configurations of Co-MoSx/Graphene structure and morphologies. Also, Raman, Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) were conducted to investigating the binding structure and chemical states. Furthermore, The internal electric field (IEF) within heterojunction, which induced from the differing electron density of the bimetallic species and the sandwiched graphene are contribute not only electron density structure optimization for enhancing reaction kinetics but also accelerating electron-hole exchange. The IEF in the microporous-heterostructure accelerates the diffusion of reaction intermediate with sufficient mass transport and facilitates a Graphene/MoS2-to-Co-MoSx pathway for enhancing redox kinetics of sluggish OER and ORR. Consequently, the OER and ORR-inactive MoS2, HER, and ORR-inactive Co3S4, along with less catalytically effective graphene, demonstrate outstanding performance when combined in the bimetallic sulfide based highly active heterojunctional structure. To investigate the electrochemical catalytic properties of Co-MoSx/Graphene, Rotating disk electrode(RDE) was used with three electrode measurment. The presence of MoS2/Graphene on Co3S4 and Co-MoSx bonding species in Co-MoSx/Graphene enhances the alkaline electrochemical catalytic activity by reducing overpotential and Tafel slopes(220 mV, 110 mV dec-1 in HER and 320 mV, 55.8 mV dec-1 in OER) under 1M KOH solution. Moreover, the ORR performance was evaluated by using Koutecky-Levich (K-L) Plot with different rotating speeds under 0.1M KOH. The electron transfer number (n) is closed theoretical value of 4.0 also shows outstanding performance of the onset potential, half-wave potential and kinetic current density (0.88 V, 0.67 V, and 10.4 mA cm-2), which is comparable that of Pt/C (0.92 V, 0.8 V, and 10.3 mA cm-2). Furthermore, Co-MoSx/G based rechargeable Zinc-Air battery achieve over 85% of theoretical zinc utilization efficiency and 1.4 times higher power density than a Pt/C + RuO2 air cathode based system. We believe that this work could provide a rational strategy for achieve trifunctional electrocatalyst and high performance self-powered hydrogen production system.This research was supported by the National Research Foundation of Korea (2022M3H4A1A04096482, RS-2023-00229679) funded by the Ministry of Science and ICT.

Reconstructed MgAl hydrotalcite, LDH-immobilized Ni(II)Schiff base complex composite for the electrooxidation of methanol

A novel heterogeneous catalyst, designated MgAl-C-Ni(II)L, was prepared by the immobilization of Ni(II) Schiff base complex, derived from the condensation of 1,2-diaminopropane with 2,5-dihydroxybenzaldehyde, in the reconstituted oxide MgAl-C. The behavior of the composite catalyst was tested in the electrooxidation reaction of methanol. The Electrochemical process was followed by cyclic voltammetry experiments in a 1 M KOH solution. The physicochemical characterization revealed the formation of Ni(II) Schiff base complex and their immobilization on the LDH interlayer.Structural-textural properties were explored and the possible complex insertion setting,as well as the formed interaction in the LDH interlamellar space were also investigated by density functional theory (DFT) based simulations. The MgAl-C-Ni(II)L catalyst has been combined with graphite powder to form a modified electrode for further improvement of the electrocatalytic performance. Significant enhancements in peak currents (Ipa) with increasing methanol concentration were observed in the electrochemical process. The modified electrode exhibited high electrocatalytic oxidation activity and stability in an alkaline medium. It induced electrocatalytic oxidation peaks at low potentials with higher current densities. A systematic study was carried out to investigate the effect of parameters such as scanning rate and methanol concentration on the electrooxidation reaction. The results obtained highlight the promising potential of MgAl-C-Ni(II)L composite as an efficient and potentially suitable catalyst for recent advanced electrochemical applications.

Effect of dissolved KOH and NaCl on the solubility of water in hydrogen: A Monte Carlo simulation study.

Vapor-Liquid Equilibria (VLE) of hydrogen (H2) and aqueous electrolyte (KOH and NaCl) solutions are central to numerous industrial applications such as alkaline electrolysis and underground hydrogen storage. Continuous fractional component Monte Carlo simulations are performed to compute the VLE of H2 and aqueous electrolyte solutions at 298-423K, 10-400bar, 0-8 molKOH/kg water, and 0-6 molNaCl/kg water. The densities and activities of water in aqueous KOH and NaCl solutions are accurately modeled (within 2% deviation from experiments) using the non-polarizable Madrid-2019 Na+/Cl- ion force fields for NaCl and the Madrid-Transport K+ and Delft Force Field of OH- for KOH, combined with the TIP4P/2005 water force field. A free energy correction (independent of pressure, salt type, and salt molality) is applied to the computed infinite dilution excess chemical potentials of H2 and water, resulting in accurate predictions (within 5% of experiments) for the solubilities of H2 in water and the saturated vapor pressures of water for a temperature range of 298-363K. The compositions of water and H2 are computed using an iterative scheme from the liquid phase excess chemical potentials and densities, in which the gas phase fugacities are computed using the GERG-2008 equation of state. For the first time, the VLE of H2 and aqueous KOH/NaCl systems are accurately captured with respect to experiments (i.e., for both the liquid and gas phase compositions) without compromising the liquid phase properties or performing any refitting of force fields.

Development and characterization of engineering plastic diaphragm for alkaline water electrolysis

Research on carbon dioxide free energy sources is increasing due to climate change, with green hydrogen gaining significant attention for its eco-friendly production process. This study focused on creating a diaphragm for alkaline water electrolysis using the TIPS method, utilizing the engineering thermoplastics PEEK and PPS for their excellent mechanical properties and heat resistance. DPK was employed as a diluent, and the phase diagram was established by measuring the crystallization temperature and cloud point based on polymer content. The morphology of the diaphragm, both surface and cross-section, was observed using an SEM, while tensile strength, alkaline stability, and permeability tests assessed its suitability for alkaline electrolysis conditions. The diaphragm with a polymer content of 20 wt% demonstrated a mechanical strength of 31.9 MPa, making it viable for operational use in alkaline electrolysis. All the diaphragms exhibited exceptional alkali resistance, with weight changes of less than 1 % in a 25 to 30 wt% KOH solution. Additionally, permeability tests indicated that permeability decreased as polymer content increased. Electrochemical evaluations revealed that the 20 wt% polymer content diaphragm achieved the best performance, delivering 188.7 mA/cm². This study confirms the potential of using these diaphragms in efficient and sustainable alkaline water electrolysis systems.

Improvement in electrochemical performance of SrTiO3 with rGO via composite (SrTiO3/rGO) strategy fabricated via solvothermal approach

Developing sustainable and highly effective electrocatalysts for the oxygen evolution reaction (OER) is a significant research target for precise custody of water splitting to fulfill worldwide energy demands. This study focuses on the fabrication of SrTiO3/rGO-based composite via a solvothermal technique, which works as an electrocatalyst for evaluating the efficiency of OER in alkaline media. The material displays outstanding OER efficacy in 1 M KOH solution with its cubic structure validated by the X-ray diffraction (XRD) study. The electrochemical study reveals that the SrTiO3/rGO composite has a minimal overpotential (222 mV) compared to SrTiO3 (289 mV) and the commercial catalyst RuO2 (367 mV). The SrTiO3/rGO composite also has a minimal Tafel plot gradient of 37 mV dec−1 whereas RuO2 has a Tafel value of 72 mV dec−1. The current material has superior properties compared to RuO2, a commercial catalyst for the OER. The SrTiO3/rGO composite shows exceptional stability for 40 h. The low conductivity of oxygen-deficient SrTiO3 perovskite can be improved by incorporating carbon-based rGO into it, as demonstrated by the minimal Rct (0.07 Ω) obtained from electrochemical impedance spectroscopy (EIS) analysis and an enlarged surface area of 250 cm2, as evidenced by electrochemical surface area (ECSA). Therefore, our research indicates that a particular morphology of metal oxide can improve the efficiency of electrocatalysis when combined with reduced graphene oxide (rGO), suggesting its potential for generating effective and environmentally friendly energy. Hence, these findings may improve the smooth passage of electrons and provide a novel perspective to function as an adequate substitute for RuO2, a commercial catalyst.