Half-cell Tests Research Articles

Unlocking the Ultrafast Deposition Kinetics within Bi-Tailored Core-Shell Structured Carbon Nanofibers for Highly Efficient and Ultrastable Sodium Metal Batteries.

Sodium metal anodes (SMA), featuring high energy content, low electrochemical potential and easy availability, are a compelling option for sustainable energy storage. However, notorious sodium dendrite and unstable solid-electrolyte interface (SEI) have largely retarded their widespread implantation. Herein, porous amorphous carbon nanofiber embedded with Bi nanoparticles in nanopores (Bi@NC) was rationally designed as a 3D host for SMA. In situ and ex situ characterizations, along with theoretical simulations unlock that the in-situ formed Na-Bi alloy significantly accelerates sodium metal nucleation and sodium ion diffusion kinetics, enabling uniform sodium plating within the void spaces and a stable SEI outside the carbon nanofiber. Particularly, the Bi@NC electrode achieved a high coulombic efficiency of 99.99 % at 3 mA cm-2 and 3 mAh cm-2 in half-cell tests, a cycle life of 1000 hours at 5 mA cm-2 and 10 mAh cm-2, and sustained performance over 600 cycles under harsh conditions under 30 mA cm-2 and 3 mAh cm-2 within symmetrical cells. The full battery assembled with a Na3V2(PO4)3@C cathode and Bi@NC anode delivered long-term cyclability over 800 cycles, demonstrating its potential for flexible application of sodium-based energy storage systems. This work highlights the Bi@NC electrode as a promising candidate for high-performance and flexible sodium metal batteries.

In-situ synthesis of Mn2SiO4 and MnxSi dual phases through solid-state reaction to improve the initial Coulombic efficiency of SiO anode for Lithium-Ion batteries

Silicon monoxide(SiO)-based anode materials have been extensively examined as high energy density for lithium-ion batteries, but still suffer from low initial Coulombic efficiency(ICE). Here, A novel SiO-MnO/Mn2SiO4-MnxSi anode material, prepared through scalable ball milling and heat treatment, is proposed for the first time, in which Mn2SiO4 and MnxSi alloy through solid-state reaction are embedded in the silicon oxide matrix to improve ICE. Half-cell testing shows that the ICE of pristine SiO increased from 52.5 % to 70.5 %, thanks to the solid-state reaction between SiO and MnO during the heat treatment, in which MnO consumed the SiO2 generated during the disproportionation of SiO, thereby reducing the first irreversible loss of Li+ during the lithiation process. In addition, the MnxSi alloy phase can improve lithium-ion diffusion ability to a certain extent. This report provides a new approach to alleviate the ICE performance of SiO-based anode materials.

Assembling Biodegradable Non-Metal Quinone-Based Supercapacitor with High Energy Density

Quinone-based materials have drawn a lot of attention particularly because of its large ion storage capacities from its low-molecular-weight moiety while having an eco-friendly element structure. Quinones, however, do not show any conductivity and are soluble to in organic solvent. Many reports have shown how to utilize such quinones as electrochemical capacitor’s active material, of which acetone impregnation is the simplest and the most practical method. However, battery cell configuration consisting of, current collector composed of metal, activated carbons (ACs) loaded with quinones synthesized from petroleum, and industrialized carbon black used as a conductive additive, are not eco-friendly. In this study, we conducted a thorough examination of the crucial parameters involved in the impregnation process of ACs to clarify the potential of biomass-based ACs in achieving enhanced electrochemical performance when employed as an organic battery. Subsequently, we applied the ACs to metal-free, organic supercapacitor, utilizing a carbon-based collector and woody biomass-based conductive additives.It was prepared that 7 different AC samples, including a commercially available petroleum-derived AC sample called Maxsorb®, and impregnated chloranil (CHL) and 1,5 dichloroanthraquinone (DCAQ) to each of the samples. Subsequently, a half-cell test was conducted on the sample to determine the extent to what CHL and DCAQ functions as a redox-active material when impregnated into each sample. To characterize each sample, we performed a Brunauer-Emmett-Teller (BET) surface area measurement, Barrett-Joyner-Halenda (BJH) pore distribution measurement, electrical resistivity measurement, and X-ray photoelectron spectroscopy (XPS) analysis to discuss the crucial parameters of quinone impregnation. To create a high-voltage aqueous organic supercapacitor with a metal-free and wood-based structure, we conducted the half-cell on each sample and utilized the best AC sample, a current collector synthesized from natural graphite, a conductive additive derived from a bamboo charcoal to fabricate a practical-sized electrode.From the BET surface area analysis and the half-cell test, one of the AC samples with a great peak in < 5 nm of diameter had a high utilization rate of 95.3% for the 30% CHL impregnated into the AC sample. Though the AC sample had only a surface area of 2271 m2/g compared to that of Maxsorb®which was 2989 m2/g, it achieved the utilization ratio comparable to that of Maxsorb® which was 94.6%. Samples with a peak diameter > 9 nm showed no redox capacity, while samples with a small broad peak in the range of 1–10nm, exhibited an approximately 60% utilization ratio. Hence, the pore size distribution was found to be a crucial aspect for quinone-impregnation, and the specific surface area plays a crucial role in determining the amount of CHL that can be effectively impregnated, as it provides more pore sites with diameters < 5 nm throughout the sample. As for DCAQ, it had a similar result compared to the CHL-impregnation, however in a slightly higher diameter range at about 5 nm for its optimized impregnation pore size. Therefore, identifying the pore size distribution of ACs is crucial in discovering new biomass-based material used for quinone-based supercapacitor.From the half-cell test with CHL, it was observed that the overpotential significantly increased from gold to SUS316 to graphite sheet as current collectors. To reduce the overpotential, we introduced a bamboo charcoal as a conductive additive, which effectively reduced the overpotential from 0.1 V to 0 V for SUS316 and from > 1 V to 0 V for graphite sheet at 1 C, while maintaining > 95% utilization rate. Subsequently, we fabricated a practical sized electrode (9 cm x 9 cm, 1 g) with CHL impregnated cathode and DCAQ impregnated anode from the best biomass-based AC, graphite sheet, and biodegradable 3D-printed battery cell case. The resulting full-cell supercapacitors exhibited a high energy density, demonstrating the feasibility of eco-friendly, metal-free wood-based organic supercapacitors.

Hydrothermally Synthesized SnS2 Anode Materials with Selectively Tuned Crystallinity as an Asset for Self-Healing Property and One Step in Situ Solid State Carbonization and Synthesis of C-SnS2

Tin-based chalcogenides such as SnS2 have been investigated as potential anode active materials for Li-ion batteries due to their high theoretical reversible capacities (e.g., 644 mAhg-1 for SnS2). These high capacities are associated with the reversible alloying of Sn with Li after the conversion reaction of SnS2 to Sn and Li2S. In this work, SnS2 was prepared via two approaches: hydrothermal synthesis of SnS2 and one step solid state synthesis of carbon coated SnS2. In the hydrothermal reaction, different molar ratios of tin chloride to thioacetamide were employed to synthesize SnS2 nanocrystals with varying fractions of the crystalline and amorphous states. An increase in molar ratio showed more crystalline SnS2 products with intensified different crystal plane orientations and formation of monolayers on the surface grains. During electrochemical analysis vs Li/Li+, partial reversibility of Sn and Li2S back to SnS2 was observed, leading to a unique self-regeneration property of the electrode. The presence of nano crystals and their level of crystallinity was examined by ex-situ Transmission Electron Microscopy (TEM) and X-ray Diffraction analysis (XRD). Galvanostatic Intermittent Titration (GITT) with in-situ Electrochemical Impedance Spectroscopy (EIS) after each galvanostatic step was used to evaluate the lithium diffusion coefficients (DLi+) to elucidate the lithium intercalation kinetics of SnS2 and its conversion to Sn and Li2S phases up to x ≈ 2.08 moles of lithiation or 300 mAh g-1. The SnS2 anode samples showed good cycling stability across 100 cycles at 0.1 C rate (560 mAh g-1) in half cell testing against Li chip. In full cell mode against NCM 811 cathodes, the cell retained a specific capacity of 160 mAh g-1 at 300th cycle.Further, we introduce a low cost, scalable solid state heat treatment method to produce SnS2-C materials, where the carbon not only facilitates electron transport, but also assists to mitigate the volume expansion of SnS2 during lithiation and enhance its structural stability. However, due to the phase transformations of SnS2 during heating, SnS2-C materials cannot be synthesized via solid state heat treatments of SnS2 with a carbon source. However, in this work, we show a novel method of producing carbon-coated SnS2 by thermally treating Sn-precursors and S with organic polymers. Using this method, SnS2-C materials were prepared, where the SnS2 crystal structure was retained and no impurity tin-sulfides such as SnS and Sn2S3 were formed. The electrochemical performance of the SnS2-C anode active materials was tested vs Li/Li+ and excellent cycling stability can be reported when compared to non-coated SnS2.Keywords: SnS2, anodes, composite anodes, carbon coating. Acknowledgement This research work is funded by Project “RESTINA”, where the main goal is to deliver “generation 3b cells for battery electric vehicles (BEVs)”. Funding agentM-ERA.NET has defined 6 quantified priorities, both in terms of their objectives and their budgetary impact: 1) support basic research in all scientific fields, 2) intensify the strategic research, 3) amplify the international dimension, 4) develop interdisciplinary research, 5) encourage "risky" projects and 6) establish equipment and infrastructure at the service of fundamental research and innovation. Figure 1

Direct Recycling of LiNixMnyCozO2 (NMC) Cathode Materials in Molten Salts

Direct recycling is an emerging technology to retrain the added value of compound structure by healing the compositional and structural defects in spent cathode materials. In our previous work, we developed a successful lithiation via ionothermal synthesis using a cost-effective Li halide as Li source and recyclable ILs as solvents for the direct recycling of LiNi1/3Mn1/3Co1/3O2 (NMC 111) cathodes.[1] Compared to the classic solid-state sintering approach, the flux synthesis in ionic liquids can achieve high-temperature phase products under a lower temperature and ambient pressure. The relithiated NMC 111 exhibited excellent electrochemical performance as a pristine NMC 111 in both half-cell and full-cell tests. For the direct recycling of commercial Ni-rich NMC cathodes, Li containing reciprocal ternary molten salts (RTMS) flux media can serve as both Li sources and solvents to restore Li in spent NMC under relatively low temperatures (below 300 °C).[2] Surpassing the traditional binary or ternary molten salts, the reciprocal ternary molten salts (RTMS) feature two cation species and two anion species, and a lower eutectic temperature. In addition, the highly charged flux media offered by molten salts provide efficient environments for transporting ionic reaction precursors for a successful direct recycling of spent NMC cathodes.Beyond direct recycling, direct upcycling of spent cathodes to the next-generation cathodes can maximize the value of EOL LIBs (Figure 1a). In a typical Li+, Na+||Cl-, NO3 - RTMS system, the reversible reaction: NaNO3 + LiCl ⇌ LiNO3 + NaCl enables a low eutectic melting point for the effective flux process under 300 °C and can provide an oxygen-rich environment, which are critical indexes for a low-temperature upcycling of spent NMC 111 to Ni-rich NMCs (eg. NMC 622).[3] After upcycling, the chemical composition of Up-NMC 622 is Li1.08Ni0.63Co0.19Mn0.18O2, having a restored Li content and higher Ni content compared to spent NMC 111 (Li0.93Ni0.33Co0.33Mn0.33O2), suggesting the successful upcycling in chemical composition. In the half-cell battery tests, the first charge/discharge capacities of Up-NMC 622 are larger than those of spent NMC 111 (charge capacity: 188.6 vs 140.1 mAh/g; discharge capacity: 153.6 vs 119.5 mAh/g at 20 mA/g). Thus, molten salts are promising and effective for the direct recycling/upcycling of spent NMC cathodes.

Enhancing Anode-Free Lithium Battery Stability By One-Step Thermal Treatment of Porous Carbon Fibers for Controlled SEI Formation and Surface Activation

Anode-free lithium batteries (AFLBs) hold great promise for high energy density, yet challenges such as low coulombic efficiency and dendrite formation impede their practical use. Herein, we present an optimal defect design of a carbon current collector that markedly enhances stable cycling reactions in AFLBs. A one-step thermal treatment is introduced to create defective surfaces with nano-sized pores on carbon fibers, guided by a comparative analysis of defect evolution under varying thermal energy and oxidation conditions. The thermally derived atomic vacancies and functional groups on the graphitized surface create uniform edge planes on the basal background of graphite, thereby facilitating lithium-ion diffusion and electrolyte reduction. Additionally, molecular dynamics simulations are employed to model the lithiated nano-defects and calculate lithium adsorption energy according to the lithiation and defect configurations. The experimental/computational analyses demonstrate the beneficial role of carbon defects in inducing uniform lithium deposition and controlling the properties of a robust solid electrolyte interphase (SEI), which is crucial for suppressing lithium dendrite. Consequently, the highly defective carbon current collector exhibits much longer cycling stability and higher coulombic efficiency compared to pristine carbon current collector and copper foil in half-cell tests. Furthermore, it shows a stable high-rate capacity at the high cut-off voltage (4.5 V) in full cell with NMC cathode. The results suggest innovative design strategies for carbon-based electrodes, focusing on the correlations between intercalation and plating mechanisms. Moreover, the rapid yet systematic thermal process demonstrates significant utility in carbon treatment, indicating its promising potential for making next-generation lithium batteries.

High-Loading Intermetallic PtCo Nanoparticles Supported on S-Doped Carbon for Oxygen Reduction Reaction Catalysts

Improving catalysts for the oxygen reduction reaction (ORR) is crucial for commercialization of proton exchange membrane fuel cells (PEMFCs) due to the sluggish kinetics of ORR at the cathode. Current ORR catalysts face challenges such as high costs associated with precious metals and poor durability. A common approach to improve catalyst activity is to alloy Pt with transition metals, such as cobalt and nickel, to control the d-band center. Instead of the disordered PtM, Pt intermetallic compounds show improved ORR intrinsic activity and enhanced stability. Also, doping carbon supports with heteroatoms such as nitrogen and sulfur is a feasible strategy to enhance the interaction between the metal nanoparticles of the catalyst and its support, which leads to improved performance and stability of the catalysts.In this study, we synthesized high-loading intermetallic PtCo nanoparticles supported on sulfur-doped carbon. High metal loading catalysts have significant advantages for practical PEMFC applications as they accelerate mass transport, leading to a reduction in voltage loss, especially under high current densities. To synthesize high-loading intermetallic PtCo nanoparticles, uniform sulfur doping on commercial carbon support is introduced, since sulfur sites can anchor metal nanoparticles even during a harsh heat treatment process. The sulfur sites not only minimize sintering, but also improve the electrochemical performance. Using this approach, high-loading (52.5 wt%) sub-5 nm PtCo intermetallic compounds with a Pt-rich shell (PtCo@Pt/S-BP) were successfully synthesized. The morphology and characteristics of the PtCo nanoparticles were confirmed through various techniques, including XRD, TEM, ICP-OES, HAADF-STEM, EDS mapping, and XPS analysis. In the half-cell test, PtCo@Pt/S-BP exhibited over 5-fold enhancement in mass activity and 6-fold increase in specific activity compared to commercial Pt/C. Additionally, the performance of PtCo@Pt/S-BP was maintained even after 50,000 cycles due to thermodynamically stable structure of the intermetallic phase and Pt-rich shell. This synthesis strategy provides a promising pathway for practical application of Pt-based catalysts in future PEMFCs.

Enhanced Oxygen Evolution Reaction Performance in Anion Exchange Membrane Water Electrolysis by Ru-Doped Ni-Fe Catalysts

Research on future energy is underway due to the problems caused by global warming and fossil fuel depletion. Of particular interest among these is hydrogen energy, which is garnering significant attention due to its high energy density per unit mass and its abundance in space. Additionally, it has the advantage of being eco-friendly since it can be produced by electrolyzing water and does not produce carbon dioxide as a by-product when used.The methods for electrolyzing water include alkaline water electrolysis (AWE), proton exchange membrane water electrolysis (PEMWE), and anion exchange membrane water electrolysis (AEMWE). In alkaline water electrolysis (AWE), achieving high current density is challenging due to significant ohmic losses arising from the considerable distance between the anode and cathode. For proton exchange membrane water electrolysis (PEMWE), the electrodes are closely situated within the membrane electrode assembly (MEA) structure, allowing for high current density. However, it suffers from the drawback of requiring precious metals due to the harsh corrosion conditions. AEMWE combines the advantages of PEMWE's compact structure and AWE's utilization of transition metals as catalysts. However, further research is needed on AEMWE as it has not yet reached the performance level of PEMWE, which uses noble metal catalysts known for their high reactivity in electrolysis.In water electrolysis, the hydrogen evolution reaction (HER) occurs at the cathode, while the oxygen evolution reaction (OER) takes place at the anode. In the HER, two electrons are involved in the reaction, whereas in the OER, four electrons are involved, resulting in a slower reaction rate for OER. Therefore, since the overall reaction rate of water electrolysis is determined by OER, research on the OER catalyst is essential. Among transition metals, Ni is known to be a good catalyst for OER, and research is underway on Ni-based catalysts enhanced in activity and durability through synergy effects with other transition metals such as Fe, Co, and Mo. However, as the performance still falls short compared to precious metals, incorporating a small amount of precious metals alongside can enhance the catalyst's performance. Precious metals such as Ir and Ru are known for their good activity in the OER. Nonetheless, Ir is considerably more expensive than Ru, and since Ru exhibits slightly superior activity, we intend to use Ru.There are several methods for synthesizing catalysts, including chemical precipitation, chemical vapor deposition, hydrothermal synthesis, sol-gel method, and electrodeposition. Among them, electrodeposition allows for the variation of catalyst composition, morphology, thickness by changing the composition of the solution, applied voltage, and time. Moreover, it occurs at room temperature and pressure and offers rapid fabrication times, making it advantageous for scaling up from lab scale to industrial scale in the future.Galvanic replacement is a spontaneous substitution reaction that occurs due to the standard reduction potential difference between two metals. The metal with a relatively higher (more negative) standard reduction potential undergoes oxidation to form ions, while the metal with a lower standard reduction potential is reduced from ions to metal. Through this reaction, a small amount of precious metals can be doped onto the surface in nanoparticle form. Since this reaction occurs spontaneously, no additional devices are required, and it can occur at room temperature and pressure, similar to electrodeposition, making it suitable for scaling up to industrial scale.Here in, we synthesized NiFe catalysts on SUS paper via the electrodeposition method. Moreover, we incorporated a small amount of Ru through galvanic replacement. We evaluated the performance of the catalysts under 1 M KOH conditions. In the half-cell test, NiFe/SUS exhibited an overpotential of 256 mV at 10 mA/cm2, which was reduced to 229 mV with Ru doping. In the single-cell test, Ru-NiFe/SUS showed excellent performance, achieving 8.3 A at 80°C and 2 V.

Design Principles for Improved Electrochemical Performance and Stability of Nonaqueous Mg-Electrolytes

Discovery of stable and efficient electrolytes that are compatible with magnesium metal anodes and high-voltage cathodes is crucial to enabling energy storage technologies that can move beyond existing Li-ion systems. Many promising electrolytes for magnesium anodes have been proposed with chloride as a co-anion that helps with reversible plating and stripping, however, Cl-containing electrolytes lack the oxidative stability required by high-voltage cathodes. We have previously demonstrated as a proof-of-principle that an oxygen-containing co-anion with higher oxidative stability (triflate) can be used as a co-anion to replace Cl–, albeit, with higher plating/stripping overpotentials (1). Given that Cl– has a higher tendency to bind to Mg2+ than triflate, in this work we focus on anions beyond halides with higher anion association strength in order to minimize these overpotentials. For this purpose, we employed a theory-guided screening approach to sample a wide chemical space and enable targeted synthesis of new salts. Based on the DFT-predicted anion association strengths, we identified alkoxide-based salts as a new family of co-anions with very favorable binding properties and oxidative stability. In order to probe the applicability of these co-anions in magnesium batteries, we have performed electrochemical evaluation using cyclic voltammetry and galvanostatic stripping and plating. We demonstrate that the addition of computationally-predicted alkoxide co-anions to a weakly coordinating electrolyte containing Mg(TPFA)2 (TPFA = tetrakis(perfluoro-tert-butoxy)aluminate) results in significantly lower stripping overpotentials (up to ~400 mV). We further show that there is a correlation between the stripping overpotential and the anion association strength, where alkoxides that have higher tendencies for Mg binding exhibit lower overpotential. Finally, the applicability of newly developed electrolytes was probed using half-cell battery testing, where we observe improved Coulombic efficiency and lower plating/stripping overpotentials. Collectively, this work outlines design principles for new electrolyte discovery and opens a new class of stable salts for next-generation magnesium batteries.

Comparative Electrochemical Analysis of Lithium and Lithium-Indium Alloy in All-Solid-State Battery

Lithium-ion batteries (LIBs) are widely used in a variety of applications due to their high energy and power densities, and long cycle life. With the expanding use of LIBs in electric vehicles and energy storage systems, there is very active research into all-solid-state batteries (ASSBs), which offer greater energy density than traditional LIBs and eliminate the inherent fire hazards. Since most of the detailed reactions involved in the performance and degradation of a battery are temperature-sensitive, so-called thermal activation processes, it is very important to accurately assess whether a battery can have the high performance and low degradation characteristics required under different climatic conditions. To evaluate the electrochemical properties of electrode materials in LIBs, a half-cell is typically constructed with the electrode of interest as the working electrode (WE) and lithium metal as auxiliary electrode (AE). Here, lithium metal is close to an ideal non-polarizable material, has a large capacity, and maintains a constant potential during charge/discharge, so it is widely used as AE material in LIB research. However, several issues arise when lithium is used as AE in ASSBs: Lithium metal undergoes mechanical deformation due to the relatively high internal pressure required to ensure good contact between lithium and solid electrolyte; When in contact with sulfide-based solid electrolytes, which are currently of interest due to their high ionic conductivity, side reaction products can lead to an increase in interfacial resistance; the growth of lithium dendrites, often observed in conventional LIBs, is still unavoidable. These issues all affect the half-cell signal, potentially causing a distorted evaluation of the WE’s characteristics.Lithium-indium alloy is being utilized as AE for ASSB half-cells to replace lithium metal. It exhibits excellent mechanical ductility and maintains a constant reduction potential over a wide stoichiometric range, ensuring excellent contact property and voltage stability. Moreover, it is very easy to fabricate through simple compression at room temperature. Nevertheless, the limited study on its electrochemical properties leaves uncertainty regarding its full functionality as AE for accurate evaluation of WE, particularly in extreme operational conditions. For instance, lithium-indium alloy are primarily based on alloying/dealloying reactions involving solid-state diffusion of lithium, which is generally considered to be a relatively slow process kinetically, while lithium only involves a kinetically favorable plating/stripping process on the surface. Therefore, a comparative analysis of these different reaction mechanisms in terms of kinetics is necessary. This presentation presents a comparative analysis of the electrochemical properties of lithium metal and lithium-indium alloys used as AEs in ASSB half-cells. In particular, the electrochemical properties of lithium-indium alloys with different reaction mechanisms with lithium are investigated over a range of temperatures and current densities, and these differences are discussed from a kinetic point of view. For this purpose, first, using a three-electrode half-cell with lithium or lithium-indium alloy as AE, we compared the electrochemical properties of these two AEs during half-cell operation by interpreting their potential and over-potential changes, and quantifying their detailed resistances. Then, through dc experiments on lithium and lithium-indium symmetrical cells, we identified differences in overvoltage behavior due to differences in their reaction mechanism. In particular, we noted distinct differences in the overpotential behavior of these two electrodes at low temperatures and high current densities. Furthermore, based on the results of a combined dc/ac electrochemical analysis, we derived the overvoltage that dominates the overall overvoltage at each of the two electrodes. Based on these results, we analyzed how the kinetic differences between the two electrodes affect the cathode half-cell signal, in order to derive key considerations for reliable ASSB half-cell evaluation. In this presentation, the advantages and disadvantages of lithium-indium alloy compared to lithium metal as AE will be discussed from a kinetic perspective, focusing on interfacial and bulk resistance (overpotential). Furthermore, methods for utilizing AE to conduct accurate and reliable half-cell tests will be proposed.

Highly Active NiRu/C Cathode Catalyst Synthesized by Displacement Reaction for Anion Exchange Membrane Water Electrolysis.

Anion exchange membrane water electrolysis (AEMWE) is highly promising for cost-effective green hydrogen production due to its basic operating conditions facilitating the use of non-noble catalysts. While non-noble Ni/Fe-based catalysts are utilized at the anode, its cathode catalyst still requires precious Pt. Due to the high cost of Pt and the sluggish hydrogen evolution reaction (HER) at the cathode in basic conditions, developing alternative catalysts to replace Pt is highly important. Here, a synthesis procedure for a Ru-based catalyst is reported and its high activity toward the HER in alkaline media is demonstrated in both half-cell and single-cell tests. The catalyst is synthesized in a two-step approach. A highly dispersed Ni catalyst is prepared on carbon support in the first step. In the second step, Ru is deposited on its surface using a galvanic displacement reaction. The uniqueness of this method is that Ru is deposited over the entire electrically conductive surface, resulting in an isotropic and homogeneous Ru distribution within the catalyst powder. It is demonstrated that this material remarkably outperforms state-of-the-art Pt/C catalysts in half-cell and single-cell tests. The single cell only requires 1.73V at 1A cm-2 with an overall PGM content of 0.05mg cm-2.

3D-stacked electrospun iron-doped nickel cobalt oxide nanofibers as integrated electrodes for anion exchange membrane water electrolysis

The commercialization of anion-exchange membrane water electrolysis (AEMWE) requires the development of highly active, stable, and cheap anode catalysts for the oxygen evolution reaction (OER). In this study, we proposed electrospun iron-doped NiCo2O4 (NCO) nanofibers on nickel foam (NF) and evaluated the performances of the resulting samples (FeX-NCO/NF; X = iron loading in NCO (0, 5, 10, and 15 at %)) as unitized anodes for the OER. Among the fabricated electrodes, Fe10-NCO/NF exhibited the lowest overpotential of 352 mV at a current density of 50 mA cm−2 in a half-cell test owing to its improved intrinsic activity. In an AEMWE single-cell test, Fe10-NCO/NF as anode showed high current density (932 mA cm-2 at 1.8 V) and long-term stability for 150 h The improved AEMWE performance of Fe10-NCO/NF was attributed to efficient mass transport enabled by superhydrophilic three-dimensional porous structure featuring stacked nanofibers.

SnO2–SnS2/graphene heterojunction composite promotes high-performance sodium ion storage

The design of electrode material nanostructures including reducing material sizes and designing appropriate heterostructures, has great potential in improving charge storage dynamics and enhancing practical performance. In this study, we present the innovative synthesis of SnO2-SnS2/graphene heterojunction composite materials via a controlled vulcanization reaction process. The unique structure endows the composite with high electronic conductivity, rapid ion diffusion rates, elevated electrochemical activity, excellent structural stability, and abundant reaction sites, making it a highly efficient anode material for sodium-ion batteries (SIBs). Half-cell tests demonstrate that the SnO2–SnS2/r–G composite achieves a first Coulombic efficiency of 77.3% at a high current density of 5 A/g, showing remarkable cycling stability. Remarkably, the composite retains a reversible capacity of 330 mA·h/g after 1000 cycles, with a capacity retention rate of 77.5%. Moreover, we elucidate the specific sodium storage mechanisms of the heterojunction composite electrode via in-situ and ex-situ characterization methods. Furthermore, a full battery utilizing Na0.53MnO2 as the cathode and SnO2–SnS2/r–G composite as the anode exhibits outstanding rate performance and long-term cycling stability. This method of heterostructure design and fabrication, coupled with the exceptional performance metrics, suggests that the SnO2–SnS2/r–G heterostructure is a promising candidate for advanced anode materials in SIBs applications.

Ultralow Ru-doped NiFe catalyst on stainless-steel fibers for enhanced oxygen evolution reaction in anion-exchange membrane water electrolysis

Designing high-performance, stable electrodes for the oxygen evolution reaction (OER) is essential for anion-exchange membrane water electrolysis (AEMWE) in industrial-scale hydrogen production. AEMWE has not yet been commercialized due to the high cost of precious metal catalysts and unsatisfactory performance of non-precious metal catalysts. Although various anodes are being developed to replace expensive Ir-based catalysts, low-cost catalysts that demonstrate a balance of performance and stability remain limited. In the present study, we fabricated a NiFe catalyst on a corrosion-resistant stainless-steel fiber paper substrate using a simple electrodeposition method and introduced small amounts of Ru via galvanic displacement. In half-cell tests, an enhanced overpotential of 229 mV was observed for the Ru-NiFe/SS anode at 10 mA/cm2. Using Ru-NiFe/SS as an anode for OER in AEMWE assembled with a commercial Pt/C cathode exhibited high performance with a current density of 8.73 A cm−2 (at 2.05 Vcell and 80℃). Long-term stability tests also showed that the Ru-NiFe/SS anode had higher stability than commercial IrO2 electrodes at 1 A cm−2 and 80℃ for 50 h. Therefore, Ru-NiFe/SS can be considered an alternative to conventional Ir-based electrodes to reduce hydrogen production costs.

Enhancing Efficiency and Durability of PEM Water Electrolysis with Low Iridium Loading through Nanofiber-Modified Porous Transport Electrodes

Hydrogen plays a significant role in the transition of the global energy system towards achieving net-zero emissions. According to the “Hydrogen for Net-Zero” report by Hydrogen Council and McKinsey & Company, the demand for clean hydrogen could reach 140 metric tons (MT) by 2030, with a further increase to 660 MT by 2050. For future high-volume production of green hydrogen, Proton Exchange Membrane Water Electrolysis (PEMWE) is a crucial technology due to its advantages of high-purity hydrogen, large operational current densities, and great energy conversion efficiency [1]. However, the use of precious metal-based catalysts for the sluggish oxygen evolution reaction (OER) on the anode side hinders the high-volume manufacturability of PEMWE. To ensure cost-effectiveness in large-scale PEMWE deployment for hydrogen production, developing strategies to reduce Iridium loading to 0.1 - 0.2 mg Ir/cm2 without compromising overall performance is essential. The challenge of reducing Ir loading also involves improving or maintaining the electrical contact between the catalyst layers and the substrate [2-3].Smoltek Hydrogen has made significant strides in achieving low iridium loading through our innovative Porous Transport Electrode (PTE) concept. This approach involves modifying a Porous Transport Layer (PTL) by growing vertically aligned Carbon Nanofibers (CNFs) using our in-house patented technology, efficiently increasing surface area [4]. Following this modification, a protective layer of corrosion-resistant and conductive material (e.g., Platinum) is applied to the CNFs. Subsequently, an OER catalyst layer is deposited utilizing a three-electrode cathodic electrodeposition method (Fig. 1a and 1b). The electrodeposited Ir catalyst exhibits strong adhesion to the CNF PTEs, resulting in a high electrical conductivity [5].In this work, we successfully reduced Ir loadings to 0.1 mg/cm2 in the PTE, demonstrating excellent mass activity in the half-cell tests (Fig. 1c). In the PEMWE tests, the polarization curves of electrodes with low Ir loading exhibited superior performance compared to cells with significantly higher Ir loading (Fig. 1d). The next step of our research involves conducting constant current durability tests for over 600 hours on PEMWE operation using low Ir loaded PTEs. The aim is to minimize degradation and overcome mass transport limitations, particularly at higher current densities.These unique PTEs developed by Smoltek Hydrogen, with CNF technology, maximize the electrode surface area and pave a new way to increase the utilization ratio of catalyst surface at a low loading amount, which makes it a competitive anode material in today’s PEMWE market. References https://www.iea.org/reports/hydrogen-2156#dashboardMöckl et al. J. Electrochem. Soc., 2022, 169, 064505.Bernt et al. Chem. Ing. Tech., 2020, 92, 31-39.https://www.smoltek.com/applications/electrolyzers/Krivina et al. Adv.Mater., 2022, 34, 2203033.https://publications.jrc.ec.europa.eu/repository/handle/JRC104045 Figure 1

A Simple Approach for Modulating the Active Site in Fe-Based Electrocatalysts

Proton Exchange Membrane Fuel Cells (PEMFCs) have garnered attention as a next-generation, environmentally friendly energy solution to address issues like the climate crisis and depletion of fossil fuels resulting from excessive usage. Nevertheless, the commercialization of PEMFCs faces challenges due to the use of expensive platinum catalysts for the Oxygen Reduction Reaction (ORR). In contrast, Anion Exchange Membrane Fuel Cells (AEMFCs) offer advantages by utilizing cost-effective non-platinum catalysts, making ongoing research on non-platinum catalysts for AEMFCs essential. Numerous studies have been conducted to develop M-N-C catalysts in nanoparticle units using transition metals such as Fe, Co, and Ni for AEMFCs. Notably, Fe-based catalysts with FeNx active sites are considered representative candidates for AEMFCs. Moreover, recent research aims to advance Fe catalysts by incorporating single-atom active sites to enhance mass transfer and improve reaction efficiency at the atomic level.We have developed a straightforward method for synthesizing an Fe catalyst. The catalyst, synthesized through a redox reaction between aniline and a metal ion, followed by pyrolysis, exhibited remarkable durability and activity for the Oxygen Reduction Reaction (ORR). Notably, it possesses an active FeNx site crucial for ORR. Furthermore, by simply altering the solvent during the synthesis process, we observed a variation in the Fe-to-N ratio. Particularly noteworthy was the synthesis of Fe4N, which demonstrated activity for the Oxygen Evolution Reaction (OER). This synthesis method allows for the controlled manipulation of the catalyst's chemistry by varying the solvent, resulting in the production of Fe-based catalysts with either FeNx or Fe4N active sites, active for ORR and OER, respectively. To understand the catalyst's characteristics based on the solvent used during synthesis, we conducted a comprehensive characterization using techniques such as Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The electrochemical activity was investigated through a half-cell test, and efforts were made to interpret the results based on the catalyst's properties.

Unravelling Effects of Microstructural Electrode Architecture on Cell Performance and Aging - a Combined Experimental and Simulation-Based Study on Commercial 21700 Lithium-Ion High-Energy Cells

In order to balance energy and power density of Li-ion batteries – and to ensure a long battery life – it is crucial to understand in detail how the composition and the microstructural design of the electrodes affects their capacity and kinetics.In our study we compare different commercial 21700 high-energy cells with very similar capacities (5 Ah) and energy densities (264 Wh/kg, 735 Wh/l) according to the supplier’s data sheets. However, in electrochemical tests, these cells showed significant differences with respect to rate capability and cyclic ageing. Detailed microstructural, chemical as well as electrochemical tests utilizing rebuilt half cells and symmetrical cells were done to identify microstructure-property relationships and the most critical microstructural parameters. In doing so, our study contributes to derive guidelines for optimized microstructural electrode design that combines energy with power and a long battery life.For material and microstructural analyses of fresh and aged cells, we used complementary methods such as optical and scanning electron microscopy, µCT- and FIB/SEM tomography, EDS and XRD to characterize the architecture of the electrodes at different length scales. We combined these results with results from detailed electrochemical studies such as OCV and half-cell tests with rebuilt cells as well as electrochemical impedance spectroscopy. Moreover, the 3D data from FIB/SEM tomography has been used as the input for microstructure-resolved simulations in the framework BEST, which allows for further investigation of the electrode microstructure and its effect on the electrochemical behaviour. In doing so, we gained a comprehensive dataset that allowed us to understand the different electrochemical behaviour of the different cells in the pristine state as well as their different behaviour during cyclic ageing.Some of the main findings are: (i) Different suppliers realize the same nominal capacity and energy densities of their cells by different electrode loadings; we observed differences of about 25 %; (ii) All suppliers strive to highly densify both, cathode and anode. Typical densities are 3.4 – 3.6 g/cm³ for the cathode and 1.5 – 1.6 g/cm³ for the anode. (iii) All investigated cells contain Si-rich phases within the anode, however, the chemical composition and the morphology is quite different and affects the electrochemical behaviour; (iv) We found significant differences in the binder-additive content; microstructure-resolved simulations indicate that this critically affects the electronic conductivity of the electrodes and thus, their electrochemical behaviour; (iv) The rate capability of the cells is significantly affected by the areal capacity of the electrodes (and presumably, their electronic conductivity); (vi) This in turn affects the cyclic aging behaviour of the cells. The investigated cells exhibit significant differences under various cycling protocols; we varied upper and lower cut-off voltage as well as the C-rate to investigate how microstructural features affect aging under different conditions.Within the talk, we will provide detailed insights into the results briefly outlined above and try to put the individual pieces of the puzzle together into an overall picture to elucidate how different microstructural features in combination determine the performance and cycling stability of the cells. Figure 1

Thin Film Based Membrane Electrode Assemblies for Solid-State Ammonia Synthesis

Ammonia is the of the most crucial chemicals and currently primarily produced through the Haber-Bosch process causing the industrial ammonia production to emit more CO2 than any other chemical-making reaction. While the current primary function of ammonia lies within the fertilizer production, it can also be directly used as a fuel for power generation or in the maritime industry. Compared to hydrogen, ammonia has superior storage and transportation capabilities due to its greater volumetric energy density and mild conditions for liquefication. Given the need of reducing global carbon emissions, ammonia could be synthesized electrochemically using air, water and electricity by the Solid-State Ammonia Synthesis (SSAS). Protonic ceramic cells operate within an intermediate temperature regime of around 450 - 550 °C which is well suited for this process. Within our work, we present a tubular membrane electrode unit entirely made of ceramic components based on a barium zirconate thin film electrolyte. An ammonia production rate of 9.06 × 10-10 mol s-1 cm-2 and a Faradaicefficiency of 6.58% were achieved using a NiO-BaZr0.7Ce0.2Y0.1O3- δ | BaZr0.8Y0.2O3- δ | Ru@Ba0.5Sr0.5TiO3-δ cell.A key innovation lies in the production of dense BaZr0.8Y0.2O3-δ electrolyte layers, ranging from 1 to 5 µm in thickness, utilizing a Closed-Field Unbalanced Magnetron Sputtering (CFUMS) process. This technique allows precise adjustments of stoichiometric ratios within the perovskite structure, offering improved sputtering yields compared to conventional methods. Furthermore, the crystallinity, phase purity, and microstructure of sputter-deposited thin films are enhanced through selective laser annealing (SLA), resulting in high-density films composed of single-phase BaZr0.8Y0.2O3-δ with average crystallite sizes of 200 nm while avoiding substrate damage from thermal stress. Electrochemical performance was evaluated through impedance spectroscopy, half-cell tests and full cell tests providing insights into the efficacy of the developed tubular membrane reactor for the electrochemical synthesis of ammonia. The results demonstrate the feasibility of utilizing ceramic proton conductors in SSAS, particularly highlighting the potential of high-pressure operation up to 80 bars in tubular cells at relatively low temperatures around 450 °C, thereby achieving attractive NH3 production rates.This research contributes to the evolving landscape of sustainable ammonia synthesis by presenting a novel approach that integrates advanced materials and manufacturing techniques. Electrification and decentralization of the ammonia supply chain will expand the market by supporting its current use as fertilizer source and enable a new route as green energy carrier paving the way for an ammonia-based economy. Figure 1

Bringing GDE Half-Cell and MEA Single Cell Testing Closer Together

In the context of the energy transition, the fuel cell represents a key technology. On the way to higher performance and efficiency, the development and testing of catalysts for the oxygen reduction reaction (ORR) is crucial [1]. Over the past years, the gas diffusion electrode (GDE) half-cell setup has been introduced as a bridging tool between RDE half-cell testing and MEA single cell testing for catalyst characterization [2,3]. Compared to the MEA testing, the GDE proved to be pronounced faster and cheaper, while still reaching relevant current densities (3 A cm-2) other than RDE setups. In recent studies the potential and reliability of this technique has been proven. It was shown, that the GDE can correctly predict trends of catalytic activity in the MEA until the mass transport limitation in the MEA appears. Furthermore, the mass transport influence of ionic liquid modifications of the catalyst layer could also be deduced in the GDE half-cell, without the tedious ink development needed for MEA preparation [4]. Proton transport is not limited in the GDE half-cell, if the catalyst layer is directly immersed within the liquid electrolyte. Depending on if the intrinsic activity of the catalyst or the proton resistance wants to be studied this is an advantage or disadvantage. This opens the question, whether proton mass transport resistance can also be studied in the GDE setup, when separating the catalyst layer from the liquid electrolyte through a membrane. Adding a membrane will change the mass transport of the system by two aspects: First, the protons must be transported through the membrane to reach the catalyst layer and second, the formed water during the reaction can no longer be flushed away from the liquid electrolyte but must leave through the gas diffusion layer (GDL). Developing such a manufacturing procedure and measurement protocol to gain valid, reproducible, and reliable results is scope of this study.In the first step the membrane (Nafion™ NR211) was spray coated via an ultra-sonic spray coater with a commercial Pt/C catalyst (HiSPEC®3000, 20 wt% Pt). Afterwards the catalyst coated membrane (CCM) was hot-pressed to the GDL (Toray™ TP-090-T5). Different pressing times and pressures were examined. The resulting electrode was characterized using a commercial GDE half-cell (Flexcell® PTFE, Gaskatel GmbH) and the measurement protocol according to Schmitt et al. [5].On the way towards the final manufacturing procedure many challenges have been overcome. The biggest was how to deal with membrane swelling and detachment when measuring at high current densities where large quantities of water are produced. To cope this issue a GDL without a microporous layer was chosen to support the water transport. Furthermore, the application of a membrane in a GDE half-cell brings up - yet unsolved – challenges, when using impedance spectroscopy for iR-correction.With our final manufacturing procedure and measurement protocol additional mass transport resistances and limitations can be captured in the ohmic region and at high current densities in the GDE half-cell-setup.In summary we showed a working proof of concept for the membrane application in GDE half-cell setups, which give comparable results to actual MEA measurements and remaining the advantages of GDE testing.Literature:[1] Banhamet al. ACS Energy Lett. 2017, 2, 629. [2] Ehelebe et al. ACS Energy Lett. 2022, 7, 816. [3] Schmitt et al. Journal of Power Sources 2022, 539, 231530. [4] Schmitt et al. Energy Adv. 2023, 2, 854. [5] Schmitt et al. Electrochemistry Communications 2022, 141, 107362.

Boosting the Oxygen Reduction Performance of Fe–N–C Catalyst Using Zeolite as an Oxygen Reservoir

Non-precious metal electrocatalysts (such as Fe–N–C materials) for the oxygen (O2) reduction reaction demand a high catalyst loading in fuel cell devices to achieve workable performance. However, the extremely low solubility of O2 in water creates severe mass transport resistance in the thick catalyst layer of Fe–N–C catalysts. Here, we introduce silicalite-1 nanocrystals with hydrophobic cavities as sustainable O2 reservoirs to overcome the mass transport issue of Fe–N–C catalysts. The extra O2 supply to the adjacent catalysts significantly alleviated the negative effects of the severe mass transport resistance. The hybrid catalyst (Fe–N–C@silicalite-1) achieved a higher limiting current density than Fe–N–C in the half-cell test. In the H2–O2 and H2–air proton exchange membrane fuel cells, Fe–N–C@silicalite-1 exhibited a 16.3% and 20.2% increase in peak power density compared with Fe–N–C, respectively. The O2-concentrating additive provides an effective approach for improving the mass transport imposed by the low solubility of O2 in water.