Cell Setup Research Articles

Low-Cost and Sustainable Aqueous Lithium-Ion Batteries by All-Organic PTCDI Anodes

Electrolyte engineering has been key to the advancement of aqueous lithium-ion batteries (ALIBs), for example, the introduction of water-in-salt electrolytes (WiSEs) has enabled ALIBs to cycle well and to operate at potentials far beyond the electrochemical stability window of water. WiSEs are, however, intrinsically based on high concentrations of salt(s) which furthermore often are expensive and fluorinated, and therefore defeats the aim of ALIBs being low-cost and sustainable. Strategies to circumvent this issue have been to add co-solvents and/or diluents to decrease the overall electrolyte concentration or customize the anion and salt concentration to each battery chemistry. The clean and green ethos of ALIBs can be enhanced by using organic active materials (AMs), but these are unfortunately often water soluble and therefore requires an electrolyte designed to mitigate dissolution/electrode de-attachment.Herein, we for the first time implement perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) as the anode AM for ALIBs. We demonstrate that by appropriate aqueous electrolyte selection we can truly mitigate electrode de-attachment, leading to excellent properties in terms of capacity, rate capability, cycling stability, and Coulombic efficiency. All things considered, this endeavour intends to further reduce the kWh/€ and thereby reinforcing the feasibility of more cost-effective large-scale battery energy storage solutions Fig 1. Long term galvanostatic cycling of an all-organic PTCDI electrode in a PTCDI/low conc. aqueous el./LFP cell set-up. Inset shows the chemical structure of PTCDI and the corresponding charge/discharge voltage curves. Figure 1

Carbon Corrosion Behavior of Carbon Support Materials for PGM-Based Catalysts in PEM Fuel Cells

The proton exchange membrane fuel cell (PEMFC) is a promising device for the transportation sector of a fossil free society, using green hydrogen from water electrolysis as a clean and sustainable option. However, sluggish kinetics as well as durability issues limit the implementation until this day. Therefore, modifications to the platinum catalysts [1] and the carbon supports [2] are made to improve the overall performance and durability of the cathode catalyst system.Herein, we present the investigation of the carbon corrosion behavior of different carbon support materials in PEMFCs using online nondispersive infrared (NDIR).The different carbon supports used for this study are commercial materials such as Vulcan, Ketjenblack EC-300J and Ketjenblack EC-600JD as well as self-synthesized mesoporous carbon nanodendrites (MCND). [3] The MCND support material is a highly porous high surface area carbon, which makes it a suitable candidate for fuel cell applications. Onto the support materials, Pt nanoparticles were deposited using a customized fluidized bed reduction reactor [4], resulting in similar Pt particle size and distribution onto the support material, thus making a comparison between different supports possible. Beginning of life (BOL) measurements in a single cell setup, as shown in Figure 1, show promising performance of the platinum catalyst supported on MCND (Pt/CMCND) compared to the platinum catalysts on commercial supports. Furthermore, we will present the investigated carbon corrosion behavior of the different support materials conducted by accelerated stress tests (AST) based on the DOE support degradation protocol. The online quantification of the evolved CO and CO2 from the cathode catalyst layer is measured using our online NDIR giving insight in the carbon corrosion resistivity of the different support materials. Together with the performance measurements, we develop a better understanding of the impact of the carbon support material on the performance and durability of the cathode catalyst layer.Literature:[1] Strasser, P; Kühl, S. Nano Energy 2016, 29, 166.[2] Ott, S. et. al., Nat. Mater. 2020, 19 (1), 77-85.[3] Numao, S. et al., Carbon 2009, 47, 306-312.[4] Hornberger, E. et. Al. J. Electrochem. Soc. 2020, 167, 114509. Figure 1: Air polarization curves of the four different catalysts under the following conditions: 80° C, 100% RH, 150 kPaabs backpressure, stoich.: 1.5 (H2) and 2 (air), min. flow: 50 ml/min (H2) and 800 ml/min (air). Figure 1

Linking Microstructure and Ionic/Electronic Conductivity in Composite Cathodes for Thiophosphate-Based All-Solid-State Lithium-Ion Batteries

Compared to conventional lithium-ion batteries (LIBs) with liquid electrolytes, ASSBs (all-solid-state batteries) have the potential to improve safety and achieve higher performance and energy density1. However, there are still many challenges to tackle in order to achieve ASSBs with sufficient cell performance, and one of them is to optimize the microstructure regarding its ionic and electronic conductivity. To achieve a high energy density, the fraction of AM must be as high as possible, and pores must be avoided. At the same time, an ionic conductive network of the SE has to be established; thus, both phases have to be distributed homogeneously with the composite cathode. On the other hand, the degradation of the solid electrolyte (SE) with cathode active material (CAM) and conductive additive (CA) has to be tackled with protective coatings that hinder the degradation but at the same time, keep the charge transport pathways open2,3. Therefore, the composite cathode microstructure (i.e., composition ratios CAM:SE:CA, particle characteristics, distribution of the phases) must be designed for different materials systems to ensure the sufficient percolation of ions and electrons for high performance4-9.In this study, we aim to understand the effect of the CAM fraction, morphology, and coating on the transport properties within the composite cathode. For this purpose, effective ionic and electronic conductivity of different cathode mixtures of Li6PS5Cl and NMC622 (coated, uncoated, single crystal, polycrystal) were analyzed and correlated with the microstructures. Moreover, a conductive matrix comprising Li6PS5Cl and C65 was introduced to the composite cathode system. Electronic and ionic conductivities were measured via impedance spectroscopy with ion- or electron-blocking electrodes in a symmetric cell configuration under constant pressure. To do so, a specially designed cell setup comprising a force sensor and a spring to adjust the pressure was used. The impedance spectra were fitted using T-type transmission line model (TLM) with equivalent circuit components with the RelaxIS 3 software package. Microstructural characterization was conducted on the powder mixtures and Ar- polished cross sections via scanning electron microscope using a transfer shuttle. We found the ionic and electronic transport limitations for the prepared composite cathode mixtures by varying the abovementioned parameters and optimized the CAM fraction accordingly. The results presented contribute to an improved understanding of the structure-property relationships and provide guidance on how to design a suitable microstructure.for improved cell performance. Acknowledgement The authors gratefully acknowledge the support of the German Federal Ministry of Education and Research within the program “FH‐Impuls” (Project SmartPro, Subproject SMART‐BAT, Grant no. 13FH4I07IA), Dr. Veit Steinbauer (Aalen University), Sebastian Puls and Dr. Nella Vargas-Barbosa (Helmholtz Institute Münster (IEK-12) - Forschungszentrum Jülich). References Janek, Jürgen, and Wolfgang G. Zeier.,Nature Energy 1.9 (2016): 1-4.Ma, Yuan et al., Advanced Functional Materials 32.23 (2022): 2111829.Sun, Shuo et al., Materials Futures 1.1 (2022): 012101.Noh, Sungwoo et al., Journal of Electroceramics 40 (2018): 293-299.Dewald, Georg F., et al., Batteries & Supercaps 4.1 (2021): 183-194.Ohno, Saneyuki, and Wolfgang G. Zeier., Accounts of Materials Research 2.10 (2021): 869-880.Bielefeld, Anja, Dominik A. Weber, and Jürgen Janek., ACS applied materials & interfaces 12.11 (2020): 12821-12833.Dixit, Marm et al., Solid State Batteries Volume 2: Materials and Advanced Devices. American Chemical Society, 2022. 113-132.Hendriks, Theodoor A. et al. ," Batteries & Supercaps (2023): e202200544

Role of Ionic Liquids As Modifiers of Ru-Based Catalysts for Water Electrolysis

The generation of hydrogen through electrocatalytic water splitting has attracted tremendous attention in the past years [1,2]. Although water electrolysis has been already established in industrial settings, a large amount of research is still being carried out to further improve the catalytic efficiency and stability to exploit the full potential of this technology. One approach in this endeavor is the utilization of ionic liquids (ILs) as modifiers of electrocatalysts and electrode surfaces [3, 4]. The special physicochemical properties of the IL can affect and ideally improve the characteristics of the electrocatalyst, e.g., in terms of mass and electron transport [3]. Furthermore, the hydrophilic nature of certain ILs can in addition influence gas bubbles removal on the working electrode and improve the stability of the catalysts (e.g., Ru) by acting as a monomer-like binder [4].In this study, we compared the effect of four different ILs that are based on the same cation chain (1-butyl-3-(4-methylphenethyl)-1H-imidazol-3-ium) but different anions (-OAc, -NTf2, -Br, and -MeSO3) on Ru nanoparticles as catalysts for hydrogen and oxygen evolution reactions (HER and OER). To this end, carbon nanotubes were functionalized using different ILs and subsequently decorated with 1-2 nm Ru nanoparticles (Ru NPs) following an established organometallic approach [5]. We analyze how the catalytic activity/stability for HER, as well as OER, is influenced by the metal-ILs combination by established electrochemical methods utilizing a rotational disc electrode setup, with a particular focus on the different hydrophilic natures (depending on the anion) of the four ILs. To obtain a more comprehensive picture of how the different ILs affect Ru dissolution during the reaction, the IL/catalyst systems are additionally investigated by inductively coupled plasma-optical emission spectroscopy (ICP-OES) in a flow cell setup, as well as by electrochemical quartz crystal microbalance (EQCM) measurements.In this work, we discuss the use of ILs as modifiers for catalyst/electrode systems in water-splitting reactions, highlighting the importance of careful IL selection as well as the necessity for more future research in this field to fully explore the potential of IL/NPs-systems in electrochemistry.

Scalable Diastereoselective Electrosynthesis of Spiro[benzofuran-2,2'-furan]-3-ones.

Spirobenzofuran scaffolds, because of their three-dimensional structure, are incorporated into several valuable natural products and drug candidate molecules. Herein, with the assistance of electrosynthesis, we introduce a novel electrochemical approach for achieving spirobenzofurans in a user-friendly and operationally simple undivided cell setup under constant current. This metal-catalyst-free electrochemical procedure afforded spiro[benzofuran-2,2'-furan]-3-ones with high diastereoselectivity. Compatibility with gram-scale synthesis along with the convenient accessibility of reaction instruments and starting materials collectively raised the importance of this protocol compared to previous challenging methods. Furthermore, mechanistic cognizance of this reaction is obtained by the investigation of the cyclic voltammetry spectra of reactants.

Single fluid-driven crack propagation in analogue rock assisted by chemical environment

During the operation of hydraulic fracturing as used in many geo-energy and geo-environment applications, chemical stimulation is often incorporated for cracking enhancement in low-permeability geological formations for the purpose of an optimization of energy recovery. The mechanism of subcritical crack propagation in a chemically reactive environment is essential for understanding of the involved coupled chemo-mechanical process and a better control of acid-assisted hydraulic fracturing. It has been postulated that the rate of crack propagation under environmental loads is inherited from the chemical processes involved including the reaction and the diffusive transport. However, laboratory explorations focusing on the evolving interplay between the propagation of a fluid-pressurizing individual crack and the environment it is subject to via a variable chemical intensity imposed have been rare. Here we present an experimental investigation on a single tensile crack propagation in alginate hydrogel as an analogue material for brittle rocks, driven by the injection of a chemically reactive fluid kept at constant pressure using a Hele-Shaw cell setup. We show that an intensified chemical environment can accelerate tensile crack propagation in both subcritical crack growth and fracturing regimes, while leading to the Region III fracturing of less brittle characteristics. During the experiment, crack-tip blunting upon injection of reactive solutions was observed, suggesting a competing mechanism between the crack-tip geometry induced toughening and the chemically induced softening within the process zone as the crack advances. Our results provide quantitative insights into how a chemically reactive environment facilitates the growth of a single macroscopic crack of mode I opening in a low-permeability matrix through coupled chemo-mechanical feedback. The imposed chemical environment promotes crack propagation while alleviating the stress concentration at the advancing crack tip, suggesting a more energy-efficient method compared to pure water fracturing. We anticipate our experimental investigation presented here to be a starting point of sound laboratory support for future studies towards a more controllable technique of chemical stimulation in geomaterials as well as complementing the ongoing modeling efforts in reactive chemo-mechanics.

Quantification of Organic Solvent Concentration Profiles in Ion Exchange Membranes Via Confocal Raman Microscopy

AbstractThe perfluorinated sulfonic acid membranes used in direct alcohol fuel cells cause low faradaic efficiency and performance due to alcohol absorption and permeation. Thus, a measurement setup is sought that enables a direct evaluation of the suitability of polymer electrolytes for this application. A 3D‐printed diffusion cell setup capable of measuring the interaction between the organic solvents, such as alcohols, and a proton exchange membrane via confocal Raman microscopy is introduced. The cell design employs flow channels to mimic the flow fields of electrochemical cell tests. Exemplarily, information on the interaction of membranes like Nafion 212 and the composite membrane Nafion XL with 1 m solutions of organic solvents such as 2‐propanol, acetone, and ethanol are provided to demonstrate the applicability of this setup. The Raman diffusion cell is capable of quantifying the preferred solvent uptake, which is characterized by the sorption coefficient, the permeability, and the concentration gradient within the membrane. These properties can be obtained in situ and in a time‐resolved manner. Thus, this diffusion cell setup is a powerful and accessible tool for screening membrane compatibility with various liquids.

Industrially Relevant Conditions in Lab‐Scale Analysis for Alkaline Water Electrolysis

AbstractAlkaline water electrolysis remains one of the most promising technologies for the large‐scale production of green hydrogen. However, further increases in efficiency remain elusive, as new electrode materials that are highly efficient in the laboratory cannot maintain their performance under industrial conditions. Within this work, we present a beaker cell setup, in which the industrial relevance of research materials can already be investigated in the laboratory by applying industrial conditions. Thus, the setup allows for testing at 80 °C in 30 wt. % KOH for more than 300 hours. Electrodes are contacted with an in‐house designed Ni tuck‐in holder and two types of reference electrodes are recommended. In addition, a protocol to unify catalyst research is introduced.

Selective electrochemical methanation of carbon dioxide using a sulphide derived CuZn catalyst

Efficient catalysts facilitate the electrochemical reduction of CO2, enabling its conversion into fuels or chemical feedstocks through proton coupled electron transfer processes. Among these catalysts, Cu-based ones stand out for their unique ability to produce hydrocarbon products with high faradaic efficiencies. This study focuses on the use of sulphide-derived (SD)-CuxZny nanoparticle catalysts, which have been found to exhibit enhanced methane selectivity during CO2 reduction in an H-Cell with 0.10 M KHCO3 as the electrolyte. The composition of the catalysts plays a crucial role in determining their catalytic behavior. At an optimal Cu/Zn ratio of 1:1, the SD-CuZn catalyst demonstrates exceptional methane production, achieving a faradaic efficiency of 76 ± 3 % at a potential of −0.98 V vs RHE. Moreover, a partial current density of −4.5 mA cm−2 was achieved at a more negative potential of −1.09 V vs RHE. Ex situ characterization highlighted the significance of partially reduced CuS species in influencing the selectivity of hydrogenated carbon products. When CO2 reduction was performed in a flow cell equipped with a gas diffusion electrode with 1.0 M KHCO3 or 1.0 M KOH electrolytes in both anodic and cathodic compartments, the current density increased due to the enhanced mass transport rate. However, the altered conditions lead to a shift in selectivity, favoring carbon monoxide over methane. It is important to note that insights garnered from H-Cell experiments may not be directly extrapolated to flow cell setups.

Electrochemical Annulation of ortho‐Alkynylbiphenyls to Fused Sulfenyl Phenanthrenes and Spiro Cyclohexenone Indenes

AbstractHere, we present an electrochemically induced synthesis of 9‐sulfenylarylphenanthrenes and 3’‐sulfenylarylspiro‐cyclohexa[4.5]trienones starting from o‐alkynylbiphenyls and diaryl disulfides. This method was accomplished through constant current electrolysis of 10 mA in an undivided cell setup by utilizing CH3CN as a solvent and LiClO4 as an electrolyte at room temperature. Notably, the present strategy enabled the formation of sulfenylphenanthrenes and sulfenyl spiro cyclohexa[4.5]trienones in 70%–95% yield. Scale‐up synthesis, mechanistic studies, and cyclic voltammetry have also been carried out.

Electrochemical Sodium Storage in Hard Carbon Powder Electrodes Implemented in an Improved Cell Assembly: Insights from In-Situ and Ex-Situ Solid-State NMR.

In this work, we report on an improved cell assembly of cylindrical electrochemical cells for 23 Na in-situ solid-state NMR (ssNMR) investigations. The cell set-up is suitable for using powder electrode materials. Reproducibility of our cell assembly is analyzed by preparing two cells containing hard carbon (HC) powder as working electrode and sodium metal as reference electrode. Electrochemical storage properties of HC powder electrode derived from carbonization of sustainable cellulose are studied by ssNMR. 23 Na in-situ ssNMR monitors the sodiation/desodiation of a Na|NaPF6 |HC cell (cell 1) over a period of 22 days, showing high cell stability. After the galvanostatic process, the HC powder material is investigated by high resolution 23 Na ex-situ MAS NMR. The formation of ionic sodium species in different chemical environments is obtained. Subsequently, a second Na|NaPF6 |HC cell (cell 2) is sodiated for 11 days achieving a capacity of 220 mAh/g. 23 Na ex-situ MAS NMR measurements of the HC powder material extracted from this cell clearly indicate the presence of quasi-metallic sodium species next to ionic sodium species. This observation of quasi-metallic sodium species is discussed in terms of the achieved capacity of the cell as well as of side reactions of sodium in this electrode material.

Nanoporous Activated Carbon Material from Terminalia chebula Seed for Supercapacitor Application

High-surface-area porous carbon materials with high porosity and well-defined pore structures are the preferred advanced supercapacitors electrode materials. Here, we report the electrochemical supercapacitive performance of novel high-porosity activated carbon materials prepared from biowaste Terminalia chebula (Harro) seed stones involving zinc chloride (ZnCl2) activation. Activation is achieved by mixing ZnCl2 with Harro seed powder (1:1 w/w) followed by carbonization at 400–700 °C under a nitrogen gas atmosphere. The amorphous carbon materials obtained exhibit excellent performance as electrical double-layer capacitor electrodes in aqueous electrolyte (1 M sulfuric acid) due to high specific surface areas (as high as 1382.6 m2 g−1) based on well-developed micropore and mesopore structures, and partial graphitic structure containing oxygenated surface functional groups. An electrode prepared using material having the optimal surface textural properties achieved a large specific capacitance of 328.6 F g−1 at 1 A g−1 in a three-electrode cell setup. The electrode achieved a good capacitance retention of 44.7% at a high 50 A g−1 current density and outstanding cycling performance of 98.2% even following 10,000 successive charge/discharge cycles. Electrochemical data indicate the significant potential of Terminalia chebula seed-derived porous carbons as high-performance electrode materials for high-energy-storage supercapacitor applications.

Simple Iron Halides Enable Electrochemically Mediated ATRP in Nonpolar Media.

An electrochemically controlled atom transfer radical polymerization (eATRP) was successfully carried out with a minimal amount (ppm-level) of FeBr3 catalyst in a nonpolar solvent, specifically anisole. Traditionally, nonpolar media have been advantageous for Fe-based ATRP, but their low conductivity has hindered any electrochemical application. This study introduces the application of electrocatalytic methods in a highly nonpolar polymerization medium. Precise control over the polymerization was obtained by employing anhydrous anisole with only 400 ppm of FeBr3 and applying a negative overpotential of 0.3 V. Additionally, employing an undivided cell setup with two simple iron wire electrodes resulted in a significant 15-fold reduction in electrical resistance compared to traditional divided cell setups. This enabled the production of polymers with a dispersity of ≤1.2. Lastly, an examination of kinetic and thermodynamic aspects indicated that the ppm-level catalysis was facilitated by the high ATRP equilibrium constant of Fe catalysts in nonpolar environments.

Impact of Nano‐sized Inorganic Fillers on PEO‐based Electrolytes for Potassium Batteries

AbstractThe low melting points of solid polymer electrolytes (SPEs) based on the KTFSI electrolyte salt allow comparatively low operation temperatures (below 50 °C) for K‐ion batteries, unlike their Li or Na counterparts. Unfortunately, for this reason the electrolyte is also rendered mechanically unsuitable in its function to act as a cell separator. Therefore, in this work the use of inorganic nanofillers (Al2O3 and SiO2) is explored with the aim to improve rheological, thermal and cation transport properties of the resulting polymer composite electrolytes. Their electrochemical properties were further examined in K‐metal symmetrical cells and K‐metal/SPE/K2Fe[Fe(CN)6] cells and compared to corresponding liquid electrolyte systems. As a result of particle‐polymer interactions, filler‐containing SPEs showed higher degrees of crystallinity combined with filler polymer interaction and thus improved mechanical integrity in the relevant temperature range of 25–55 °C, while maintaining similar ionic conductivities than a filler‐free sample above the melting temperature. Although plating‐stripping experiments in symmetrical cell setups suggested high cell resistances for various compositions and in some cases even rapid cell failure, Al2O3‐based SPEs generally displayed high capacity retention when cycled against a positive electrode (here Prussian blue analogue K2Fe[Fe(CN)6]) over 100–160 cycles and possibly beyond.

Electrochemical Synthesis of Sulfonamides in Single‐Pass Flow

AbstractAn electrochemical multicomponent synthesis of sulfonamides at room temperature in single‐pass flow is presented. In contrast to batch‐type electrolysis, an undivided flow cell setup with a stainless‐steel cathode and either a boron‐doped diamond (BDD) anode or a glassy carbon anode can be employed. Simply by using SO2 stock solutions, less atom‐economic sulfur dioxide surrogates can be avoided. Moreover, no additional supporting electrolytes are required due to the in‐situ generation of amidosulfinates, which also serve as intermediate for this transformation. This protocol allows sulfonamides to be synthesized directly from non‐prefunctionalized electron‐rich arenes with amines and SO2. In total, 10 examples are demonstrated with isolated yields up to 92 %. The robust scalability of this electrosynthesis with an easy downstream processing was also proven.

Structural Mechanics Analysis of Woven Web Reinforced Membranes in Proton Exchange Membrane Water Electrolysis

Abstract Membranes are a key component of proton exchange membrane water electrolysis (PEMWE) cells and are exposed to various stressors during operation, which can significantly reduce cell lifetime. PEMWE membranes incorporating woven web layers within the membrane structure for mechanical reinforcement are a promising, commonly-used industrial strategy to mitigate the formation of membrane defects. Here, the structural mechanics of a PEMWE cell were investigated, specifically the woven web reinforced membrane. Experimental tensile tests were conducted on the membrane to obtain stress-strain data. These measurements were utilized to parameterize a geometrically simplified model of the woven web reinforced membrane through a tensile test simulation. The validated model was applied in a 2D-cell simulation to identify resulting stresses and strains in the membrane during various electrolysis operation modes. The results herein allow the used PEMWE cell geometry to be systematically evaluated and optimized with respect to mechanical membrane stability. For the applied PEMWE cell setup, no failure is expected during normal operation, including varied temperatures and differential pressure. Increasing the gap size at the edge of the electrochemically active cell area, however, leads to large deformations when the gap becomes larger than 0.2 mm.

Analytical Solutions to Characterize Through-Plane Inhomogeneity of Porous Electrodes Using Electrochemical Impedance Spectroscopy

Characterization of through-plane inhomogeneity in porous media requires knowledge of the distribution of porosity, tortuosity, and double-layer capacitance across the thickness. The thickness-averaged or apparent values of these parameters may not be sufficient to model the transport processes in batteries and fuel cells accurately. Cleverly designed through-plane inhomogeneities can improve the performance of electrochemical systems (e.g., graded-porosity electrodes for batteries or gas diffusion media for fuel cell). In some cases, inhomogeneity can result from manufacturing steps; for example, tortuosity variation due to binder migration in the fast slurry-drying step. In this work, we extend the impedance-based approach to characterize the inhomogeneity of a porous electrode in the through-plane direction. We derive analytical expressions for the impedance response of an electrode having three types of inhomogeneities (step-wise, linear, and inverse-linear variation) in a symmetric cell setup having non-reacting electrode/electrolyte interface (blocking electrode or electrolyte method). We also provide perturbation-theory based approximate solutions and expressions for semi-infinite domain to enable the development of an impedance-based fitting tool for inhomogeneous electrodes. In the end, we provide an impedance-based experimental investigation of gas diffusion media (composite layer) using symmetric cell setup to demonstrate the applicability of the theory and understanding derived in this work.

Critical Current Density Measurements of Argyrodite Li6PS5Cl Solid Electrolyte at Ambient Pressure

Sulfide electrolytes including the argyrodite family (Li6PS5X, X = Cl, Br, I) exhibit high ionic conductivities and transference numbers and are regarded as promising electrolytes for all-solid-state lithium batteries. Although high ionic conductivity is a necessary requirement for feasible battery operation, other parameters are equally important and have often been neglected in efforts to realize all-solid-state batteries. The so-called critical current density (CCD) is among the more relevant parameters for application and indicates the maximum current an electrolyte can sustain before breakdown. When Li metal electrodes are used, this breakdown is often initiated by heavy dendrite formation and subsequent growth through the electrolyte layer, resulting in internal shorting of the cell. Very promising CCD values are reported for the argyrodite family of >1 mA cm−2 at elevated temperatures and pressures. However, non-standardized cell setups and testing procedures are employed, which renders a proper comparison of values impossible. Thus, this work investigates the impact of these often-overlooked parameters and aims at establishing more standard measurement procedures for solid electrolytes under ambient or almost ambient pressure. Furthermore, an alternative method for evaluation of CCD values is presented adopted from Tafel analysis.

Stability of Bipolar Plate Materials for Proton‐Exchange Membrane Water Electrolyzers: Dissolution of Titanium and Stainless Steel in DI Water and Highly Diluted Acid

AbstractThe widespread use of proton exchange membrane water electrolyzers (PEMWE) is hindered by their high cost, of which a colossal factor is caused by the bipolar plates (BPP). In this paper, we investigate the stability of two BPP materials on‐line with an optimized scanning flow cell setup coupled to an inductively coupled plasma mass spectrometer (SFC‐ICP‐MS), as well as scanning electron microscopy (SEM). The stability of currently used titanium and a cheaper alternative, stainless steel (SS) 316L, were characterized in deionized (DI) water and 0.5 mM H2SO4 to mimic the conditions at the BPP under operation. We show that the dissolution of Ti is negligible, whereas SS 316L degrades notably. Here, besides pH, the applied potentials play a crucial role. Nonetheless, even for the highest measured dissolution rate of SS 316L, the contamination in a full cell is estimated to remain below 1 ppm. This work illustrates the capabilities of on‐line high‐throughput stability tests for BPP materials and could therefore contribute towards optimization of cost‐effective PEMWE.

On the role of inductive loops at low frequencies in PEM electrolysis

Inductive loops at low frequencies have been observed in the electrochemical impedance spectra (EIS) of various electrochemical cells. Although different physicochemical models for this phenomenon have been suggested in many other applications, this topic has not been widely discussed in the field of proton exchange membrane (PEM) electrolysis.In this article, low-frequency inductive loops in PEM electrolysis cells and their impact on cell performance are analyzed. We show that this phenomenon is reproducible and occurs with different cell materials and setups. Its impact increases with increasing current density and decreasing temperature. At extreme conditions (7 A∙cm−2, 40 °C) we show that the negative polarization resistance of the inductive process can exceed the capacitive polarization processes by a factor of three, resulting in a direct current resistance less than the high frequency series resistance of the cell.