Electrochemical Protocols Research Articles

Revealing the Dynamic Evolution of Electrolyte Configuration on the Cathode-Electrolyte Interface by Visualizing (De) Solvation Processes.

Electrolyte engineering is crucial for improving cathode electrolyte interphase (CEI) to enhance the performance of lithium-ion batteries, especially at high charging cut-off voltages. However, typical electrolyte modification strategies always focus on the solvation structure in the bulk region, but consistently neglect the dynamic evolution of electrolyte solvation configuration at the cathode-electrolyte interface, which directly influences the CEI construction. Herein, we reveal an anti-synergy effect between Li+-solvation and interfacial electric field by visualizing the dynamic evolution of electrolyte solvation configuration at the cathode-electrolyte interface, which determines the concentration of interfacial solvated-Li+. The Li+ solvation in the charging process facilitates the construction of a concentrated (Li+-solvent/anion-rich) interface and anion-derived CEI, while the repulsive force derived from interfacial electric field induces the formation of a diluted (solvent-rich) interface and solvent-derived CEI. Modifying the electrochemical protocols and electrolyte formulation, we regulate the "inflection voltage" arising from the anti-synergy effect and prolong the lifetime of the concentrated interface, which further improves the functionality of CEI architecture.

Bottom-up designing nanostructured oxide libraries under a lab-on-chip paradigm towards a low-cost highly-selective E-nose

BackgroundThe multisensor concept has been developed as a powerful alternative to well-known gas-analytical instrumentation for applications where a fast but accurate and reliable assessment of the environment is required. The concept follows a biology-inspired approach where the selectivity towards various gases/odors is attained via pattern recognition of multisensory signal vectors. Herein, we discuss how to design a selective multisensor library based on various metal oxide nanostructures like a lab-on-chip using a simple but efficient bottom-up growth of materials over the multi-electrode chip under robust dc electrochemical protocols. ResultsIn addition to a conventional growth of oxide layers over the metal electrodes, we show that the fine nanowall-like oxide structures appear as a quasi-matrixed percolation film over the SiO2 substrate surface in the inter-electrode gaps to constitute a chemiresistive film. We have tested two directions while applying the technique to grow Co, Ni, Mn, and Zn oxides to develop on-chip sensor arrays of, (i) monoxide type employing the oxide films with gradual change of growth time, and (ii) multi-oxide type based on the four oxides. The materials were thoroughly characterized by electron microscopy, X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy/mapping to prove the composition and structure. Among tested oxides, ZnO readily appears not only at the electric potential-targeted chip zone but also in other areas to dope the films for yielding heterojunctions with other oxides that enhances a variability of functional properties in the on-chip sensor array. The gas-sensing performance of the chips has been tested versus various chemically akin alcohol vapors at the sub- and low ppm range of concentrations in a mixture with air. SignificanceWe show that the grown oxide nanostructures exhibit a high-sensitive chemiresistive signal which allows one to build a multisensor vector signal, selective to the kind of alcohols, even at sub-ppm concentrations. Moreover, the multi-oxide library yields options for a superior selectivity under LDA metrics than the gradient-grown mono-oxide one due to the versatility of materials while the low-cost growth protocols remain to be the same in both cases. The delivered method to produce multisensor arrays allows one producing low-cost but efficient electronic nose units for numerous applications.

Revealing the Dynamic Evolution of Electrolyte Configuration on the Cathode‐Electrolyte Interface by Visualizing (De) Solvation Processes

AbstractElectrolyte engineering is crucial for improving cathode electrolyte interphase (CEI) to enhance the performance of lithium‐ion batteries, especially at high charging cut‐off voltages. However, typical electrolyte modification strategies always focus on the solvation structure in the bulk region, but consistently neglect the dynamic evolution of electrolyte solvation configuration at the cathode‐electrolyte interface, which directly influences the CEI construction. Herein, we reveal an anti‐synergy effect between Li+‐solvation and interfacial electric field by visualizing the dynamic evolution of electrolyte solvation configuration at the cathode‐electrolyte interface, which determines the concentration of interfacial solvated‐Li+. The Li+ solvation in the charging process facilitates the construction of a concentrated (Li+‐solvent/anion‐rich) interface and anion‐derived CEI, while the repulsive force derived from interfacial electric field induces the formation of a diluted (solvent‐rich) interface and solvent‐derived CEI. Modifying the electrochemical protocols and electrolyte formulation, we regulate the “inflection voltage” arising from the anti‐synergy effect and prolong the lifetime of the concentrated interface, which further improves the functionality of CEI architecture.

A review of recent advances in electrochemical and photoelectrochemical late-stage functionalization classified by anodic oxidation, cathodic reduction, and paired electrolysis.

With the resurgence of electrosynthesis in organic chemistry, there is a significant increase in the number of routes available for late-stage functionalization (LSF) of drugs. Electrosynthetic methods, which obviate the need for hazardous chemical oxidants or reductants, offer unprecedented control of reactions through the continuous variation of the applied potential and the possibility of combination with photochemical processes. This capability is a substantial advantage for performing electrochemical or photoelectrochemical LSF. Ultimately, these protocols are poised to become a vital component of the medicinal chemist's toolkit. In this review, we discuss electrochemical protocols that have been demonstrated to be applicable for the LSF of pharmaceutical drugs, their derivatives, and natural substrates. We present and analyze representative examples to illustrate the potential of electrochemistry or photoelectrochemistry for the LSF of valuable molecular scaffolds.

A Comprehensive Online Analytical System Coupled with Standardized Data Analysis for the Electrochemical Reduction of CO2

The electrochemical reduction of CO2 (CO2RR) is a promising way to convert detrimental CO2 emissions into sustainable fuels and chemicals, and thus to achieve a circular carbon economy. 1 Depending on catalyst type and reaction conditions, different gaseous and liquid products can be obtained from the CO2RR, and their production rates vary with reaction time. It becomes thus imperative, for any catalytic performance analysis, to be able to assess the product distribution online during CO2RR. 2,3 However, while gaseous products are readily analyzed online by gas chromatography, liquid products are typically only assessed at the end of the reaction due to the lack of suitable automated liquid sampling and analysis methods. In addition, reaction parameters such as CO2 mass flow rates, temperatures and pressures are seldom recorded, causing the loss of significant information on catalysts, electrodes, and electrolyzers behavior.To overcome these issues, we assemble a comprehensive analytical system coupling online gas and liquid product analysis by gas and liquid chromatography leveraging a special automated liquid sampling valve with electrochemical protocols that assess CO2RR performance, electrolyzer cell resistance and electrode surface area. In addition, we record CO2 mass flow rates, electrolyzer temperatures, as well as gas and liquid flow pressures. 4 To rapidly and reproducibly handle the large and heterogeneous data volume obtained we implement a standardized data pipeline based on our own open-source software,5 which automatically parses the numerous different raw data files, composes a data set following FAIR practices,6 and post-processes and plots the data in a standardized way. We validate the analytical system by carrying out CO2RR at 200 mA/cm2 on Cu gas diffusion electrodes, following the changes in selectivity with reaction time for > 10 gaseous and liquid products, and recording mass flow rates, electrolyzer temperatures and pressures. The modular nature of our analytical system, combined with the standardized data pipeline, allows us to freely increase the number and type of sensors used with minimal impact on the data analysis time, as well as to multiplex our analysis to 8 parallel electrolyzer cells, paving the way for a much deeper and faster understanding of the function of CO2RR catalysts, electrodes, and electrolyzers.

PH dependence of noble metals dissolution: Platinum

Obtaining new information about the dissolution behavior of platinum in different pH conditions can help understand the stability of this metal in a wide variety of electrochemical devices. In this work, Pt dissolution is investigated in a pH range from 0 to 12.7 applying on-line inductively coupled plasma mass spectrometry (ICP-MS) with phosphate buffer solutions in an electrochemical scanning flow cell (SFC). Various electrochemical protocols are employed, including slow cyclic voltammetries at 5 mV s-1 and potential steps up to 1.2 and 1.6 VRHE. Results for total Pt dissolution show an inverted volcano dependence with pH in all cases, with the minimum dissolution located at pH = 7. Dissolution for pH = 0 is considerably higher than for pH = 1. In the case of the cyclic voltammetry experiments, the changes in dissolution are mainly due to the cathodic dissolution contribution. Interestingly, when phosphoric acid is used for the electrolyte with pH = 1, cathodic dissolution is higher than for the perchloric acid case. When comparing a slow reductive ramp to a direct potential jump after holding the electrode at oxidative potential, the results point out that dissolution is much higher for the slow reductive ramp in the case of acidic pH values. The results presented in this work can help improve the fundamental understanding of Pt dissolution since it is the first time such an exhaustive pH study has been carried out for on-line potential resolved experiments.

Understanding mechanical stresses upon solid-state battery electrode cycling using discrete element method

Solid-state batteries (SSBs) often fall behind conventional lithium-ion batteries (LIBs) in performance. Electrochemical cycling protocols, in particular under isostatic compression, present ample opportunities for improvement to mitigate issues like contact loss and aging among numerous other challenges. This study introduces a novel Discrete Element Method (DEM) workflow to assess the effectiveness of uniaxial and isostatic compression as proceeding electrode preparation on the conductivity and structural integrity of SSBs. Isostatic compression achieves conductivity levels comparable to uniaxial compression with significantly reduced pressure requirements. In contrast, uniaxial compression at elevated loads, while resulting in higher conductivity, subjects the particles to significant stress, increasing the risk of cracking and deformation of the SSB materials. This study shows the impact of mechanical stress during different stages of electrochemical cycling on the microstructure's integrity to provide valuable insights into electrochemistry-mechanics couplings, which can be challenging to evaluate experimentally.

Electrophotocatalysis Versus Indirect Electrolysis: Electrochemical Selenocyclization of 3-Aza-1,5-dienes Facilitated by Energy Transfer, Direct Photolysis or N-Hydroxyphthalimide.

Three hybrid electrochemical protocols, which involve the energy transfer, direct photolysis and N-hydroxyphthalimide catalyst, respectively, are presented for the selenylation/cyclization of the fragile substrates of 3-aza-1,5-dienes with diorganyl diselenides to afford 3-selenomethyl-4-pyrrolin-2-ones. The two electrophotocatalytic reactions and the indirect electrolysis one are both regioselective and external-oxidant- and transition-metal-free, and are associated with a broad substrate scope and high Se-economy, and all three methods are amenable to gram-scale syntheses, late-stage functionalizations, sunlight-induced experiments and all-solar-driven syntheses.

Attention towards chemistry agnostic and explainable battery lifetime prediction

Predicting and monitoring battery life early and across chemistries is a significant challenge due to the plethora of degradation paths, form factors, and electrochemical testing protocols. Existing models typically translate poorly across different electrode, electrolyte, and additive materials, mostly require a fixed number of cycles, and are limited to a single discharge protocol. Here, an attention-based recurrent algorithm for neural analysis (ARCANA) architecture is developed and trained on an ultra-large, proprietary dataset from BASF and a large Li-ion dataset gathered from literature across the globe. ARCANA generalizes well across this diverse set of chemistries, electrolyte formulations, battery designs, and cycling protocols and thus allows for an extraction of data-driven knowledge of the degradation mechanisms. The model’s adaptability is further demonstrated through fine-tuning on Na-ion batteries. ARCANA advances the frontier of large-scale time series models in analytical chemistry beyond textual data and holds the potential to significantly accelerate discovery-oriented battery research endeavors.

Active Hydrogen for Electrochemical Ammonia Synthesis

AbstractElectrochemical ammonia synthesis (EAS) presents an attractive alternative to the Haber–Bosch process due to the benefits of energy saving, low carbon emission, environmental friendliness, and so on. However, the competing hydrogen evolution reaction (HER) severely limits the yield, selectivity, and current efficiency of NH3. Although the accumulation and self‐aggregation of active hydrogen (H*) are the primary causes of the competing HER, it also serves as the critical active species and intermediate for the multistep hydrogenation and deoxygenation processes. Therefore, the sensible regulation of the H* generation and consumption are essential for enhancing EAS performance. And it is significant to thoroughly review the current strategies for H* control. Herein, a comprehensive introduction of H* to provide a fundamental understanding of its role in electrochemical reactions, including generation, conversion, identification, and quantification protocols is first proposed. In addition, the role and control strategies of H* in EAS are carefully summarized with a particular focus on regulating H* generation and consumption to enhance the activity, selectivity, and Faradaic efficiency. Finally, the remaining challenges and perspectives are discussed. This critical review is intended to offer a profound understanding of the regulation of H* in electrochemical reactions and the development of EAS technology.

Towards improved online dissolution evaluation of Pt-alloy PEMFC electrocatalysts via electrochemical flow cell - ICP-MS setup upgrades

Electrochemical flow cell coupled with an inductively coupled plasma mass spectrometer (EFC-ICP-MS) is a powerful electroanalytical technique to monitor in-situ dissolution of metallic electrocatalysts and to understand mechanism of degradation under operating conditions. Its utilisation has witnessed a notable increase in the electrocatalyst field in the last decade where it has been extensively used to study the stability of platinum group metals (PGMs) under oxygen reduction and oxygen evolution reaction conditions. Online ICP-MS has allowed the scientific and industrial community to optimise the activity and stability of PGMs thanks to a better understanding of the complex metal corrosion processes. Among the different setups, the electrochemical flow cell design is the most common as it is based on a commercially available design. Nonetheless, besides different materials and different electrochemical protocols, the impact of the geometry and various parameters of the setup on the recorded dissolution signal has not been studied until now. Such parameters can influence the results obtained with an EFC-ICP-MS and thus the interpretation of the dissolution mechanism and/or stability assessment. Hereby, we demonstrate that the length of the tubing between the outlet of the cell and the inlet of the ICP-MS impacts the resolution of the PtCo catalyst dissolution peaks. This, in turn, facilitates studies where the detection of extremely low concentrations is necessary, such as under a very narrow potential window. Similarly, a reduced internal volume of the cell restricts Pt redeposition, contributing to a more precise evaluation of stability. These claims were supported by dynamic continuum mechanics modelling of the ion concentration in a model EFC. Finally, we provide guidelines and advice to properly measure dissolution with an electrochemical cell coupled with ICP-MS.

Quantifying Electrochemical Degradation in Single-Crystalline LiNi0.8Mn0.1Co0.1O2 –Graphite Pouch Cells through Operando X-Ray and Postmortem Investigations

Layered nickel-rich lithium transition-metal oxides (LiNixMnyCo1−x−yO2; where ≥ 0.8), with single-crystalline morphology, are promising future high-energy-density Li-ion battery cathodes due to their ability to mitigate particle-cracking-induced degradation. This is due to the absence of grain boundaries in these materials, which prevents the build-up of bulk crystallographic strain during electrochemical cycling. Compared to their polycrystalline counterparts, there is a need to study single-crystalline Ni-rich cathodes using x-ray methods in uncompromised machine-manufactured industrylike full cells to understand their bulk degradation mechanisms as a function of different electrochemical cycling protocols. This can help us identify factors to improve their long-term performance. Here, through in-house x-ray studies of pilot-line-built LiNi0.8Mn0.1Co0.1O2–graphite A7 pouch cells, it is shown that their electrochemical-capacity fade under harsh conditions (2.5–4.4 V and 40 °C for 100 cycles at a C/3 rate) primarily stems from the high-voltage reconstruction of the cathode surface from a layered to a cubic (rock-salt) phase that impedes the Li+ kinetics and increases cell impedance. Postmortem electron and x-ray microscopy show that these cathodes can withstand severe anisotropic structural changes and show no cracking when cycled under such conditions. Comparing these results to those from commercial Li-ion cells with surface-modified single-crystalline Ni-rich cathodes, it is identified that cathode surface passivation can mitigate this type of degradation and prolong cycle life. In addition to furthering our understanding of degradation in single-crystalline Ni-rich cathodes, this work also accentuates the need for practically relevant and reproducible fundamental investigations of Li-ion cells and presents a methodology for achieving this. Published by the American Physical Society 2024

Dual Roles of Supporting Electrolytes in Organic Electrosynthesis

AbstractSynthetic electro‐organic chemistry is advancing to a well‐established methodology in academic research and industry. The simple process control minimizes reagent waste and avoids using toxic and environmentally unfriendly redox agents, providing a feasible and sustainable alternative to conventional techniques. However, a fundamental disadvantage, is the necessity of ion‐conductive components within the electrolyte. The recovery of these supporting electrolytes, as well as simple product isolation, pose challenges for work‐up strategies. This review presents the following electrochemical protocols featuring a simple material‐ and resource‐saving strategy: the dual role of supporting electrolytes as conductivity enabling components and reagents or meditators. This review is the first to conclude and categorize dual role strategies for the supporting electrolytes. It may inspire electrochemists to advance the development and optimization of electrochemical synthesis protocols towards more material‐ and resource‐efficient reaction control.

Effects of Anions and Surface Structure on Pt Single Crystal Dissolution in Acidic Electrolytes

AbstractUnderstanding the mechanisms of Pt dissolution with well‐defined surfaces is vital for developing stable catalysts for electrochemical energy conversion devices such as fuel cells. This work investigates Pt dissolution from low‐index single crystals in perchlorate, sulfate, and methanesulfonate acid solutions by on‐line inductively coupled plasma mass spectrometry (ICP‐MS), and the results are correlated with surface X‐ray diffraction (SXRD) studies. The previously reported stability trend Pt(111)>Pt(100)>Pt(110) in HClO4 was confirmed for the other acids. The application of electrochemical protocols up to high potential values demonstrated that dissolution for Pt(100) increases to a lower extent than for the other planes. Dissolution is affected by the nature of the anion, especially for Pt(111), with the dissolution rate increasing in the order H2SO4>MSA>HClO4. This influence could be due to the interaction strength of the anion with Pt and its complexing ability or different ratios of the surface coverage of different oxide species. For Pt(111), SXRD measurements show different onset potentials for extraction in HClO4 and H2SO4, which can influence the dissolution processes. These results demonstrate that fundamental studies are necessary to improve the current knowledge about Pt dissolution and how to hinder it to a practical extent.

An Ionic Liquid‐Based Gel Electrolyte: Formation Mechanism and Feasibility for Lithium Metal Batteries

AbstractQuasi‐solid‐state electrolytes (QSSEs) based on ionic liquids are recognized as one of the frontrunners of electrolytes for ensuring the safety and high energy density of next‐generation lithium batteries. However, the incapacity of such systems to meet the performance demands of batteries is significantly subject to the properties of the electrolyte and the intricacies of related interfacial processes. Recently, we have designed a high‐performing pyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI) based QSSE (Py‐Gel), with introducing LiBF4 and LiCl, which served as a system for probing the dynamic Li deposition mechanism. Herein, we focus on understanding the mechanisms of Py‐Gel formation and examining the chemistry and structure as well as the properties of the solid‐electrolyte interphases (SEIs) formed in the Py‐Gel and their influences on Li deposition. Spectroscopic characterizations suggest the existence of a cross‐linked structure in Py‐Gel, for which multiple intermolecular/intramolecular hydrogen bondings and ionic coulumbic interactions among Py cations, TFSI− anions, and Li salts are responsible. The Py‐Gel electrolyte exhibits exceptional electrical properties at room temperature. Different SEIs are prepared in the Py‐Gel via electrochemical protocols to elucidate that the synergy between a well‐featured electrolyte and an outstanding SEI is vital for stable cycling of Li metal anodes in such a QSSE.

Recent development and applications of differential electrochemical mass spectrometry in emerging energy conversion and storage solutions.

Electrochemical energy conversion and storage are playing an increasingly important role in shaping the sustainable future. Differential electrochemical mass spectrometry (DEMS) offers an operando and cost-effective tool to monitor the evolution of gaseous/volatile intermediates and products during these processes. It can deliver potential-, time-, mass- and space-resolved signals which facilitate the understanding of reaction kinetics. In this review, we show the latest developments and applications of DEMS in various energy-related electrochemical reactions from three distinct perspectives. (I) What is DEMS addresses the working principles and key components of DEMS, highlighting the new and distinct instrumental configurations for different applications. (II) How to use DEMS tackles practical matters including the electrochemical test protocols, quantification of both potential and mass signals, and error analysis. (III) Where to apply DEMS is the focus of this review, dealing with concrete examples and unique values of DEMS studies in both energy conversion applications (CO2 reduction, water electrolysis, carbon corrosion, N-related catalysis, electrosynthesis, fuel cells, photo-electrocatalysis and beyond) and energy storage applications (Li-ion batteries and beyond, metal-air batteries, supercapacitors and flow batteries). The recent development of DEMS-hyphenated techniques and the outlook of the DEMS technique are discussed at the end. As DEMS celebrates its 40th anniversary in 2024, we hope this review can offer electrochemistry researchers a comprehensive understanding of the latest developments of DEMS and will inspire them to tackle emerging scientific questions using DEMS.

Electrochemical and optical protocols for the detection and removal of an antibiotic drug rifaximin from wastewater.

Improper disposal of pharmaceutical drugs is increasing the pollution level of water reservoirs which in turn adversely impacts the ecosystem. The current study presents an electrochemical scaffold that comprises a glassy carbon electrode modified with amino-functionalized multiwalled carbon nanotubes (NH2-fMWCNTs) for the detection of a pharmaceutical drug rifaximin in wastewater. Electrochemical impedance spectroscopic characterization revealed efficient charge transport through the modified electrode surface. Square wave voltammetry was employed for probing the electro-oxidation of antibiotic rifaximin. Under optimized experimental conditions, the designed sensor demonstrated the qualities of sensitivity, repeatability, and reproducibility as required for the practical applicability of the sensing device. After the detection of a contaminant, its removal from water is imperative. In this regard an adsorption method using ZnO nanoparticles as adsorbents was developed that led to the removal of rifaximin from wastewater. At lower adsorbate concentration, adsorption was found to occur according to the Langmuir model while at higher concentration adsorption data followed the Freundlich model. The rate of rifaximin adsorption over ZnO nanoparticles followed pseudo-second-order kinetics.

Characterizing Reversible and Irreversible Degradation Effects of PEM Water Electrolyzer Stacks

Polymer electrolyte membrane water electrolyzers (PEMEL) have been identified as a key component in a decarbonized large-scale energy system, as they can produce high-purity hydrogen from renewable electricity sources for the chemical industry or energy storage. However, the long-term durability and performance of PEM electrolyzers remain a major challenge, with degradation being a critical factor that limits their lifespan and efficiency. Recent studies have focused on developing accelerated stress test (AST) protocols for PEM electrolyzers to better understand the conditions and mechanisms that lead to degradation.1, 2 Especially the reversible rise in cell potential, which in the literature is often regarded as apparent or reversible degradation, must be further investigated to find mitigation strategies for operation.3, 4 We present our research on the development of two testing protocols (static, dynamic) characterizing reversible and irreversible degradation effects for PEMEL stacks in different operation modes. Our aim is to gain a better understanding of the variance of these phenomena in general and the recovery of reversible effects across PEMEL stacks. The measurements are carried out on a commercialized Greenlight E400 test bench equipped with a 7kW 8 cell PEMEL stack (Hydrogen Innovation GmbH). The potential of all cells will be monitored during testing. The measurements include repeated electrochemical characterization protocols measuring i/E-curves, HFR and impedance spectroscopy (EIS) of the PEMEL stack and if possible, every single cell. These protocols include the introduction of low potential regeneration phases before every characterization during the test protocol to distinguish between reversible effects and the irreversible cell degradation. This was seen to be effective for potential recovery by Suermann et al. 2019 for single PEMEL cells.4 The results consist of a description of the two testing procedures and the used equipment. Due to the duration of each test protocol (3000 h) only results of the static test protocol can be presented.The contribution of the presented research is threefold. Firstly, we break down the degradation across a whole stack. Giving valuable insights regarding the distribution of cell efficiency and degradation effects. Secondly, the presented test protocols characterize and account for the reversible rise in cell/stack potential. Thirdly, the characterization of the recovery time of the cell potential across the stack will have implications for the operation of stacks to mitigate or recover these performance losses. We address both static and dynamic operation modes aiming to simulate the application of PEMEL stacks for a constant production of hydrogen used in downstream processes and the volatile operation due to a direct coupling with renewable energy sources.This publication is to be seen as presentation of first results in our ongoing research to find test protocols for short stack systems to develop operation strategies, which can be applied to large scale electrolyzer systems. Furthermore, we try to deepen the understanding of the reversible cell potential rise as well as standardize the general testing of PEMEL stacks.This work is funded by the Federal Ministry of Education and Research (BMBF) in the project “hyBit” under the grant 03SF0687E. The authors declare that the opinions expressed in this submission are their own and are based on a thorough review of existing scientific literature. Sources 1. G. Tsotridis and A. Pilenga, EU harmonized protocols for testing of low temperature water electrolysis, Publications Office of the European Union, Luxembourg (2021). 2. A. Voronova, H.-J. Kim, J. H. Jang, H.-Y. Park and B. Seo, International Journal of Energy Research, 46 (2022) 11867. 3. C. Rakousky, U. Reimer, K. Wippermann, S. Kuhri, M. Carmo, W. Lueke and D. Stolten, Journal of Power Sources, 342 (2017) 38. 4. M. Suermann, B. Bensmann and R. Hanke-Rauschenbach, Journal of The Electrochemical Society, 166 (2019) F645-F652.

Benchmarking Activity and Stability of Layered Double Hydroxides (LDHs) Electrocatalysts for Alkaline Water Electrolysis

In order to reduce the cost of producing hydrogen through water electrolysis, novel technologies must be improved. Recently, the merging of conventional alkaline electrolysis (AEL) and proton exchange membrane electrolysis (PEM) has led to the development of anion exchange membrane electrolysis (AEMWE), which offers several advantages over AEL and PEM. In a nutshell, this technique employs cheap, abundant, and easily available (non-geostrategic) transition metals with anionic exchange membranes, overcoming the drawbacks of AEL and PEM.[1]To reach the readiness level of this technology, new and scalable synthetic routes for catalysts that lower the overpotential of the sluggish oxygen evolution reaction (OER) are required. Amongst all the OER catalysts reported in the literature, Layered Double Hydroxides (LDHs) have gained increasing attention due to their low overpotentials and stabilities.[2] Besides, electrochemical protocols to determine the activity and stability of these catalysts in different electrochemical cells must be established to understand their properties. Thus, this work focuses on the advantages and limitations of different electrochemical techniques, such as rotating disk electrode (RDE), three-electrode cells, and single-cell tests, to determine the activity and stability of two different LDHs. Unlike laboratory scale LDHs ‒prepared by hydrothermal treatment (HT-LDH)‒ room temperature synthesized LDHs (RT-LDH) can be prepared in kilogram quantities and present chemical structure and morphology differences. In this work, the LDHs have been characterized with spectroscopic techniques to correlate the chemical structure and morphology of the materials to their electrochemical response by RDE, three-electrode cells, and single-cell measurements.All in all, the scalable RT-LDH presents higher activity compared to HT-LDH in all three techniques. On the one hand, small current densities can only be reached by RDE, and the short-term stability of the materials is affected by the catalyst layer interface. On the other side, single-cell test measurements require long operational times, and the contribution of the membrane degradation to the overall cell voltage is still unclear. Thus, three-electrode cell measurements offer the possibility of characterizing LDHs at relevant current densities in a fast and straightforward manner, without membrane contributions, and are further employed in this work to study the stability of these systems.

Characterization of Fuel Cell Catalyst Layers in a Gas Diffusion Electrode Setup (GDE)

Although the performance of new catalyst materials for proton exchange membrane fuel cells (PEMFC) often show very promising results in ideal rotating disc electrode (RDE) environment, these results cannot always be transferred to applicable conditions in membrane electrode assemblies (MEAs). This is mainly attributed to differences in the catalyst layer (CL) structure, which hinders the transport of reactants and products for the oxygen reduction reaction (ORR). Therefore, the chemical structure and morphology of the CL have to be considered to improve the performance of these systems in fuel cells. However, due to the various possibilities in producing CLs, many experiments must be carried out until the optimum is reached. The interaction of Pt nanoparticles, carbon support, and ionomer creates a complex triple phase interface dependent on numerous parameters. Characteristics of the carbon support,[1] the Pt loading[2] or the ionomer content[3-5] leads to intensive research efforts and a considerable amount of time as many MEA experiments have to be performed for such studies.[6] To accelerate the screening of catalyst layers, the gas diffusion electrode (GDE) was recently proposed as a half-cell to study real catalyst layers.[7] As a proof of concept study, our group recently shown that catalyst layers with different Pt loading in GDE demonstrate similar ORR trends to MEA experiments.[7] Subsequently, GDEs from different laboratories were benchmarked with standardized electrochemical protocols obtaining reproducible results.[8] Most recently, advanced electrochemical characterization methods developed for MEA technique were established as a GDE method.[9] In the present work, we focus on main aspects of catalyst development, such as the morphology of catalyst layer formation and different catalyst materials, to gain fundamental insights into catalyst layer development. We tuned the porosity of real catalyst layers using different solvent compositions. The results show that low macroporosity leads to severe O2 mass transport limitations, whereas a better performance could be achieved for higher porosity. This allows a critical consideration of key parameters in MEA manufacturing, which has hot pressing as an indispensable step.This work demonstrates the importance of morphology and treatment of the catalyst layer and how substantially it affects the performance and mass transport in GDE setups to elucidate the optimal conditions for the accessibility of the triple phase interface.Literature[1] V. Yarlagadda, M. K. Carpenter, T. E. Moylan, R. S. Kukreja, R. Koestner, W. Gu, L. Thompson and A. Kongkanand, ACS Energy Lett. 2018, 3, 618-621.[2] J. P. Owejan, J. E. Owejan and W. Gu, J. Electrochem. Soc. 2013, 160, F824.[3] E. Antolini, L. Giorgi, A. Pozio and E. Passalacqua, J. Power Sources 1999, 77, 136-142.[4] K.-H. Kim, K.-Y. Lee, H.-J. Kim, E. Cho, S.-Y. Lee, T.-H. Lim, S. P. Yoon, I. C. Hwang and J. H. Jang, Int. J. Hydrogen Energy 2010, 35, 2119-2126.[5] G. Sasikumar, J. W. Ihm and H. Ryu, J. Power Sources 2004, 132, 11-17.[6] K. Ehelebe, D. Escalera-López and S. Cherevko, Current Opinion in Electrochemistry 2021, 29, 100832.[7] K. Ehelebe, D. Seeberger, M. T. Y. Paul, S. Thiele, K. J. J. Mayrhofer and S. Cherevko, J. Electrochem. Soc. 2019, 166, F1259-F1268.[8] K. Ehelebe, N. Schmitt, G. Sievers, A. W. Jensen, A. Hrnjić, P. Collantes Jiménez, P. Kaiser, M. Geuß, Y.-P. Ku, P. Jovanovič, K. J. J. Mayrhofer, B. Etzold, N. Hodnik, M. Escudero-Escribano, M. Arenz and S. Cherevko, ACS Energy Lett. 2022, 7, 816-826.[9] P. Kaiser, V. Lloret Segura, K. Ehelebe and S. Cherevko, ECS Meeting s 2022, MA2022-01, 2071.