On-line Electrochemical Mass Spectrometry Research Articles

Lattice Oxygen Activation through Deep Oxidation of Co4N by Jahn-Teller-active Dopants for Improved Electrocatalytic Oxygen Evolution.

Triggering the lattice oxygen oxidation mechanism is crucial for improving oxygen evolution reaction (OER) performance, because it could bypass the scaling relation limitation associated with the conventional adsorbate evolution mechanism through the directly formation of oxygen-oxygen bond. High-valence transition metal sites are favorable for activating the lattice oxygen, but the deep oxidation of pre-catalysts suffers from a high thermodynamic barrier. Here, taking advantage of the Jahn-Teller (J-T) distortion induced structural instability, we incorporate high-spin Mn3+ (t2g3eg1) dopant into Co4N. Mn dopants enable a surface structural transformation from Co4N to CoOOH, and finally to CoO2, as observed by various in-situ spectroscopic investigations. Furthermore, the reconstructed surface on Mn doped Co4N triggers the lattice oxygen activation, as evidenced experimentally by pH-dependent OER, tetramethylammonium cation adsorption and on-line electrochemical mass spectrometry measurements of 18O-labelled catalysts. In general, this work not only offers the introducing J-T effect approach to regulate the structural transition, but also provides an understanding about the influence of catalyst's electronic configuration on determining the reaction route, which may inspire the design of more efficient catalysts with activated lattice oxygen.

Elucidating the Reduction Mechanism of Lithium Bis(oxalato)borate.

Electrolyte additives are indispensable to enhance the performance of Li-ion batteries. Lithium bis(oxalato)borate (LiBOB) has been explored for many years, as it improves both cathode and anode performance. No consensus regarding its reaction mechanisms has, however, been established. A model operando study combining attenuated total reflection infrared spectroscopy (ATR-FTIR), electrochemical quartz crystal microbalance (EQCM), and online electrochemical mass spectrometry (OEMS) is herein presented to elucidate LiBOB reduction and electrode/electrolyte interphases thus formed. Reduction of the BOB- ion sets in at ∼1.8 V with solid lithium oxalate and soluble oxalatoborates as the main products. The reduced BOB- ion also reacts with itself and its environment to evolve CO2, which in turn impacts the interphase formed on the negative electrode. This study provides further insights into the reduction pathways of LiBOB and how they contribute to the interphase formation.

Beneficial Effects of Oxide-Based Additives on Li-and Mn-rich Cathode Active Materials

Li- and Mn-rich layered oxides such as Li1.14(Ni0.26Co0.14Mn0.60)0.86O2 (LMR-NCM) are potential next-generation cathode active materials (CAMs) for lithium ion-batteries, promising an increased energy density at lower materials costs compared to state-of-the-art CAMs. However, its commercial viability is still inhibited by its strong gassing, poor cycling stability, and voltage fading, so various approaches such as post-treatments or additives are being investigated. Here, it will be shown that the cycling performance of LMR-NCM//graphite coin-cells is drastically improved when assembled with 300 °C dried glassfiber (GF) separators (“GF-cells”) compared to cells with Celgard (CG) separators dried at 70 °C (“CG-cells”). The origin of this phenomenon is investigated by online electrochemical mass spectrometry (OEMS), TGA-MS, water absorption, and XPS measurements. These reveal that the superior performance of the GF-cells can be ascribed to the bulk water absorption capability of the 300 °C dried glassfiber material as well as its ability to scavenge HF, whereby H2O and HF are produced by the (electro)chemical oxidation of the electrolyte and the decomposition of the LiPF6 salt. Similar performance enhancements can be observed for 300 °C dried SiO2 nanoparticles added to the LMR-NCM cathodes or for an HF/H+ scavenging electrolyte additive.

Factors Influencing Gas Evolution from High‐Nickel Layered Oxide Cathodes in Lithium‐Based Batteries

AbstractGas evolution from high‐nickel layered oxide cathodes (>90% Ni) remains a major issue for their practical application. Gaseous species, such as CO2, O2, and CO, that are evolved at high states of charge (SOC) worsen the overall safety of batteries, as pressure build‐up within the cell may lead to cell rupture. Since these gasses are produced during cathode degradation, tracking the formation of gasses is also important in diagnosing cathode failure. Online electrochemical mass spectrometry (OEMS) is a powerful in situ technique to study gas evolution from the cathode during high‐voltage charge. However, the differences in the OEMS experimental setups between different groups make it challenging to compare results between groups. In this perspective, the various factors that influence gas evolution based on the OEMS results collected in this group are presented. The focus is on the conditions that lead to gas release, with a particular emphasis on reactive oxygen formation and subsequent chemical reactions with the electrolyte. Promising strategies, such as electrolytes, compositional tuning, and surface coatings that are effective at suppressing gas evolution from the cathode are highlighted. Critical insights into mitigating cathode degradation and gas evolution are provided to guide the development of safer, high‐energy batteries.

Impact of Lithium‐Ion Battery Separators on Gas Evolution during Temperature Abuse

AbstractSeparators in lithium‐ion batteries are typically considered to be electrochemically inert under normal operating conditions. Yet, temperature abuse tests at elevated temperatures of ca. 60 °C to 132 °C show that the choice of separator material has a decisive influence on battery behavior and degradation. Using online electrochemical mass spectrometry, we analyzed the evolution of cell voltage and gas products during and after thermal abuse for different separators. Polypropylene and polytetrafluoroethylene seem exhibited little change in gas evolution, producing only modest amounts of CO2 and POF3. In contrast, glass fiber and polyethylene terephthalate separators caused additional gas release, indicating electrochemical instability. Polyethylene terephthalate produced significantly more gas, resulting in the mechanical failure of the separator and drastic performance losses. The amount of CO2 evolved with polyethylene terephthalate is four times higher than that of the glass fiber separator. However, the amount of POF3 detected was five times higher for the glass fiber separator.

Polycarbonate-Based Solid-Polymer Electrolytes for Solid-State Sodium Batteries.

Solid-polymer electrolytes comprised of polypropylene carbonate (PPC) and varied sodium bis(fluorosulfonyl)imide (NaFSI) salt concentrations are investigated for implementation as a conductive solid polymer electrolyte into solid-state cathode composites utilizing a sodium-layered oxide active material. The ionic conductivity generally increases with NaFSI salt content, reaching ≈1mScm-1 at 80°C at the highest salt concentration (PPC:NaFSI = 0.5:1). Through an all-in-one slurry casting method, Na2/3 Ni1/3 Mn2/3 O2 cathode composites are fabricated in which the dispersed PPC electrolyte acts as the primary binder. Enabled by a bilayer polymer electrolyte system, cycling performance with the PPC cathode electrolyte is optimized with respect to salt concentration and anode material. The best cyclability is achieved with a moderate salt concentration electrolyte (PPC:NaFSI = 5:1), showcasing an initial capacity of 83mAhg-1 with a remarkable 80% capacity retention after 150 cycles at C/5 rate and 60°C. The superior performance of the lower salt concentration electrolyte is attributed to better electrochemical stability, as confirmed by linear sweep voltammetry and online electrochemical mass spectrometry measurements. These results underscore the potential of carbonate-based polymer electrolytes and the importance of balancing electrolyte conductivity and stability in cell design.

Accelerating Real-Time Analysis of Gas Diffusion Electrodes Using Different Coupled Mass Spectrometry Techniques

Due to the rapid development of new catalysts, simple electrochemical screening methods are needed to evaluate the activity and stability of catalyst layers. Setups for these applications already exist: the so-called Scanning Flow Cells (SFCs) unify real-time electrochemical activity and dissolution stability analysis in a high-throughput fashion and find applications in a broad range of topics, such as battery research, 1 oxygen evolution reaction catalysts performance,2 and photo-electrochemistry.3 Yet, the low current densities reached in the system hinder the direct comparison of the results to real devices.4 Gas diffusion electrode (GDE) based setups present a promising alternative to Aqueous Model Systems (AMS) due to their ability to achieve higher current densities. Compared to two electrode full cells (fuel cell or water electrolyser), GDE half-cells are operated in a three-electrode configuration with liquid electrolyte. However, as in fuel cells, gasses reach the catalyst layer through a flow field, achieving relevant current densities up to 2 A cm-2. The GDE half- cell offers the advantage of studying the isolated reaction of the working electrode by applying controlled potentials with a reference electrode. While the GDE offers a simplified approach, the assembly process can be time-consuming, and the overall catalyst throughput analysis could be further optimised.5,6 In this context, we present a novel setup that enables the rapid examination of catalyst layers for fuel cells, providing more realistic conditions while simultaneously investigating degradation processes. The setup consists of an optimised SFC based on lower internal resistance and an additional flow field to purge the catalyst layer with different gasses. As the common SFC, the presented Scanning Gas Diffusion Electrode half cell (S-GDE) can be connected to an Inductively Coupled Plasma Mass Spectrometer (ICP-MS) to quantify the dissolution of metals in real-time. Furthermore, the gas-sensitive Mass Spectrometer can be connected to the gas stream of the cell, enabling the detection of volatile products via on-line electrochemical mass spectrometry (OLEMS). The simple replacement of catalyst layers in the S-GDE allows fast analysis of multiple catalysts consecutively. Still, as the aim is to facilitate high-throughput electrochemistry, developing the S-GDE is ongoing. Furthermore, the optimised cell can reach higher current densities than cells of a similar design, allowing accelerated stress tests (ASTs) and the performance of polarisation curves.The S-GDE will offer a new perspective on realistic catalyst layers, their performance, and catalyst/support degradation processes, e.g. Pt dissolution and carbon corrosion. The increasing demand for new catalyst materials highlights the need for their rapid evaluation under realistic conditions, taking into account not only their electrochemical performance but also their stability. Lüchtefeld J, Hemmelmann H, Wachs S, Mayrhofer KJ, Elm MT, Berkes BB. Effect of Water Contamination on the Transition Metal Dissolution in Water-Enriched Electrolyte: A Mechanistic Insight into a New Type of Dissolution. The Journal of Physical Chemistry C. 2022;126(40):17204–11.Zlatar M, Nater D, Escalera-López D, Joy RM, Pobedinskas P, Haenen K, et Evaluating the stability of Ir single atom and Ru atomic cluster oxygen evolution reaction electrocatalysts. Electrochimica Acta. 2023;444:141982.Jenewein KJ, Kormányos A, Knöppel J, Mayrhofer KJJ, Cherevko S. Accessing In Situ Photocorrosion under Realistic Light Conditions: Photoelectrochemical Scanning Flow Cell Coupled to Online ICP-MS. ACS Measurement Science Au. 2021;1(2):74–81.Ehelebe K, Escalera-López D, Cherevko S. Limitations of aqueous model systems in the stability assessment of electrocatalysts for oxygen reactions in fuel cell and Current Opinion in Electrochemistry. 2021;29:100832.Ehelebe K, Knöppel J, Bierling M, Mayerhöfer B, Böhm T, Kulyk N, et Platinum Dissolution in Realistic Fuel Cell Catalyst Layers. Angewandte Chemie (International ed in English). 2021;60(16):8882–8.Ehelebe K, Seeberger D, Paul MTY, Thiele S, Mayrhofer KJJ, Cherevko S. Evaluating Electrocatalysts at Relevant Currents in a Half-Cell: The Impact of Pt Loading on Oxygen Reduction Reaction. Journal of The Electrochemical Society. 2019;166(16):F1259-F68. Figure 1: The S-GDE unifies the real conditions approach of the GDE and the high throughput approach of the SFC and the connection to two mass spectrometer enables the real time detection of dissolved catalyst (ICP-MS) and volatile products (OLEMS). Figure 1

Temperature-Dependent Interplay of Chemical Versus Electrochemical Electrolyte Oxidation at Ni-Rich Cathodes

Increasing demands for high energy density Li-ion batteries as a source for power supply are demanding an optimization of cathode active materials (CAMs) and of the overall cell chemistry of batteries. Thus, the main interest of researchers has focused on nickel-rich (>80%) layered transition metal oxides such as NCMs (LiNixCoyMnzO2, with x+y+z=1) or NCAs (LiNixCoyAlzO2, with x+y+z=1) as CAMs, owing to their high capacity. However, as a result of the increase in Ni-content, the structural stability of these CAMs is significantly decreased at high upper cut-off potentials compared to those with lower Ni-content, resulting in capacity fading, which restricts their practically achievable capacity.[1] One possible culprit behind this capacity fading at high state-of-charge (SOC) is the release of reactive lattice oxygen, which is known for layered TM-oxides to occur at high SOC (i.e., starting at approx. 80% SOC).[2] The released oxygen is proposed to lead to the chemical oxidation of ethylene carbonate (EC), resulting in HF formation, which in turn is proposed to trigger the dissolution of TMs.[3] Furthermore, the electrochemical oxidation of the electrolyte is known to occur at high potentials, which as a result of its reactive reaction products, can induce further transition metal (TM) dissolution from the CAM.[4,5] The proposed chemical oxidation of the electrolyte by lattice oxygen suggests that this process should be strongly correlated to the dissolution of TMs from the CAM. However, as shown by operando X-ray absorption spectroscopy (XAS) and on-line electrochemical mass spectroscopy (OEMS) studies, the onset for the TM-dissolution, depending on the CAM under investigation, occurs at ~300 mV higher potentials compared to the onset for oxygen evolution.[2,3] This suggests that the dissolution of metals is rather induced by the electrochemical oxidation of the carbonate-based electrolyte, which was reported to initiate at potentials above 4.7 VLi at room temperature.[5] Both the electrochemical oxidation of battery electrolytes, as well as the dissolution of TMs from the CAM were reported to be strongly affected by temperature, while the onset potential for lattice oxygen loss is essentially unaffected, which further hints towards the significance of former.[5-7] Within this work we therefore conduct a detailed study on the temperature dependency of both the gas formation due to (electro)chemical electrolyte oxidation and the dissolution of TMs by means of OEMS and operando hard XAS, respectively. By applying a measurement protocol consisting of constant voltage-holds in steps of 50 mV at elevated potentials (see Figure 1), an excellent time as well as potential resolution enables the deconvolution of the onset for lattice oxygen release and the (electro)chemical oxidation of LP47 (1 M LiPF6 in EC:DEC 3:7 by weight) for a LiNi0.80Co0.15Al0.05O2 (NCA) CAM via OEMS. It will be shown that the onset for oxygen evolution coincides with a significant evolution of CO2 (see Figure 1b), indicating chemical oxidation of the electrolyte. However, the onset for POF3/PF5 evolution (marked in Figure 1b as “POF3”, since both gasses appear on the same mass channel)[8], which is a reaction product from the decomposition of LiPF6 caused by electrochemical electrolyte oxidation, is shifted to 300 – 450 mV higher potentials (depending on the temperature). It suggests a chemical oxidation mechanism of the electrolyte, which proceeds without significant H2O/H+ production. A change in temperature strongly affects this onset of “POF3” evolution, while O2 is released at the same degree of de-lithiation, regardless of temperature. To correlate this effect observed in the temperature-dependent gassing behavior to the dissolution of transition metals for this CAM, an operando hard XAS study at different temperatures will be conducted.

Electro-Oxidative Valorization of Biomass-Derived Furanics

Electrocatalysis poses many potential advantages for distributed scale biomass valorization. Furanic biomass derivatives such as furfural and 5-hydroxymethylfurfural (HMF) can provide access to a number of value-added chemicals by partial oxidation, including furoic acid, maleic acid, and 2,5-furandicarboxylic acid (FDCA). Here, we have utilized differential reactor studies with online electrochemical mass spectrometry (OLEMS), as well as in-situ attenuated total reflectance surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS), to probe these reaction pathways on various metal electrodes. Experimental insights are combined with computational results to piece together plausible mechanisms. We find tradeoffs between decarbonylation activity and self-assembly of furoate intermediates on late transition metals to be critical selectivity-determining and rate-determining process. We also characterize oxidative dehydrogenation paths for furanic aldehydes, which co-produce (anodic) hydrogen gas. Strategies for improved catalyst design will be discussed.

Unexplored Reaction Pathways of Ethylene Carbonate during Solid Electrolyte Interphase Formation

The solid electrolyte interphase (SEI) keeps eluding our grasp. Fundamental understanding of Li-ion battery performance will not be complete until the major underlying reaction pathways of SEI formation and growth have been described.1 Although the SEI has been observed to be a complex and highly diverse matrix of in-/organic crystalline and amorphous aggregates, likely only few compounds are functional, i.e. passivate the electrode while at the same time sustaining the Li+ transport. The aim of the presentation is to provide experimental evidence for hitherto largely unexplored reaction pathways of several commonly observed SEI compounds (such as lithium ethyl dicarbonate, abbr. LEDC) and prove how the formation of the same can be altered by the choice of electrolyte additives. For instance, Electrochemical Quartz Crystal Microbalance with Dissipation monitoring complemented by Online Electrochemical Mass Spectrometry is demonstrated to separate electrochemical from chemical reactions in a multistep SEI formation process.2-3 Based on our experimental findings, the role and implication of each compound (be it LiOH, Li2O, LEDC, etc.) in the SEI formation process will be discussed.4

(Poster Award Winner 1) Investigating the Impact of Ethylene Carbonate Reaction Pathways on the Solid Electrolyte Interphase in Li-Ion Batteries

A high-performing Li-ion battery relies heavily on the solid electrolyte interphase (SEI), which is composed of various decomposition products, primarily from reduced additives or electrolyte species such as ethylene carbonate (EC). The composition of the SEI evolves and continues to form during the operation of a Li-ion battery, making it challenging to fully understand through post-mortem analysis alone. To gain a complete understanding of the EC reaction pathways and their respective contributions to the SEI, it is necessary to employ analytical techniques that monitor the battery during operation. Online Electrochemical Mass Spectrometry (OEMS) is one such technique that can sample the gas composition of a battery, providing an overview of voltage-dependent gas evolution processes.1 This presentation focuses on two EC reaction pathways that occur on a model carbon electrode.2 The first pathway, the "EC ring-opening" reaction pathway, is initiated by hydroxides/alkoxides at potentials above 1.5 V vs. Li+/Li and is associated with CO2 evolution.3 , 4 The second pathway, the "EC reduction" pathway, occurs at potentials below 0.9 V vs. Li+/Li and is identified by C2H4 evolution.5 Both reaction pathways contribute to the formation of the SEI, and they compete with each other. If EC ring-opening is favoured, it can suppress EC reduction. Figure 1 illustrates the competing relationship between the two different EC reaction pathways, where the addition of EC ring-opening initiators (H2O) increases CO2 and reduces C2H4. It is essential to consider all possible EC reaction pathways, not just the desired one, when forming the SEI. The presentation concludes with a discussion of the potential implications that EC ring-opening may have on a Li-ion cell. Figure 1 . Comparison between the total CO2 and C2H4 evolution during the initial cyclic voltammetry cathodic sweep in a Glassy carbon | 1 M LiPF6 EC:DEC | LiFePO4 cell. References R. Lundström and E. J. Berg, J. Power Sources, 485, 229347 (2021).R. Lundström, N. Gogoi, X. Hou, and Berg Erik J., Submitted (2023).M. Metzger, B. Strehle, S. Solchenbach, and H. A. Gasteiger, J. Electrochem. Soc., 163, 1219–1225 (2016).L. Gireaud, S. Grugeon, S. Laruelle, S. Pilard, and J.-M. Tarascon, J. Electrochem. Soc., 152, A850 (2005).R. Imhof and P. Novák, J. Electrochem. Soc., 145, 1081–1087 (1998). Figure 1

Bridging Aqueous and Organic Electrolytes: Intercalation Mechanism of TiS2 in Sustainable Aqueous Li-Ion Batteries

Aqueous Li-ion batteries (ALiBs) are a promising alternative for large-scale grid storage owing to water's non-flammability, low cost, and ease of purification. However, the narrow electrochemical stability window (ESW) of water (1.23 V) significantly limits the energy density of ALiBs, compared to their non-aqueous counterpart. The use of a highly concentrated electrolyte, such as 21 mol kg-1 (molality, m) of LiTFSI in water, known as the “water-in-salt” (WiS) electrolyte, can widen the water ESW to ~3 V, but its high cost and low environmental sustainability hinder the commercialization of ALiBs. Therefore, we explored the feasibility of cycling layered TiS2 anodes in ALiBs containing dilute electrolytes (i.e. 2 m LiTFSI in water).We obtained a reversible discharge capacity of ca. 80 mAh g-1 at a current density of 50 mA g-1. By employing three-electrode cycling with online electrochemical mass spectrometry, we identified potential-dependent gas evolution from the cell triggered by multiple chemical/electrochemical reactions, such as (1) solvent co-intercalation, (2) partial TiS2 exfoliation, and (3) TiS2-catalyzed water splitting in dilute aqueous electrolytes. We also identified a completely different potential profile of TiS2, when cycled in an aqueous electrolyte, with two distinct redox plateaus at 2.95 V and 2.88 V, followed by a sloping region until 2.3 V (all vs. Li+/Li0). Recall that in classic non-aqueous electrolytes, TiS2 shows a characteristic sloping profile centered at ca. 2.2 V, the peculiar potential profile suggests a different intercalation mechanism of TiS2 in aqueous electrolytes.In this presentation, we will share our latest findings from complementary physicochemical and computational methods to tackle the complex interfacial reactivity between layered anodes and aqueous electrolytes. Operando synchrotron X-ray diffraction data revealed the reversible uptake-release of water molecules between TiS2 layers, which was also confirmed energetically favorable by theoretical modeling. By introducing triethyl phosphate (TEP) as a co-solvent, we successfully tuned the electrochemical intercalation behavior of TiS2 from purely Li-intercalation (as in non-aqueous systems, when using only TEP as the solvent) to hydrated-Li-intercalation (as in concentrated and dilute aqueous electrolytes, when using water/TEP mixtures as the solvent). These findings suggest that solvent co-intercalation can be a promising strategy for ALiBs. The general implication of these results on the electrode-electrolyte interface and interphase in aqueous batteries will be systematically discussed in the talk. Overall, our work provides new perspectives on developing sustainable energy storage technologies. Figure 1

An Insight into the Lithium Plating – Operando Gas Evolution Study

Lithium-ion batteries (LiBs) play a major role in the electrification of transportation systems as a step forward in achieving a sustainable carbon neutral society [1]. Fast-charging is regarded as one of the most necessary features for lithium-ion batteries in order to speed the widespread adoption of electric vehicles [2]. However, we have previously shown that charging LiBs at high C-rate cause the evolution of high amount of ethylene gas along with capacity fade [3]. It is well known that fast charging is also may result in lithium plating and allied parasitic reactions [4]. Since many of the side reactions in LiBs are associated with evolution of products in gaseous phase, operando mass spectrometric techniques can be used to better understand these unwanted reactions. We have developed an Online Electrochemical Mass Spectrometry (OEMS) set-up to study the gases formed on a Li-plated electrode, to provide the fundamental understanding of the reaction mechanism at the electrode/electrolyte interface.

Porous lithiophilic Cu-Sn solid solution current collector for dendrite-free lithium metal batteries

Lithium metal batteries (LMBs) have high energy density but suffer from the formation of Li dendrites and unstable solid electrolyte interface. Herein, a three-dimensional porous Cu-Sn solid solution was designed as current collector for LMBs and was fabricated through the combination of vapor phase alloying with subsequent vapor phase dealloying. The effect of the Sn addition on electrochemical performances and Li plating/stripping behaviors was investigated using in-situ X-ray diffraction, ex-situ scanning electron microscopy, as well as density functional theory calculations. As benchmarked with porous Cu (3D-Cu), the addition of lithiophilic Sn can efficiently improve the Li plating/stripping performance, especially for the 1.5 at.% Sn addition (3D-Cu98.5Sn1.5). The 3D-Cu98.5Sn1.5 current collector maintains coulombic efficiency of 95 % up to 200 cycles at 1 mA cm−2. Moreover, the existence of Sn in solid solution exhibits a much lower binding energy (-3.223 eV) and nucleation overpotential (28.9 mV) compared with those of 3D-Cu, indicating that the metallic Li is extremely susceptible to nucleation and growth on the surface. Additionally, the gas evolution scenarios were probed by on-line differential electrochemical mass spectrometry. Our findings show that the 3D-Cu98.5Sn1.5 current collector effectively enhances the uniformity of Li plating and suppresses the generation of dendrites in LMBs.

Combining Renewable Electricity and Renewable Carbon: Understanding Reaction Mechanisms of Biomass-Derived Furanic Compounds for Design of Catalytic Nanomaterials.

ConspectusDespite the growing deployment of renewable energy conversion technologies, a number of large industrial sectors remain challenging to decarbonize. Aviation, heavy transport, and the production of steel, cement, and chemicals are heavily dependent on carbon-containing fuels and feedstocks. A hopeful avenue toward carbon neutrality is the implementation of renewable carbon for the synthesis of critical fuels, chemicals, and materials. Biomass provides an opportune source of renewable carbon, naturally capturing atmospheric CO2 and forming multicarbon linkages and useful chemical functional groups. The constituent molecules nonetheless require various chemical transformations, often best facilitated by catalytic nanomaterials, in order to access usable final products.Catalyzed transformations of renewable biomass compounds may intersect with renewable energy production by offering a means to utilize excess intermittent electricity and store it within chemical bonds. Electrochemical catalytic processes can often offer advantages in energy efficiency, product selectivity, and modular scalability compared to thermal-driven reactions. Electrocatalytic reactions with renewable carbon feedstocks can further enable related processes such as water splitting, where value-adding organic oxidation reactions may replace the evolution of oxygen. Organic electroreduction reactions may also allow desirable hydrogenations of bonds without intermediate formation of H2 and need for additional reactors.This Account highlights recent work aimed at gaining a fundamental understanding of transformations involving biomass-derived molecules in electrocatalytic nanomaterials. Particular emphasis is placed on the oxidation of biomass derived furanic compounds such as furfural and 5-hydroxymethylfurfural (HMF), which can yield value-added chemicals, including furoic acid (FA), maleic acid (MA), and 2,5-furandicarboxylic acid (FDCA) for renewable materials and other commodities. We highlight advanced implementations of online electrochemical mass spectrometry (OLEMS) and vibrational spectroscopies such as attenuated total reflectance surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS), combined with microkinetic models (MKMs) and quantum chemical calculations, to shed light on the elementary mechanistic pathways involved in electrochemical biomass conversion and how these paths are influenced by catalytic nanomaterials. Perspectives are given on the potential opportunities for materials development toward more efficient and selective carbon-mitigating reaction pathways.

Comparing the Lithiation and Sodiation of Hard-Carbon Using Online Electrochemical Mass Spectrometry

Sodium-ion batteries (SIBs) are a promising alternative to lithium-ion batteries (LIBs), especially for applications in which weight and size play a subordinate role.1 In contrast to LIBs, graphite is not a viable anode active material for SIBs since sodium cannot be inserted into graphite. So-called hard-carbons are promising anode active materials for SIBs because of their easy synthesis, high capacity, and high cycling stability.2 Major challenges are the high irreversible capacity in the first cycle and the stability of the solid electrolyte interphase (SEI).3 - 4 Online electrochemical mass spectrometry (OEMS) is a powerful tool for identifying and quantifying evolved gasses during SEI formation, giving insight into the mechanism of SEI formation. For LIB research, our group had developed a two-compartment OEMS cell design that enables the investigation of evolved gases from one of the electrodes of a battery cell without interference from the gases evolved from the other electrode, which is particularly useful for the mechanistic study of electrolyte additives or impurities without influences of the counter electrode.5–8 In this study, we investigate the gas evolution during the first lithiation/delithiation cycles of a hard-carbon anode active material using our existing two-compartment cell design. This will then be compared to the gas evolution during the first sodiation/desodiation cycles of the same hard-carbon material using a newly developed two-compartment OEMS-cell design for the study of sodium-ion batteries, which is based on a gas impermeable solid electrolyte separator composed of sodium ion conducting β-alumina. We compare the quantities of evolved gasses and look at the onset potentials of gas evolution during the first alkaline metal insertion. On the basis of gassing and impedance data,9,10 the differences in SEI formation and its properties will be discussed.Acknowledgments: We gratefully acknowledge funding by the BMBF (Federal Ministry of Education and Research, Germany) for its financial support under the auspices of the ExZellTUM III project, grant number 03XP0255

Gas Analysis of Large-Format Automotive Lithium-Ion Battery Cells during Formation

Due to the decision by the European Union to stop sales of combustion-based vehicles after 2035, all car manufacturers are in search to close this gap with alternative solutions. As Lithium-Ion batteries (LIBs) are already an integral part of our everyday life, battery based electric vehicles (BEVs) are expected to be one possible alternative for the individual mobility of tomorrow. Therefore, all original equipment manufacturers (OEMs) who want to produce their own battery cells must deal with many challenges as the LIB is the most expensive single component used in EVs. Reducing costs of LIB production is making EVs more affordable and even more sustainable. One major production-related factor is the dwell-time under dry-room conditions as its disproportionately increases the overall production costs. Dry-Room conditions can´t be avoided as materials like the electrolyte and active material rely on water-free handling conditions [2-3, 5].Battery cells are typically assembled in a dry state. Cells are then filled with electrolyte and a so-called precharge step is performed. During this, the solid-electrolyte interface (SEI) is formed on the negative electrode when the electrolyte is partially reduced. The formation process results in a significant gas evolution, where typical gasses like CO, CO2, H2, O2, C2H4 can be formed [1, 4, 5]. After main gas evolution, the cells can be sealed and transported into normal atmosphere, where further charging and evaluation protocols are performed. In order to understand the voltage-related gas evolution during first charging, new analytical methods are needed. The hyphenation of electrochemical cycling and mass spectrometry to so-called Online-Electrochemical Mass Spectrometry (OEMS) is a powerful technique to investigate the gas evolution inside LIBs.In this project the development of OEMS for large-format prismatic LIBs will be outlined. The feasibility of studying battery cell formation reactions and the influence of typical parameters, like temperature or charging rate onto the gassing rate will be discussed. The obtained experiments are designed to give new insights into the gas formation during first charge and how the results compare in size to already well described model-cell OEMS-experiments [2, 3]. The cells are based on a graphite / NMC811 system with ethylene carbonate (EC) and ethyl methyl carbonate (EMC) 5/7 w% (LP57-electrolyte). The cells are produced by our BMW inhouse prototype production line and provide a clear as simple composition of all components. In contrast, commercially available LIBs differ in many aspects, e.g., containing a complex mixture of different volatile organic carbonates as well as quite often unknown additives, which may complicate the analysis [4]. The inhouse production also allows a unique integration of a commercially available Swagelok fitting in the lid of the LIB.

Quantitative Electrochemistry-Mass Spectrometry: Real-Time Detection of Volatile Products for Electrocatalysis and Batteries

A major challenge both within electrocatalysis and battery research concerns the real-time (i) identification and (ii) quantification of volatile reaction products as a function of the applied electrochemical parameters and the reaction conditions. Analysis of both steadily evolving gases and of fast- and transient reaction phenomena can reveal key insights into reaction mechanisms. To this end, methods like Differential Electrochemical Mass Spectrometry (DEMS)1 and On-line Electrochemical Mass Spectrometry (OLEMS)2 have been used successfully to study reaction mechanisms to an ever-increasing degree in recent years, primarily in aqueous electrolytes. Similarly, Online Electrochemical Mass Spectrometers (OEMS)3 have been essential for the study of gas evolution in batteries.However, to gain an in-depth understanding of these mechanisms, the ability to accurately relate the electrochemical charge transferred in the reaction to the amount of evolved product is essential. To this end, accurate calibration of MS signals is paramount. Calibration procedures available for DEMS systems are by themselves cumbersome and unreliable and full quantification is not possible for OLEMS.Herein, we show how a simple gas-based calibration procedure using chip-based Electrochemistry-Mass Spectrometry (EC-MS) can be used for reliable, fully quantitative real-time analysis of volatile electrochemical reaction products. We validate this calibration with electrochemistry-based calibration methods described previously.4,5 The new procedure allows to extend the quantitative analysis to systems with no a priori knowledge of faradaic efficiencies. We demonstrate calibration of important gases like H2, O2 and C2H4 in aqueous and non-aqueous electrolytes and exemplify the calibration methodology’s usefulness on standard electrochemical reactions. References H. Baltruschat, J Am Soc Mass Spectrom, 15, 1693–1706 (2004).A. H. Wonders, T. H. M. Housmans, V. Rosca, and M. T. M. Koper, J Appl Electrochem, 36, 1215–1221 (2006).N. Tsiouvaras, S. Meini, I. Buchberger, and H. A. Gasteiger, J Electrochem Soc, 160, A471–A477 (2013).D. B. Trimarco et al., Electrochim Acta, 268 (2018).S. B. Scott, PhD thesis, Technical University of Denmark (2019). Figure 1: a) Schematic of the MS inlet chip’s working principle. b) Uncalibrated M2 and M32 signals (dotted lines) and the same signals after calibration for H2 and O2 (full lines) in a cyclic voltammogram of PtPoly in 0.1 M HClO4 obtained at room temperature at 20 mV/s. Figure 1

Solid-Electrolyte Interphase of Molecular Crowding Electrolytes

Molecular crowding electrolyte was proposed to improve the stability of water at a low concentration of Li salt (2 m LiTFSI )1. Low-cost and safe poly (ethylene glycol) (PEG, Mn=400) is adopted as a crowding agent to confine water molecules through hydrogen bonding and strengthen the covalent bond of H-O (H2O), leading to effective suppression of water decomposition (especially HER). However, the mechanism behind the improved cathodic stability of molecular crowding electrolyte is not yet fully understood. Specifically, the composition of the SEI and the impact of salt on the electrochemical stability of PEG-based electrolyte are still unknown. To gain a deeper insight into the stability mechanism in molecular crowding electrolytes, we investigated the cathodic stability of PEG-based molecular crowding electrolytes with LiTFSI and LiClO4 as the electrolyte salt. We characterized the composition and structure of SEI on Li4Ti5O12 electrode (LTO) derived from LiTFSI- and LiClO4-containing electrolytes, and correlated cathodic stability to the composition of the SEI. Comprehensive characterizations including linear sweep voltammetry (LSV), online electrochemical mass spectroscopy (OEMS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) are used to study the cathodic stability of water. The enhance mechanism will be discussed.[1] Xie, J., Liang, Z. & Lu, Y. C. Molecular crowding electrolytes for high-voltage aqueous batteries. Nat. Mater. 2020, 19, 9, 1006-1011[2] Xie, J., Guan, Y., Huang, Y., & Lu, Y. C. Solid–electrolyte interphase of molecular crowding electrolytes. Chem. Mater. 2022, 34, 11, 5176–5183AcknowledgementThis work is supported by a grant from the Research Grant Council of Hong Kong Special Administrative Region, China (Project No. RFS2223-4S03) and a grant from the Innovation and Technology Commission of the Hong Kong Special Administrative Region, China (Project No. ITS/219/21FP).

Temperature-Dependent Gassing Analysis By on-Line Electrochemical Mass Spectrometry of Lithium-Ion Battery Cells with Commercial Electrolytes

Li-ion batteries (LiBs) are known to evolve gases during their first few formation cycles due to the formation of a solid electrolyte interphase (SEI) at the anode active material particle surface. Simultaneously, the electrolyte can react by other mechanisms leading to the formation of volatile species. 1,2 At a high state-of-charge, the cathode can also release reactive oxygen which causes the formation of CO and CO2 from the oxidative decomposition of the electrolyte.3,4 Consequently, by the analysis of evolved gas species one can study the effect of electrolyte additives, reveal substantial degradation processes within LiBs, and rationalize optimized formation strategies.4–6 The evolution of gaseous species is typically quantified in-situ by monitoring the cell pressure (e.g., via the so-called Archimedes principle) or by online mass spectrometry.5,7 Concerning the latter, an on-line electrochemical mass spectrometer (OEMS) was developed for the application in LiB research and proved to be particularly powerful, since it allows a quantitative analysis and the identification of the evolved and consumed gas during the operation of a battery.4,7 The quantification of OEMS data, however, is challenging when the vapor pressure of the electrolyte is high, which, e.g., is the case for linear carbonates, particularly at elevated temperatures. Mixtures of linear and cyclic carbonates are widely used in LiB applications due to their low viscosity, high salt solubility, and high conductivity. In contrast to the cyclic ethylene carbonate (EC) with a vapor pressure of 0.25 mbar, the vapor pressure for the typically used linear carbonates dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) can vary from 23 to 80 mbar at room temperature.8 Their vapor pressure further increases by a factor of ~3 when increasing the temperature from room temperature to 45 °C.9 Thus, a significant share of the gas in the head-space of the OEMS cell consists of electrolyte vapor. As they undergo fragmentation in the mass spectrometer, a background signal is superimposed on the relevant mass traces related to hydrogen, ethylene, carbon monoxide, oxygen, and carbon dioxide.1 Furthermore, the cell pressure inherently decreases due to the continuous leak through the capillary (with a leak rate of ~1 µL/min) that connects the OEMS cell (~10 mL volume) with the mass spectrometer. Because of the liquid reservoir of electrolyte in the OEMS cell and its constant vapor pressure, this results in an enrichment of the gas phase with electrolyte vapor. Analyzing the pressure-dependent flow of gaseous species into the mass spectrometer allowed us to introduce corrections for signal normalization, electrolyte background change, and signal quantification.In the present study, we applied these corrections in the investigation of the influence of LP57 (1 M LiPF6 in EC:EMC 3:7wt/wt) and LP47 (1 M LiPF6 in EC:DEC 3:7wt/wt) electrolyte on the gassing characteristics during the formation of full-cells with a graphite anode and a Ni-rich cathode from low (10 °C) to high (45 °C) temperatures. From that, we were able to conclude how the formation temperature influences the gas evolution related to SEI formation as well as the trans-esterification of the electrolyte and the lattice oxygen reactivity towards different electrolytes. A comparison to a model electrolyte (1.5 M LiPF6 in EC) with a low vapor pressure (< 0.25 mbar) allowed us to assess the detection limits of all the signals depending on the electrolyte’s vapor pressure and to evaluate the validity of our proposed signal corrections. Acknowledgment: The authors thank BMW AG for their financial support.