Metal Surface Research Articles

(Invited) Visualizing Electrode Assembly Movement and Lithiation Gradients in Lithium-Metal Batteries

In this presentation we will introduce dilatometry and profilometry using Operando Energy Dispersive X-Ray Diffraction conducted at the Advanced Photon Source, Argonne National Laboratory. This approach is applied to a Li metal battery with a high-voltage NMC811 cathode but the method is suitable for any and all materials and electrodes.In the technique, micrometer-wide collimated X-rays traverse the electrode assembly, and the Bragg peaks from different crystalline phases are used to track the hard edges of the solid materials as they move due to volume changes in the cell. We visualize, with submicron resolution, the movement of the oxide cathode and microporous separator: the latter is observed through the diffraction of X-rays off the lamellae in the polymer matrix. One can map movement of the cathode and also compression in the porous separator – a task that is beyond the capabilities of mechanical dilatometers. We use our approach to show periodic expansion and contraction of metallic lithium during delithiation and relithiation of the cathode and to quantify formation of mossy lithium on the metal surface. The method is universal, easy to implement in-operando, and is selective in distinguishing between different phases in materials.Another dividend of this method is that it allows the profiling of lithiation gradients in the layered-oxide cathode. In our NMC811/Li cells, the cathode gradients are seen even with weak currents, they occur only during relithiation of the cathode, and they persist as the currents abate during constant-voltage discharge.Other particulars of our experimental approach and observations will also be discussed during the talk.Acknowledgement: This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.

Molecular Level Insights into the Chemical Reactivity of Metal Porphyrins and Iodine at the Solution/Solid Interface

Highly oxidized metalloporphyrins (MP) exhibit unusual electronic properties and unique reactivities and are known to serve as intermediates in a number of biological reactions. Of special interest are MP systems that can electronically communicate during the oxidative processes. Model synthetic porphyrins substituted with first row transition metals can react with dihalides and undergo metal oxidation or form MP p-cation radicals. MP dimers that are covalently connected by short alkane or alkene bridges exhibit electronic coupling between the macrocycles which can strongly influence the outcome of the oxidation reaction by dihalides. Metal surfaces also can serve as a conduit for electron transfer and promote cooperative behavior during reactions between adsorbed MP and axial ligands. In this contribution, we present STM experimental results and supporting theoretical calculations of the reactions dynamics of I2 and metal (Co, Zn, and Ni) porphyrins adsorbed on metallic supports. Single molecule level STM imaging was accomplished in-situ under ambient solution conditions. We uncovered unusual surface chemistry and surface modulated cooperativity in the redox reactions. Computations corroborate our experimental findings. The high-resolution images obtained for these reactions at the single molecule level combined with theoretical studies offer insights into surface redox chemistry, surface cooperativity, and surface-driven catalysis.

Material Changes of Bimetallic Ag–Cr, Fe, Co, Ni, Cu, Sn Electrocatalysts during Alkaline Oxygen Reduction in Fundamental Versus Alkaline Membrane Exchange Fuel Cell Conditions

The more apparent challenges of climate change drastically increase the global demand for sustainable fuel production and usage.1 In this context, hydrogen fuel cells (FCs) powered by renewable electricity are among the promising technologies.2 Addressing the sluggish cathode reaction in FCs, the oxygen reduction reaction (ORR), these devices hold immense potential for sustainable energy conversion and storage. An alkaline environment allows for the utilization of more abundant and cost-effective metals in contrast to current platinum-based catalysts. Silver (Ag), for instance, exhibits high selectivity for the ORR, i.e., forming hydroxide instead of peroxide.3 When combined with secondary metals, bimetallic Ag catalysts show enhanced activity, making them viable alternatives to platinum-group materials for ORR.In our highly collaborative research, we investigated the material transformations of bimetallic Ag thin films with chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and tin (Sn) as secondary metals for ORR electrocatalysis in fundamental rotating disk electrode (RDE) setups and the application device, anion-exchange membrane FC (AEMFC). Grazing-incidence X-ray diffraction (GI-XRD) conducted prior to electrochemical testing reveals no evidence of alloying except for the Ag-Sn bimetallic thin film. However, X-ray photoelectron spectroscopy (XPS) indicates a shift of the Ag 3d peaks to higher binding energies for all catalysts, suggesting a hybridization of Ag and the secondary metals. The composition of the metal surface, native oxide formation, ORR performance, and material changes post-RDE testing vary distinctly among the Ag bimetallic catalysts depending on the secondary metal. Intriguingly, performance is either enhanced (Ag-Co, Ag-Sn), maintained with reduced Ag content (Ag-Fe, Ag-Cr), or falls in between the two monometallic materials (Ag-Ni) compared to monometallic Ag thin films. Density functional theory (DFT) calculations offer insights into the catalyst performances and changes in metal oxidation states and surface composition prior and post electrocatalysis. AEMFC tests reveal promising performances under device conditions contradicting our fundamental RDE measurements. The integration of fundamental and application device tests, along with material characterization and DFT calculations, enables a comprehensive exploration of material changes under varying electrochemical conditions. This underscores the complexity of bimetallic catalysts and the importance of testing under device conditions, positioning Ag-bimetallic catalysts as highly promising alternatives to platinum-group metal catalysts for alkaline ORR.

On-Surface Chemistry: Probing the Presence of Adatoms on Differently Terminated Surfaces by Porphyrin Metalation

Reactive adsorbates in on-surface reactions and in heterogeneous catalysis on different substrates are of emerging importance. This is for the crucial roles they take in reaction pathways and for their decisive influence on reaction kinetics. [1] The thermally activated 2D mobility [2] of reaction precursors and reactive adatoms as well as their spatial and temporal coincidence at reaction sites is of mechanistic importance for many interface-specific reactions. In our work, we use the well-studied metalation reaction of H2-porphyrins to investigate the action of adatoms on metallic and passivated surface substrates. Porphyrin metalation has been established on atomically clean metallic substrates [3] as well as on metal-oxides [4] and metallic surfaces modified by oxygen [5].We perform spectro-microscopy correlation experiments combining X-ray Photoelectron Spectroscopy, Ultraviolet Photoelectron Spectroscopy, Low Energy Electron Diffraction and Scanning Tunnelling Microscopy on Cl- and N terminated Cu(001). Thereby we find extended layers of adsorbate-induced superstructures that have decisive and contrasting impact on the reactivity of the surface, as well as on molecular self-assembly. The O and N termination of Cu facilitates the metalation reaction and self-assembled domains of CuTPP are formed at room temperature. Cl termination on the contrary, fully inhibits the metalation reaction and causes 2HTPP to assemble into small ‘magic’ clusters.

On-Surface Synthesis of Open-Shell Nanographenes through the π-Extension of Dibenzo[Hi,St]Ovalene

Graphene nanostructures are attracting attentions for their intriguing optical, electronic, and magnetic properties that are critically dependent on their chemical structures. Whereas it is challenging to obtain atomically precise structures by typical top-down fabrication methods, such as lithographic patterning of graphene and unzipping of carbon nanotubes, bottom-up synthesis enables the preparation of molecular nanographenes and graphene nanoribbons (GNRs) with pre-designed structures. In addition to the solution synthesis based on the methods of synthetic organic chemistry, such graphene nanostructures can also be synthesized on metal surfaces under ultrahigh vacuum conditions and directly visualized by atomic resolution scanning probe microscopy (SPM) [1]. Using carefully designed and solution-synthesized molecular precursors, this on-surface synthesis method can provide various nanographenes, including the structures that are highly unstable under ambient conditions. We have previously developed the solution synthesis of dibenzo[hi,st]ovalene (DBOV) with strong red fluorescence [2], and achieved its π-extension to circumpyrene [3]. Following the successful synthesis of rhombus-shaped nanographenes with four zigzag edges, showing a closed-shell or an open-shell depending on the size [4], we functionalized DBOV and circumpyrene with two 2,6-dimethylphenyl groups for their on-surface π-extension to unprecedented zigzag-edged nanographenes. The resulting structures were clearly visualized by scanning tunneling microcopy and their open-shell characters were indicated by theoretical and experimental investigations, revealing large magnetic exchange couplings of up to 190 meV [5]. We have more recently also achieved further π-extension of these open-shell nanographenes on surface and obtained initial results for their polymerization.[1] Chen, Z.; Narita, A.; Müllen, K.; Adv. Mater. 2020, 32, 2001893.[2] Paternò, G. M.; Chen, Q.; Wang, X.-Y.; Liu, J.; Motti, S. G.; Petrozza, A.; Feng, X.; Lanzani, G.; Müllen, K.; Narita, A.; Scotognella, F., Angew. Chem. Int. Ed. 2017, 56, 6753–6757.[3] Chen, Q.; Schollmeyer, D.; Müllen, K.; Narita, A., J. Am. Chem. Soc. 2019, 141, 19994–19999.[4] Mishra, S.; Yao, X.; Chen, Q.; Eimre, K.; Gröning, O.; Ortiz, R.; Di Giovannantonio, M.; Sancho-García, J. C.; Fernández-Rossier, J.; Pignedoli, C. A.; Müllen, K.; Ruffieux, P.; Narita, A.; Fasel, R.; Nat. Chem. 2021, 13, 581.[5] Biswas, K.; Soler, D.; Mishra, S.; Chen, Q.; Yao, X.; Sánchez-Grande, A.; Eimre, K.; Mutombo, P.; Martín-Fuentes, C.; Lauwaet, K.; Gallego, J. M.; Ruffieux, P.; Pignedoli, C. A.; Müllen, K.; Miranda, R.; Urgel, J. I.; Narita, A.; Fasel, R.; Jelínek, P.; Écija, D. J. Am. Chem. Soc. 2023, 145, 2968–2974.

Anhydride Photolysis on a Semiconductor Surface

The on-surface synthesis (OSS) method has facilitated the growth of diverse carbon-based nanomaterials, with the goal of integrating them into electronic devices. However, the reliance on metallic substrates in OSS restricts these materials' applications, necessitating strategies for transferring these materials into technological relevant substrates or direct synthesis on non-metallic surfaces, where the low absorption energies and lack of catalytic activity from the substrate complicate this approach. Addressing these limitations, we explore on-surface photochemistry as an alternative to thermally induced reactions, enabling controlled chemical processes at lower temperatures. While prior works have demonstrated light-induced reactions on metallic surfaces, where the hot electrons photogenerated from the metallic surface play a crucial role, synthesizing nanostructures directly on semiconducting or insulating surfaces through a purely intramolecular energy absorption remains challenging.The photolysis and pyrolysis of anhydrides has proven to be a suitable approach for the formation of arynes, as schematically shown in the Figure. Our study focuses on the selective photodissociation of maleic anhydride-containing precursors on a semiconductor surface (SnSe), unveiling their distinct photochemical behaviors. Specifically, tetraphenylphthalic anhydride (TPPA) undergoes successful photolysis on SnSe, forming tetraphenyl benzyne (TPBY) intermediates, and eventually, tetraphenyl benzene (TPBE) products. Furthermore, TPPA photolysis occurs efficiently also at room temperature, leading to the direct formation of TPBE. Contrastingly, benzo[ghi]perylene-1,2-dicarboxylic anhydride (BPA) possesses an extended pi-conjugated backbone and exhibits no photoactivity upon irradiation on the same semiconductor surface. Our calculations of TPPA and BPA excited states predict different behaviors, demonstrating the relationship between molecular structure, pi-conjugation, and photochemical reactivity, offering insights into the design principles for light-induced reactions on inert surfaces. Figure 1

Corrosion of Copper-Nickel Alloys in Seawater-Based Electrolytes

Copper nickel materials are used for their corrosion resistance due to the protective film that forms in seawater. The development of this film over time depends on the exposure condition, and it is critically important to understand the aging process for CuNi components used in marine systems to ensure passivity under sulfide contaminated conditions. Here we study the formation of the protective film over time and its effect on corrosion performance. Electrochemical impedance spectroscopy (EIS) measurements during exposure are used to develop a model of film growth on CuNi 70/30 alloys. These electrochemical measurements are coupled with surface analytical techniques such as glow discharge-optical emission spectroscopy (GD-OES) and X-ray photoelectron spectroscopy (XPS) to characterize the composition of the surface oxide. GD-OES results show that as the protective layer forms, nickel mainly remains at the metal surface and the outer layers are copper enriched oxides and chlorides. There is also incorporation of various elements from the seawater within the film. The rate of this film growth is correlated to the resulting decrease in corrosion rate. Different exposure conditions, such as under flow, are investigated.The translation of these protective film mechanisms to additively manufactured CuNi materials is also of interest, to ensure similar performance with these materials. Evaluating corrosion performance of these newly developed materials involves careful comparison to existing knowledge of film growth and potential for breakdown.

Atmospheric Pressure Plasma Jet Synthesis and Characterization of Copper-Silver Bimetallic Materials as Electrocatalysts for CO2 Reduction

Copper-silver (Cu-Ag) bimetallics and alloys are attractive due to their enhanced performance compared to their parent metals in various fields including electronics, batteries, biomedicine, solar technology, energy storage, and catalysis.[1] Existing methods for synthesizing Cu-Ag bimetallics suffer from major drawbacks such as intense temperature and pressure conditions, pre and post-treatment processes, and multiple time-consuming steps.[2, 3]In this work, Cu-Ag bimetallic films were synthesized under various ratios for the first time using a newly developed Atmospheric Pressure Plasma Jet (APPJ) system. Synthesis was done in a single step, in under 15 minutes. The samples exhibited strong adhesion onto various substrates such as glass and glassy carbon. This direct-deposition technique requires low power input (<50 W) without the need for any pre- or post-treatment processes and with little to no waste. This contrasts with wet chemistry, where deposition normally takes 12-24 hours followed by thermal processes that produce several waste products.[4] Considering the high melting points (MP) of pure Cu and Ag (MP of Cu is ca. 1,085 °C and MP of Ag is ca. 962 °C), and the fact that they are immiscible, the formation of Cu-Ag alloys usually requires a high amount of energy under intense conditions.[5]These Cu-Ag films were characterized via cyclic voltammetry (CV), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Here, we demonstrate that by only mixing low-concentration metal salt solutions and using a neutral gas (helium), we can readily synthesize metal alloys while controlling their thickness, shape, composition, and metal ratios. From an electrochemical point of view, APPJ drives the reduction of metal cations from the presence of free electrons. This suggests the presence of a medium that is considered either as an electrode, due to the presence of electrons, or as an electrolyte, due to their electrical conduction.[6]These plasma-synthesized materials were tested as electrocatalysts for reducing atmospheric carbon dioxide (CO2) under various potentials. The performance of these catalysts was assessed via electrochemical surface area (ECSA), electrochemical impedance spectroscopy (EIS), and pulse voltammetry techniques. Copper is the only heterogeneous catalyst that converts CO2 into valuable chemicals, such as hydrocarbons, aldehydes, and alcohols.[7] Interestingly, we illustrate that the addition of silver improves the catalytic activity of copper toward CO2 reduction under low potentials. This is a desirable property given the anticipated transition to green energy. References Tantawy, H.R., et al., Novel synthesis of bimetallic Ag-Cu nanocatalysts for rapid oxidative and reductive degradation of anionic and cationic dyes. Applied Surface Science Advances, 2021. 3: p. 100056. Zhang, X., et al., Microstructures and properties of 40Cu/Ag (Invar) composites fabricated by powder metallurgy and subsequent thermo-mechanical treatment. Metallurgical and Materials Transactions A, 2018. 49: p. 1869-1878. Rajashekhar, B., et al., Electro co-deposition of copper-silver nanocrystallite alloy cluster: A way for tunable SERS substrate development. Materials Letters: X, 2022. 15: p. 100157. Jie, S., et al., Preparation of copper–silver alloy with different morphologies by a electrodeposition method in 1-butyl-3-methylimidazolium chloride ionic liquid. Bulletin of Materials Science, 2019. 42: p. 1-4. Banhart, J., et al., Electronic properties of single-phased metastable Ag-Cu alloys. Physical Review B, 1992. 46(16): p. 9968. Rumbach, P., et al., The solvation of electrons by an atmospheric-pressure plasma. Nature communications, 2015. 6(1): p. 7248. Kuhl, K.P., et al., New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces. Energy & Environmental Science, 2012. 5(5): p. 7050-7059.

Probing the Structure of the Electrochemical Interface Using in-Situ Surface X-Ray Scattering Techniques

Surface X-ray Scattering (SXS) or Surface X-ray Diffraction (SXRD) using synchrotron radiation is a powerful tool for the study of single crystal metal electrodes in the electrochemical environment. The single crystal surfaces have well defined adsorption sites and this enables fundamental links to be made between the surface atomic structure and the electrochemical response as has been illustrated, for example, in electrocatalysis [1]. As the development of electrochemical surface science progresses, there is a growing need for a comprehensive understanding of the atomic sturcture of electrochemical interface, both of the solid electrode and in the liquid electrolyte. This is because changes in the atomic structure across the interface induced by changes in the electric field can affect the system’s reactivity and stability [2]. These processes can be subtle and do not always involve the direct transfer of charge between electrode and electrolyte. Examples include metal surface relaxation and surface reconstruction, as well as charging of the double layer, which leads to rearrangement of the electrolyte side of the interface [3]. To further extend the fundamental understanding of the electrochemical interface structure, we have been developing resonant surface x-ray diffraction (RSXRD), a technique which combines diffraction with spectroscopy, to investigate the charge distribution in the double layer region. Combining experimental data and first-principles calculations, in-situ RSXRD was used to establish the charge distribution both at the Pt(111) electrode surface and at the Cu(001)-c(2x2)-Br electrode surface [5,6].In this talk results of recent studies of single crystal metal electrodes to probe the liquid side of the interface, particularly the role of cations in the electrochemical double layer, will be presented. The results include a systematic study of the low index Ag(hkl) surfaces to explore the role of the surface atomic geometry in determining the electrolyte layering and an exploration of the role that Cs+ cations play in forming the double layer structures on single crystal Au and Pt electrodes.[1] Y. Gründer and C. A. Lucas, Surface X-ray Diffraction Studies of Single Crystal Electrocatalysts, Nano Energy, 29, 378 (2016)[1] O. M. Magnussen and A. Groß, Toward an Atomic-Scale Understanding of Electrochemical Interface Structure and Dynamics. Journal of the American Chemical Society, 141, 4777 (2019)[2] Y. Gründer and C.A. Lucas, Potential-induced structural deformation at electrode surfaces. Current Opinion in Electrochemistry, 19, 168 (2020)[3] Y. Soldo-Olivier et al., Unraveling the Charge Distribution at the Metal-Electrolyte Interface Coupling in Situ Surface Resonant X-ray Diffraction with Ab Initio Calculations, ACS Catalysis, 12, 2375 (2022)[4] Y. Gründer et al., Charge Reorganization at the Adsorbate covered Electrode Surface probed through in-situ resonant X-ray Diffraction Combined with Ab-initio Modelling, Journal of Physical Chemistry C, 126, 4612 (2022)

Advancing Towards Commercialization with Enhanced Stability and Efficiency in Lithium Metal Batteries Using TTE as a Co-Solvent in Carbonate Electrolytes

Lithium metal batteries are considered ideal anode materials for next-generation battery systems due to their high theoretical specific capacity (3,860 mAh g-1) and low negative electrochemical potential (−3.040 V vs. the standard hydrogen electrode), which are essential for high energy density. However, the fatal dendritic growth on the lithium metal surface, which occurs during repetitive cycling, acts as a significant barrier to commercially successful lithium metal battery application. Therefore, regulating the morphology of lithium plating in commercial carbonate-based electrolytes is a critical challenge for the stable operation of lithium metal batteries. Additionally, this leads to the formation of inhomogeneous lithium dendrites in carbonate-based electrolytes, manifesting as uneven current density and lithium-ion concentration gradients. The uneven current leads to inconsistent charging/discharging rates in the corresponding Ni-rich cathode, which in turn causes overpotentials and deteriorates cell safety, culminating in a reduction of capacity. this has been clarified through Kelvin probe force microscopy analysis to demonstrate an uneven state of charge distribution in the Ni-rich cathode.In this work, we propose a new strategy for high-performance lithium metal batteries, utilizing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) as a co-solvent with carbonate electrolytes. By using TTE as a co-solvent, we observed a reduction in the viscosity of the electrolyte, leading to improved ionic conductivity and a decrease in the overpotential during the lithium plating/stripping process via in-situ electrochemical atomic force microscopy. This resulted in more uniform Li deposition compared to conventional carbonate-based electrolytes, forming a dense and stable Li metal layer. Furthermore, by leveraging our control over stable lithium plating morphologies via TTE co-solvent system, we observed long-term cycling stability (capacity retention of 78% at 300 cycles) with the use of an ultra-thin Li layer (40 µm). Through these results, we have effectively enhanced the stability and efficiency of high-energy-density (380 Wh kg-1) electrodes based on carbonate electrolytes, and we believe that this study can contribute to the commercialization of lithium metal batteries. Figure 1

(Keynote) Unified Quantum Theory of Electrochemical Kinetics Based on Coupled Ion-Electron Transfer

A general theory of coupled ion–electron transfer (CIET) is presented, which unifies quantum kinetics of electron transfer (ET) with classical kinetics of bond-breaking ion transfer (IT) in a general framework of non-equilibrium thermodynamics [1]. In the limit of large reorganization energy, the theory predicts Marcus kinetics of “electron-coupled ion transfer” (ECIT). In the limit of large ion-transfer energies, the theory predicts generalized Butler–Volmer kinetics of “ion-coupled electron transfer” (ICET), where the charge transfer coefficient and exchange current are connected to microscopic properties of the electrode/electrolyte interface. In the ICET regime, the reductive and oxidative branches of Tafel’s law are predicted to hold over a wide but finite range of overpotentials, bounded by the ion-transfer energies for oxidation and reduction, respectively. The probability distribution of transferring electron energies in CIET smoothly interpolates between a shifted Gaussian distribution for ECIT (as in the Gerischer–Marcus theory of ET) to an asymmetric, fat-tailed Meixner distribution centered at the Fermi level for ICET. The latter may help interpret asymmetric line shapes in x-ray photo-electron spectroscopy (XPS) and Auger electron spectroscopy (AES) for oxidized metal surfaces in terms of shake-up relaxation of the ionized atom and its image polaron by ICET. In the limit of large overpotentials, the theory predicts a transition to inverted Marcus ECIT, leading to a universal reaction-limited current for metal electrodes, dominated by barrierless quantum transitions. Uniformly valid, closed-form asymptotic approximations are derived that smoothly transition between the limiting rate expressions for ICET and ECIT for metal electrodes, using simple but accurate mathematical functions. The theory is applied to lithium intercalation in lithium iron phosphate (LFP) and found to provide a consistent description of the observed current dependence on overpotential, temperature and concentration, learned from x-ray images [2]. CIET theory thus provides a critical bridge between quantum electrochemistry and electrochemical engineering.[1] M. Z. Bazant, Unified quantum theory of electrochemical kinetics by coupled ion-electron transfer, Faraday Discussions 246, 60-124 (2023).[2] H. Zhao, H. D. Deng, A. E. Cohen, J. Lim, Y. Li, D. Fraggedakis, B. Jiang, B. D. Storey, W. C. Chueh, R. D. Braatz, and M. Z. Bazant, Learning heterogeneous reaction kinetics from X-ray movies pixel-by-pixel, Nature 621, 289-294 (2023). Figure 1

Effect of Crystal Structure on Dealloying Behavior in PtCo Alloy and Its Impact on the Oxygen Reduction Reaction

The proton exchange membrane fuel cell (PEMFC) is considered ideal for power generation due to its high energy conversion efficiency, low operating temperature, and environmentally friendly features. However, the performance of PEMFC is limited by the slow oxygen reduction reaction (ORR) at the cathode, necessitating the use of catalysts such as Pt to enhance the reaction. The Pt catalyst, although effective, poses the challenge of high cost. Consequently, numerous studies have been undertaken to develop more cost-effective catalysts that can match the excellent activity of platinum while maintaining high stability. In particular, the development of alloy nano-catalysts has garnered attention, and promising results have been reported for enhancing catalyst performance through dealloying on the surface of the alloy catalyst. Alloy catalysts prepared by the dealloying method offer the advantage of improving performance by selectively dissolving less-noble metal surfaces and constructing a Pt-rich shell layer. In this study, we synthesized two PtCo alloy catalysts with distinct crystal structures: face-centered cubic (FCC) and face-centered tetragonal (FCT). To prevent particle growth during the transformation from FCC to FCT when subjected to high-temperature heat treatment for an extended duration, we employed the carbon shell encapsulation technique. Subsequently, the synthesized catalyst underwent acid treatment for dealloying. We investigated the variations in dealloying characteristics based on crystal structures and examined their impact on electrochemical performance. Various characterizations, including X-ray diffraction (XRD), High-Resolution Transmission Electron Microscopy (HR-TEM), Scanning Electron Microscopy (SEM), Thermo-Gravimetric Analysis (TGA), and Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), were conducted to validate the structure of the synthesized PtCo alloy nano-catalyst. Half-cell and unit-cell experiments were carried out to verify electrochemical properties and performance, following the testing protocol suggested by the Department of Energy (DOE) in 2020. Finally, we explored the relationship between the dealloying feature of FCC and FCT and their impact on electrochemical activity and stability.

In-Situ Investigation of Surface Modifiers Dithiocarbamates on Au Electrodes for Electrochemical CO2 Reduction

Molecular functionalization of metal electrodes via self-assembled monolayers (SAMs) can introduce synthetically tunable properties to metal surfaces and has exhibited great potential in electrocatalysis. Alkanethiols are commonly used organic ligands because of their strong affinity to Au but they are prone to desorption at negative potentials. Alternatively, dithiocarbamates (DTC) show superior electrochemical stability. In this study, a series of DTCs, differing in hydrophobicity, size, and steric bulk, were synthesized to prepare SAM-functionalized Au electrodes. The properties of the resulting surfaces (e.g. wettability, surface coverage, and reductive stability) were investigated by analytical and electrochemical techniques. Particularly, in-situ approaches such as surface-enhanced infrared absorption spectroscopy (SEIRAS) are employed to characterize the molecularly modified interface. The novel catalyst platforms were explored for electrochemical CO2 reduction.

Efficient Electrochemical Reduction through Flow Cells Using Spherical-Polymer Based Carbon Supported Catalysts as Fixed-Bed Electrode

The transition to economically friendly feedstocks and the electrification of chemical synthesis reactions gained much attention in the recent years. To be able to compete with the conventional processes, it is crucial not only to concentrate on the electrochemical reactions itself but also to constantly improve the reactor concepts. A vast variety of designs are imaginable and already well-described – from a simple, undivided beaker cell setup to a divided flow cell with separate electrolytes at cathode and anode. [1] As electrode material not only flat metal electrodes are studied, but also the concept of using carbon supported metal nanoparticles is well-known to employ high dispersion to lower the total amount of required metal. [2,3] While there are already commercial flow reactors and electrodes available for electrosynthesis with flat standard electrodes, reactors using a fixed-bed of porous carbon with nanodispersed metals as electrode just recently started to attract attention. [4] Dealing with the pressure drop over the catalyst bed, while the electrical contact is still ensured, are key challenges for this reactor design. Spherical polymer-based carbons (SPBC) combine porous carbons properties with a high purity and especially spherical character. [5] While these advantages led already to commercial products for chromatographic applications (e.g. Carboxen®) the potential regarding flow-electrochemistry has not been leveraged. Key developments for this are reproducible synthesis procedures to deposit active metal on the SPBCs and the design of an electrochemical flow cell using these catalysts in a fixed-bed electrode configuration.The first part of this work presents the deposition of Cu through different impregnation and reduction procedures on a SPBC (Carboxen® 1032, 50 µm, Merck). The carbon was characterized by physisorption, TPD-MS, TPO, Raman and SEM. The resulting metal-impregnated carbon catalysts were additionally investigated regarding the metal loading. Using the applied impregnation and reduction parameters targeted metal loadings (3 – 20 wt%) could be well achieved. The second part focuses on the design and commissioning of a flow-cell for the application of the SPBC-supported catalysts as a fixed-bed at the cathode side. Electrochemical synthesis reactions are targeted in the cell and the reduction of 5-HMF to BHMF was chosen as the test reaction in this work. In the framework of the cell development multiple aspects not only regarding the construction but also reaction engineering issues had to be considered: material stability of the pump, fixation and pressure drop of catalyst bed, choice of electrolyte, effect of dissolved oxygen in the catholyte, optimal flow rate, reliable electrochemical protocol and selection of contact material. The latter has to be a compromise between chemical inertness and an enhanced electron transfer between the catalyst bed and the contact material (e.g. soft foil vs. hard metal). Figure 1A shows the current voltage characteristics of two possible contact materials (graphite foil, boron-doped diamond (BDD)) in the targeted electrolyte (0.5M borate buffer with 0.25M potassium chloride). Here, the graphite foil clearly shows a higher activity towards the hydrogen evolution reaction which may result in a less effective electrolysis later on. The comparison of BDD as contact material without and with a catalyst bed (Carboxen® 1032 loaded with 20 wt% Cu) resulted in a significant shift in the current voltage characteristic to lower overpotentials. Therefore, the electronic contact with the carbon bed is clearly enabled and the carbon spheres loaded with copper catalyze the reaction. Figure 1B presents the results of the test reaction with the conversion of the educt 5-HMF as well as the selectivity to the targeted product BHMF over the reaction time with BDD as contact material without and with a fixed bed of Cu/SPBC catalyst. The experiments prove full 5-HMF conversion within 23 h on stream in combination with a high selectivity towards BHMF with the catalyst bed. The mass-based productivity reaches values of up to 1.78 mmol h-1 gCu -1 and is therefore about 15 times higher compared to the use of conventional Cu foil (Pliterature = 0.11 mmol h-1 gCu -1 [6]). It is possible that due to the metal-support approach in the fixed-bed configuration, the copper is leveraged more efficiently and small amounts allow to provide sufficient metal surface area for the catalytic reaction.

Effects of Lithium Metal Storage Environment on Its Reactivity Toward Polyethylene Oxide-Based Blend Electrolytes

Lithium metal has generated significant interest as an anode material because of its high theoretical capacity (3860 mAh/g). However, issues such as dendrite growth and lithium loss during cycling make this material incompatible with current liquid electrolytes. Solid polymer electrolytes (SPE) have been proposed as a potential replacement as they are non-flammable, able to resist dendrite growth, have decent ionic conductivity and good interfacial contact with lithium metal.One aspect that is often overlooked is the fact that passivation layers, initially reported by Naudin et Al (1), often form on the lithium metal surface and are hence intrinsic to the chemical composition of the lithium surface (2, 3). According to Otto et Al (4), residual quantities of atmospheric gases are often present in lithium metal storage environments, thus electrode surface modification is inevitable. This passivation layer is expected to impact the reactivity of the lithium metal anode (LMA) towards SPE. Moreover, such phenomenon was originally described by Peled et Al as the solid electrolyte interface (SEI) (5). Lithium metal reactivity towards PEO, suspected by Galluzo et Al (6), was recently reported by Liu et Al (7), under optimized conditions (ultra-thin neat materials), but the impact of this phenomenon in a realistic LMA environment has not been extensively investigated.In this study, the impact of gas exposure on a LMA was investigated by exposing freshly cut lithium rods to O2, CO2 and N2. The resultant passivation layers were characterized via XPS. The effect of passivation layer formation on LMA reactivity towards SPE was measured by exposing samples with pre-characterized passivation layers to common SPE materials. The resultant interface was characterized using Raman spectroscopy. SPE-passivation layer reactivity was correlated to ageing properties by EIS and kinetic charge transfer characteristics in galvanostatic linear polarization at the LMA-SPE interface, in a symmetric Li – SPE – Li stack.This study revealed that the chemical composition of the lithium metal passivation layer affects its reactivity towards SPE as well as the electrochemical performance of a Li-SPE-Li symmetric cell. A thorough characterization of the lithium metal passivation layer is essential for the understanding of some of the fundamental factors affecting all solid-state lithium metal battery performance and is therefore consubstantial with the development of modified LMA. C. Naudin et al., Characterization of the lithium surface by infrared and Raman spectroscopies. Journal of Power Sources 124, 518-525 (2003).S.-K. Otto et al., In-Depth Characterization of Lithium-Metal Surfaces with XPS and ToF-SIMS: Toward Better Understanding of the Passivation Layer. Chemistry of Materials 33, 859-867 (2021).P. R. G. Zhuang, F. Kong, F. McLarnon The reaction of clean Li surfaces with small molecules in ultrahigh vacuum: II. Journal of The Electrochemical Society, 159-164 (1998).S.-K. Otto et al., Storage of Lithium Metal: The Role of the Native Passivation Layer for the Anode Interface Resistance in Solid State Batteries. ACS Applied Energy Materials 4, 12798-12807 (2021).E. Peled, Film forming reaction at the lithium/electrolyte interface. Journal of Power Sources 9, 253-266 (1983).M. D. Galluzzo et al., Dissolution of Lithium Metal in Poly(ethylene oxide). ACS Energy Letters 4, 903-907 (2019).P. Liu et al., Increasing Ionic Conductivity of Poly(ethylene oxide) by Reaction with Metallic Li. Advanced Energy and Sustainability Research 3, 2100142 (2022).

A Ceramic/Lithiophilic Metal Dual Protective Layer for Stable Lithium Metal Anodes Fabricated via Transfer-Printing Methods

Lithium metal has attracted researcher’s attention because of its superior theoretical capacity (3860mAh g-1 or 2061 mAh cm-3), which is nearly 10 times higher than commercialized anode materials, for example, graphite (372 mAh g-1). However, lithium metal is not currently used in commercial lithium metal batteries due to safety and efficiency issues that arise during long-term battery operation. The high reactivity of lithium metal causes almost all available electrolytes to be spontaneously reduced on the Li surface to form a solid-electrolyte interface (SEI) layer. Unfortunately, this passivating SEI layer is typically too fragile to withstand significant mechanical deformation of the electrode during cycling, resulting in crack formation. These cracks expose fresh Li underneath, which locally enhances Li-ion flux and promotes morphological deformation of the lithium metal surface. This often leads to dendritic Li deposition that can cause internal short circuits and compromise battery safety. Additionally, repeated failures and repairs of SEIs result in the continued loss of both Li and electrolyte, leading to low coulombic efficiency (CE) and rapid capacity decrease.To mitigate these problems, researchers have attempted to suppress lithium dendrite growth by slurry coating on the lithium metal surface such as ceramic layer and lithiophilic metal. These materials and conventional lithium metal protection coating methods partially inhibit the growth of lithium dendrites; however, they come with several significant drawbacks. The ceramic layer possesses high mechanical properties that physically inhibit the growth of lithium dendrites. However, it exhibits poor interfacial characteristics with lithium metal, leading to increased resistance. This heightened resistance results in the formation of uneven lithium deposition layers at high current densities, causing cracks in the ceramic layer. Lithiophilic metals exhibit an advantage in reducing nucleation resistance through alloying reactions with lithium prior to nucleation, thereby facilitating uniform lithium ion deposition. However, their low mechanical properties limit their potential for enhancing electrochemical performance. Furthermore, the conventional coating method used for lithium metal protection involves the direct application of solvent-containing slurries onto the lithium metal surface using slurry coating techniques. Given the inherent reactivity of lithium metal, the presence of residual moisture and impurities within the solvent may induce sub-reactions, ultimately compromising the stability of lithium metal.In this study, we propose an approach to improve the cycling stability of lithium metal through Ceramic/lithiophilic metal dual protective layer fabricated via transfer-printing methods. The dual lithium metal protection layer, consisting of Ceramic/lithiophilic, involves coating a lithiophilic metal layer between the ceramic layer and the lithium metal. This method aims to maximize electrochemical performance improvement through a synergistic effect that utilizes the high mechanical properties of ceramics and solves the problem of interfacial resistance between the ceramic layer and lithium metal through the lithiophilic metal. Furthermore, we propose a coating process for lithium metal protection layers using a method based on transfer printing. This method involves applying pressure to the lithium metal surface through transfer printing of pre-finished composite protective layers on a film, rather than directly applying slurry onto the lithium metal surface. Transfer printing offers the advantage of maintaining the stability of lithium metal by avoiding direct application of slurry onto the lithium metal surface, thereby ensuring the integrity of the protection layer.

On-Surface Synthesis of 1D and 2D π-Conjugated Polymers from Heterotetrabromo-P-quinodimethanes (HTBQs)

Molecules bearing gem-dibromoolefines functionalities have been employed in wet chemistry as intermediates in the well-known Corey-Fuchs homologation of carbonyls to alkynes. This gem-dibromoolefines can be embedded into tetrabromo-p-quinodimethanes (TBQs), which efficiently undergo dehalogenative homocoupling on coinage metal surfaces, namely Au(111) and Ag(111), forming one-dimensional (1D) acene and periacene π-conjugated polymers able to exhibit non-trivial topological properties.[1,2]However, the synthesis of more complex π-conjugated polymers to determine the scope of this new reaction, as well as the synthesis of two-dimensional (2D) polymers by following this chemical methodology are still important challenges. In this context, new dimeric TBQs have been synthesized by wet chemical protocols for their further use in the synthesis of double-strand oligomers. Interestingly, the new systems exhibit many defects, due to the intrinsic nature of the synthesized precursors.[3] In this work, we firstly take advantage of the introduction of heteroatoms at the edges of the monomers in order to grow 1D new π-conjugated polymers which, eventually, collapse into amazing large 2D networks by non-covalent interactions. Moreover, when suitable designed TBQs with both the presence of heteroatoms and steric hindrance, unprecedented 1D and covalently linked 2D π-conjugated polymers are formed. These results have allowed the study of new topologically non-trivial polymers which will be presented and discussed in this communication.[1] Cirera, B., Sánchez-Grande, A., de la Torre, B., Santos J. et al. Nat. Nanotechnol. 2020, 15, 437–443.[2] González-Herrero, H., Mendieta-Moreno, J. I., Edalatmanesh, S., Santos, J. et al. Advanced Materials 2021, 33, 2104495.[3] Vicent, D. J., Perez-Escribano, M. et al. Chem. Sci., 2023, 14, 10112-10120.

Advanced Hybrid Polymer/Ceramic PEO-SnF2 Protective Mechanism for Sodium Metal Anodes

In the face of mounting global energy requirements and pressing environmental issues, the scientific community turned to lithium-metal batteries, celebrated for their superior capacity and efficiency. However, challenges arising from the scarcity and increasing costs of lithium have redirected research efforts towards sodium batteries. Sodium metal anodes, with their remarkable theoretical specific capacity of ~1166 mAh/g, low anode potential of -2.714 V vs standard hydrogen electrode, and cost benefits, are increasingly recognized as promising candidates for conventional energy storage systems. Notwithstanding their advantages, the unstable and fragile solid electrolyte interphase (SEI) due to the spontaneous reaction between metallic Na and a liquid electrolyte remains a significant limitation. As this SEI layer expands, it hinders ion transport, causing increased polarization and diminishing the battery's energy efficiency. Specifically, during the plating process, Na ions are deposited beneath the SEI layer, causing significant expansion. This expansion fractures the fragile SEI, allowing dendrites to grow through these defects. As these dendrites grow, they can pierce the separator, posing a risk of short-circuiting the battery. While numerous studies have proposed designs for protecting sodium metal interphase, to overcome these challenges, this study amalgamates mechano-electrochemical protective strategies to enhance sodium metal anode stability, offering groundbreaking solutions to these challenges.Central to our exploration were tin fluoride (SnF2) and silicon nitride (Si3N4), both established as effective in generating robust artificial SEI layers on the sodium metal surface. These layers, rich in NaF and NaxN respectively, demonstrated a notable improvement in cycling performance, effectively suppressing dendrite growth and enhancing the battery's cycling stability by nearly 3.5 times compared to bare sodium anodes.Building upon these foundational insights, a novel approach was conceptualized: a hybrid protective mechanism combining polyethylene oxide (PEO) with the presence of SnF2 as an additive, is particularly efficacious. This combination was specifically chosen to provide chemical stability, morphological conformality, and mechanical flexibility to accommodate the mechano-electrochemical instability upon sodiation/desodiation processes. Through this novel strategy, we aimed to amalgamate the strengths of both components, ensuring optimal outcomes. This composite artificial SEI under a 0.25 mA/cm2 current density, delivers a cycling performance 10 times superior to bare sodium metal and survived up to 1800 hours of cycling. Impressively, at a high current density of 0.5 mA/cm2, the hybrid system still performed much better than its untreated counterpart and continued cycling for up to 800 hours of cycling. The synergy of PEO and SnF2 remarkably minimized electrolyte decomposition, inhibited dendrite formation, and stabilized Na plating/stripping processes, all of which consolidated its promise for sodium metal battery technology.

Covalently Immobilized Anthraquinone on Carbon and Its Use As a Proton-Exchange Counter Electrode in Impurity Sensitive Electrochemical Measurements

The choice of counter electrode has emerged as an important topic in our search for non-platinum group metal (PGM) materials that can catalyze reactions that are important for fuel cells and electrolyzers such as oxygen reduction reaction (ORR), H2 evolution reaction (HER), and the CO2 reduction reaction. Recent investigations on the stability of Pt materials have revealed that significant dissolution occurs during O2 evolution, making the use of Pt as a counter electrode unsuitable for developing non-PGM materials for ORR and HER, in particular. That has led to increased use of carbon as the counter electrode, which can also oxidize at high voltages and generate partial oxidization compounds such as CO and other small organic molecules, which in turn, are detrimental to metal surfaces. Therefore, developing a stable counter electrode material is key for artifact-free electrocatalytic measurements. In this work, we will discuss the synthesis and application as a counter electrode of a proton-exchange anthraquinone-based reversible redox pair that was covalently grafted onto a high-purity (e.g. 99.99995%) carbon rod. The anthraquinone-grafted counter electrodes were evaluated in aqueous electrolytes using metal single crystals such as Pt(111) and Ir(111) surfaces as the working electrodes, given their extreme sensitivity to impurities in the electrochemical cell. Our results show that the counter electrode voltage is far more stable and centered around the proton-exchange process happening at the anthraquinone centers. This is in contrast to the wide-range voltage changes observed when using the un-grafted carbon rod. There were no differences in the single-crystal surface cyclic voltammetry profile, even after performing HER or OER, which typically causes the biggest swings in the counter electrode voltages. Lastly, there were no detectable amounts of grafted material leaching or exfoliated carbon, confirming that the use of a known redox pair such as from anthraquinone is an effective strategy to prevent artifacts in electrocatalysis research.

Chemistry and Formation of Solid-Electrolyte Interphase (SEI) at Li-Metal Potential

Li metal batteries (LMBs) have long been considered a solution to address the energy density limitations of Li-ion batteries. However, the widespread adoption of LMBs has faced challenges due to operational issues, notably safety concerns arising from the formation of Li dendrites and uncontrolled reactivity at the interfaces, leading to continuous consumption of the electrolyte. To enhance the reversibility of the Li-metal anode (LMA), a promising approach has emerged involving the development of a novel liquid electrolyte comprising an ether solvent and LiFSI salt. Notably, this electrolyte formulation has achieved impressive Coulombic efficiency (CE) values surpassing 99.5%. Despite this progress, the underlying causes of Coulombic inefficiency (CI) and its connection with the formation of a solid-electrolyte interphase (SEI) on the Li metal surface remain inadequately understood.Gaining fundamental insights into these essential processes occurring during continuous cycling of the LMA can provide valuable guidance for optimizing CE more effectively. This presentation focuses on recent advancements that systematically unravel the underlying chemistry and formation of SEI derived from FSI anions at the interface of the Li metal anode in contact with various liquid electrolytes. By employing a non-washing protocol and a Cu current collector, we successfully captured and identified crucial reaction intermediates from SEI chemistry, enabling precise determination of the decomposition pathway for FSI anions. Our discoveries unveil a dynamic scenario at the electrode/electrolyte interface, where these reaction byproducts can significantly dissolve into the liquid layer, and their relative solubility dictates their role in passivating the electrode surface. Furthermore, we demonstrate a strong correlation between faster interfacial passivation in higher-performing electrolytes and the reduced solubility of diverse inorganic species within the liquid electrolyte. These fresh insights into SEI chemistry and formation open new avenues for enhancing LMA performance by mitigating undesired side reactions at the interface.