Journal Of Physical Chemistry Research Articles

(Invited) Unraveling Hot Carrier Transfer Processes in Plasmonic Catalysis

In the last decade, plasmonic nanoantennas have revolutionized light manipulation and control at the nanoscale. Interestingly, generation of hot carriers in metals upon light absorption have opened new pathways for controlling photo(electro)chemical processes and engineering photocatalysts. Yet, fundamental questions remain about the microscopic details of these complex light-matter interactions.We have recently developed a well-controlled platform for micro-scale plasmonic photoelectrochemistry studies that leverages the unique properties of monocrystalline microflakes [1] as well as precise nanofabrication methods. Interestingly, the microflakes exhibit well-defined crystal facets and can bridge the properties of bulk metals with those of nanoscale plasmonic antennas, accessing ultra-thin film dimensions (sub 15-nm) that are challenging for polycrystalline films. By performing careful absorption measurements, we explore the photoelectrochemical performance of these hot carrier micro-scale photoelectrodes for inner- and outer-sphere reactions [2], concurrently comparing them to cm-scale devices [3]. This allows us to unravel the interplay of hot carrier generation and transport at metal-liquid and metal-semiconductor interfaces and identify bottlenecks for charge transfer.[1] Kiani F., Tagliabue G. - High‐Aspect Ratio Au Microflakes via Gap‐Assisted Synthesis – Chemistry of Materials 34 (3), 1278-1288, 2022[2] Kiani F. et al - Transport and Interfacial Injection of d-band Hot Holes Control Plasmonic Chemistry - ACS Energy Letters, 8 (10), 4242-4250, 2023[3] Ma J., Oh K., Tagliabue G. - Understanding Wavelength-Dependent Synergies between Morphology and Photonic Design in TiO2-Based Solar Powered Redox Cells – Journal of Physical Chemistry C, 127 (1), 11-21, 2022

Revealing the Functionality of Li2CO3 in the Li-Metal SEI Via Study of Gas-Reacted Li Films

The solid electrolyte interphase (SEI) governs transport and reactivity at lithium interfaces, so its structure and composition are essential factors in improving the cyclability of next-generation lithium-metal anodes (1). An ideal SEI should passivate Li against continuous reactions with electrolyte while promoting facile transport of Li+ ions. However, achieving these properties is challenging, in part because our understanding of the relative desirability of different SEI materials is often based on qualitative relationships between characterization and cell performance; quantitative experimental conductivity (2, 3) and stability (4) measurements are limited. As a further complication, the highly reductive conditions (-3.04 V vs SHE) and the complex nanoscale structure of the SEI can lead to markedly different behavior in practical contexts compared to bulk environments (2, 5, 6). In previous work, our group developed techniques to synthesize single-component, nanoscale films of LiF and Li2O on Li, enabling direct measurements of their transport properties and reactivity in relevant electrolytes (6-8). Here, we turn to Li2CO3, which has a mixed reputation as an SEI material. While many papers assert its desirability based on high ionic conductivity (9-12), others raise concerns related to reductive instability (13-15).In this work, we synthesized Li2CO3 films via sequential reactions of O2 and CO2 on polished lithium surfaces at slightly elevated temperature (175-200°C). Scanning electron microscopy (SEM) and air exposure tests showed that the prepared films are conformal, tens of nanometers thick, and relatively pinhole-free. Fourier transform infrared spectroscopy (FTIR) was used to confirm the speciation of the films, and titration-based quantification yielded insights into their composition. We found that the formation of Li2CO3 is associated with generation of Li2O and Li2C2, confirming that the reductive instability of Li2CO3 results in the evolution of a more reduced inner SEI layer at the Li | Li2CO3 interface. We also studied the stability of films at the SEI | electrolyte interface, performing electrolyte soak tests then assessing native SEI evolution using FTIR and titration-based quantification of LiF. We found that Li2CO3 is poorly-passivating in fluorinated electrolytes, leading to continuous formation of native SEI. However, in 1M LiClO4 PC electrolyte, the Li2CO3 film remains intact, enabling the use of electrochemical impedance spectroscopy (EIS) to study film transport properties. This analysis reveals an ionic conductivity of ~4-8 nS/cm, which is substantially greater than ionic conductivities previously measured in Li2O (~1 nS/cm) and LiF (~0.5 nS/cm) (6). Together, these results show that though Li2CO3 has some stability limitations, it could promote facile Li+ ion transport as a stable meso-SEI layer in less-fluorinated electrolytes.This work was funded by the 2022-2023 ECS Toyota Young Investigator Fellowship award. References E. Peled and S. Menkin, Journal of The Electrochemical Society, 164, A1703 (2017).S. Lorger, K. Narita, R. Usiskin and J. Maier, Chemical Communications, 57, 6503 (2021).P. Lu and S. J. Harris, Electrochemistry Communications, 13, 1035 (2011).B. S. Parimalam, A. D. MacIntosh, R. Kadam and B. L. Lucht, Journal of Physical Chemistry C, 121, 22733 (2017).S. Shi, Y. Qi, H. Li and L. G. Hector, (2013).R. Guo and B. M. Gallant, Chemistry of Materials, 32, 5525 (2020).R. Guo, D. N. Wang, L. Zuin and B. M. Gallant, Acs Energy Letters, 6, 877 (2021).M. F. He, R. Guo, G. M. Hobold, H. N. Gao and B. M. Gallant, Proceedings of the National Academy of Sciences of the United States of America, 117, 73 (2020).E. Plichta, S. Slane, M. Uchiyama, M. Salomon, D. Chua, W. B. Ebner and H. W. Lin, J. Electrochem. Soc., 136, 1865 (1989).D. Aurbach, A. Zaban, Y. Gofer, E. Ely, I. Weissman, O. Chusid and O. Abramson, Recent studies of the lithium-liquid electrolyte interface Electrochemical, morphological and spectral studies of a few important systems, in Journal of Power Sources, p. 76 (1995).T. Osaka, T. Momma, Y. Matsumoto and Y. Uchida, Journal of Power Sources, 68, 497 (1997).J. Besenhard, M. W. Wagner, M. Winter, A. D. Jannakoudakis, P. D. Jannakoudakis and E. Theodoridou, Journal of Power Sources, 413 (1993).K. Leung, F. Soto, K. Hankins, P. B. Balbuena and K. L. Harrison, Journal of Physical Chemistry C, 120, 6302 (2016).N. Tian, C. Hua, Z. Wang and L. Chen, Journal of Materials Chemistry A, 3, 14173 (2015).B. Han, Z. Zhang, Y. C. Zou, K. Xu, G. Y. Xu, H. Wang, H. Meng, Y. H. Deng, J. Li and M. Gu, Advanced Materials, 33 (2021). Figure 1

(Invited) In Situ spectroscopy of Electrocatalytic and Photocatalytic Interfaces

We explore various aspects of electrochemistry and photoelectrochemistry using in situ spectroscopy of electrode (metal) and photoelectrode (semiconductor) interfaces in situ under electrochemical working conditions. These spectroscopies include sum frequency generation (SFG), transient reflectance/absorption spectroscopy (TAS/TRS), and surface enhanced Raman spectroscopy (SERS). Using surface enhanced Raman scattering (SERS) spectroscopy, we monitor local electric fields using Stark-shifts of nitrile-functionalized silicon photoelectrodes.6 We also report several spectroscopic methods for monitoring local electric fields (within the double layer), local pH,1 photo-induced surface potential and charge transfer2 at electrode surfaces using surface reporter molecules. The Figure below illustrates two surface reporter molecules for determining the local pH, local surface potential, and charge transfer at electrode and photoelectrode surfaces. We also measured the stacking dependence and Resonant interlayer excitation of monolayer WSe2/MoSe2 heterostructures for photocatalytic energy conversion.3 Using sum frequency generation (SFG) spectroscopy, we measure the voltage dependence of the orientation of D2O molecules at a graphene electrode surface, which is related back to the “stiffness of the ensemble”.4 Using transient absorption spectroscopy (TAS), we measure the lifetime of hot electrons photoexcited in plasmon resonant nanostructures.5 Using transient reflectance spectroscopy (TRS), we measure the photoexcited carrier dynamics in a GaP/TiO2 photoelectrode, as well as the electrostatic field dynamics at this semiconductor-liquid interfaces in situ under various electrochemical potentials.6 Here, the electrostatic fields at the surface of the semiconductor are measured via Franz−Keldysh oscillations (FKO). These spectra reveal that the nanoscale TiO2 protection layer enhances the built-in field and charge separation performance of GaP photoelectrodes.7 1 Wang, Y.Y., et al., Measuring Local pKa and pH Using Surface Enhanced Raman Spectroscopy of 4‐Mercaptobenzoic Acid. Langmuir, DOI:10.1021/acs.langmuir.3c02073 (2023).2 Li, R., et al., SERS Detection of Charge Transfer at Electrochemical Interfaces Using Surface-Bound Ferrocene. The Journal of Physical Chemistry C, 127, 14263 (2023).3 Chen, J., et al., Stacking Independence and Resonant Interlayer Excitation of Monolayer WSe2/MoSe2 Heterostructures for Photocatalytic Energy Conversion. ACS Applied Nano Materials, DOI:10.1021/acsanm.9b01898 (2020).4 Montenegro, A., et al., Field-Dependent Orientation and Free Energy of D2O at an Electrode Surface Observed via SFG Spectroscopy. Journal of Physical Chemistry C, 126, 20831 (2022).5 Wang, Y., et al., In Situ Investigation of Ultrafast Dynamics of Hot Electron-Driven Photocatalysis in Plasmon-Resonant Grating Structures. Journal of the American Chemical Society, 144, 3517 (2022).6 Xu, Z.H., et al., Direct In Situ Measurement of Quantum Efficiencies of Charge Separation and Proton Reduction at TiO2-Protected GaP Photocathodes. Journal of the American Chemical Society, 2860-2869 (2023).7 Wang, Y. and S.B. Cronin, Performance Enhancement of TiO2-encapsulated Photoelectrodes Based on III–V Compound Semiconductors, in Ultrathin Oxide Layers for Solar and Electrocatalytic Systems. 2022, Royal Society of Chemistry. p. 103-134. Figure 1

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)

Harmonic Light Scattering to Study Supramolecular Assembly Processes

Characterization of complex dynamical processes such as supramolecular aggregation, (electro)chemical reactions or phase transitions, requires in-situ measurement techniques to provide insight into morphology changes, symmetry changes, concentration, or phase changes during the process. Currently available techniques are often not sensitive to all these aspects or too slow for in-situ studies. Instead, very fast and sensitive techniques are needed. Recently, we developed a method based on second-and third harmonic scattering that partially satisfies these requirements (1-3).Second-harmonic scattering is a nonlinear scattering process in which two incident photons of frequency ω are annihilated to create a new photon at the double frequency 2ω. It is a very sensitive tool to study dynamical processes since it is fast, sensitive to the symmetry of the scatterer and extremely sensitive to aggregation.For molecular scatterers, the intensity of the scattered second-harmonic light I2ω is given by:I2ω ∼ N<β2> Iω 2 With N the number scatterers, β the first hyperpolarizability, Iω the intensity of the incident light and < > refers to orientational averaging. Information about the point group symmetry of the scatterer can be inferred by analyzing the polarization components of the scattered light. For aggregated or correlated scatterers I2ω is given by: I2ω ∼ N'<(Mf(β))2> Iω 2 with N’ the number of scatterers, M the number of molecules in each aggregate, and f(β) a combination of molecular hyperpolarizability components. Also in this case, an analysis of the polarization components of the scattered light will yield information about the symmetry of the aggregated scatterers.Similar formula’s hold for third harmonic scattering where part of the incident light at frequency ω is scattered at the triple frequency 3ω . For molecular scatterers I3ω is given by I3 ω ∼ N<γ2> Iω 3 and for correlated scattersI3 ω ∼ N'<(Mf(γ))2> Iω 3 with γ the second hyperpolarizability.While both techniques may seem similar, there is an important difference: the symmetry selection rules are very different. Second-harmonic scattering is only allowed if the scatterer is non centrosymmetric, while third-harmonic scattering does not have any symmetry constraints. As such, both techniques are highly complementary. The combination of both, referred to as harmonic scattering, has been used as a very versatile method to study in-situ supramolecular aggregation of macrocycles and conjugated polymers with the ability to completely unravel the nucleation and aggregation dynamics.Now, we have extended this measurement platform to also include multi-photon fluorescence, linear light scattering, UV/Vis absorption and optical rotation. Hence, in total we can monitor 6 observables for any dynamical process in-situ. Several examples will be given on how this methodology can provide new insights in the mechanism and dynamics of supramolecular aggregation processes.References1) Moris, M. et al., Harmonic light scattering study reveals structured clusters upon the supramolecular aggregation of regioregular poly(3-alkylthiophene). COMMUNICATIONS CHEMISTRY, 2, Art.No. ARTN 130 (2019).2) Hattori, S., et al. Vortex-Induced Harmonic Light Scattering of Porphyrin J-Aggregates. JOURNAL OF PHYSICAL CHEMISTRY B, 125 (10), 2690-2695 (2021)3) Dok, A.R., et al. Nonlinear optical probes of nucleation and crystal growth: recent progress and future prospects. JOURNAL OF MATERIALS CHEMISTRY C, 9 (35), 11553-11568 (2021).

Effective Lithium Polysulfides Anchoring on Vanadium Disulfide Facets for Lithium-Sulfur Batteries – A Computational Study

The commercialization of Li-S batteries is hindered by the shuttle effects of lithium polysulfides (LiPS) and the sluggish reaction kinetics. Hence, effectively trapping and promoting the conversion rates of LiPSs is of prime importance1. However, the fundamental kinetics of the electrocatalytic charging and discharging of Li-S batteries and the underlying mechanism have not been sufficiently explored yet.2 Therefore, by taking the 2D transition metal sulfide, VS2 as a model, we conducted a systematic investigation using density functional theory to study the ability of dominant exposed crystal planes of VS2 to trap LiPSs from leaching into electrolyte solvents and to act as an electrocatalyst to increase the Sulfur Reduction Reaction (SRR) kinetics3. To reflect a realistic environment of a battery, the effect of electrolyte solvents on the electrocatalytic activity was further investigated. Our calculations show that VS2 has moderate binding energy toward LiPSs which inhibits LiPS from leaching into electrolytes while fulfilling the key prerequisite to act as an electrocatalyst simultaneously.4 At the discharge, the conversion of S8 to the long chain Li2S8 was facile with a lower energy barrier while the rest of the reactions were sluggish explaining the accumulation of LiPSs. Further, the VS2 (001) facet exhibits excellent electrocatalytic activity for the SRR and Li2S decomposition reaction at charging compared to other dominant crystal planes, which significantly lowers the energy barriers of LiPS conversion during the charging and discharging process, ensuring high-rate performance and longer cycle life4. References Manthiram, A., Fu, Y., Chung, S.-H., Zu, C., & Su, Y.-S. (2014). Rechargeable Lithium–Sulfur Batteries. Chemical Reviews, 114(23), 11751–11787.Abraham, A. M., Thiel, K., Shakouri, M., Xiao, Q., Paterson, A., Schwenzel, J., Ponnurangam, S., & Thangadurai, V. (2022). Ultrahigh Sulfur Loading Tolerant Cathode Architecture with Extended Cycle Life for High Energy Density Lithium–Sulfur Batteries. Advanced Energy Materials, 2201494.Abraham, A. M., Boteju, T., Ponnurangam, S., & Thangadurai, V. (2022). A global design principle for polysulfide electrocatalysis in lithium–sulfur batteries—A computational perspective. Battery Energy, 20220003.Boteju, T., Abraham, A. M., Ponnurangam, S., & Thangadurai, V. (2023). Theoretical Study on the Role of Solvents in Lithium Polysulfide Anchoring on Vanadium Disulfide Facets for Lithium–Sulfur Batteries. The Journal of Physical Chemistry C.

In-Situ X-Ray Absorption Spectroscopy Investigations on the Transition Metal Cations Intercalation in Ti3C2Tx MXene for Electrochemical Applications

Synchrotron X-ray absorption spectroscopy (XAS) serves as a robust and powerful technique for probing the oxidation state and coordination surrounding of specific elements. In particular, operando XAS has been employed to elucidate charge storage mechanisms by monitoring changes in the oxidation state through the absorption edge energy of metals in electrodes such as MnO2 and RuO2 during charging/discharging[1] [2]. Herein, we utilized in-situ XAS technique to uncover the charge storge mechanisms of transition metal (TM)-intercalated MXenes (Ti3C2Tx). We specifically probed the K-edges of intercalated TM and Ti MXene to reveal their oxidation states changes, shedding light on their respective contributions to capacitance. Aiming to gain further insights into the confined environment between MXene layers, we also employed ab-initio molecular dynamics (AIMD) to further interpret and validate the coordination environment obtained through in-situ extended X-ray absorption fine structure (EXAFS). This investigation lays the groundwork for tailoring the electronic and electrochemical properties of MXenes by the intercalation of various transition metal cations across diverse electrochemical systems.[1] J.-K. Chang, M.-T. Lee, W.-T. Tsai, Journal of Power Sources 2007, 166, 590-594.[2] Y. Mo, M. R. Antonio, D. A. Scherson, The Journal of Physical Chemistry B 2000, 104, 9777-9779.

Quantification of O2 Crossover and Concurrent Faradaic Efficiency Loss of H2 Production Via PEM Water Electrolysis

PEM water electrolyzers (PEMWEs) are considered to be a key technology for the decarbonization of major sectors by being able to store fluctuating renewable energy as chemical energy in the form of hydrogen gas. While the scarcity of the necessary iridium catalyst on the anode limits widespread application minding the high loadings still needed today,1 there are additional efficiency losses that are still to be fully understood.By employing a proton exchange membrane, PEMWEs are able to produce hydrogen at elevated pressure on the cathode while keeping the balance of plant costs low as the anode can still be operated with liquid water at close to ambient pressure. Hydrogen crossover to the anode compartment through the membrane is significantly increased at elevated cathode pressures, which is majorly considered a safety issue. As the anode catalyst does not serve as a good hydrogen oxidation reaction catalyst, explosive mixtures of hydrogen and oxygen can form at the anode (and its exhaust) depending on the membrane type and thickness, current density, temperature, hydrogen partial pressure at the cathode, cathode catalyst layer structure etc.2-4 Aside of safety concerns – which can be bypassed by the use of recombination interlayers in the membrane5 – gas crossover also reduces the Faradaic efficiency of the system as parts of the hydrogen produced cannot be used further because it does not reach the cathode exhaust.A so far not majorly considered additional Faradaic efficiency loss stems from oxygen crossover from the anode to the cathode. As the platinum based cathode catalyst is very active for the oxygen reduction reaction, basically all of the oxygen crossing over to the cathode compartment recombines with the hydrogen present, forming liquid water.6 The permeability of oxygen through common PEM materials is significantly lower than that of hydrogen.7 But due to the osmotic drag from the anode to the cathode as well as possibly high bubble pressures of oxygen at the anode catalyst layer / membrane interface,8 oxygen crossover deserves closer attention.In this study we show quantification of the oxygen crossover in operating PEMWE single cells by a full balance of the gases detected at both the anode and cathode exhaust using an online mass spectrometer. A direct correlation of Faradaic efficiency of the oxygen and hydrogen produced matches the expected chemical recombination on the cathode, which serves as a direct measure of the oxygen crossover to the cathode compartment during PEMWE operation. Depending on the exact operating conditions the Faradaic efficiency loss caused by oxygen crossover can easily be in the percentage range, stressing the importance of having a closer look at the oxygen crossover characteristics of PEMWE cells in order to improve the Faradaic efficiency of the system. Taie, Z.; Peng, X.; Kulkarni, D.; Zenyuk, I. V.; Weber, A. Z.; Hagen, C.; Danilovic, N., Pathway to Complete Energy Sector Decarbonization with Available Iridium Resources using Ultralow Loaded Water Electrolyzers. ACS Appl Mater Interfaces 2020, 12, 52701-52712.Bernt, M.; Schröter, J.; Möckl, M.; Gasteiger, H. A., Analysis of Gas Permeation Phenomena in a PEM Water Electrolyzer Operated at High Pressure and High Current Density. J. Electrochem. Soc. 2020, 167.Ito, H.; Miyazaki, N.; Ishida, M.; Nakano, A., Cross-permeation and consumption of hydrogen during proton exchange membrane electrolysis. Int. J. Hydrogen Energy 2016, 41, 20439-20446.Trinke, P.; Keeley, G. P.; Carmo, M.; Bensmann, B.; Hanke-Rauschenbach, R., Elucidating the Effect of Mass Transport Resistances on Hydrogen Crossover and Cell Performance in PEM Water Electrolyzers by Varying the Cathode Ionomer Content. J. Electrochem. Soc. 2019, 166, F465-F471.Zhang, Z.; Han, Z.; Testino, A.; Gubler, L., Platinum and Cerium-Zirconium Oxide Co-Doped Membrane for Mitigated H2 Crossover and Ionomer Degradation in PEWE. J. Electrochem. Soc. 2022, 169.Schalenbach, M.; Carmo, M.; Fritz, D. L.; Mergel, J.; Stolten, D., Pressurized PEM water electrolysis: Efficiency and gas crossover. Int. J. Hydrogen Energy 2013, 38, 14921-14933.Schalenbach, M.; Hoefner, T.; Paciok, P.; Carmo, M.; Lueke, W.; Stolten, D., Gas Permeation through Nafion. Part 1: Measurements. The Journal of Physical Chemistry C 2015, 119, 25145-25155.Weber, C. C.; Wrubel, J. A.; Gubler, L.; Bender, G.; De Angelis, S.; Buchi, F. N., How the Porous Transport Layer Interface Affects Catalyst Utilization and Performance in Polymer Electrolyte Water Electrolysis. ACS Appl Mater Interfaces 2023, 15, 34750-34763.

Photoexcited States Dynamics on Cu(II) Porphyrines-Nanographenes Dyads

Donor-acceptor systems have garnered significant attention in the fields of semiconducting materials and light harvesting.1 Particularly intriguing are porphyrin diads, wherein porphyrins are covalently bonded to nanographenes, forming a dyad with an expected electron transfer from the porphyrin to the nanographene. In our study, we leverage the excellent charge transport properties of Hexabenzocoronene (HBC) in combination with the superior light harvesting capabilities of Cu(II) porphyrins.The steady-state absorption spectra of the dyads exhibit a linear combination of HBC and porphyrin spectra, suggesting a low degree of electronic coupling in the ground state. Femtosecond optical transient absorption spectroscopy (TAS) has been employed to investigate the dynamics of photoexcited states. The TAS spectrum of the dyad displays a first derivative shape of the steady-state absorption, indicative of a photoinduced electron transfer within the system.2 These findings underscore the potential application of these systems as donor-acceptor systems, wherein the Cu(II) porphyrine serves as the source, transferring electrons to the HBC nanographene. This points towards promising applications of this system in photovoltaic devices. Figure 1. A) Cu(II) porphyrine B) Cu (II) porphyrine, HBC and Cu(II) porphyrine-HBC dyad absorption spectra C) Cu (II) porphyrine with C-H chains, HBC and Cu(II) porphyrinewith C-H chains-HBC dyad absorption spectra D)u (II) porphyrine with C-H chains.______________________________________________[1] H. Imahori, T. Umevama, Journal of Physical Chemistry C 2009, 113, 9029–9039.[2] Shengqiang Xiao; Mohamed E. El-Khouly; Yuliang Li; Zhenhai Gan; Huibiao Liu; Li Jiang; Yasuyuki Araki; Osamu Ito; Daoben Zhu J. Phys. Chem. B 2005, 109, 8, 3658–3667 Figure 1

Study of Antimony and Fluorine Doped Tin Oxide in Acidic Medium

In recent decades, the high-energy demand has generated interest in renewable energies and has become a more pressing issue for the development of cost-effective and eco-friendly conversion and storage technologies.1 Solar conversion systems are very attractive to address this problem, either in photovoltaic systems or in systems that store solar energy in chemical form ("solar fuels").2-3 However, there are challenges in terms of functionality, such as (1) finding suitable materials for photon absorption and (2) developing materials for the water electrolysis reaction to produce hydrogen as a solar fuel.4 Materials include catalysts and catalyst supports that allow a stable operation of a cell. Sb-doped tin oxide (ATO) has recently been used as an electrocatalyst support under acidic conditions and proposed as an alternative to F-doped tin oxide (FTO). In this talk, we will address our studies in acidic media of the fundamental electrochemistry of ATO to determine the potential window corresponding to the operation of the material in acid solutions. Experimental. The experiments were performed in a 3-electrode cell. A glassy carbon electrode of 0.0706 cm2 surface area was used as working electrode (WE), a graphite rod of 0.618 cm diameter as counter electrode (CE), and an Ag/AgCl as reference electrode (RE). The RE was placed in a double junction, and the electrolyte used was a 0.5 M H2SO4 solution (Ultrex® II Ultrapure Reagent). Electrochemical measurements were made on a CH instruments electrochemical workstation potentiostat (CHI 760D). Open circuit potential (OCP) and cyclic voltammograms (CV) were collected. The electrolyte was deoxygenated with Ar, and an Ar blanket was kept on top of the electrochemical cell surface.Cavaliere and coworkers had synthesized an antimony-doped tin oxide (ATO) with microwaves5 and carried out different studies regarding the applications of ATO as support toward proton-exchange membrane fuel cell (PEMFC)6. Our studies of ATO were mainly focused on the electrochemical activity of anodic potentials. Figure 1 shows two oxidation peaks: one at 0.147 V and the other at -0.253 V both vs NHE. We have assigned the peak at 0.147 V to tin dissolution because of the potentials for SnO2 reduction:7 The material exhibits a potential window of more than one volt in acidic media, which we propose corresponds to the thermodynamic stability of ATO. The anodic and cathodic limits, and the effect of Sb doping on the SnO2 material will be discussed in detail in the presentation. Acknowledgment The authors express their gratitude to the National Science Foundation (NSF) for the financial support through NSF project CHE-2108462. References Zhao, Y.; Adiyeri Saseendran, D. P.; Huang, C.; Triana, C. A.; Marks, W. R.; Chen, H.; Zhao, H.; Patzke, G. R., Oxygen Evolution/Reduction Reaction Catalysts: From In Situ Monitoring and Reaction Mechanisms to Rational Design. Chemical Reviews 2023.Bordet, A.; Leitner, W., Adaptive Catalytic Systems for Chemical Energy Conversion. Angewandte Chemie International Edition 2023, 62 (33), e202301956.Bagdanavicius, A., Energy and Exergy Analysis of Renewable Energy Conversion Systems. Energies 2022, 15 (15), 5528.Montoya, J. H.; Seitz, L. C.; Chakthranont, P.; Vojvodic, A.; Jaramillo, T. F.; Nørskov, J. K., Materials for solar fuels and chemicals. Nature Materials 2017, 16 (1), 70-81.Cavaliere, S.; Subianto, S.; Savych, I.; Tillard, M.; Jones, D. J.; Rozière, J., Dopant-Driven Nanostructured Loose-Tube SnO2 Architectures: Alternative Electrocatalyst Supports for Proton Exchange Membrane Fuel Cells. The Journal of Physical Chemistry C 2013, 117 (36), 18298-18307.Dubau, L.; Maillard, F.; Chatenet, M.; Cavaliere, S.; Jiménez-Morales, I.; Mosdale, A.; Mosdale, R., Durability of Alternative Metal Oxide Supports for Application at a Proton-Exchange Membrane Fuel Cell Cathode—Comparison of Antimony- and Niobium-Doped Tin Oxide. Energies 2020, 13 (2), 403.Bard, A. J. P., R; Jordan, J. , Standard Potentials in Aqueous Solution. 1st edition ed.; CRC Press, 1985: 1985; Vol. Volume 6 of Monographs in Electroanalytical Chemistry and Electrochemistry, p 848. Figure 1

Material Dynamics of Nickel (oxy)Hydroxide As an Alcohol Oxidation Electrocatalyst

Electrochemical alcohol oxidation is an attractive reaction for renewable-energy driven production of value-added chemicals, like precursors for acrylic (acrolein from glycerol) and nylon (adipic acid from cyclohexanol). Implementing selective, earth-abundant catalysts for alcohol oxidation can improve electrolyzer efficiency and economics. For example, replacing the energy intensive oxygen evolution reaction (OER) in CO2 electrolyzers with alcohol oxidation can decrease operating voltage by about 0.85 V and reduce electricity requirements up to 53% while also reducing carbon emissions from chemical production.1 Electrochemical alcohol oxidation catalyzed by as synthesized nickel oxyhydroxide (NiOOH) is hypothesized to proceed through two pathways, a chemical, redox pathway preferred by aldehydes (geminal diols in alkaline electrolyte), and a potential dependent pathway preferred by alcohols.2 Many studies have focused on understanding reaction mechanisms and device performance, however, transition metal alcohol oxidation catalysts, such as NiOOH, are known to undergo reduction/oxidation, phase changes, and even dissolution in the same potential window as alcohol oxidation.3 It is still unclear how these processes affect catalyst material stability and electrochemical performance.In this work, we probe the performance stability and material stability of Ni(OH)2 for alcohol oxidation in alkaline media through electrochemical cycling and chronoamperometry. We use a rigorously Fe-free environment to mitigate performance impacts from Fe-contamination common in non-purified alkaline electrochemical studies.4 We show that the rate of change of alcohol oxidation current density (mA cm-2) depends on reaction pathway (redox vs. potential dependent), alcohol concentration, and side chain structure. Using EC-MS and NMR, we also probe changes in performance in yield and selectivity by quantifying oxidation products, including oxygen gas. These changes in performance are correlated to material changes through monitoring dissolution with on-line ICP-MS. Furthermore, to disentangle the role of potential and reactant (e.g. alcohol or water) on stability, we elucidate oxidation state and local structural changes using in situ X-ray Absorption Spectroscopy (XAS). Insights from this rigorous model system are directly translatable to the broader goal of developing efficient, long-lasting catalysts for industrial deployment of electrochemical organic reactions powered by clean energy. References. Verma, Sumit, Shawn Lu, and Paul JA Kenis. Nature Energy 4.6 (2019): 466-474.2.Bender, Michael T., and Kyoung‐Shin Choi. ChemSusChem 15.13 (2022): e202200675.Klaus, Shannon, et al. The Journal of Physical Chemistry C 119.13 (2015): 7243-7254Wei, Lingze, et al. ACS Catalysis 13.7 (2023): 4272-4282.

Redox Behavior of Arsenic (III) and Copper (II) Mixtures on Ultraflat Au (111) Thin Film Electrodes

The electrochemical behavior of arsenic on gold (Au) electrodes surfaces is of great interest as As is well-recognized as a highly toxic and relatively ubiquitous ground water species. The United States Environmental Protection Agency (USEPA) and World Health Organization (WHO) drinking water standards for arsenic are 10 PPB, or 𝜇g L-1 [1]. These minute ion concentrations necessitate the use of analytical methods with high sensitivity and a low susceptibility to cross interferences. Electrochemical stripping voltammetry is a well-established electroanalytical method for arsenic ions [2]. Polycrystalline gold electrodes are often used due to their high redox stability and relatively low overpotential for hydrogen evolution. We recently explored the use of ultra-flat, thin film, Au(111) electrodes to replace polycrystalline Au for As stripping voltammetry. Previous studies on oriented single crystals showed relatively narrow stripping peaks with greatly improved peak to background ratios on the (111) surfaces [3]. We observed comparatively similar or better stripping behavior on the Au(111) thin film electrodes with correspondingly far less gold usage per electrode. Unfortunately, copper is a known interference for arsenic stripping electroanalysis, with a strong affinity for UPD deposition on gold. We therefore studied the deposition behavior of Cu on Au(111) thin film electrodes and the co- deposition of Cu and As on the Au(111) thin film electrodes to evaluate cross interference effects. Copper redox behavior in 0.5M H2SO4 was characterized by cyclic voltammetry, electro- deposition and linear stripping voltammetry (LSV) measurements. Strong Cu UPD behavior was observed on Au(111) thin films with sharper, better defined redox peaks than polycrystalline electrodes. Arsenic and Cu ions were also co-deposited over a wide range of Cu (II) and As (III) concentrations. Complex redox behavior was observed with strong indications of Cu-As alloy formation. This was confirmed via angle resolved, X-ray Photoemission Spectroscopy (XPS) measurements. Our results also indicate that the electrodeposition efficiency during LSV of As is increased by the co-deposition of Cu. The results of this study have important implications for understanding the nature of Cu (II) interference with electrochemical detection of trace As (III) in water.[1] USEPA. National Secondary Drinking Water Regulations. 2009. https://www.epa.gov/sdwa/drinking-water- regulations-and-contaminants (accessed.[2] USEPA. METHOD 7063: ARSENIC IN AQUEOUS SAMPLES AND EXTRACTSBY ANODIC STRIPPING VOLTAMMETRY (ASV). 1996.[3] Casuse-Driovínto, T. Q.; Rizo, R.; Benavidez, A.; Brearley, A. J.; Cerrato, J. M.; Garzon, F. H.; Herrero, E.; Feliu, J. M. Increased Sensitivity and Selectivity for As(III) Detection at the Au(111) Surface: Single Crystals and Ultraflat Thin Films Comparison. The Journal of Physical Chemistry C 2022, 126 (48), 20343-20353. DOI: 10.1021/acs.jpcc.2c05541.

Multiple Diffusion Processes in Lithium-Ion Battery Electrolytes

Numerical simulations are a powerful tool for the development and improvement of Li-ion batteries[1]. Modelling the mass transport of the involved electrolytic solutions requires precise determination of the corresponding electrolyte parameter. However, the determination methods are still controversially discussed.In this work, we attempt to measure the complete set of electrolyte parameter for a system of 0.5 M LiPF6 dissolved in a blend of ethylene carbonate and ethyl methyl carbonate (EC:EMC, 3:7 weight) at 20°C and 50°C. In order to determine the conductivity, the diffusion coefficient, the transference number and the thermodynamic factor we conduct a combination of concentration cell measurements, galvanostatic polarization experiments and electrochemical impedance spectroscopy[2].While the conductivity and concentration cell measurements show comparable results to the literature, we find the potential response in the polarization experiments deviating from theoretical expectations. Applying galvanostatic polarization experiments to symmetrical metal Li | electrolyte + separator | Li metal cells result in slower, impeded diffusion processes. This indicates the presence of additional, undesired porous structures on the Li electrodes, preventing a reliable evaluation of the electrolyte parameters[3]. To spectrally resolve the diffusive processes, we conduct very low frequency impedance spectroscopy in an attempt to identify the impedance for the sole diffusion through the separator[4].1. Max Schammer et al 2021 J. Electrochem. Soc. 168 0265112. Johannes Landesfeind and Hubert A. Gasteiger 2019 J. Electrochem. Soc. 166 A30793. Talian et al. The Journal of Physical Chemistry C 2019 123 (46), 27997-280074. F. Wohde et al 2016 J. Electrochem. Soc. 163 A714Figure 1: VLF-IS measurements with amplitudes of 60µA, 500µA and 10µA together wit the corresponding equivalent circuits, fits and Kramers-Kronig transformations at 20° C and 50°C respectively Figure 1

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

(Poster Award - Honorable Mention) Probing the Catalyst-Ionomer Interface in Catalyst Layers with Sulfo-Phenylated Polyphenylene Ionomers Using CO-Displacement and Stripping Techniques

Sulfo-phenylated polyphenylene ionomers (sPPP) are a class of hydrocarbon Ionomer being explored as a replacement for the perfluorinated sulfonic acid (PFSA) ionomer in fuel cell membranes and catalyst layers because they do not contain fluorinated compounds. Integration of sPPP ionomers into catalyst layers is challenging, as they have significantly different morphology compared to PFSA-based ionomers. Furthermore, little is known about the resulting ionomer-catalyst interface and whether characterization techniques developed for catalysts layers with PFSA-based ionomers will perform well for catalyst layers containing an sPPP ionomer. In this work, we examine the usefulness of CO displacement and stripping techniques to probe both the electrochemically active surface area (ECSA) of Pt/C in the catalyst layer and adsorbed species on the Pt catalyst sites. For catalyst layers containing PFSA, we measure a strong CO displacement reduction peak at potentials above potential of zero charge, when CO is introduced to the system, corresponding to sulfonic acid groups being displaced from active sites. The range of sulfonic acid groups adsorbed on the surface is 15- 25 % depending on the carbon support used. When the catalyst layers contain an sPPP ionomer instead of PFSA, the CO displacement peak is almost entirely suppressed, resulting in less than 10 % of sulfonic acid group adsorption. This is indicative that sPPP ionomer orientation near the Pt surface is very different compared to PFSA-based ionomer and that sulfonic acid groups do not “poison” Pt when in contact with the sPPP ionomer. However, mass activity increase is not observed for the sPPP ionomer-based catalyst layers, indicating there might be different “poisoning” mechanisms present, perhaps associated with the phenyl rings adsorption [1]. ECSA measurements for MEAs containing the non-fluorinated ionomer catalyst layers align with those measured for PFSA MEAs with the same catalysts type, loading, and comparable ionomer content, indicating that CO stripping is still a useful tool for assessing the ECSA for MEAs.[1] Zhai, Y., Baturina, O., Ramaker, D., Farquhar, E., St-Pierre, J., & Swider-Lyons, K. (2015). Chlorobenzene Poisoning and Recovery of Platinum-Based Cathodes in Proton Exchange Membrane Fuel Cells. Journal of Physical Chemistry C, 119(35), 20328–20338. https://doi.org/10.1021/acs.jpcc.5b06362

Scaling a Gas Phase Residual Lithium Conversion Process on Ni-Rich NMC Cathode Materials in Commercial Fluidized Bed Reactors

‘Residual lithium’, the LiOH and Li2CO3 surface contamination that is ubiquitous to Ni-rich NMC manufacturing, is a significant obstacle in the large-scale production and handling of high-nickel layered oxides. These hydroxide and carbonate surface phases influence reproducibility and shelf stability of the NMC powder and cause gelation and particle aggregation during electrode casting. There is ample evidence in the literature that atomic layer deposition (ALD) possesses a two-fold solution to this problem.1-3 First, reactive organometallic species such as trimethylaluminum (TMA) can convert insulating residual lithium to a Li-rich LixAlyO conducting layer. Customizable ALD layers can then be added to inhibit the re-formation of the carbonate layer and to deter negative side reactions of the CAM surface with the liquid electrolyte. While highly impactful, these studies have mostly been relegated to small, lab-scale demonstrations of <50 g. As such, there remains a need to enable this ALD-assisted-technology for high-throughput commercial applications.In this talk, we will explore the progression of a residual lithium conversion process from lab (10 – 1000 mL) to industrial-scale (10 L – 100 L) fluidized bed equipment and how scale and material-dependent parameters can impact performance. Using a commercial NMC 811 cathode as a case study, we first applied aluminum phosphate ALD coatings on a lab-scale fluidized bed reactor to examine the interfacial and electrochemical changes of the CAM material under various process conditions. ICP-OES measurements confirmed linear and reproducible deposition versus ALD cycle number between 200- 300°C. XPS analysis showed the ALD coated NMC 811 powder had an 80% reduction in Li2CO3 versus the pristine material and that a reduction persisted even after 10 days of storage in atmospheric conditions. At standard (0.5C/1C) cycling to 4.4V, AlPO4 coatings increased cycle life by 44% versus the uncoated powder. Under optimized conditions, the process was scaled first to 1 kg and finally to 10 kg in a pilot-scale reactor. In-situ mass spectrometry indicated that residual lithium conversion byproducts such as CO2 could be used to monitor reaction progress and optimize chemical usage efficiency. Fluidization aids including vibration and mechanical stirring were used to inhibit and break up powder agglomerates. ICP-OES and electrochemical cycling data confirmed reproducible deposition and cycle life benefits versus the small scale runs and pristine materials, demonstrating a pathway for these ALD-enhanced materials to transition from lab-scale demonstration to viable product. We will discuss strategies for continuing the scaling process to 100 kg batches for commercial applications.[1] M. Young et al., The Journal of Physical Chemistry C 2019 123 (39), 23783-23790[2] P. Darapaneni et al., ACS Applied Energy Materials 2022, 5, 8, 9870–9876[3] J. Li et al., Coatings 2022, 12(1), 84

Electrodeposition of 3D Au1-XAgx Nanowire Networks – Influence of Ag on the Electrochemical Properties

We present the synthesis of free-standing Au1-xAgx alloy nanowire networks with controlled geometry and atomic composition, by ion track nanotechnology and electrodeposition, and their electrochemical characterization.Polycarbonate polymer templates with interconnected nanochannels are fabricated by sequential irradiation from four directions with 1-2 GeV Au ions at the UNILAC accelerator of GSI, followed by selective chemical etching of the ion tracks. [1] Au1-xAgx alloy nanowires are subsequently synthesized by potentiostatic electrodeposition inside the channels. Nanowire growth rate and atomic composition are tuned by varying the deposition potential and the electrolyte composition. The technique provides precise control of the nanowire size, interconnectivity, and composition. [2,3,4] By dissolving the polymer template, free standing nanowire networks are obtained showing good mechanical stability. Geometry, crystallinity, and composition of the alloy Au1-xAgx nanowires were analysed by TEM, EDX, and XPS. The results demonstrate that the Ag molar fraction can be precisely adjusted between 10% and 90%.The electrochemically active surface area was determined by measuring the double layer capacitance of the nanowire network surface, and is in good agreement with the calculated theoretical surface area. The 3D network exhibit surface areas up to 200 times larger than their planar counterpart, which makes them highly interesting for catalytic processes. Their electrochemical activity in alkaline solution is investigated by cyclic voltammetry in 0.1 M KOH electrolyte, and will be discussed in this presentation.[1] M.E. Toimil-Molares, Beilstein Journal of Nanotechnology, 3.1, 860-883 (2012).[2] M. Rauber, I. Alber, S. Müller et al. Nano Letters, 11.6, 2304-2310 (2011).[3] L. Burr, I. Schubert, W. Sigle et al. The Journal of Physical Chemistry C, 119.36, 20949-20956 (2015).[4] M. Li, N. Ulrich, I. Schubert et al. RSC Advances, 13, 4721-4728 (2023).

CO-Driven Au Recovery and Nanoparticle Synthesis By in-Situ CO2 Reduction on Gas-Diffusion Electrodes

Effective synthesis methods for gold nanoparticles (NPs) have been extensively researched due to their wide-ranging applications in biomedicine, bioanalytical processes, and electrochemistry. Chemical reduction is the most common technique for producing precious metals nanoparticles, with the synthesis method greatly influencing the morphology of the resulting product. In most instances, the formation of polydisperse nanoparticles (NPs) is obtained (Reverberi, Kuznetsov et al. 2016). CO is a known reducing agent for and , offering fast reduction rates (Pretzer, Nguyen et al. 2010) and easy removal, resulting in fewer purification steps.We recently reported a synthesis method called Gas-Diffusion Electrocrystallization (GDEx), which can be applied to the platinum group metals (PGMs). The precipitation of the water-soluble PGM precursors is accomplished by the in situ production of H2 and CO, issued from the electrochemical reduction of CO2 and water electrolysis, respectively. This is typically accomplished using gas diffusion electrodes (Martinez Mora, Pozo et al. 2023). H2 acts as a reducing agent and CO as a size-controlling agent. In this work, we propose the synthesis of Au0 NPs driven by the GDEx process fed by CO2 in aqueous media.Different current densities (i.e., 10 and 40 mA cm-2) and two gas-flow regimes were tested –flow-by (FB) and flow-through (FT). Under FB, excess gas was fed into the gas chamber of the electrochemical set-up (i.e., 200 mL min-1), while under FT, the gas chamber overpressure was increased to force the gas through the GDE in convective regime, (i.e., the outlet of the gas chamber was closed and the flow rate was set to 5 mL min-1).In the first instance, the CO-driven Au(III) reduction process was modeled, including the CO(g)-CO(l) mass transport and equilibrium. It was discovered that the CO mass transport is the bottleneck in the reduction rate.In the GDEx electrochemical set-up, lower current densities and FT conditions achieved smaller particle size (i.e., 46 nm at -10 mA cm-2 and FT, table 1) and higher current efficiencies for CO production (~19 %, where the competing reaction was H2 evolution, table 1). Conversely, higher current densities led to faster reduction kinetics, yet lower current efficiencies (see Fig. 1).The GDEx process enables Au recovery and nanoparticle synthesis from Au(III)-containing synthetic streams, and can be applied to industrial leachates from end-of-life products. Conditions favoring CO mass transport and availability in the electrolyte improved the reduction kinetics. Furthermore, GDEx allows controlled CO production, mitigating the risk associated with using pure CO.Table 1. Summary of CO yield, current efficiencies and NP size for the different operating conditions j / mA cm-2 FB/FT CO generation / mmol min-1 CECO / % CEAu / % NP Size / nm Crystallite size / nm -10 FB 0.0023 7.3 4.2 70 ± 32 29 ± 7 FT 0.0081 18.6 6.6 46 ± 17 29 ± 6 -40 FB 0.0046 3.3 2.0 91 ± 36 31 ± 6 FT 0.0081 5.5 2.1 72 ± 20 27 ± 6 This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 958302 (PEACOC project). Martinez Mora, O., G. Pozo, L. F. Leon-Fernandez, J. Fransaer and X. Dominguez-Benetton (2023). "Synthesis of platinum group metal nanoparticles assisted by CO2 reduction and H2 cogeneration at gas-diffusion electrodes." RSC Sustainability.Pretzer, L., Q. Nguyen and M. Wong (2010). "Controlled Growth of Sub-10 nm Gold Nanoparticles Using Carbon Monoxide Reductant." The Journal of Physical Chemistry C 114.Reverberi, A. P., N. T. Kuznetsov, V. P. Meshalkin, M. Salerno and B. Fabiano (2016). "Systematical analysis of chemical methods in metal nanoparticles synthesis." Theoretical Foundations of Chemical Engineering 50: 59-66. Figure 1

Exploring the Efficiency of Lithium Stripping/Plating in Solid Polymer Anode-Free Lithium Cells

Traditional Li-ion batteries (LIBs) are widely used in various electronic devices due to their advantages in energy storage applications. However, finding ways to push the energy densities even higher would be highly desirable for the further rapid development of electric vehicles and electromobility. Li metal batteries and anode-free batteries (AFBs) – where the Li metal is plated in situ from Li+ ions taken from the cathode – have received extensive attention and research due to their very high specific capacity.[1] However, Li ions are unevenly deposited on the surface of anodes to form Li dendrite during the charging and discharging process, which severely deteriorates their electrochemical performance and battery safety.[2] To solve this problem, many researchers choose solid polymer electrolytes (SPEs) instead of liquid electrolytes in the batteries, because of the stability of SPEs towards Li metal.Long-term cycling of AFBs requires high-efficiency Li metal stripping and plating, which in a solid polymer cell is highly dependent on the polymer electrolyte system used, so finding appropriate host materials and salts to for the SPEs is very necessary. Poly(ethylene oxide) (PEO)-based SPEs are one of the most popular host materials for SPEs, due to their excellent chemical stability. Poly(ε-caprolactone) (PCL)-based SPEs have higher ionic conductivity and can be cycled at room temperature.[3] Poly(trimethylene carbonate) (PTMC)-based SPEs have high lithium transference number and better mechanical properties.[4] Lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) is one of the most popular salts used for SPEs. Recently, lithium difluoro(oxalate)borate (LiDFOB) and lithium bis(oxalato)borate (LiBOB) have been considered a promising alternative as electrolyte because they can passivate electrode surfaces and protect electrode materials.[5] Combinations of these materials are all potentially relvant for application in AFBs.In this work, three different polymer host materials, PEO, PTMC, and PCL, were explored as polymer electrolytes together with LiTFSI salt for their performance in anode-less cell setups, testing the plating/striping coulombic efficiency (CE) in Cu || Li cells. The results reveal clear issues for the CE of cycling in the PEO:LiTFSI system, while low-concentration PTMC:LiTFSI instead shows much more promising results. Changing the LiTFSI salt for LiBOB or LiDFOB also improves the CE of the cells.[1] Beyene, T. T., Jote, B. A., Wondimkun, Z. T., Olbassa, B. W., Huang, C. J., Thirumalraj, B., Wang C. H., Su W. N., Dai H., Hwang B. J., Effects of concentrated salt and resting protocol on solid electrolyte interface formation for improved cycle stability of anode-free lithium metal batteries, ACS applied materials & interfaces, 2019, 11(35), 31962.[2] Huang W. Z., Zhao C. Z., Wu P., Yuan H., Feng W. E., Liu Z. Y., Lu Y., Sun S., Fu Z. H., Hu J. K., Yang S. J., Anode‐Free Solid‐State Lithium Batteries: A Review, Advanced Energy Materials, 2022, 12(26), 2201044.[3] Chiu, C. Y., Chen, H. W., Kuo, S. W., Huang, C. F., Chang, F. C., Investigating the effect of miscibility on the ionic conductivity of LiClO4/PEO/PCL ternary blends. Macromolecules, 2004, 37(22), 8424.[4] Li Z., Mogensen R., Mindemark J., Bowden T., Brandell D., Tominaga Y., Ion‐conductive and thermal properties of a synergistic poly (ethylene carbonate)/poly (trimethylene carbonate) blend electrolyte. Macromolecular rapid communications, 2018, 39(14):1800146.[5] Shkrob, I. A., Zhu, Y., Marin, T. W., Abraham, D. P., Mechanistic Insight into the Protective Action of Bis (oxalato) borate and Difluoro (oxalate) borate Anions in Li-Ion Batteries, The Journal of Physical Chemistry C, 2013, 117(45), 23750.

Modeling the Environment-Dependent Kinetics of Oxygen Reduction Reaction – a Continuum Model for Electric Double Layer

For proton-exchange-membrane fuel cells (PEMFCs) to achieve broad commercialization, improved energy-conversion efficiency with minimal Pt-based electrocatalyst is required [1]. Because the sluggish rate of oxygen reduction reaction (ORR) limits the efficiency of PEMFCs [2], the efficiency improvement requires a better understanding of ORR kinetics and mechanism to design better catalyst. To understand the ORR mechanism, theoretical and experimental analyses have been conducted. While previous studies reasonably explained the catalyst-dependent activity on single crystal catalysts in 0.1 M perchloric acid solution [3, 4], the explicit effect of electrolyte and related microenvironments [5, 6] is not thoroughly understood. The change in the electrolyte alters the electric-double-layer (EDL) structure and thus the local microenvironment at the electrode/electrolyte interface. Thus, the structure of the EDL should be carefully analyzed to uncover the electrolyte-dependent reaction kinetics. In this talk, we propose a multiscale continuum model to predict the EDL structure and examine the effect of perchloric acid concentration on ORR activity on Pt (111). The model includes Density Potential Functional Theory (DPFT) for electron density and Modified Poisson Boltzmann equation for species’ density and electric potential [7]. Also, the interaction between adsorbents and electric field is taken into account by minimizing the grand potential. After model validation with experimentally measured double-layer capacity data as a function of applied potential and concentration, the effect of the perchloric acid concentration (0.02 M – 0.2 M) on ORR activity is analyzed and discussed. It is shown that the model reproduces the specific activity obtained in the experiments when assuming the oxygen adsorption is limiting the rate, which can be attributed to the large energetic barrier for solvent reorganization [8]. Then, extension of the model to PEMFC ionomer electrolytes will be introduced. Overall, the model framework and findings provide insights into the ORR mechanism and guidance on how to tailor catalyst materials for increased PEMFC performance. Acknowledgements: This work was partially supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE) through the Million Mile Fuel Cell Truck (M2FCT) consortia, technology managers G. Kleen and D. Papageorgopoulos, under contract number DE-AC02- 05CH11231, as well as by a CRADA with Toyota Central R&D Labs., Inc.. Reference [1] D. A. Cullen, K. C. Neyerlin, R. K. Ahluwalia, R. Mukundan, K. L. More, R. L. Borup, A. Z. Weber, D. J. Myers and A. Kusoglu, Nature Energy, 6, 462 (2021).[2] I. E. L. Stephens, A. S. Bondarenko, U. Grønbjerg, J. Rossmeisl and I. Chorkendorff, Energy & Environmental Science, 5 (2012).[3] M. Shibata, M. Inaba, K. Shinozaki, K. Kodama and R. Jinnouchi, Journal of The Electrochemical Society, 169 (2022).[4] H. A. Hansen, V. Viswanathan and J. K. Nørskov, The Journal of Physical Chemistry C, 118, 6706 (2014).[5] K. Kodama, K. Motobayashi, A. Shinohara, N. Hasegawa, K. Kudo, R. Jinnouchi, M. Osawa and Y. Morimoto, ACS Catalysis, 8, 694 (2017).[6] M. Luo and M. T. M. Koper, Nature Catalysis, 5, 615 (2022).[7] J. Huang, J Chem Theory Comput, 19, 1003 (2023).[8] D. T. Limmer, A. P. Willard, P. Madden and D. Chandler, Proceedings of the National Academy of Sciences, 110, 4200 (2013).