Ambient-pressure Photoelectron Spectroscopy Research Articles

Using Ambient Pressure Photoelectron Spectroscopy to Investigate the Time Dependence of Electrostatic Potential Difference over the Interphase between an Electrode and an Electrolyte

Ambient pressure photoelectron spectroscopy (APPES) is a method well-suited for measuring the change ∆φ in electrostatic potential difference φ over an interphase between an electronic conductor and an insulator. APPES had previously been used to compare ∆φ over an interphase between an electrode and an electrolyte with the change in electrochemical potential difference ∆UWE-RE between the working and the reference electrode UWE-RE .[1] The relationship between ∆φ and ∆UWE-RE at low current-transient had been shown to follow two distinct trends depending on whether charge transfer of Li+ ions between an electrode and an electrolyte occurs or not.[1,2] In this work, APPES was used to investigate the time dependence of ∆φ after changing UWE-RE . The studied electrochemical system consisted of Au (working electrode), Li4Ti5O12 (reference electrode) and a second Li4Ti5O12 (counter electrode) with 0.008 M LiClO4 in propylene carbonate (PC) as the electrolyte. Pressure in the sample compartment was equal to the saturated PC pressure. APPES experiments were performed at HIPPIE beamline at MAX IV in Lund and were conducted as follows. After applying a potential step ∆UWE-RE , a C 1s spectrum was measured every 7 s. Incident photon energy was 1800 eV. Each spectrum was fitted using a Python code written especially for the obtained C 1s spectra. Time dependence of ∆φ was extracted from the shift in the kinetic energy ∆KE of the C=O peak (∆φ = ∆KE). Experiments were performed in both regimes, i.e. when the working electrode behaves as an ideal polarizable electrode and when it behaves as an ideal non-polarizable electrode, and have shown the time dependence of ∆φ to differ for the two regimes. Behaviour of ∆φ(t) as well as the experimental setup and spectral fitting using the Python code will be discussed.Figure 1: a) Schematic depiction of the electronic electrostatic potential φ between a working (WE) and a reference electrode (RE). Electrostatic potential profile is not to scale. b) An example of the experimentally obtained time dependence of the C=O peak kinetic energy KE(t). KE(t) is related to φ(t) as ∆φ(t) = ∆KE(t).

Co3O4 for sustainable CO2 reduction and possible fine-tuning towards selective CO production

Two main challenges involved in heterogeneous catalytic CO2 reduction are: (a) decreasing the consumption of H2 to the minimum required level with possibly the maximum CO2 conversion, and (b) concurrently enhancing the selectivity of the desired CO, at the cost of methane. Towards meeting these two challenges, Co3O4 spinel has been identified as a potential catalyst and it exhibits predominant CO selectivity ≥ 673 K at atmospheric pressure. CO2 conversion begins ≥ 523 K, with 100% CO selectivity observed ≥ 673 K with CO2:H2 = 3:2. Current work shows a sustainable catalytic CO2 conversion to 100% CO selectivity with Co3O4-Nanocube (NC). Critically, CO selectivity and yield is observed to increase at the cost of methane with smaller amount of H2. 1:1 and 3:2 CO2:H2 ratio exhibits 88–100% CO selectivity with 24–32.5% CO2 conversion between 623 and 823 K. Irrespective of the input CO2:H2, ratio of CO2:H2 uptake changes from around 1:3 at 523 K to 1:1–1.5 at 823 K with concurrent production of significant methane to predominant CO, respectively. Surface electronic state changes was explored by near ambient pressure photoelectron spectroscopy, and the results suggests that Co3O4 is the active phase that promotes CO2 reduction selectively to CO. Broadening observed with the vibrational feature of the CO2 molecules at high temperature underscores the heterogeneous character of the catalyst surface, under operating conditions, due to changing electron density. By optimizing the gas hourly space velocity (GHSV), H2-lean CO2:H2 ratio, and the reaction temperature/pressure, 100% CO selectivity could be broadened to a range of operating conditions.

Atomic Structural Origin of the High Methanol Selectivity over In2O3–Metal Interfaces: Metal–Support Interactions and the Formation of a InOx Overlayer in Ru/In2O3 Catalysts during CO2 Hydrogenation

CO2 hydrogenation to methanol is of great environmental and economic interest due to its potential to reduce carbon emissions and produce valuable chemicals in one single reaction. Compared with the unmodified traditional Cu/ZnO/Al2O3 catalyst, an indium oxide (In2O3)-based catalyst can double the methanol selectivity from 30–50 to 60–100%. It is worth noting that over catalysts involving various active metals dispersed on indium oxide (M/In2O3, M = Pd, Ni, Au, etc.), although the methanol yield is boosted, the selectivity remains similar to that of plain In2O3 despite the distinct chemical properties of the added metals. To investigate the phenomena behind this behavior, here we used RuO2/In2O3 as a test catalyst. The results of ambient pressure photoelectron spectroscopy, in situ X-ray absorption fine structure, and time-resolved X-ray diffraction indicate that the structure of the RuO2/In2O3 catalyst is highly dynamic in the presence of a reactive environment. Specifically, under CO2 hydrogenation conditions, Ru clusters facilitate the reduction of In2O3 to generate In2O3–x aggregates, which encapsulate the Ru systems in a migration driven by thermodynamics. In this way, the Ru0 sites for CH4 production are blocked while creating RuOx–In2O3–x interfacial sites with tunable metal–oxide interactions for selective methanol production. In an inverse oxide/metal configuration, indium oxide has properties not seen in its bulk phase that are useful for the binding and conversion of CO2. This work reveals the dynamic nature of In2O3-based catalysts, providing insights for a rational design of materials for the selective synthesis of methanol.

Dip-and-pull ambient pressure photoelectron spectroscopy as a spectroelectrochemistry tool for probing molecular redox processes.

Ambient pressure x-ray photoelectron spectroscopy (APXPS) can provide a compelling platform for studying an analyte's oxidation and reduction reactions in solutions. This paper presents proof-of-principle operando measurements of a model organometallic complex, iron hexacyanide, in an aqueous solution using the dip-and-pull technique. The data demonstrates that the electrochemically active liquid meniscuses on the working electrodes can undergo controlled redox reactions which were observed using APXPS. A detailed discussion of several critical experimental considerations is included as guidance for anyone undertaking comparable experiments.

Following the Kinetics of Undercover Catalysis with APXPS and the Role of Hydrogen as an Intercalation Promoter

While improved catalytic properties of many surfaces covered by two-dimensional materials have been demonstrated, a detailed in situ picture of gas delivery, undercover reaction, and product removal from the confined space is lacking. Here, we demonstrate how a combination of gas pulses with varying compositions and time-resolved ambient pressure photoelectron spectroscopy can be used to obtain such knowledge. This approach allows us to sequentially form and remove undercover reaction products, in contrast to previous work, where co-dosing of reactant gases was used. In more detail, we study CO and H2 oxidation below oxygen-intercalated graphene flakes partially covering an Ir(111) surface. We show that hydrogen rapidly mixes into a p(2 × 1)-O structure below the graphene flakes and converts it into a dense OH–H2O phase. In contrast, CO exposure only leads to oxygen removal from the confined space and little CO intercalation. Finally, our study shows that H2 mixed into CO pulses can be used as a promoter to change the undercover chemistry. Their combined exposure leads to the formation of OH–H2O below the flakes, which, in turn, unbinds the flakes for enough time for CO to intercalate, resulting in a CO structure stable only in coexistence with the OH–H2O phase. Altogether, our study proves that promoter chemistry in the form of adding trace gases to the gas feed is essential to consider for undercover reactions.

Investigating Surface Sensitivity of Ni-Rich Cathode Material Towards CO2 and H2O

Layered Ni-rich transition metal oxide materials have been considered as the most promising cathode utilized in Li-ion batteries, e.g., LiNi0.8 Mn0.1 Co0.1 O2 (NMC 811). However, one of the drawbacks of NMC 811 is its high air sensitivity, leading to a degradation layer forming on the surface, and a lower cycling performance. Since the degradation mechanism is not fully understood, in this work, we use ambient pressure photoelectron spectroscopy (APPES)1 to investigate the surface sensitivity of NMC 811 towards CO2 and H2O in situ, aiming to determine the factor triggering the degradation. Before gas exposure, NMC 811 surface was Ar+ sputtered to remove the pre-existing boron oxide coating. The changes in surface chemical composition were monitored as a function of time and gas pressure. Results show that carbonate compounds are formed on the surface when NMC 811 is exposed to CO2. The carbonate compounds start to appear already within 2 minutes in CO2 at around 10-5 mbar. More interestingly, this reaction is reversed at around 3x10-6 mbar. Changes induced by water are slower, however, the water vapour effect on NMC 811 surface is irreversible. Results indicate that lithium hydroxide is formed, where Li+/H+ exchange on the surface is a possible route.2 Kokkonen, E.; Lopes Da Silva, F.; Mikkelã, M.-H.; Johansson, N.; Huang, S.-W.; Lee, J.-M.; Andersson, M.; Bartalesi, A.; Reinecke, B. N.; Handrup, K.; Tarawneh, H.; Sankari, R.; Knudsen, J.; Schnadt, J.; Såthe, C.; Urpelainen, S., Upgrade of the SPECIES beamline at the MAX IV Laboratory. Journal of Synchrotron Radiation 2021, 28 (2), 588-601.Hartmann, L.; Pritzl, D.; Beyer, H.; Gasteiger, H. A., Evidence for Li+/H+ Exchange during Ambient Storage of Ni-Rich Cathode Active Materials. Journal of The Electrochemical Society 2021, 168 (7), 070507. Figure 1

Potentials in Li-Ion Batteries Probed by Operando Ambient Pressure Photoelectron Spectroscopy.

The important electrochemical processes in a battery happen at the solid/liquid interfaces. Operando ambient pressure photoelectron spectroscopy (APPES) is one tool to study these processes with chemical specificity. However, accessing this crucial interface and identifying the interface signal are not trivial. Therefore, we present a measurement setup, together with a suggested model, exemplifying how APPES can be used to probe potential differences over the electrode/electrolyte interface, even without direct access to the interface. Both the change in electron electrochemical potential over the solid/liquid interface, and the change in Li chemical potential of the working electrode (WE) surface at Li-ion equilibrium can be probed. Using a Li4Ti5O12 composite as a WE, our results show that the shifts in kinetic energy of the electrolyte measured by APPES can be correlated to the electrochemical reactions occurring at the WE/electrolyte interface. Different shifts in kinetic energy are seen depending on if a phase transition reaction occurs or if a single phase is lithiated. The developed methodology can be used to evaluate charge transfer over the WE/electrolyte interface as well as the lithiation/delithiation mechanism of the WE.

New insights on the electronic factor of the SMSI effect in Pd/TiO2 nanoparticles

Whereas observed and explored for over 40 years, there are still open questions regarding the nature of the Strong Metal-Support Interaction (SMSI) effect. The lack of a precise determination of the atomic mechanisms of electronic and geometrical factors of the SMSI effect hinders the application of metal-support systems towards several catalytic reactions. The present study sheds light on the electronic factor of the SMSI effect in Pd/TiO2 nanoparticles by using Near Ambient Pressure Photoelectron Spectroscopy (NAP-XPS), Ultraviolet Photoelectron Spectroscopy (UPS), and Density Functional Theory (DFT) calculations. The electronic and geometrical factor of the SMSI effect were observed during reduction treatment at 300 °C and 500 °C, respectively. The results enable mapping the electronic factor during reduction treatment at 300 °C, where a charge transfer from Pd nanoparticles to TiO2 support through Pd-O-Ti entities existing at the Pd-TiO2 interface is observed. Furthermore, the charge transfer is mediated by O p states present at the Pd-TiO2 interface.

Stroboscopic operando spectroscopy of the dynamics in heterogeneous catalysis by event-averaging

Heterogeneous catalyst surfaces are dynamic entities that respond rapidly to changes in their local gas environment, and the dynamics of the response is a decisive factor for the catalysts’ action and activity. Few probes are able to map catalyst structure and local gas environment simultaneously under reaction conditions at the timescales of the dynamic changes. Here we use the CO oxidation reaction and a Pd(100) model catalyst to demonstrate how such studies can be performed by time-resolved ambient pressure photoelectron spectroscopy. Central elements of the method are cyclic gas pulsing and software-based event-averaging by image recognition of spectral features. A key finding is that at 3.2 mbar total pressure a metallic, predominantly CO-covered metallic surface turns highly active for a few seconds once the O2:CO ratio becomes high enough to lift the CO poisoning effect before mass transport limitations triggers formation of a √5 oxide.

Gas Pulse-X-Ray Probe Ambient Pressure Photoelectron Spectroscopy with Submillisecond Time Resolution.

A setup capable of conducting gas pulse–X-ray probe ambient pressure photoelectron spectroscopy with high time resolution is presented. The setup makes use of a fast valve that creates gas pulses with an internal pressure in the mbar range and a rising edge of few hundreds of microseconds. A gated detector based on a fast camera is synchronized with the valve operation to measure X-ray photoemission spectra with up to 20 μs time resolution. The setup is characterized in several experiments in which the N2 gas is pulsed either into vacuum or a constant flow of another gas. The observed width of the pulse rising edge is 80 μs, and the maximum internal pulse pressure is ∼1 mbar. The CO oxidation reaction over Pt (111) was used to demonstrate the capability of the setup to correlate the gas phase composition with that of the surface during transient supply of CO gas into an O2 stream. Thus, formation of both chemisorbed and oxide oxygen species was observed prior to CO gas perturbation. Also, the data indicated that both the Langmuir–Hinshelwood and Mars-van-Krevelen mechanisms play an important role in the oxidation of carbon monoxide under ambient conditions.

Probing Electrochemical Potential Differences over the Solid/Liquid Interface in Li-Ion Battery Model Systems.

The electrochemical potential difference (Δμ̅) is the driving force for the transfer of a charged species from one phase to another in a redox reaction. In Li-ion batteries (LIBs), Δμ̅ values for both electrons and Li-ions play an important role in the charge-transfer kinetics at the electrode/electrolyte interfaces. Because of the lack of suitable measurement techniques, little is known about how Δμ̅ affects the redox reactions occurring at the solid/liquid interfaces during LIB operation. Herein, we outline the relations between different potentials and show how ambient pressure photoelectron spectroscopy (APPES) can be used to follow changes in Δμ̅e over the solid/liquid interfaces operando by measuring the kinetic energy (KE) shifts of the electrolyte core levels. The KE shift versus applied voltage shows a linear dependence of ∼1 eV/V during charging of the electrical double layer and during solid electrolyte interphase formation. This agrees with the expected results for an ideally polarizable interface. During lithiation, the slope changes drastically. We propose a model to explain this based on charge transfer over the solid/liquid interface.

Internal Oxidation of High Strength Steels during Short-Term Annealing: Observation of Significant Enhancement of the Internal Oxidation in Fe-Mn-Si Ternary Alloys

In different production steps steels are exposed for short times, from a few minutes to up to a few hours, to high temperatures, either under reducing conditions for iron (e.g. N2-H2 during recrystallization annealing) or in oxidizing environments (e.g. during hot rolling and cooling after hot rolling). These processes are accompanied by external and internal oxidation, which can affect further processing steps. For example, during cooling after hot rolling of high strength steels especially grain boundary oxidation can lead to significant problems during pickling and cold rolling. For some alloys, e.g in the Fe-Mn-Si system, a surprisingly pronounced and deep grain boundary oxidation is observed.In this paper a fundamental investigation of grain boundary oxidation during annealing under model atmospheres simulating the oxygen partial pressure beneath the scale and also under significant lower partial pressure will be addressed, based on model alloys which are relevant to industrial high strength steel grades. The focus will be on questions such as how the different alloying elements and different annealing conditions influence the internal selective oxidation.In order to develop a fundamental understanding, the internal oxidation of dedicated binary and ternary model alloys (Fe-Mn, Fe-Si, Fe-Mn-Si, of different composition) was investigated in depth. Besides a thorough analysis of the oxide morphology, one important focus was on monitoring the mass gain in-situ during isothermal oxidation for short term exposures of up to 2h. The partial pressure of oxygen during the experiments was kept just below the equilibrium pressure for FeO/Fe and for comparison also at much lower partial pressure. As the mass changes during internal oxidation are very low, errors from buoyancy effects in a standard set-up are in the same range as the mass change to be investigated. Hence, a novel under-pressure TG set-up was developed and applied here. Furthermore, in-operando photoelectron spectroscopy of the oxide evolution at the surface by Ambient Pressure Photoelectron Spectroscopy (APXPS) was carried out, which provided important additional information for achieving a fundamental understanding of the observed oxidation kinetics. Based on the results the enhancing effect of the combination of Si and Mn on internal oxidation will be discussed.

Tracking Nafion Evolution in a Humidified Environment through Near-Ambient Pressure X-Ray Photoelectron Spectroscopy

Near ambient pressure X-ray photoelectron spectroscopy (nAP-XPS) affords unparalleled insight into the physicochemical processes that drive electrocatalytic devices.1 Studies featuring nAP-XPS span a broad range of materials and reactions, with many focused on thin films or other well-defined materials. Experiments featuring a water vapor atmosphere, or a humidified atmosphere (often with O2 or H2 as the other vapor component) have been effectively used to study the fundamentals of the electrocatalytic reactions occurring in polymer electrolyte membrane fuel cells and water electrolyzers (PEMFCs and PEMWEs).2,3 However, many of these studies have solely focused on the interaction between gas and catalyst, even if ionomer was also present within the catalyst layer. This talk focuses on the investigation of the evolution of ionomer species, and the catalyst-ionomer interface under conditions relevant to the operation of PEM devices.Analyzing the catalytically relevant surfaces and interfaces present in PEMFC and PEMWE electrodes with nAP-XPS is a complex challenge, due in part to the subtlety of the changes induced in nAP-XP spectra by interactions between the catalyst, ionomer, and gas. Adsorption of a gaseous reactant species onto a catalyst’s surface results in a weak interaction and a small chemical shift in the adsorbent species,5 while ionomer may undergo protonation, re-orientation or degradation upon exposure to reactants, also altering the spectra. Indeed, few studies feature XPS measurements of Nafion, as it has been shown to degrade over the course of standard XPS operation.6 This issue is likely exacerbated through the use of much more intense synchrotron radiation sources most commonly used for nAP-XPS experiments in the literature. Within this work, we present an evaluation of the degree of Nafion degradation during our measurements using a unique Scienta Omicron HiPP-3 nAP-XPS system, and the results of an approach to data collection developed to mitigate the induced damage. This enables the reliable study of both Nafion films and Nafion present within platinum-catalyst based PEMFC cathodes in a water vapor atmosphere using a laboratory-based, commercially available nAP-XPS system. This work lays the foundation for future study of different classes of electrocatalysts at the electrode scale, with the goal of deconvoluting complex changes at the electrode surfaces and interfaces, both in inert and catalytically relevant environments.(1) Starr, D. E.; Liu, Z.; Hävecker, M.; Knop-Gericke, A.; Bluhm, H. Investigation of Solid/Vapor Interfaces Using Ambient Pressure X-Ray Photoelectron Spectroscopy. Chem. Soc. Rev. 2013, 42, 5833–5857.(2) Yamamoto, S.; Bluhm, H.; Andersson, K.; Ketteler, G.; Ogasawara, H.; Salmeron, M.; Nilsson, A. In Situ X-Ray Photoelectron Spectroscopy Studies of Water on Metals and Oxides at Ambient Conditions. J. Phys. Condens. Matter 2008, 20 (18).(3) Casalongue, H. S.; Kaya, S.; Viswanathan, V.; Miller, D. J.; Friebel, D.; Hansen, H. A.; Nørskov, J. K.; Nilsson, A.; Ogasawara, H. Direct Observation of the Oxygenated Species during Oxygen Reduction on a Platinum Fuel Cell Cathode. Nat. Commun. 2013, 4.(4) Saveleva, V. A.; Savinova, E. R. Insights into Electrocatalysis from Ambient Pressure Photoelectron Spectroscopy. Curr. Opin. Electrochem. 2019, 17, 79–89.(5) Dzara, M. J.; Artyushkova, K.; Shulda, S.; Strand, M. B.; Ngo, C.; Crumlin, E. J.; Gennett, T.; Pylypenko, S. Characterization of Complex Interactions at the Gas − Solid Interface with in Situ Spectroscopy : The Case of Nitrogen-Functionalized Carbon. J. Phys. Chem. C 2019, 123 (14), 9074–9086.(6) Paul, D. K.; Giorgi, J. B.; Karan, K. Chemical and Ionic Conductivity Degradation of Ultra-Thin Ionomer Film by X-Ray Beam Exposure. J. Electrochem. Soc. 2013, 160 (4), F464–F469.

Stochastic Analysis of Electron Transfer and Mass Transport in Confined Solid/Liquid Interfaces

Molecular-level understanding of electrified solid/liquid interfaces has recently been enabled thanks to the development of novel in situ/operando spectroscopic tools. Among those, ambient pressure photoelectron spectroscopy performed in the tender/hard X-ray region and coupled with the “dip and pull” method makes it possible to simultaneously interrogate the chemical composition of the interface and built-in electrical potentials. On the other hand, only thin liquid films (on the order of tens of nanometers at most) can be investigated, since the photo-emitted electrons must travel through the electrolyte layer to reach the photoelectron analyzer. Due to the challenging control and stability of nm-thick liquid films, a detailed experimental electrochemical investigation of such thin electrolyte layers is still lacking. This work therefore aims at characterizing the electrochemical behavior of solid/liquid interfaces when confined in nanometer-sized regions using a stochastic simulation approach. The investigation was performed by modeling (i) the electron transfer between a solid surface and a one-electron redox couple and (ii) its diffusion in solution. Our findings show that the well-known thin-layer voltammetry theory elaborated by Hubbard can be successfully applied to describe the voltammetric behavior of such nanometer-sized interfaces. We also provide an estimation of the current densities developed in these confined interfaces, resulting in values on the order of few hundreds of nA·cm−2. We believe that our results can contribute to the comprehension of the physical/chemical properties of nano-interfaces, thereby aiding to a better understanding of the capabilities and limitations of the “dip and pull” method.

(Invited) Ambient Pressure X-Ray Photoelectron Spectroscopy of Electrochemical Systems

Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) enables investigation of surfaces and interfaces under in-situ and in-operando conditions providing improved fundamental understanding of the physicochemical processes that occur during industrially relevant catalytic reactions and operation of electrochemical devices.1–4 Combining traditional ex situ characterization methods, performance testing, and in-situ diagnostics with AP-XPS studies yields a more comprehensive understanding of both catalyst and electrode properties, and their evolution during operation of electrochemical devices. While many AP-XPS studies of electrocatalytically active materials focus on thin films or other model/well-studied materials,5 it is critical to investigate more complex systems.6 This is particularly important to advance the understanding of surfaces and interfaces in low temperature polymer electrolyte membrane devices, such as electrolyzers and fuel cells. In these systems, multiple interfaces exist between the catalyst, support, ionomer, and other additives, in addition to the presence of gas reactant(s). Studies of such complex systems necessitate holistic approaches to data analysis in conjunction with multi-technique studies. Progress has been made on this front,7 however there are still many additional experimental and analytical considerations. This talk will discuss a variety of challenges in collecting and analyzing AP-XPS data towards the goal of better understanding gas-solid interfaces in electrochemical devices. This includes sample preparation and necessary processing steps prior to XPS measurements, conditions during XPS data acquisition, and approaches to data analysis of these complex systems. Additional considerations for experiments on electrodes/composites, as opposed to just a catalyst material will be discussed. (1) Bluhm, H.; Hävecker, M.; Knop-Gericke, A.; Kiskinova, M.; Schlögl, R.; Salmeron, M. In Situ X-Ray Photoelectron Spectroscopy Studies of Gas-Solid Interfaces at near-Ambient Conditions. MRS Bull. 2007, 32 (12), 1022–1030. (2) Crumlin, E. J.; Bluhm, H.; Liu, Z. In Situ Investigation of Electrochemical Devices Using Ambient Pressure Photoelectron Spectroscopy. J. Electron Spectros. Relat. Phenomena 2013, 190, 84–92. (3) Starr, D. E.; Liu, Z.; Hävecker, M.; Knop-Gericke, A.; Bluhm, H. Investigation of Solid/Vapor Interfaces Using Ambient Pressure X-Ray Photoelectron Spectroscopy. Chem. Soc. Rev. 2013, 42, 5833–5857. (4) Stoerzinger, K. A.; Hong, W. T.; Crumlin, E. J.; Bluhm, H.; Shao-Horn, Y. Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy. Acc. Chem. Res. 2015, 48 (11), 2976–2983. (5) Liu, Q.; Han, Y.; Cai, J.; Crumlin, E. J.; Li, Y.; Liu, Z. CO2 Activation on Cobalt Surface in the Presence of H2O: An Ambient- Pressure X-Ray Photoelectron Spectroscopy Study. Catal. Letters 2018, 148 (6), 1686–1691. (6) Artyushkova, K.; Matanovic, I.; Halevi, B.; Atanassov, P. Oxygen Binding to Active Sites of Fe–N–C ORR Electrocatalysts Observed by Ambient-Pressure XPS. J. Phys. Chem. C 2017, 121, 2836–2843. (7) Dzara, M. J.; Artyushkova, K.; Shulda, S.; Strand, M. B.; Ngo, C.; Crumlin, E. J.; Gennett, T.; Pylypenko, S. Characterization of Complex Interactions at the Gas − Solid Interface with in Situ Spectroscopy : The Case of Nitrogen-Functionalized Carbon. J. Phys. Chem. C 2019, 123 (14), 9074–9086.

Probing a battery electrolyte drop with ambient pressure photoelectron spectroscopy

Operando ambient pressure photoelectron spectroscopy in realistic battery environments is a key development towards probing the functionality of the electrode/electrolyte interface in lithium-ion batteries that is not possible with conventional photoelectron spectroscopy. Here, we present the ambient pressure photoelectron spectroscopy characterization of a model electrolyte based on 1M bis(trifluoromethane)sulfonimide lithium salt in propylene carbonate. For the first time, we show ambient pressure photoelectron spectroscopy data of propylene carbonate in the liquid phase by using solvent vapor as the stabilizing environment. This enables us to separate effects from salt and solvent, and to characterize changes in electrolyte composition as a function of probing depth. While the bulk electrolyte meets the expected composition, clear accumulation of ionic species is found at the electrolyte surface. Our results show that it is possible to measure directly complex liquids such as battery electrolytes, which is an important accomplishment towards true operando studies.

Insights into electrocatalysis from ambient pressure photoelectron spectroscopy

Near ambient pressure X-ray photoelectron spectroscopy has recently emerged as a powerful tool for studies of electrocatalytic materials. This article provides a brief overview of the opportunities, which near ambient pressure X-ray photoelectron spectroscopy offers for furthering the understanding of electrocatalysis, and challenges, which have to be met in order to avoid certain pitfalls.

Design and performance of bending-magnet beamline BL02B at the SSRF.

The BL02B bending-magnet beamline at the Shanghai Synchrotron Radiation Facility (SSRF) has been constructed and is now operational for ambient-pressure photoelectron spectroscopy (APPES) and photon-in/photon-out spectroscopy (PIPOS) experimental use. Optical optimization was implemented for realization of high performance, e.g. photon flux, energy-resolving power and focus spot size. X-ray photoelectron spectroscopy experiments show that the energy range extends from 40 to 2000 eV. Argon, nitrogen and neon gas core-shell excitation spectra indicate energy-resolving powers of over 1.4 × 104 @ 244 eV, 1.0 × 104 @ 401 eV and 7.0 × 103 @ 867 eV, respectively. The measured photon flux is 1.3 × 1011 photons s-1 @ E/ΔE = 3700 at 244 eV at the expected sample position, for the SSRF electron energy of 3.5 GeV and electron current of 240 mA. The spot sizes are 177 µm × 23 µm and 150 µm × 46 µm at the APPES and PIPOS samples, respectively.

Interface Science Using Ambient Pressure Hard X-ray Photoelectron Spectroscopy

The development of novel in situ/operando spectroscopic tools has provided the opportunity for a molecular level understanding of solid/liquid interfaces. Ambient pressure photoelectron spectroscopy using hard X-rays is an excellent interface characterization tool, due to its ability to interrogate simultaneously the chemical composition and built-in electrical potentials, in situ. In this work, we briefly describe the “dip and pull” method, which is currently used as a way to investigate in situ solid/liquid interfaces. By simulating photoelectron intensities from a functionalized TiO2 surface buried by a nanometric-thin layer of water, we obtain the optimal photon energy range that provides the greatest sensitivity to the interface. We also study the evolution of the functionalized TiO2 surface chemical composition and correlated band-bending with a change in the electrolyte pH from 7 to 14. Our results provide general information about the optimal experimental conditions for characterizing the solid/liquid interface using the “dip and pull” method, and the unique possibilities offered by this technique.

Ambient Pressure Photoelectron Spectroscopy: Opportunities in Catalysis from Solids to Liquids and Introducing Time Resolution

AbstractPhotoelectron spectroscopy is an excellent technique to explore chemically complex systems in catalysis. However, due to a small mean free path of photoelectrons in gas, liquid, and solid media, the study of the gas–solid, liquid–gas, solid–liquid interfaces, as well as liquid homogeneous systems are a serious challenge. With differentially pumped analyzers this limitation ceases to exist and no longer restricts photoelectron spectroscopy only to ultra‐high vacuum conditions. Presently, photoemission studies at tens of mbar of pressure are possible. To reach atmospheric pressure and even higher, membrane‐covered closed cells have been developed. Graphene membranes are impermeable to molecules and almost transparent to photoelectrons. They are used as a pressure barrier between the enclosed cell at atmospheric pressure and the electron analyzer at vacuum while allowing transmission of photoelectrons. By accessing to atmospheric pressure range, with this kind of cell, photoemission studies will become a versatile in situ and operando tool for catalysis. Studies involving liquids in static conditions are an important aspect in this direction, which can be extended to homogeneous catalytic systems. Liquids are presently accessible using micro‐jets. Another aspect which is of paramount interest to investigate catalysts is time resolution. By improving the time resolution of photoemission measurements to the sub‐second regime it is possible to follow the kinetic changes that are crucial of a catalytic reaction, the changes that occur during catalyst pretreatment and activation, and notably to differentiate active species from spectator ones, which may be the dominating species in a classical experiment.