Surface Oxidation Research Articles

Natural Surface Frustrated Lewis Pairs: The Concept and Beyond.

The reusable and separable surface frustrated Lewis pairs (SFLPs) open up a novel approach to efficient small-molecule activation and conversion in heterogeneous catalysis. However, SFLPs have only been reported on limited systems due to the difficulty in the design and synthesis process. The inherent Lewis pairs on various solid materials offer promising opportunities for finding natural SFLPs, providing a straightforward and efficient strategy to overcome the current limitations. In this concept, we retrospect the concept of natural SFLPs proposed on wurtzite crystal surfaces and identify other natural SFLPs that probably exist on solid materials, including reduced oxide surfaces, corrugated graphene, and perovskite quantum dots. Having focused on the reactivity of natural SFLPs in small-molecule activation, we discuss the current challenges, propose possible research directions, and highlight potential applications of natural SFLPs in heterogeneous catalysis.

(Invited) Self-Recovery of Photodegraded CsPbBr3 Perovskite Nanocrystals and Problems By Irreversible Damage

CsPbBr3 perovskite nanocrystals (NCs) synthesized by a typical hot injection method are adsorbed with surface modifiers. The authors have investigated photodegradation and self-recovery phenomena due to photo-induced desorption by excitation light irradiation and re-adsorption of the surface modifiers in the dark, respectively [1-4]. These phenomena occurred when a dry solid sample of NCs was placed in a sample holder covered with a glass plate to shut out the atmosphere. On the other hand, the dried NCs exposed to the air did not show the self-recovery after photodegradation. This was due to irreversible degradation caused by surface oxidation by atmospheric oxygen. When the dried NCs were covered with a resin film instead of a glass plate, the resin with lower gas barrier properties did not prevent oxidation. However, the use of a resin with higher gas barrier properties confirmed the occurrence of photodegradation and subsequent self-recovery. The authors will present recent results including experiments on nanocomposite films of the NCs dispersed in resin.References K. Kidokoro, Y. Iso, T. Isobe, J. Mater. Chem. C, 7, 8546 (2019).K. Miyashita, K. Kidokoro, Y. Iso, T. Isobe, ACS Appl. Nano Mater., 4, 12600 (2021).I. Enomoto, Y. Iso, T. Isobe, J. Mater. Chem. C, 10, 102 (2021).K. Kano, Y. Iso, T. Isobe, ECS J. Solid State Sci. Technol., 12, 056003 (2023). Figure 1

Electrochemical and in Situ Raman Spectroscopic Characterization of Ni Surface Using Inorganic Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

・Introduction Anion exchange membrane water electrolyzer (AEMWE) is expected to reduce the production cost by using base metals for the electrocatalysts and to have high electrolytic efficiency due to its membrane electrode assembly (MEA) structure. The improvement of electrochemical activity and durability of the catalysts remains one of the essential issues for practical application. At present, Ni based oxide is one of the essentially candidate catalysts for both the anode and cathode of AEMWE.Ni is easily oxidized and formed the oxygen-containing adsorbates. The formation of Ni surface oxides depends strongly on the synthesis condition, dopant elements, and the applied potentials. Their peak assignment in the potential-dependent spectra are only possible with well-controlled surfaces. Therefore, an accurate understanding of the surface states and the catalytic reaction process on Ni oxide surface requires the Ni catalyst with well-controlled surface and a highly sensitive analytic technique. Herein, we introduced the inorganic shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) to confirm the surface states and surface reaction precisely.The SHINERS is the advanced mode of the surface-enhanced Raman Scattering (SERS) and can detect the Raman signals enhanced by the local electromagnetic field generated on the surface of the nano-amplifier by an applied laser. The SERS has some priorities to detect the signals non-destructively at in situ/operando conditions from extremely small amount of samples at the molecular level, such as self-assembled monolayers and partial surface adsorbates. Introduction of the inorganic shell on the surface of nano-amplifier prevents direct contact and interaction between the sample and the nano-amplifier, selectively detecting intrinsic surface information of samples. In this experiment, the SHINERS technique can provide spectral features of the thin layers of the Ni oxide with high sensitivity and surface selectivity to detect the surface adsorbates in detail.・Experiment In situ SHINERS measurements were performed in 0.1 mol L-1 KOH aqueous electrolyte (Ar-saturated) at room temperature, using a homemade in situ Raman cell equipped with a Ag/AgCl reference electrode and a Pt counter electrode, while all potentials were quoted vs. the reversible hydrogen electrode (RHE). In the Raman measurements, Au nanoparticles coated with an alkaline-resistant zirconia shell were introduced as an optical nano-amplifier at the surface coverage of ca. 20%. Raman spectra were acquired using the Confocal Microscope Laser Raman Spectrometer (Horiba Jobin Yvon LabRAM HR Evolution). The excitation laser source was 632.8 nm He-Ne laser with the typical power of max. 0.1 mW on the surface. The spectrometer was equipped with an 800 mm focal length monochrometer with a long working distance objective lens (50× magnification, OLYMPUS).・Results and discussion Electrochemical measurements and in situ SHINERS have captured a detail surface features at different potential range, including the redox profile between metallic Ni and α-Ni(OH)2, the phase transition from α-Ni(OH)2 to β-Ni(OH)2, as well as the oxidation process from β-Ni(OH)2 to β-Ni(O)OH on a flat Ni electrode in alkaline condition, together with the formation of the γ-Ni(O)OH and the precursor species of the oxygen evolution reaction (OER) on the Ni electrode. Weak bands of each oxygen-containing adsorbate in the few layers of surface oxide film were assigned in the function of applied potential, revealing difference with those in literatures observed on the thick layers of Ni oxides. In situ SHINERS studies, incorporated with the electrochemical studies, on a flat Ni electrode allow us to propose a general scheme presenting relationships between the metallic Ni and various oxygen-containing adsorbates formed during the potential scan in the range between hydrogen and oxygen evolution reaction. In addition, the potential-dependent catalytic activity of Ni surface and nano-catalysts with be discussed at the conference. Figure 1

(Invited) Metallization for Advanced Semiconductor Technology Nodes: Wet-Chemical Deposition and Etching, Characterization, and (Semi) Damascene Approaches

To ensure semiconductor technology scaling to continue for the decades to come, the industry focuses on identifying alternative metals (elemental or alloys), that can replace copper in the back end of line (BEOL) integration scheme, for which the metal is used as main conductor for most of the metallization levels. Recently, the semi-damascene process is being developed, in which the interconnect metal is first deposited and then patterned using a dry etching process (‘direct metal etch’), in a fashion closely resembling the traditional Al metallization. One of the advantages is that any metal that can be deposited as a blanket thin film (either by physical vapor deposition (PVD), electrochemical deposition (ECD), electroless deposition (ELD), chemical vapour deposition (CVD), or atomic layer deposition (ALD)) can subsequently be patterned, provided that the critical requirement for dry etching of ‘volatilization’ of the metal is fulfilled. Furthermore, it allows the integration of materials for which no ECD, ELD, CVD or ALD process is available to fill damascene trenches.In this contribution, intrinsic material properties (bulk resistivity, electromigration, ...) and composition (surface versus bulk composition as well as surface oxide) of a wide range of metals and alloys of interest to the BEOL will be compared. An overview of wet-chemical deposition approaches of a few selected metals (Cu and Rh) will be given. For ELD, the focus will be on discussing the mechanistic understanding of the intrinsically complex process, for which the stability and reactivity of the reducing agent is affected by solution pH and composition as well as the presence of oxygen. For ECD, results will be discussed for Rh and Ni, for which an electrochemical quartz crystal microbalance (EQCM) was used to quantify the amount of material deposited and interpret the various features detected in cyclic voltammograms. Metal ion solution speciation as well as stability, of importance for both deposition methods, has been studied using UV-vis spectroscopy and electrochemical characterization (linear sweep and cyclic voltammetry). Deposits were analysed morphologically using transmission electron microscopy and the chemical composition was assessed by elemental mapping.During process integration, the surface-chemical composition of metals / alloys needs to be carefully controlled, as this can, for instance, critically impact metal line resistance or result in wet etching or corrosion. A few example cases in which this is relevant will be presented, e.g. the reversible surface oxidation and reduction of Cu was studied using EQCM, the surface chemistry of NiAl was characterized using electrochemical measurements, and the reversible surface nitridation of a model metal (Mo) is demonstrated as a method to protect against unwanted metal dissolution.

Native Oxidation of HgCdTe Compound Semiconductors and Its Impact on Infrared Detectors Performances

The development of high-operating temperature (HOT) infrared imaging systems is motivated by the growing demand to reduce the size, weight, power consumption, and total cost of infrared detectors. HgCdTe photodiodes have unique material properties, making them one of the most promising candidates to produce infrared detectors with background-limited performances at room temperature, as predicted by the "Law 19" photodiode performance metric [1]. However, in state-of-the-art devices, the fraction of anomalous pixel responses increases alongside the detectors' operating temperature and cut-off wavelength. Numerous studies have already identified surface states induced by manufacturing processes as one of the main sources of this issue. As a result, the assessment and understanding of HgCdTe surface chemistry will be critical for future technological advancements.HgCdTe surface processing and its exposition to the environment promotes the formation of surface oxides reported to influence the interface electrical behavior and the global material electronic properties [2]. Nonetheless, the complexity of the HgCdTe surface chemistry makes it challenging to characterize the nature of the surface states caused by the presence of native oxide. As a result, there is no consensus in the literature on the effect of the alloy composition on the formed surface native oxide and its subsequent effects on the passivation quality.The purpose of this work is to investigate the mechanisms underlying the formation of HgCdTe native oxides and discuss their impact on the devices’ electrical performances. Therefore, X-ray Photoelectron Spectroscopy (XPS) and Spectroscopic Ellipsometry (SE) studies were performed in an attempt to understand HgCdTe oxidation as a function of its nominal bulk composition.The samples used in this study were epitaxial Hg(1-x)Cd(x)Te layers grown on CdZnTe substrate with multiple cadmium molar fractions (x ≃ 0.2 to 0.7). A technologically relevant standard wet etching procedure was used to achieve clean, oxide-free surfaces. Freshly etched samples were transported to the XPS in an inert atmosphere using a transfer vessel to representative surfaces and prevent alterations. The surfaces showed no oxides identifiable by XPS, thus showing the effectiveness of the transfer procedure. Furthermore, it was found that the HgCdTe components of these surfaces were not stoichiometric. Particularly, the surfaces were enriched in tellurium regardless of the alloy composition under study. These differences from the nominal composition are induced by the preferred etching of the alloy's components (Cd > Hg >> Te).Dynamic SE measurements were used to monitor native oxide formation in real-time, with scans taken every few seconds for the first hour after exposure to a clean-room environment. Furthermore, the long-term evolution of the surfaces was assessed by taking further measurements over several days. SE trends revealed a two-stage formation of native HgCdTe oxides, with an initial fast oxide growth (<1 hour) followed by a slower oxidation. The findings were supported by XPS measurements on additional samples exposed to air and kept in an airtight plastic box to obtain surface oxides of different thicknesses. Regardless of the alloy composition, the excess surface tellurium is oxidized during early oxide formation. While lengthier environment exposures resulted in oxide thicknesses correlated to the alloy cadmium molar fraction. Therefore, indicating for the first time a clear experimental demonstration of the cadmium contribution to further oxidize the material.Consequently, the combination of surface characterization techniques used in this work allowed us to investigate the formation mechanisms surrounding the native oxide of wet-etched HgCdTe surfaces and to discuss the effect of their formation on the device's performance. Acknowledgements :This work, carried out on the Platform for Nanocharacterisation (PFNC), was supported by the “Recherche Technologique de Base” and "France 2030 - ANR-22-PEEL-0014" programs of the French National Research Agency (ANR) References :[1] M. Kopytko and A. Rogalski, New Insights into the Ultimate Performance of HgCdTe Photodiodes, Sensors Actuators A Phys. 339, 113511 (2022).[2] E. R. Zakirov, V. G. Kesler, G. Y. Sidorov, and A. P. Kovchavtsev, Effect of HgCdTe Native Oxide on the Electro-Physical Properties of Metal-Insulator-Semiconductor Structures with Atomic Layer Deposited Al2O3, Semicond. Sci. Technol. 35, 0 (2020).

Engineering Surface Oxidation States in Co-Free, High-Ni Core/Shell Cathode Precursors: Impact on Physicochemical Properties and Lithium-Ion Battery Performance

This work explores the core/shell structure (Ni-rich core, Mn-rich shell) as a promising approach to improve interfacial stability in high-nickel cathode materials. This structure reduces surface reactivity without sacrificing capacity. Traditionally, co-precipitation is used to synthesize these materials. Here, we investigate the impact of manganese (Mn) oxidation state during drying on the physicochemical and electrochemical properties. We focus on how this state depends on the sintering temperature. Our findings reveal that the presence of oxidized Mn in the precursor lattice can mitigate further transition metal (TM) oxidation at lower sintering temperatures. This also induces oxygen vacancies on the particle surface. However, this leads to poor electrochemical performance due to two factors: the magnetic frustration effect and the “cross-talk effect” caused by TM dissolution and deposition on the graphite anode. In contrast, higher sintering temperatures promote complete Mn oxidation in the precursors. This kinetically suppresses Mn diffusion, preserving the core/shell structure and minimizing surface defects. This approach also demonstrably suppresses the cross-talk effect.This study highlights the profound influence of surface Mn oxidation state in core/shell high-nickel cathode material precursors. The oxidation state impacts surface properties, intrinsic characteristics, and reaction kinetics during heat treatment. Consequently, this research emphasizes the critical role of precursor surface chemistry and offers valuable insights for developing strategies to enhance cathode material interface stability.Keywords: Ni-rich cathode / Core-Shell structure / Precursor surface oxidation / Transition metal dissolution / Magnetic Frustration

Impact of the Cathode Platinum Distribution on the Proton Transport Resistance Measurement in a PEMFC

The cathode of a proton exchange membrane fuel cell (PEMFC) could have inhomogeneous platinum distribution through its thickness either by design (e.g., graded Pt loading electrodes) or as a result of degradation (e.g., Pt dissolution and migration to the membrane) [1,2]. The assessment of electrode properties such as inherent proton transport resistivity with electrochemical impedance spectroscopy (EIS) could be impacted by this inhomogeneity. Regarding protonic resistivity in the cathode, typically a transmission line model is fit to the corresponding EIS spectrum collected in the H2/N2 environment [3]. However, the model assumes a homogeneous distribution of capacitance and proton resistance through the electrode thickness and does not account for the inhomogeneity in Pt distribution. In this study, a bilayer electrode model system with variation in Pt loading is proposed to investigate the corresponding EIS spectrum as a function of Pt loading distribution in the cathode. 10 and 40wt% Pt on Vulcan were used to make low- and high-loading catalyst layers with a constant ionomer-to-carbon ratio of 0.85, which is supposed to result in similar proton transport resistivity in all designed electrodes. Artificially designed bilayer electrode structures of Low-Low, Low-High, High-Low, and High-High (first term: loading near membrane and second term: loading near the gas diffusion layer) have been successfully fabricated to simulate the cathode layer with homogeneous and heterogenous Pt mass loading through the electrode thickness. Potentiostatic EIS spectra of the bilayers at 0.45V bias potential revealed similar Rp for all samples (Avg. 51.7 Ω.cm2), while the measured Rp at 0.2V deviated by 22% for the High-Low and 55% for the Low-High sample from the corresponding value at 0.45V. Homogeneous bilayers maintained similar Rp at both bias potentials. Considering the cyclic voltammogram of the samples, the total capacitance is highly affected by a pseudo capacitive contribution from the Pt surface at potentials < 0.35V (Hydrogen adsorption-desorption) and > 0.65 (Pt surface oxidation). Even though the total capacitance is similar for High-Low and Low-High samples, the EIS spectra collected at 0.2V suggest that the distribution of capacitance through the electrode thickness can highly impact the spectra and corresponding Rp estimate.

Monolithic Integration of Lead Chalcogenide Thin Films on Silicon Substrates via Surface Morphology Engineering for Low-Cost Mid-IR Photodetector Applications

In this study, we assess the impact of surface modification techniques on the signal-to-noise ratio and opto-electrical properties of lead chalcogenide thin films grown on silicon substrates using chemical bath deposition (CBD). Our research supports the development of cost-effective mid-wavelength infrared (mid-IR) photodetectors. We focus on the adhesion stability and physical properties of lead chalcogenide films on Si substrates treated with surface oxidation and plasma. We employ atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and current-voltage (I-V) measurements to characterize these films.

The Future of Die-to-Die Copper Interconnects and Epoxy Dielectrics

Recent Die-to-Die (D2D) interconnects require high data rates operating at high frequencies (> 10 GHz) in multichip packages. Mechanical adhesion was utilized to improve the reliability of traditional packages by increasing interface roughness between epoxy dielectrics and electrochemically deposited copper interconnects. The classical packages, operating at low frequencies below 1 GHz, showed a negligible scattering of electromagnetic waves (S21 < 0.5 dB/m) on the rough surface [1, 2]; however, recent interconnects present considerable degradation in power losses (S21 > 1.0 dB/m) on the rough surface due to skin effect at high frequencies (> 10 GHz) [2]. While previous works have shown the impact of surface roughness on adhesion enhancement, a trade-off between adhesion and power losses has not been precisely considered.This study investigates the trade-off between reliability and performance. We explore the impact of surface roughness on adhesion and power efficiency of electrochemically deposited copper interconnects at high frequencies up to 18 GHz. Wet etching was performed to modify surface roughness for low-cost production. The root-mean-square roughness (RRMS) is regulated at ~10-100 nm to examine smooth copper-epoxy interfaces for future D2D interconnects. The surface morphology is analyzed by atomic force microscopy (AFM). Adhesion and insertion losses are investigated by peel test and vector network analyzer. A direction for future work is provided to improve chemical adhesion at a smooth copper-epoxy interface. Chemical adhesion is expected to improve the reliability of future multichip packages while maintaining power integrity. For example, surface oxidation and silane coupling agents are discussed to improve chemical adhesion at the smooth interface (< 100 nm RRMS).REFERENCES:[1] Lau, J.H., Recent Advances and Trends in Advanced Packaging. IEEE Transactions on Components, Packaging and Manufacturing Technology, 2022. 12(2): p. 228-252.[2] Gold, G. and K. Helmreich, A physical surface roughness model and its applications. IEEE Transactions on Microwave Theory and Techniques, 2017. 65(10): p. 3720-3732.

High Activity pH-Universal Oxygen Reduction Reaction Catalyst: Tri-Doped Porous Carbon Material Derived from Agricultural and Mining Wastes

Introduction Fuel cells still command great attention even as the need for an alternative source of energy increases annually. Following the unison conclusion by various researchers on the use of platinum and precious group metals (PGM) catalysts, as an expensive venture, many researchers are still committed to alternative and effective catalysts for fuel cell application. First-row transitional metals (TM) have been proposed as effective alternatives for oxygen reduction reaction (ORR) applications due to their promising high ORR activity and durability besides their abundance and cheaper unit cost compared to PGM [1]. In the last decade in particular, many researchers have reported catalysts derived from carbon doped with iron (Fe) and nitrogen (N). Such catalysts have shown high ORR activity, especially under alkaline conditions. The formation of Fe-N4 moieties in the carbon lattice through the interaction between the doped heteroatoms has been reported as an effective active site during the ORR process [2,3]. However, most of these catalysts have only shown high activity under alkaline conditions while their activity in neutral and acidic mediums still lags hindering wide applications in fuel cells [4]. This negative trend has been attributed to the limited number of active sites and the ease of catalyst degradation in acidic or neutral medium hence low durability in these media. To address these challenges, an increase in the number and concentration of dopants has been considered and shown positive results towards increasing the activity. However, such ventures have a net effect on the sustainability of this technology. Herein an eco-friendly and sustainable approach is presented. In this approach, we harness waste rice husk biomass rich in silica as a source of carbon (C) and self-doped silica (Si) together with pyrite, an abundant byproduct of chalcopyrite smelting following the increased demand of copper for the electric vehicle (EV) industry, as a source of Fe. These materials are then synthesized through a chain of hydrothermal and template carbonization synthesis processes to yield a tri-doped catalyst which is referred to as Fe-N-Si-C in this work. The synthesized catalyst was characterized for both physiochemical properties using TEM, SEM, XAFS and DFT while the electrochemical properties were analyzed using linear sweep voltammetry, cyclic voltammetry, and durability in both alkaline, neutral, and acidic mediums. Results and discussion The template carbonization method adopted in the synthesis in this work, resulted in a porous carbon material with successfully doped heteroatoms as confirmed by the TEM and SEM analysis. A homogenous and evenly distributed of C, Fe, N and Si elements was further confirmed by the EDS mapping. The significance of this heteroatom doping that was achieved from wastes was exhibited in the Fourier transform EXAFS where the coexistence of Fe-N4 moieties and Fe clusters with surface oxides was confirmed by the presence of Fe-N and Fe-O peaks were detected on the catalyst spectrum. Similarly, a Si-K-edge X-ray absorption revealed the formation of an amorphous SiO2 peak on the Fe-N-Si-C catalyst. These Fe-N4 porphyrin-like moieties and the SiO2 provided effective active sites for ORR as demonstrated in the LSV analysis in all universal pH media, where Fe-N-Si-C showed an onset potential of 1.02V, 0.96V and 0.86V which was close to those of commercial PtC ;1.04V, 0.99V and 0.91V in ORR analysis conducted in 0.1M KOH (alkaline),0.1M PB (neutral) and 0.1M HClO4 (acidic) respectively as highlighted in Table 1. Motivated by superior ORR performance in alkaline conditions, a Zn-air battery (ZAB) was assembled with 6M KOH and 0.2M Zinc acetate. Fe-N-Si-C cell achieved a 103mW/cm2 power density, nearly 50% higher than what the PtC (78mW/cm2) cell achieved. This work not only showcases value addition to unused environmental waste resources considered pollutants but also introduces a cost-effective and environmentally friendly catalyst, serving as a substitute for precious and expensive metal-derived electrocatalysts.

Catalyst Deactivation on Transition Metal Oxides during Ammonia Electrooxidation

Electrochemical ammonia oxidation reaction (AOR) offers a sustainable approach for waste ammonia remediation, energy conversion, and valuable product production.[1] Despite the promise of transition metal oxides as effective catalysts, the AOR mechanism on their surface remains elusive, along with factors leading to deactivation, which often involve surface poisoning species formation and site corrosion. Moreover, the AOR potential overlaps with the oxygen evolution reaction (OER), leading to the formation of O2 as a byproduct and an overall decline in energy efficiency. Therefore, it is critical to understand the molecular behavior of ammonia and other species on the oxide surface under reaction conditions.In this work, we systematically investigate the AOR mechanism on NiOOH and CuOOH, emphasizing the influence of OER and dissolved O2, which has been previously largely overlooked. Utilizing three in situ techniques: differential electrochemical mass spectrometry (DEMS) for detecting gaseous intermediates and products, Raman spectroelectrochemistry for monitoring surface transformations, and UV-vis spectroelectrochemistry for observing species within the electrical double layer, we reveal that the formation of NiOOH/CuOOH, the AOR catalytic activity and selectivity, and the deactivation pathway are all significantly modulated by OER and the presence of O2.It is established that AOR on NiOOH is potential-dependent, with N2 production being initiated at potentials coinciding with OER commencement and the generation of NOx species being favored at elevated potentials (Figure 1 left). Moreover, OER competes with the AOR to N2 pathway but promotes the AOR to NOx (N2O, NO, and NO2), which is further elucidated through the protective role of O2 to remove *N poisoning species, mitigating surface deactivation and decreasing charge transfer resistance (Figure 1 right). On CuOOH, however, the O2 can promote NO formation and Cu dissolution from the CuOOH layer, leading to complete deactivation at high potential. Our findings offer an in situ insight into the AOR mechanisms on metal oxides with co-existing OER and provide a critical direction for designing electrocatalysts for environmental applications, particularly for systems where long-term electrolysis is desired. Figure 1. Left: DEMS results during linear sweep voltammetry of NiOOH electrode in Ar/O2-saturated electrolytes (1.0 M KOH + 100 mM NH3). Right: Electrolysis results of NiOOH electrode in Ar/O2 saturated electrolytes (1.0 M KOH + 100 mM NH3) at various potentials. References MacFarlane, D. R.; Cherepanov, P. V.; Choi, J.; Suryanto, B. H. R.; Hodgetts, R. Y.; Bakker, J. M.; Ferrero Vallana, F. M.; Simonov, A. N. Joule, 4 (6), 1186-1205 (2020). Figure 1

Nanoparticels Exsolution on Perovskite Oxides: From Growth Mechanism to Energy Conversion Applications

Exsolution method is a bottom-up process for growing uniformly distributed nanoparticles embedded on the oxide surface, exhibiting excellent activity and stability in energy conversions. Despite suggestions of diverse techniques for controlling and optimizing nanoparticle exsolution, research for quantitative control remains insufficient. Herein, we investigate the distribution of endogenous nanoparticles in the bulk of the fully reduced oxide, providing evidence of ion diffusion limitation rather than surface reduction limitation. Thus, we suggest a diffusion limitation model to understand the growth behavior of exsolved nanoparticles on the oxide support. Based on the experimental results, a theoretical model is developed using Fick’s laws and confirmed in designed perovskite oxides in which their Ni doping levels are controlled within the range of solubility. Their exsolution tendencies in the gas reduction, depending on doping level, reduction temperature, and time, are matched with the theoretical model. According to experimental and theoretical results, highly Ni-doped perovskite oxides are employed to improve exsolution and achieve high performance in energy conversions, including solid oxide cells and reforming. This framework between experimental and theoretical approaches provides insight for understanding and controlling nanoparticle exsolution on perovskite oxides.

Diode-Type Hydrogen Sensor Employing Pd-coated Pt Electrodes and Anodized Titania under Gaseous Atmosphere and Its Application to Oil-Deterioration Monitoring

Numerous efforts have been directed to developing highly sensitive and selective H2 sensors, because H2, which is the most promising alternative to fossil fuels, is highly flammable and explosive in a wide concentration range (4–75% in air). However, general gas sensors (e.g., semiconductor-type and catalytic combustion-type gas sensors) cannot operate under O2-free atmosphere, because the effective reaction of H2 with negatively-charged oxygen adsorbates on the oxide surface is essential for the large H2 response. The diode-type gas sensors using noble-metal (N) sensing electrodes and an anodized titania film (N/TiO2 sensors) show extremely large H2 response even under oxygen-free atmosphere as well as relatively good selectivity to other inflammable gases, compared with other types of gas sensors [1–4], and thus the diode-type gas sensors have been quite promising as a H2-sensing device for the next generation. Typically, the titania films are fabricated by the anodization of a polished Ti plate at a current density of 50 mA cm−2 in 0.5 M H2SO4 aqueous solution at 20°C, and a pair of N films is deposited on the surface of both the titania film and the Ti plate by magnetron sputtering. The H2-sensing properties of the sensors are generally measured under a forward-bias voltage of 100 mV (N(+)–TiO2–Ti(−)) to H2 balanced with air or N2 (e.g., 5–8000 ppm) under dry or wet atmosphere at elevated temperatures (e.g., 250°C). The use of a Pd film as the N-sensing electrode resulted in quite large H2 response, and the alloying of Pd with Pt for the sensing electrode effectively improved the H2 response and the long-term stability. However, the H2 response of these sensors was too sensitive to a change in oxygen concentration. On the other hand, a Pt/TiO2 sensor showed lower H2 response, and the optimal coating of the Pt-sensing electrode with a slight amount of Au drastically enhanced the magnitude of H2 response in air especially under humidified atmosphere, due to a decrease in the amount of oxygen adsorbates on the Pt electrode. In addition, the sensor also showed quite excellent H2 selectivity against other inflammable gases such as methane, propane and propene. Recently, a thermally oxidized titania film has also attempted to be utilized as an oxide film of diode-type gas sensors to improve the operation stability under any condition. The N/TiO2 sensors can monitor the deterioration of oils, too. The deterioration of oils increases its acidity, which decreases the performance and lifetime of various machines and instruments. The acidity is generally evaluated as total acid number (TAN, the amount of KOH in milligrams, which is needed to neutralize all acid components in 1 g of oil) by batch process such as titration, and thus the new monitoring devices is required to measure TAN inline in real time. We have already demonstrated that ion-selective field-effect transistor (IS-FET)-based devices coated with a cation-conducting polymer can monitor TANs of deteriorated oils [5]. In addition, we have recently attempted to monitor the deterioration of oils by the diode-type N/TiO2 sensors [6]. For example, the Pt/TiO2 sensor clearly showed nonlinear current (I)–voltage (V) characteristics not only under gaseous atmosphere but also in the oils at 30°C, and the magnitude of current monotonically increased with an increase in TANs of the oils at forward-bias voltages of +0.8 V and +1.0 V. These results obviously indicate that the output of the Pt/TiO2 sensor is well correlated to TANs of the deteriorated oils. T. Hyodo, T. Yamashita, Y. Shimizu, Sens. Actuators B 207 (2015) 105–116. doi: 10.1016/j.snb.2014.10.005.T. Hyodo, W. Sakata, T. Ueda, Y. Shimizu, ECS Sens. Plus 1 (2022) Article No. 013602. doi: 10.1149/2754-2726/ac5b9f.T. Hyodo, T. Okusa, W. Sakata, T. Ueda, Y. Shimizu, ACS Sens. 8 (2023) 51–60. doi: 10.1021/acssensors.2c01702.T. Ueda, T. Kurano, T. Hyodo, M.i Hamano, H. Taka, Y. Shimizu, Chem. Sens. 39(B) (2023) 22–24.T. Hyodo, M. Yuto, H. Tanigawa, M. Tsuruoka, H. Sakamoto, T. Ueda, K. Kamada, Y. Shimizu, ECS Trans. 98(12) (2020) 59–66. doi: 10.1149/09812.0059ecst.S. Yamanaka, T. Ueda, M. Kasai, T. Hyodo, and Y. Shimizu, . of The 19th International Meeting on Chemical Sensors (IMCS2023), Oct. 4–8, Changchun, China (2023) p. 19.

(Invited) Stabilization and Activation of Cuprous Oxide Photocathodes for Effective Reduction of Carbon Dioxide

Among representative examples of semiconducting materials for the selective reduction of carbon dioxide to desired small organic molecules (fuels, utility chemicals), there are transition metal oxides (p-type semiconductors), in particular Cu-based oxides, such as Cu2O, CuFeO2, CuBi2O4, CuNb2O6, CuO and Cu2O) that are capable of generating electrons with use of solar visible light. Selectivity of the catalytic systems largely depends on the activing adsorptive (CO2) phenomena and the affinity of catalytic centers to the adsorbed carbon monoxide intermediates leading to their protonation or hydrogenation. Here application of aqueous or water-containing electrolytes is generally preferred. Furthermore, a compromise must be reached between the activity of a catalyst toward hydrogen evolution (water splitting), its ability to promote reductive adsorption of CO2 and to generate moderate coverages of H atoms capable of stabilizing subsequent reduced intermediates.Our interest concentrates on copper(I) oxides but their practical use requires means of stabilization without poisoning or deactivation. To improve stability against photocorrosion, to assure the sufficient electron-hole pair separation, as well as to increase population of electrons in the conduction band, mixed oxide systems combining the p-type semiconductor (e.g. Cu2O) with n-type semiconductors such as TiO2, SrTiO3 or KTaO3 have been proposed. To meet requirements for practical Cu2O-based photocathodes, not only the ability to absorb efficiently visible light and to assure fast interfacial electron transfers but also the stability issues need to be addressed.Contrary to the poor performance of the pristine (bare) copper(I) oxide photocathode, the visible-light-illuminated photoelectrochemical reduction of carbon dioxide has been successfully performed using the p-type Cu2O-semiconductor (deposited onto the transparent fluorine-doped conducting glass electrode) over-coated with the ultra-thin films of various polymer (poly(4-vinyl pyridine, oligoaniline) or polynuclear type materials (titanium, zirconium and tungsten oxides).. In this respect, ultra-thin films of functionalized carbon nanostructures, supramolecular complexes (with nitrogen containing ligands and certain transition metal sites) or robust bacterial biofilms could also be advantageous. For example, A biofilm formed by a strain of Yersinia enterocolitica (Y. enterocolitica) is characterized by high physicochemical stability over a wide pH range (4-10) and temperatures (0-40°C).Also oligoaniline or tungsten oxide over-layers could be fabricated on copper(I) oxide surfaces. Under such conditions, the copper(I) oxide photoelectrode does not change the oxidation state during photoelectrochemical diagnostic experiments. Thus certain robust (not necessarily thin) over-layers could exhibit the effect of stabilization of Cu2O against photocorrosion. Among important issues is the ability of CO2 to undergo adsorption (and activation toward reduction to CO) at both bare and modified surfaces of Cu2O. The proposed bi-layered photocathode has been demonstrated to produce such simple organic fuels as alcohols. Introduction of co-catalytic centers, e.g. palladium in a form of supramolecular complexes could also be advantageous.

Solid-State Electrochemical Oxide Pattern Formation on Au Surface Utilizing Polyelectrolyete Membrane Stamps

Nanoscale patterned gold (Au) surfaces are promising for a wide range of applications such as bio/chemical sensors and high-performance electrodes. However, pattern formation by conventional methods, which typically involves the use of resist, is complex, cost-consuming, and poses a high environmental burden. In this study, we report an investigation into the interfacial chemical reaction occurring between the polymer electrolyte membrane (PEM) and Au surfaces and its application for microscale pattern formation. Introducing a PEM instead of a liquid electrolyte can realize solid-state electrochemical surface processing. Room temperature and highly efficient electrochemical oxidation of Si, Ti [1], GaN [2], and SiC [3] can be achieved without the use of harsh liquid chemicals. The proposed method can be used for the rapid modification and etching of metal and semiconductor surfaces on the micro and nanoscale. This simple and direct pattern formation method, leading to the absence of resist film, liquid chemicals, and high-temperature treatment, offers significant advantages in terms of processing cost and environmental impact. As shown in Fig. 1, patterning was performed using an electrochemical system where the PEM was sandwiched between the Au (anode) and a cathode. The PEM can transport ions through nanoscale water channels within the membrane, effectively functioning as a solid-state electrolyte. The PEM stamps were prepared via a hot embossing process: The pattern structure of a master mold was transferred onto the PEM surface by plastic deformation of the membrane. A PEM stamp with a pattern on its surface was used, and the electrochemical reaction proceeded only at the contact area of the PEM stamp, thereby transferring the pattern onto the Au surface. Electrochemical oxidation using the wet PEM stamp under a bias of 3V effectively oxidized the Au surface and formed dot patterns with diameters and heights of approximately 2 µm and 400 nm, respectively. The time-dependent change in the morphology of the patterned Au surface was investigated. The patterned Au surface, after 30 days of exposure in air, still maintained the dot pattern structure. However, the pattern height decreased to approximately 250–300 nm after 30 days, which was 70% of the height of the pattern on the as-oxidized sample. This decrease in pattern height was likely caused by the reduction of the oxide to metallic Au after air exposure, as observed in the electrochemical oxidation of the Au surface using liquid electrolyte as reported by Nishio et al. [4]. According to a report by Takimoto et al. [5], an LSPR tip containing Au dots of approximately 60 nm in height can be applied for toxic gas sensors. The present patterned Au surface maintained a height of several hundred nanometers even after 30 days of air exposure, which is significantly larger than that of the previously reported LSPR tip, and therefore, this process can be applied for the preparation of LSPR templates. Chemical composition analysis by XPS confirmed that the Au3+ peak, which is associated with Au2O3 or Au(OH)3, was observed on the Au surface treated by solid-state electrolysis using PEM, while only metallic Au peaks exist in the spectrum from the untreated surface. After the treated sample was exposed to the air atmosphere for 12 weeks, the intensity of the Au3+ peaks significantly decreased, indicating that the oxidation film was reduced to form metallic Au by air exposure. Although further investigation of the patterning characteristics, such as the lifetime of the PEM stamps and the limitation of the pattern resolution, should be clarified, the present imprinting method on the Au surface based on solid-state electrochemical oxidation is promising as a fast and facile approach to preparing micro and nanoscale Au patterns that can potentially be applied for localized surface plasmon resonance templates for bio/chemical sensors.Figure 1. Schematics of the electrochemical imprint lithography method using PEM stamp.

(Invited) Zinc Oxide and Titanium Oxide Photocatalysts Fabricated By Electrochemical Methods and Boron Doped Diamond Electrochemistry

Photocatalytic Properties of Transparent ZnO Films Prepared by Anodization of Zinc PlateTransparent zinc oxide films were prepared by anodizing of zinc plate when the electrolyte was kept at low temperature（＜10℃）in low concentration of alkaline solution and under high bias voltage，Obtained transparent film was uniform，and it showed transparency even if it might be thick．Thus obtained transparent film is confirmed to be a pure zinc oxide，and its absorption edge is 380nm，which corresponds to the optical band gap energy of 3.2 eV，Moreover，it had high photocatalytic activity which was superior to the one prepared under no cooling. We have already reported that the photocatalytic properties were closely correlated with their orientation preference of（1010）. In this case，thus obtained transparent film also showed preferred orientation of the（1010），Effects of Electrolytic Condition to Photocatalytic Activity for Cathodically Deposited ZnO Films. Zinc oxide film was prepared easily by cathodic deposition from zinc nitrate aqueous solutions. Deposited film was evaluated as photocatalytic film under different deposition conditions. The Photocatalytic activity was evaluated by measuring acetaldehyde gas degradation. Film prepared in dilute solutions of Zn (NO3)2 showed superior photocatalysis activity. Film prepared under high current density showed superior photocatalysis. We monitored mass changes during cathodic deposition and confirmed that ZnO was completely deposited under the above conditions and that additional reactions took place under other preparation conditions. These additional reaction deactivated photocatalytic activity.Photocatalytic Properties of Titanium Oxide Film Prepared by Electrophoretic Sol－Gel Deposition Electrophoretic Sol-Gel Deposition was introduced to immobilize the TiO2 photocatalysis．Thus prepared coatings showed quite high－photocalytic activities without successive heat treatment．It is suggested that Non-heated coating showed high photocalytic activity because it responds effectively for light，which is attributed to the nano-structure of the deposited coating．Fabrication and Characterization of Diamond Quartz Crystal Microbalance Electrode Boron-doped diamond film on a quartz crystal electrode was prepared by a reflow technique. The mass sensitivity of this diamond-quartz crystal microbalance (QCM) sensor was determined by performing Fe electrodeposition. This novel electrochemical QCM sensor was quite stable under several electrochemical experimental conditions. Its wide potential window and significantly low background current are just the same as the performance of a diamond electrode. We also showed that the fabricated diamond-QCM electrode worked satisfactorily as a useful tool for electrochemical microgravimetry by examining hydrogen evolution, oxygen evolution, and oxidation of the diamond surface in acidic solutions. It was found that evolved H2 inserted into the bulk of as-grown diamond with a storage volume of 0.06 mol/dm3 in 0.5 mol/dm3 HCl solution, after sweeping the potential from 0 to -2.3 V at a scan rate of 10 mV/s, in contrast to O-terminated diamond-QCM, which inhibited hydrogen intercalation.Oxygen reduction on Au nanoparticle deposited boron-doped diamond films Nanoparticle Au was deposited on as grown boron-doped diamond (BDD). The coverage and the morphology of the deposited Au particles were investigated by means of the linear sweep voltammetry and scanning electron microscopy (SEM). From SEM, the gold electrodeposited randomly as small spherical particles with an average diameter of 60nm. The applications of the as grown BDD film deposited by Au for electrocatalytic reduction of the oxygen in acidic solution were investigated. The catalytic efficiency of the Au deposited as grown BDD with the coverage of 0.06 is near 20 times larger than that of polycrystalline gold. The mechanism of the highly electrocatalytic active was investigated by ac impedance and hydrodynamic voltammetric methods.Photoelectrodeposition of Copper on Boron-Doped Diamond Films: Application of Conductive Pattern Formation on Diamond. The Photographic Diamond Surface Phenomenon The photoelectrodeposition of copper on semiconducting B-doped diamond films was investigated. There were clear morphology differences between photoelectrodeposited and electrodeposited copper. Photoelectrodeposition proceeded by a uniform two-dimensional growth process, whereas electrodeposition involved isolated random deposition. By applying this effect we have succeeded in forming a conductive copper pattern on semiconducting B-doped diamond with the aid of a photo-mask. Interestingly, it was further found that changes occurring on the diamond surface during photoelectrochemical polarization in the absence of copper in solution facilitate subsequent copper electrodeposition in the dark, possibly due to the formation of subsurface hydrogen. We refer to this as the `photographic diamond surface phenomenon'.

Impact of Electrode Reversal Method on Electrode Degradation By High-Potential Environment in Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) are key energy conversion devices, that address global energy challenges and climate change and are prized for various applications due to their high efficiency, low operating temperature, fast startup, and low toxic emissions. Enhancing PEMFC durability is crucial for advancing commercialization. Thus, prioritizing research on Catalyst Layer (CL) degradation mechanisms of Membrane Electrode Assembly (MEA) and developing analytical methods to understand extreme degradation conditions are becoming imperative.In PEMFCs’ operational scenarios, various issues deteriorate the membrane electrode assembly (MEA) of PEMFCs, leading to irreversible performance declines. These include Pt dissolution, ionomer degradation, carbon corrosion [1], and occasional membrane mechanical issues. Of these, the electrochemical carbon oxidation reaction is particularly detrimental, causing a significant reduction in electrochemical double layer capacitance (EDLC), the formation of oxygen functional groups in carbon supports, and substantial deterioration in electrochemical surface area (ECSA) [2, 3], ultimately leading to degraded PEMFC performance.On the other hand, reversible performance degradation occurs during fuel cell operation, which specific operational recovery procedures can rectify. Mechanisms contributing to reversible voltage degradation include the platinum oxide formation, adsorption of impurity ions and contaminants on the catalyst surface, water flooding/dehydration, and oxidation of the carbon support surface to create hydrophilic oxygen-containing groups [4]. Understanding reversible degradation mechanisms and recovery strategies is important for efficient operation, improved durability, and prolonged cell lifespan. Typically, the "electrode reversal" method is practical and economical, allowing power output during recovery without additional equipment, thereby minimizing recovery operation runtime.In this study, we examine the impact of the electrode reversal method on PEMFC performance and the deterioration tendency of MEA during carbon corrosion of cathode CL (Figure 1). Accelerated stress tests (AST) were conducted at high potentials exceeding 1.0 V (vs. RHE), specifically investigating the relationship between electrode degradation behaviors, porous carbon structural properties including ionic resistance and EDLC, and overall PEMFC performance.Particularly noteworthy after the electrode reversal recovery method were the discernible variations in degradation behaviors and diverse rates of performance decline observed through electrochemical impedance spectroscopy (EIS) analysis. EIS can be used to isolate the contribution of many processes to performance loss, allowing investigation of the effect of carbon corrosion-induced catalyst layer changes on fuel cell performance [5]. The EIS data underwent evaluation via parametric fitting utilizing the transmission line model (TLM) applied to the EIS spectrum. Furthermore, relaxation time distribution (DRT) analysis was employed to directly analyze internal resistance factors as a diagnostic tool for assessing electrode degradation by enhancing the TLM-based impedance analysis results. During the ASTs, electrochemical measurements (i-V, CV, LSV, and EIS) were performed to estimate the degree of PEMFC degradation, we also conducted ex-situ surface analysis of MEA using SEM, TEM, and XPS to elucidate the specific degradation components. Fig. 1 Electrode Reversal Recovery method during Anode cycling AST of the PEMFC single cell (a) polarization curves (i-V curves); 10 A constant current test (b)-(d): (b) fresh MEA, (c) after 250 cycles, (d) after 500 cycles of Anode cycling AST References [1] Sorrentino, Antonio, Kai Sundmacher, and Tanja Vidakovic-Koch. "Polymer electrolyte fuel cell degradation mechanisms and their diagnosis by frequency response analysis methods: a review." Energies 13.21 (2020): 5825.[2] Macauley, Natalia, et al. "Carbon corrosion in PEM fuel cells and the development of accelerated stress tests." Journal of The Electrochemical Society 165.6 (2018): F3148.[3] Kwon, JunHwa, et al. "Identification of electrode degradation by carbon corrosion in polymer electrolyte membrane fuel cells using the distribution of relaxation time analysis." Electrochimica Acta (2022): 140219.[4] Yang, Wenbin, et al. "Investigation of an electrode reversal method and degradation recovery mechanisms of PEM fuel cell." Electrochimica Acta 449 (2023): 142181.[5] Kwon, JunHwa, et al. "A Comparison Study on the Carbon Corrosion Reaction under Saturated and Low Relative Humidity Conditions via Transmission Line Model-Based Electrochemical Impedance Analysis." Journal of The Electrochemical Society 168.6 (2021): 064515. Figure 1

Integration of Automated Anomaly Detection with Real-Time Fish Stress Monitoring Using QR Code-Enabled Biosensors in Diverse Aquatic Environments

Background and Objectives:In our laboratory, we have developed a biosensor capable of monitoring fish blood glucose levels as an indicator of stress response in real time. Previous studies faced challenges with traditional communication systems using radio waves or visible light, which were susceptible to interference from water mediums and ambient light. Therefore, this research aimed to develop a stress response monitoring system that could transmit information even in seawater and freshwater environments, utilizing QR code technology with error correction capabilities and automatically detecting abrupt anomaly changes in sensor response values.Materials and Methods:The glucose biosensor was constructed using a needle-type electrode with a Pt/Ir wire (φ: 0.178 mm) as the working electrode and Ag/AgCl as the reference electrode, with glucose oxidase immobilized on the working electrode surface for glucose oxidation. A microcontroller development kit (M5Stack Core2) was employed to convert sensor response values into QR codes, allowing for voltage application to the sensor and QR code display based on sensor response values. An iOS application was developed as a reading module to enable communication via QR codes. Stress response was monitored using freshwater fish (Nile tilapia, Oreochromis niloticus) and saltwater fish (Largescale Blackfish, Girella punctata). Additionally, a model capable of detecting abnormal sensor data using a One-Class Support Vector Machine was created utilizing baseline glucose concentration data. This model was integrated into a webcam control program to attempt real-time and automatically detect abnormal data.Results and Discussion:The QR code display system using M5Stack Core2 proved effective in applying voltage to the glucose biosensor, converting sensor response values to QR codes, and displaying them on the LCD screen. Stress response monitoring of freshwater and saltwater fish resulted in data retrieval rates of 100% and 84.6%, respectively, demonstrating the feasibility of wireless monitoring via QR codes regardless of water type. Furthermore, the stress response monitoring system incorporating abnormal data detection capabilities successfully identified communication issues and variations in response values due to stress induction, providing user feedback. These results highlight the capability of the system to monitor fluctuations in fish blood glucose levels in real time, potentially contributing to addressing issues such as the spread of fish diseases and mortality caused by stress. Future efforts will incorporate cloud storage and remote access features to enable real-time data monitoring and analysis from any location.Conclusion:Developing a real-time wireless monitoring system using QR code technology significantly advances understanding and addressing fish stress responses. By enabling continuous monitoring of glucose levels in fish, the system has the potential to mitigate the adverse effects of stress-related diseases and mortality. Further enhancements, including cloud integration and remote access, aim to enhance the system's usability and accessibility for researchers and aquaculture professionals, ultimately contributing to improved fish welfare and management practices. Figure 1

The Relationship between d-Band Center of Pt in Pt-Based Catalysts and Catalytic Activity for Methanol Oxidation in an Alkaline Aqueous Solution

In this study, in order to examine the relationship between d-band center of platinum (Pt) in Pt-based catalysts and catalytic activity for methanol electrochemical oxidation in an alkaline aqueous solution, Pt-based nanoparticle catalysts were synthesized and then their electrocatalytic activity and d-band center of Pt in the Pt-based catalyst surfaces were analyzed with X-ray photoelectron spectroscopy. Finally, the plots of electrocatalytic activity vs. d-band center of Pt atoms on the catalyst surface were obtained. The plots exhibited a so-called volcano-type correlationship (Fig. 1), indicating that there is an optimum electronic state of Pt atoms on the catalyst surfaces for the methanol oxidation. In addition, the existence of the optimum electronic state was also confirmed from the relationship between the change in the d-band center due to the elution of the second element from the Pt-based alloy catalyst and the catalytic activity.Fig.1 Relationship between d-band center of the Pt atoms in Pt NPs/CB and Pt-based NPs/CB and current density at -0.1 V for the methanol oxidation. Figure 1

XAS and XPS Analysis on Surface Reconstruction By Chemical Treatment of Ba0.5Sr0.5Co0.8Fe0.2O3

Alkaline water electrolysis is expected to play a vital role in hydrogen production systems using renewable electricity. However, the intermittent nature of renewable electricity can often cause electrolysis cells to shut down. Such interruptions result in reverse currents that accelerate catalyst degradation. Extensive studies of catalytic activity have elucidated that the oxygen evolution reaction (OER) is contingent on certain descriptors [1]. Recently, the focus has been placed on the surface structure of the catalysts, as the actual OER occurs on the catalyst surface [2]. Previous research has demonstrated that the surfaces of numerous oxide materials with high OER activity undergo surface reconstruction under OER, resulting in the formation of metal oxyhydroxide phases [3]. This surface reconstruction has been reported after OER experiments, although it is challenging to analyze large numbers of samples in this manner. In order to efficiently study and utilize the state of the catalyst surface for material design, a method is needed to induce the surface reconstruction through chemical treatments. Consequently, the present study examines the chemical state of the surface following chemical treatment of perovskite-type oxide Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) by stirring in an alkaline solution, employing X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). BSCF was synthesized using the sol-gel process. The as-prepared samples were subjected to stirring under four different conditions: in 1 M or 7 M KOH solutions with either oxygen or nitrogen bubbling for a duration of 21 hours. The structural and chemical properties were characterized using X-ray diffraction (XRD), XAS, and XPS. XAS measurements were conducted at the BL-2 and BL-11 beamlines of the Ritsumeikan University SR Center. Both total electron yield and partial fluorescence yield modes were employed. XRD analysis did not reveal any significant peak shifts or the formation of a second phase, indicating that the bulk structure of the samples remained unchanged. Comparative studies of the O K-edge XAS for both as-prepared and chemically treated BSCF samples in 7 M KOH with oxygen bubbling were conducted. The peak at approximately 530 eV is attributed to the transition from O 1s to the 3d orbitals of transition metals combined with O 2p. In the as-prepared sample, this peak exhibited low intensity. However, in the chemically treated sample, sharp peaks were observed at approximately 529 eV and 532 eV. These findings indicate that the surface of the perovskite-type oxide underwent a transformation to an oxyhydroxide of Co or Fe, as evidenced by the presence of peaks characteristic of transition metal oxyhydroxides. Despite these surface changes, the results from Co and Fe L-edge XAS showed no peak shifts, indicating that the valence states of Co and Fe remained unchanged. XPS analysis revealed a decrease in the surface concentrations of Ba and Sr. This work is based on results obtained from the project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. (JPNP 20003). [1] J. Suntivich, K. May, H. Gasteiger, J. Goodenough, and Y. Shao-Horn, Science, 334, 1383-1385 (2011). [2] I. C. Man, H. Su, F. Call-Vallejo, H. A. Hansen, J. I. Martínez, N. G. Inoglu, J. Kitchin, T. F. Jaramillo, J. K. Nørskov, and J. Rossmeisl, ChemCatChem, 3, 1159-1165 (2011). [3] E. Fabbri, M. Nachtegaal, T. Binninger, X. Cheng, B. Kim, J. Durst, F. Bozza, T. Graule, R. Schaublin, L.Wiles, M. Pertisi, N. Danilovic, K. E. Ayers, and T. J. Schmidt, Nat. Mater., 16, 925-934 (2017).