Near-ambient Pressure X-ray Photoelectron Spectroscopy Research Articles

Exploring the Gas-Sensing Mechanism of a WO3 Nanowires-Based Sensor for Ethanol Detection by Near-Ambient Pressure XPS

The WO3 nanowires (NWs), fabricated on a commercial Al2O3-based sensor platform, underwent near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) analysis during ethanol detection. Our findings revealed challenges that may appear in utilizing NAP-XPS studies for studying a real gas sensor in operando conditions. Through NAP-XPS analysis, we explored the gas-sensing mechanisms of pristine and Pt-decorated WO3 NWs for ethanol sensing at different temperatures, demonstrating a combination of several mechanisms commonly observed in metal-oxide chemiresistors. For ethanol sensing, the primary driving force for the sensor's macroscopic electrical response at low temperatures was the adsorption of ethanol molecules. Conversely, at high temperatures, it involved the adsorption of ethoxy groups along with the reducing effect of ethanol on the WO3 surface. It is shown that the surface oxygen vacancies play a crucial role in the ethanol sensing mechanism of WO3 NWs-based gas sensors. Figure 1

CeO2-Supported Single-Atom Cu Catalysts Modified with Fe for RWGS Reaction: Deciphering the Role of Fe in the Reaction Mechanism by In Situ/Operando Spectroscopic Techniques.

Reverse water-gas shift (RWGS) reaction has attracted much attention as a potential approach for CO2 valorization via the production of synthesis gas, especially over Fe-modified supported Cu catalysts on CeO2. However, most studies have focused solely on investigating the RWGS reaction over catalysts with high Cu and Fe loadings, thus leading to an increase in the complexity of the catalytic system and, hence, preventing the gain of any reliable information about the nature of the active sites and reaction mechanism. In this work, a CeO2-supported single-atom Cu catalyst modified with iron was synthesized and evaluated for the RWGS reaction. The catalytic results reveal a significant synergistic effect between CuCeO2 and Fe, demonstrating an activity up to three times higher than the combined catalytic activities of monometallic catalysts (Fe/CeO2 + CuCeO2) under identical conditions. Various ex situ and in situ/operando techniques are employed to unveil the concealed role of Fe in catalyst activity enhancement. The combined findings from hydrogen temperature-programmed reduction (H2-TPR) and operando electron paramagnetic resonance spectroscopy (EPR) reveal that the added Fe predominantly interacts with Cu-containing surface sites, resulting in the stabilization of higher proportions of Cu single sites. Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and operando EPR results unveil a synergistic interplay of Fe with Cu-containing sites and CeO x domains, efficiently enhancing both the reoxidation of Cu+ in Cu+-Ov-Ce3+ moieties and the reducibility of Ce4+ in CeO x domains under RWGS conditions. Detailed mechanistic studies reveal that the RWGS reaction predominantly proceeds via the redox mechanism.

Tuning the Size of TiO2-Supported Co Nanoparticle Fischer-Tropsch Catalysts Using Mn Additions.

Modifying traditional Co/TiO2-based Fischer-Tropsch (FT) catalysts with Mn promoters induces a selectivity shift from long-chain paraffins toward commercially desirable alcohols and olefins. In this work, we use in situ gas cell scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) elemental mapping, and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to demonstrate how the elemental dispersion and chemical structure of the as-calcined materials evolve during the H2 activation heat treatment required for industrial CoMn/TiO2 FT catalysts. We find that Mn additions reduce both the mean Co particle diameter and the size distribution but that the Mn remains dispersed on the support after the activation step. Density functional theory calculations show that the slower surface diffusion of Mn is likely due to the lower number of energetically accessible sites for the Mn on the titania support and that favorable Co-Mn interactions likely cause greater dispersion and slower sintering of Co in the Mn-promoted catalyst. These mechanistic insights into how the introduction of Mn tunes the Co nanoparticle size can be applied to inform the design of future-supported nanoparticle catalysts for FT and other heterogeneous catalytic processes.

Dynamic restructuring of nickel sulfides for electrocatalytic hydrogen evolution reaction

Transition metal chalcogenides have been identified as low-cost and efficient electrocatalysts to promote the hydrogen evolution reaction in alkaline media. However, the identification of active sites and the underlying catalytic mechanism remain elusive. In this work, we employ operando X-ray absorption spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy to elucidate that NiS undergoes an in-situ phase transition to an intimately mixed phase of Ni3S2 and NiO, generating highly active synergistic dual sites at the Ni3S2/NiO interface. The interfacial Ni is the active site for water dissociation and OH* adsorption while the interfacial S acts as the active site for H* adsorption and H2 evolution. Accordingly, the in-situ formation of Ni3S2/NiO interfaces enables NiS electrocatalysts to achieve an overpotential of only 95 ± 8 mV at a current density of 10 mA cm−2. Our work highlighted that the chemistry of transition metal chalcogenides is highly dynamic, and a careful control of the working conditions may lead to the in-situ formation of catalytic species that boost their catalytic performance.

Redox dynamics and surface structures of an active palladium catalyst during methane oxidation

Catalysts based on palladium are among the most effective in the complete oxidation of methane. Despite extensive studies and notable advances, the nature of their catalytically active species and conceivable structural dynamics remains only partially understood. Here, we combine operando transmission electron microscopy (TEM) with near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and density functional theory (DFT) calculations to investigate the active state and catalytic function of Pd nanoparticles (NPs) under methane oxidation conditions. We show that the particle size, phase composition and dynamics respond appreciably to changes in the gas-phase chemical potential. In combination with mass spectrometry (MS) conducted simultaneously with in situ observations, we uncover that the catalytically active state exhibits phase coexistence and oscillatory phase transitions between Pd and PdO. Aided by DFT calculations, we provide a rationale for the observed redox dynamics and demonstrate that the emergence of catalytic activity is related to the dynamic interplay between coexisting phases, with the resulting strained PdO having more favorable energetics for methane oxidation.

Understanding the Decomposition of Dimethyl Methyl Phosphonate on Metal-Modified TiO2(110) Surfaces Using Ensembles of Product Configurations.

The decomposition of dimethyl methyl phosphonate (DMMP), a simulant for the nerve agent sarin, was investigated on Cu4/TiO2(110) and K/Cu4/TiO2(110) surfaces using a combination of near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and density functional theory calculations (DFT). Mass-selected Cu4 clusters and potassium (K) atoms were deposited onto TiO2(110) as a metal catalyst and alkali promoter to improve the reactivity and recyclability of the TiO2 surface after exposure to DMMP. Surface reaction products resulting from decomposition of DMMP were probed by NAP-XPS measurements of phosphorus (P) 2p and carbon 1s core-level spectra. The Cu4/TiO2(110) surface is found to be very active for DMMP decomposition with highly reduced P-species observed even at room temperature (RT). The codeposition of K atoms and Cu4 clusters further improves the reactivity with no intact DMMP detectable. Temperature-dependent measurements show that the presence of K atoms promotes the removal of residual P-species at temperatures > 600 K. Detailed DFT calculations were performed to determine the surface structures and energetically accessible pathways for DMMP decomposition on Cu4/TiO2(110) and K/Cu4/TiO2(110) surfaces. The calculations show that DMMP and P-containing reaction products preferentially bind to the TiO2 surface, while the molecular fragments, i.e., methoxy and methyl, bind to both the Cu4 clusters and TiO2. The Cu4 clusters make the P-O, O-C, and P-C bond cleavages of DMMP markedly more exothermic. The Cu4 clusters are highly fluxional with atomic structures that depend on the configuration of fragments bound to them. Finally, the manifold of P 2p chemical shifts calculated for a large number of energetically favorable configurations of decomposition products is in good agreement with the observed XPS spectra and provides an alternative way of interpreting incompletely resolved core-level spectra using an ensemble of observed structures.

Importance of Metal-Support Interactions for CO2 Hydrogenation: An Operando Near-Ambient Pressure X-ray Photoelectron Spectroscopy Study on Gold-Loaded In2O3 and CeO2 Catalysts.

Metal-support interactions, which are essential for the design of supported metal catalysts, used, e.g., for CO2 activation, are still only partially understood. In this study of gold-loaded In2O3 and CeO2 catalysts during CO2 hydrogenation using near-ambient pressure X-ray photoelectron spectroscopy, supported by near edge X-ray absorption fine structure, we demonstrate that the role of the noble metal strongly depends upon the choice of the support material. Temperature-dependent analyses of X-ray photoelectron spectra under reaction conditions reveal that gold is reduced on CeO2, enabling direct H2 activation, but oxidized on In2O3, leading to decreased activity of Au/In2O3 compared to bare In2O3. At elevated temperatures, the catalytic activity of the In2O3 catalysts strongly increases as a result of facilitated CO2 and (In2O3-based) H2 activation, while the catalytic activity of Au/CeO2 is limited by reoxidation by CO2. Our results underline the importance of operando studies for understanding metal-support interactions to enable a rational support selection in the future.

Low-temperature gas sensing mechanism in β-Ga2O3 nanostructures revealed by near-ambient pressure XPS

Ga2O3 is a promising gas-sensing material that can operate over a wide temperature range. However, despite its relevance for practical applications, there is a lack of understanding regarding its sensing mechanism at temperatures below 800 °C. To reveal the sensing mechanism, GaOOH nanorods were grown on β-Ga2O3 seed layers by chemical bath deposition, then converted to β-Ga2O3 by annealing in the air at 500 °C, and the surface properties were investigated by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) in the presence of oxidizing/reducing gases. Time-stable shifts in the XPS spectra were used to estimate the relative changes in conductivity in compliance with the ionosorption model. Our results indicate that the sensing mechanism at lower temperatures is governed by redox reactions, leading to an increase/decrease in the conductivity for reducing/oxidizing gases. Furthermore, we provide a detailed description of the ethanol-sensing mechanism at different temperatures.

Investigating methanol decomposition at low temperatures on polycrystalline Pt using near ambient pressure XPS (NAP-XPS)

In this work, methanol was frozen on the surface of polycrystalline Pt and the decomposition of methanol was monitored from its frozen state to 195 K. This works shows that methanol spontaneously decomposes to CO on Pt even at 160 K. CO was observed to adsorb onto the top and bridge site of Pt based on the C 1s and O 1s binding energy assignment from the NAP-XPS measurement. At low temperatures, CO is preferred to bind onto the top site with a bridge to top coverage ratio of 0.4, while CO is found to be predominantly on the bridge site at room temperature, with a CO bridge to top ratio of 4. The difference in the energy of the CO binding sites were found to be 6.4 (±1.0) kJ/mol, which is in good agreement with literature.

The Effect of Mn Doping and Ti3+ Defects at TiO2 Surfaces in NO and SO2 Gas Capture Investigated Using Near-Ambient Pressure X-ray Photoelectron Spectroscopy

The removal of air pollutants is an important research topic in order to improve the environment. In addition, many common pollutants can affect human health to varying degrees. In this work, we investigate NO and SO2 conversion by reaction with a commonly used metal oxide catalyst, TiO2. Rutile TiO2(110) single crystals and industrial powder samples used in sunscreen are studied using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) as a main tool. This allows in situ monitoring of the gas conversion process. We find Ti3+ defects (oxygen vacancies) or Mn oxides/cations (MnO) at the TiO2 surfaces can improve the conversion of NO and SO2 to surface-bound species. MnO and Ti3+ defects at the surface of rutile TiO2(110) exhibit a synergistic effect on the conversion of NO and SO2 that is significantly improved by nearly an order of magnitude. The by-products are mainly in the form of NO3−, SO32−, and SO42−. We find the main oxidation products formed on the single crystals are subtly different from those on the industrial powder samples. For TiO2 nanopowders (undoped and Mndoped), the presence of Mn also shows improvement in toxic gas adsorption capacity. Overall, it is believed that the outcome obtained from NAP-XPS in this research provides useful insights for the future use of TiO2 in pollutant gas capture.

Confining isolated Pt atoms into the porous SnO2 for efficient gas sensing

Highly dispersed isolated sites offer opportunities to rationally design sensing materials with desired performance, but their stability under harsh reaction conditions is still challenging. Herein, we deposited the highly dispersed atomic layer deposition (ALD) platinum (Pt) species into optimized porous SnO2 nanorods derived from the Sn-based metal organic frameworks (MOFs). With confining isolated Pt into porous SnO2, the optimum operating temperature of the sensor based on SnO2–Pt2 nanorods was decreased from 275 °C to 190 °C. And the response (Ra/Rg) to 5 ppm acetone was improved from 2.63 to 6.33, along with the decrease of response time from 23 s to 9 s. Combined with X-ray adsorption, near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and density functional theory (DFT) simulation, the highly dispersed Pt confined within SnO2 nanorods are confirmed to heighten the adsorption of acetone at working temperature and lower the reaction activation energy. The confined structure enriches the acetone in hole, further enhancing its adsorption on Pt. The highly dispersed isolated Pt sites and confined effects dramatically promote the sensing performance. The understanding of structure-activity relationships offers a novel strategy to design the ultrasensitive and stable acetone sensing materials, and it shows potential applications in design of other gas sensing or catalytic materials.

Dehydrogenative oxidation of hydrosilanes using gold nanoparticle deposited on citric acid-modified fibrillated cellulose: unveiling the role of molecular oxygen.

Efficient and environmentally friendly synthesis of silanols is a crucial issue across the broad fields of academic and industrial chemistry. Herein, we describe the dehydrogenative oxidation of hydrosilane using a gold nanoparticle catalyst supported by fibrillated citric acid-modified cellulose (F-CAC). Au:F-CAC catalysts with various particle sizes (1.7 nm, 4.9 nm, and 7.7 nm) were prepared using the trans-deposition method, a technique previously reported by our group. These catalysts exhibited significant catalytic activity to produce silanols with high turnover frequency (TOF) of up to 7028 h-1. Recycling experiments and transmission electron microscopy (TEM) observation represented the high durability of Au:F-CAC under the reaction conditions, allowing kinetic studies on size dependency. Mechanistic studies were conducted, including isotope labelling experiments, kinetics, and various spectroscopies. Notably, the near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) of the model catalyst (Au:PVP) revealed the formation of catalytically active cationic Au sites on the surface through the adsorption of molecular oxygen, providing a new insight into the reaction mechanism.

Electro-tuned catalysts: voltage-controlled activity selection of bimetallic exsolution particles.

In this work, we show how the activity states of bimetallic Ni0-Fe0 catalysts exsolved from Nd0.6Ca0.4Fe0.97Ni0.03O3-δ (NCFNi) can be influenced electrochemically. The NCFNi parent oxide was employed in the form of thin film mixed conducting model electrodes, which were operated in a humid hydrogen atmosphere. By precisely controlling the oxygen chemical potential in the parent oxide electrode via applying an electrochemical polarisation, we managed to selectively exsolve Ni nanoparticles from the perovskite lattice and study their catalytic activity switching characteristics. To be able to track the surface chemical changes during the switching process, electrochemical polarisation experiments were combined with near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) measurements. This in situ analytical approach allowed relating the difference we observed in the switching behaviour of Ni particles here and of Fe particles in a recent study, to a different kinetic interplay between electrochemical driving force and atmosphere. We propose that slow oxygen transport through nickel oxide, located at the particle/perovskite interface, is mainly responsible for the observed difference to iron exsolutions, which becomes especially evident for larger nickel particles. In addition, in the case of bimetallic exsolutions and with applied bias voltage as a control parameter, we are able to reversibly switch between three different activity states, namely bimetallic Ni0-Fe0 (medium activity), pure Ni0 (high activity), and the inactive oxides.

Operando observation of the dynamic SEI formation on a carbonaceous electrode by near-ambient pressure XPS

Operando near-ambient pressure XPS was carried out on a glassy carbon electrode. For the first time, the dynamic formation of the SEI in contact with the liquid electrolyte was detected by XPS.

Enhancing the performance of a novel CoRu/CeO2 bimetallic catalyst for the dry reforming of methane via a mechanochemical process

A mechanochemical synthesis method has been used to synthesize CoRu nanoparticles supported on CeO2 for methane dry reforming. In this work, we study the effect of Ru addition to Co/CeO2-based catalysts and of the synthesis method by screening their catalytic activity, using synchrotron X-ray diffraction (XRD), and operando near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). Ruthenium addition directly impacts the reducibility of cobalt species and results in smaller particle sizes, as demonstrated by H2-temperature programmed reduction and XRD. NAP-XPS shows that Ru modifies the metal-support interaction, as evidenced by the higher Ce3+/Ce ratios for the bimetallic samples and tuning the oxidation state of Ru. The synthesis method also influences the dispersion of Co and Ru on the surface. Mechanochemically-prepared samples (mono- and bimetallic) outperformed the conventionally-synthesized counterparts by reaching higher CH4 and CO2 conversions, resulting in a stable CoRu/CeO2 catalyst for 24 h at 700 °C and yielding an H2/CO ratio close to 1.

Elucidation of the Interplay between the Features of the Precursor and the Physicochemical Properties of “Core-Shell” Hierarchical Carbon Nitride Electrocatalysts for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is a major bottleneck in the operation of proton-exchange membrane fuel cells (PEMFCs) since it introduces large overpotentials (no less than 250-300 mV), which degrade significantly the energy conversion efficiency of the device. In addition, the electrocatalysts (ECs) yielding the lowest ORR overpotentials in the acidic environment found at the PEMFC cathode are based on Pt, a very scarce critical raw material (CRM). Pt raises concerns as it might trigger serious supply bottlenecks in the event of a practical widespread implementation of PEMFCs in the framework of today’s energy transition. Hence, the development of high-performing and durable ECs for the ORR is a major stepping stone towards the large-scale rollout of PEMFCs.In our research group a new breakthrough approach has been devised for the synthesis of ORR ECs, that is completely different form the preparation routes that are commonly adopted in the state of the art [1, 2]. Briefly, the approach consists in the pyrolysis and subsequent treatment of a precursor obtained by coupling suitable carbon species/sacrificial supports with a zeolitic inorganic-organic polymer electrolyte (Z-IOPE). The latter comprises anionic complexes including the Pt “catalyst” and other “co-catalysts”, which are bridged by organic binders [1,2].On one hand, the proposed approach has already shown its potential to yield ECs exhibiting a performance and durability improved with respect to Pt/C benchmark ECs. On the other hand, the proposed approach is extremely flexible, especially with respect to the synthesis of the initial EC precursor. In principle, it is possible to modulate a number of crucial features of such EC precursor, with a particular reference to: (i) the chemical composition (e.g., in terms of Pt, other “co-catalysts” and N; the latter plays a crucial role to stabilize the active sites into “coordination nests” on the EC surface, raising durability); and (ii) the morphology, that can be “templated” on suitable species (e.g., carbon species, sacrificial supports). The very flexibility of the proposed synthetic process needs to be leveraged appropriately to maximize the performance of the final ORR ECs, at the same time minimizing the efforts wasted on approaches with a low development potential.Herein it is elucidated how the modulation in the parameters involved in the synthesis of the EC precursor (e.g., the binder and the approaches to couple the Z-IOPE with the support) impact the physicochemical and electrochemical properties of the final ECs, with a particular reference to the chemical composition, morphology and distribution of the ORR active sites. An extensive characterization of the final ECs is carried out. Inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and microanalysis are adopted to determine the bulk chemical composition. Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is used to elucidate the surface chemical composition and the chemical states of the surface elements. Ultra-high resolution scanning electron microscopy (UHR-SEM) and transmission electron microscopy (TEM) allow for the elucidation of EC morphology. The porosimetric features are probed by automatic gas adsorption instrumentations. Wide-angle X-ray diffraction (WAXD) is crucial to resolve the crystal structure. Cyclic voltammetry with the rotating ring-disk electrode method (CV-TF-RRDE) is used to clarify the “ex-situ” electrochemical performance and ORR reaction mechanism. Finally, the most promising ECs are used in the fabrication of single PEMFCs, that are tested as a function of the operating conditions.It is revealed that, in comparison with the Pt/C benchamark, some ECs are characterized by a much higher intrinsic kinetic performance due to the electronic and bifunctional effects bestowed by the carbon nitride support and the «co-catalysts». Finally, the binder has a marked effect on the stoichiometry, size, and distribution of the PtMx aggregates bearing the active sites.

Pathways of Water-Induced Lead-Halide Perovskite Surface Degradation: Insights from In Situ Atomic-Scale Analysis.

While organic-inorganic hybrid perovskites are emerging as promising materials for next-generation photovoltaic applications, the origins and pathways of perovskite instability remain speculative. In particular, the degradation of perovskite surfaces by ambient water is a crucial subject for determining the long-term viability of perovskite-based solar cells. Here, we conducted surface characterization and atomic-scale analysis of the reaction mechanisms for methylammonium lead bromide (MA(CH3NH3)PbBr3) single crystals using ambient-pressure atomic force microscopy (AP-AFM) and near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) in environments ranging from ultrahigh vacuum to 0.01 mbar of water vapor. MAPbBr3 single crystals, grown by a solution process, were mechanically cleaved under UHV conditions to obtain an atomically clean surface. Consecutive topography and friction force measurements in low-pressure water (pwater ≈ 10-5 mbar) revealed the formation of degraded patches, one atomic layer deep, gradually increasing their coverage until the surface was entirely covered at a water exposure of 4.7 × 104 langmuir (L). At the perimeters of these degraded patches, a higher friction coefficient was observed, along with an interstitial step height, which we attribute to a structure equivalent to that of the MA-Br terminated surface. Combined with NAP-XPS analysis, our results demonstrate that water vapor induces the dissociation of surface methylammonium ligands, eventually resulting in the depletion of the surface MA and the full coverage of hydrocarbon species after exposure to 0.01 mbar of water vapor.

Surface-Phosphorylated Ceria for Chlorine-Tolerance Catalysis.

An improved fundamental understanding of active site structures can unlock opportunities for catalysis from conceptual design to industrial practice. Herein, we present the computational discovery and experimental demonstration of a highly active surface-phosphorylated ceria catalyst that exhibits robust chlorine tolerance for catalysis. Ab initio molecular dynamics (AIMD) calculations and in situ near-ambient pressure X-ray photoelectron spectroscopy (in situ NAP-XPS) identified a predominantly HPO4 active structure on CeO2(110) and CeO2(111) facets at room temperature. Importantly, further elevating the temperature led to a unique hydrogen (H) atom hopping between coordinatively unsaturated oxygen and the adjacent P═O group of HPO4. Such a mobile H on the catalyst surface can effectively quench the chlorine radicals (Cl•) via an orientated reaction analogous to hydrogen atom transfer (HAT), enabling the surface-phosphorylated CeO2-supported monolithic catalyst to exhibit both expected activity and stability for over 68 days during a pilot test, catalyzing the destruction of a complex chlorinated volatile organic compound industrial off-gas.

Revealing the effect of metal-support interactions at the Ni/In2O3(111) interface on the selective CO2 hydrogenation

In2O3-supported Ni catalysts exhibit remarkable catalytic activity and selectivity in CO2 hydrogenation to methanol, but the underlying mechanisms and metal-oxide interactions during the reaction remain elusive. Herein, we investigate the Ni-In2O3 interaction by physical vapor deposition of Ni onto well-defined In2O3(111) thin films. In-situ near ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) was employed to probe the CO2 hydrogenation processes on these Ni/In2O3(111) model systems. Our results reveal that the small Ni clusters supported on the In2O3(111) surface at low Ni coverages exhibit cationic states. The chemical bonding and associated electron transfer at the Ni/In2O3(111) interface play crucial roles in the activation of H2 and CO2. Importantly, reaction intermediates (CO3*, OH, and HCOO*) are readily formed and desorbed under CO2 hydrogenation conditions. Our study highlights the significance of metal-support interactions on the selectivity of CO2 hydrogenation. These findings provide valuable insights into the rational design of advanced In2O3-based catalysts for CO2 hydrogenation.

Electrocatalytic Enhancement of CO Methanation at the Metal–Electrolyte Interface Studied Using In Situ X-ray Photoelectron Spectroscopy

For the direct reduction of CO2 and H2O in solid oxide electrolysis cells (SOECs) with cermet electrodes toward methane, a fundamental understanding of the role of elemental carbon as a key intermediate within the reaction pathway is of eminent interest. The present synchrotron-based in situ near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) study shows that alloying of Ni/yttria-stabilized-zirconia (YSZ) cermet electrodes with Cu can be used to control the electrochemical accumulation of interfacial carbon and to optimize its reactivity toward CO2. In the presence of syngas, sufficiently high cathodic potentials induce excess methane on the studied Ni/yttria-stabilized-zirconia (YSZ)-, NiCu/YSZ- and Pt/gadolinium-doped-ceria (GDC) cermet systems. The hydrogenation of carbon, resulting from CO activation at the triple-phase boundary of Pt/GDC, is most efficient.