This work experimentally identifies the charge-transfer energy as a key factor governing the catalytic oxygen evolution reaction (OER) activity and mechanism across a wide range of perovskite chemistries.

Precise control of elemental configurations within multimetallic nanoparticles (NPs) could enable access to functional nanomaterials with significant performance benefits. This can be achieved down to the atomic level by the disorder-to-order transformation of individual NPs. Here, by systematically controlling the ordering degree, we show that the atomic ordering transformation, applied to AuCu NPs, activates them to perform as selective electrocatalysts for CO reduction. In contrast to the disordered alloy NP, which is catalytically active for hydrogen evolution, ordered AuCu NPs selectively converted CO to CO at faradaic efficiency reaching 80%. CO formation could be achieved with a reduction in overpotential of ∼200 mV, and catalytic turnover was enhanced by 3.2-fold. In comparison to those obtained with a pure gold catalyst, mass activities could be improved as well. Atomic-level structural investigations revealed three atomic gold layers over the intermetallic core to be sufficient for enhanced catalytic behavior, which is further supported by DFT analysis.

The water-gas shift (WGS) reaction (where carbon monoxide plus water yields dihydrogen and carbon dioxide) is an essential process for hydrogen generation and carbon monoxide removal in various energy-related chemical operations. This equilibrium-limited reaction is favored at a low working temperature. Potential application in fuel cells also requires a WGS catalyst to be highly active, stable, and energy-efficient and to match the working temperature of on-site hydrogen generation and consumption units. We synthesized layered gold (Au) clusters on a molybdenum carbide (α-MoC) substrate to create an interfacial catalyst system for the ultralow-temperature WGS reaction. Water was activated over α-MoC at 303 kelvin, whereas carbon monoxide adsorbed on adjacent Au sites was apt to react with surface hydroxyl groups formed from water splitting, leading to a high WGS activity at low temperatures.

Dense LLZO (Al-substituted Li7La3Zr2O12) pellets were processed in controlled atmospheres to investigate the relationships between the surface chemistry and interfacial behavior in lithium cells. Laser induced breakdown spectroscopy (LIBS), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, synchrotron X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption spectroscopy (XAS) studies revealed that Li2CO3 was formed on the surface when LLZO pellets were exposed to air. The distribution and thickness of the Li2CO3 layer were estimated by a combination of bulk and surface sensitive techniques with various probing depths. First-principles thermodynamic calculations confirmed that LLZO has an energetic preference to form Li2CO3 in air. Exposure to air and the subsequent formation of Li2CO3 at the LLZO surface is the source of the high interfacial impedances observed in cells with lithium electrodes. Surface polishing can effectively remove Li2CO3 and dramatically improve the interfacial properties. Polished samples in lithium cells had an area specific resistance (ASR) of only 109 Ω cm(2) for the LLZO/Li interface, the lowest reported value for Al-substituted LLZO. Galvanostatic cycling results obtained from lithium symmetrical cells also suggest that the quality of the LLZO/lithium interface has a significant impact on the device lifetime.

Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties for the carbon dioxide reduction reaction (CO 2 RR). Using in situ Ambient Pressure Xray Photoelectron Spectroscopy (APXPS) and quasi in situ Electron Energy Loss Spectroscopy (EELS) in a Transmission Electron Microscope (TEM), we show that there is a substantial amount of residual oxygen in nanostructured, oxide-derived copper electrocatalysts, but no residual copper oxide. Based on these findings in combination with Density Functional Theory (DFT) simulations, we propose that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy. If such sites are stable under the strongly reducing conditions found in CO 2 RR, these findings would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multi-carbon compounds such as ethylene.

A national priority is to convert CO 2 into high-value chemical products such as liquid fuels. Because current electrocatalysts are not adequate, we aim to discover new catalysts by obtaining a detailed understanding of the initial steps of CO 2 electroreduction on copper surfaces, the best current catalysts. Using ambient pressure X-ray photoelectron spectroscopy interpreted with quantum mechanical prediction of the structures and free energies, we show that the presence of a thin suboxide structure below the copper surface is essential to bind the CO 2 in the physisorbed configuration at 298 K, and we show that this suboxide is essential for converting to the chemisorbed CO 2 in the presence of water as the first step toward CO 2 reduction products such as formate and CO. This optimum suboxide leads to both neutral and charged Cu surface sites, providing fresh insights into how to design improved carbon dioxide reduction catalysts. T he discovery of new electrocatalysts that can efficiently convert carbon dioxide (CO2) into liquid fuels and feedstock chemicals would provide a clear path to creating a sustainable hydrocarbon-based energy cycle (1). However, because CO2 is highly inert, the CO2 reduction reaction (CO2RR) is quite unfavorable thermodynamically. This makes identification of a suitable and scalable catalyst an important challenge for sustainable production of hydrocarbons. We consider that discovering such a catalyst will require the development of a complete atomistic understanding of the adsorption and activation mechanisms involved. Here the first step is to promote initiation of reaction steps.Copper (Cu) is the most promising CO2RR candidate among pure metals, with the unique ability to catalyze formation of valuable hydrocarbons (e.g., methane, ethylene, and ethanol) (2). However, Cu also produces hydrogen, requires too high an overpotential (>1 V) to reduce CO2, and is not selective for desirable hydrocarbon and alcohol CO2RR products (2). Despite numerous experimental and theoretical studies, there remain considerable uncertainties in understanding the role of Cu surface structure and chemistry on the initial steps of CO2RR activity and selectivity (3, 4). To reduce CO2 to valuable hydrocarbons, a source of protons is needed in the same reaction environment (2), with water (H2O) the favorite choice. Thus, H2O is often the solvent for CO2RR, representing a sustainable pathway toward solar energy storage (1). However, we lack a comprehensive understanding of how CO2 and H2O molecules adsorb on the Cu surface and interact to first dissociate the CO2 (5, 6). An overview of the various surface reactions of CO2 on Cu(111) is reported in Fig. 1, illustrating the transient carbon-based intermediate species that may initiate reactions.Previous studies using electron-based spectroscopies observed physisorption of gas-phase g-CO2 at 75 K, whereas a chemisorbed form of CO2 was stabilized by a partial negative charge induced by electron capture (CO δ− 2 ) (Fig. 1A) (7, 8). The same experiments showed th...

We report a new method to probe the solid-liquid interface through the use of a thin liquid layer on a solid surface. An ambient pressure XPS (AP-XPS) endstation that is capable of detecting high kinetic energy photoelectrons (7 keV) at a pressure up to 110 Torr has been constructed and commissioned. Additionally, we have deployed a “dip & pull” method to create a stable nanometers-thick aqueous electrolyte on platinum working electrode surface. Combining the newly constructed AP-XPS system, “dip & pull” approach, with a “tender” X-ray synchrotron source (2 keV–7 keV), we are able to access the interface between liquid and solid dense phases with photoelectrons and directly probe important phenomena occurring at the narrow solid-liquid interface region in an electrochemical system. Using this approach, we have performed electrochemical oxidation of the Pt electrode at an oxygen evolution reaction (OER) potential. Under this potential, we observe the formation of both Pt2+ and Pt4+ interfacial species on the Pt working electrode in situ. We believe this thin-film approach and the use of “tender” AP-XPS highlighted in this study is an innovative new approach to probe this key solid-liquid interface region of electrochemistry.

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