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Electroreduction of CO2 to value‐added products is a promising strategy for CO2 reuse, where copper has a unique ability to produce oxygenates and C2+ products. Unfortunately, the electronic factors making copper so unique are unknown, which limits the ability to design improved catalysts. By combining in situ surface‐sensitive X‐ray resonant photoelectron spectroscopy with density functional theory calculations, the complex electronic structure of copper is uncovered during the electrocatalytic reduction of CO2. It is found that the pseudocapacitive charging of copper, produced by the incorporation of protons and electrons into the subsurface, facilitates the activation of CO2, while simultaneously increasing the barrier for H‐H coupling. The net result is that cathodic pseudocapacitive charge suppresses the hydrogen evolution reaction and promotes the production of hydrocarbons and oxygenated products on copper. These results represent a new paradigm in the understanding of CO2 reduction, highlighting the key role of pseudocapacitive charge in the reaction. [ABSTRACT FROM AUTHOR]

Transition‐metal nitrogen‐doped carbons (TM‐N‐C) are emerging as a highly promising catalyst class for several important electrocatalytic processes, including the electrocatalytic CO2 reduction reaction (CO2RR). The unique local environment around the singly dispersed metal site in TM‐N‐C catalysts is likely to be responsible for their catalytic properties, which differ significantly from those of bulk or nanostructured catalysts. However, the identification of the actual working structure of the main active units in TM‐N‐C remains a challenging task due to the fluctional, dynamic nature of these catalysts, and scarcity of experimental techniques that could probe the structure of these materials under realistic working conditions. This issue is addressed in this work and the local atomistic and electronic structure of the metal site in a Co–N–C catalyst for CO2RR is investigated by employing time‐resolved operando X‐ray absorption spectroscopy (XAS) combined with advanced data analysis techniques. This multi‐step approach, based on principal component analysis, spectral decomposition and supervised machine learning methods, allows the contributions of several co‐existing species in the working Co–N–C catalysts to be decoupled, and their XAS spectra deciphered, paving the way for understanding the CO2RR mechanisms in the Co–N–C catalysts, and further optimization of this class of electrocatalytic systems. [ABSTRACT FROM AUTHOR]

A special membrane electrode assembly to measure operando X‐ray absorption spectra and resonant photoemission spectra of mesoporous templated iridium oxide films is used. These films are calcined to different temperatures to mediate the catalyst activity. By combining operando resonant photoemission measurements of different films with ab initio simulations these are able to unambiguously distinguish µ2‐O (bridging oxygen) and µ1‐O (terminal oxygen) in the near‐surface regions of the catalysts. The intrinsic activity of iridium oxide scales with the formation of µ1‐O (terminal oxygen) is found. Importantly, it is shown that the peroxo species do not accumulate under reaction conditions. Rather, the formation of µ1‐O species, which are active in O−O bond formation during the OER, is the most oxidized oxygen species observed, which is consistent with an O−O rate‐limiting step. Thus, the oxygen species taking part in the electrochemical oxidation of water on iridium electrodes are more involved and complex than previously stated. This result highlights the importance of employing theory together with true and complementary operando measurements capable of probing different aspects of catalysts surfaces during operation. [ABSTRACT FROM AUTHOR]

Detailed knowledge about the relationship between the electronic structure and the catalytic properties of a material is a fundamental brick to rationally design better oxygen evolution reaction (OER) catalysts. Here, resonant photoelectron spectroscopy (RPES) is used to elucidate the electronic structure and active state of the most broadly employed OER catalyst, Ni–Fe (oxy)hydroxides. We implemented a graphene-capped catalyst-coated ionomer membrane approach. Starting from a well-characterized iron nickel oxide precursor, the changes in the electronic structure of oxygen and nickel species with different applied electrode potentials were studied. In particular, RPES measurements helped to distinguish between formal Ni3+ and Ni4+ species emerging upon catalyst oxidation, which indicate charge accumulation in adjacent hole states. Based on RPES, the core-level binding energy and partial electron yield absorption spectroscopy (PEY-XAS), we identify the contributions to the oxygen partial density of states (p-DOS) that are crucial for OER catalysis. Our results reveal the occurrence of metal–oxygen hybridized holes, which we can correlate to the Fermi-level at oxidizing potentials. These states potentially promote the active sites as indirect electron acceptors. The nature of this metal–oxygen charge redistribution influencing catalytically active surface-structure motifs is crucial for the formation of OER intermediates. Our findings allow the role of metal and oxygen species in the OER mechanism from the viewpoint of electronic structure to be revisited. [ABSTRACT FROM AUTHOR]

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N‐Heterocyclic carbenes (NHCs) have superior properties as building blocks of self‐assembled monolayers (SAMs). Understanding the influence of the substrate in the molecular arrangement is a fundamental step before employing these ligands in technological applications. Herein, we study the molecular arrangement of a model NHC on Cu(100) and Cu(111). While mostly disordered phases appear on Cu(100), on Cu(111) well‐defined structures are formed, evolving from magic‐number islands to molecular ribbons with coverage. This work presents the first example of magic‐number islands formed by NHC assemblies on flat surfaces. Diffusion and commensurability are key factors explaining the observed arrangements. These results shed light on the molecule‐substrate interaction and open the possibility of tuning nanopatterned structures based on NHC assemblies. [ABSTRACT FROM AUTHOR]

Single‐atom (SA) catalysis presently receives much attention with its promise to decrease the cost of the active material while increasing the catalyst's performance. However, key details such as the exact location of SA species and their stability are often unclear due to a lack of atomic level information. Here, we show how vibrational spectra measured with surface action spectroscopy (SAS) and density functional theory (DFT) simulations can differentiate between different adatom binding sites and determine the location of Ni and Au single atoms on Fe3O4(001). We reveal that Ni and Au adatoms selectively bind to surface oxygen ions which are octahedrally coordinated to Fe ions. In addition, we find that the Ni adatoms can activate O2 to superoxide in contrast to the bare surface and Ni in subsurface positions. Overall, we unveil the advantages of combining SAS and DFT for improving the understanding of single‐atom catalysts. [ABSTRACT FROM AUTHOR]

Atomically dispersed precious metals on oxide supports have recently become increasingly interesting catalytic materials. Nonetheless, their non‐trivial preparation and limited thermal and environmental stability constitutes an issue for their potential applications. Here we demonstrate that an oxygen plasma pre‐treatment of the ceria (CeO2) surface serves to anchor Pt single atoms, making them active and resistant towards sintering in the CO oxidation reaction. Through a combination of experimental results obtained on well‐defined CeO2 films and theory, we show that the O2 plasma causes surface nanostructuring and the formation of surface peroxo (O22−) species, favoring the uniform and dense distribution of isolated strongly bonded Pt2+ atoms. The promotional effect of the plasma treatment was further demonstrated on powder Pt/CeO2 catalysts. We believe that plasma functionalization can be applied to other metal/oxide systems to achieve tunable and stable catalysts with a high density of active sites. [ABSTRACT FROM AUTHOR]

Sub 10 nm cobalt ferrite CoxFe3−xO4 (x ≤ 1.75) nanoparticles and cobalt-rich wüstite (Cox/3Fe(1−x)/3)O nanoparticles (x ≥ 2) were synthesized in a solvothermal approach and characterized by powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), transmission electron microscopy (TEM) as well as energy dispersive X-ray spectroscopy (EDX), IR, Raman, and 57Fe-Mössbauer spectroscopy. Their electrocatalytic activity in the oxygen evolution reaction (OER) was evaluated and the active state formation was tracked by operando X-ray absorption spectroscopy (XAS). Our studies demonstrate that the cobalt-rich wüstite (Cox/3Fe(1−x)/3)O nanoparticles underwent a phase-transformation into the spinels CoxFe3−xO4 (x ≥ 2) under the applied OER conditions. The overpotential η10 at 10 mA cm−2, serving as a benchmark for the OER activity of the cobalt ferrite nanoparticles in alkaline media, was lower than that of magnetite Fe3O4 even with low cobalt concentrations, reaching a minimum of 350 mV for Co2.25Fe0.75O4 with a Tafel slope of 50 mV dec−1. Finally, we identified that the catalytic activity is linked to the nanoparticle size as well as to the degree of Co redox activity and change in coordination during OER. [ABSTRACT FROM AUTHOR]