The question of whether the metal chalcogenides (phosphides) that have been acknowledged to be efficient materials for bifunctional electrocatalysts really perform as the active species or just “pre-catalysts” has been debated. Herein, a series of operando measurements, including in situ X-ray absorption spectroscopy, liquid-phase transmission electron microscopy, and in situ Raman spectroscopy, were conducted to unravel in real time the structural and chemical stability of P-substituted CoSe2 electrocatalysts under both hydrogen and oxygen evolution reactions (HER and OER, respectively) in an alkaline electrolyte. It can be conclusively revealed that, in an alkaline electrolyte, the P-substituted CoSe2 electrocatalyst was acting as the “pre-catalyst” rather than the real reactive species. The introduction of phosphorus is speculated to generate more vacancies or defects around Co cations in the initial CoSe2 and considerably facilitates the structural transformation into the “real reactive species”, such as metallic cobalt (for HER) and cobalt oxyhydroxide (for OER).

Understanding the dynamic structural reconstruction/transformation of catalysts during electrochemical CO2 reduction reaction (CO2RR) is highly desired for developing more efficient and selective catalysts, yet still lacks in-depth realization. Herein, we study a model system of copper nanowires with various degrees of silver modifications as electrocatalysts for CO2RR. Among them, the Cu68Ag32 nanowire catalyst achieves the highest activity and selectivity toward methane with an extremely high faradaic efficiency of ∼60%, about 3 times higher than that of primitive Cu nanowires, and even surpasses the most efficient catalysts for producing methane. By using in situ grazing-angle X-ray scattering/diffraction, X-ray absorption spectroscopy, and Raman techniques, we found that the Cu68Ag32 nanowires underwent an irreversible structural reconstruction and well-stabilized chemical state of Cu on the catalyst surface under the working CO2RR conditions, which greatly facilitates the CO2 to methane conversion. Further analysis reveals that the restructuring phenomenon can be ascribed to a reoxidation/reduction-driven atomic interdiffusion between Cu and Ag. This work reveals the first empirical demonstration by deploying comprehensive in situ techniques to track the dynamic structural reconstruction/transformation in a model bimetallic system, which not only establishes a good understanding of the correlation between catalyst surface structure and catalytic selectivity but also provides deep insights into designing more developed electrocatalysts for CO2RR and beyond.

to develop OER electrocatalysts with a low overpotential in order to scale down the energy expenditure of water electrolysis.To date, noble metal oxides, such as iridium oxide and ruthenium oxide, are regarded as the benchmarked OER electrocatalysts, [10][11][12][13] but their scarcity and high cost hinder them from the wide utilization. [14] For these reasons, it is of the essence to explore earth-abundant substances showing comparable performance as costly noble-metal electrocatalysts. Recently, earth-abundant transition-metalbased materials exhibited high performance and superb stability toward OER, especially for the cobalt and nickel-based oxides/nonoxides. [15][16][17][18][19][20][21][22] Furthermore, various metal dopants would greatly affect the activities and intrinsic attributes. For example, tungsten, chromium, iron, and zinc-doping have been discovered to improve the activities in contrast to pristine metal oxides owing to the optimization of adsorption energy for surface intermediates or the increment of roughness factor. [23][24][25][26][27][28][29] Interestingly, among these elements, iron can commonly perform significant enhancement in catalytic activities toward oxygen evolution reaction as compared to other elements. [30,31] Boettcher's group proposed that Fe ions granted the catalytic activities while Co ions acted as the conductive oxides to transport the charge carriers in an Fe-Co metal oxide system. [32] Friebel et al. conducted a series of operando experiments and calculations to demonstrate that Fe ions in Ni 1-x Fe x OOH system would alter the adsorption energies of OER intermediates over the electrocatalytic surface and thus reduce the overpotential of OER, whereas the formation of low-activity FeOOH declined the resulting activities in the cases of higher Fe content. [33] Howbeit, the behavior of iron based on the material insight was not elaborated. Toward this end, it is crucial to establish the direct relationship between the material characteristics and the catalytic activities.Recently, we reported that the geometrical sites in spinel cobalt oxide served distinct functions. In the case of Co 3 O 4 , the cobalt ions in octahedral site (Co 3+ (Oh) ) contributed to surface double layer capacitance while those in tetrahedral site (Co 2+ (Td) ) were able to adsorb oxygen ions onto the surface for being the active species. [34,35] It suggested that even for the identical Introduction of iron in various catalytic systems has served a crucial function to significantly enhance the catalytic activity toward oxygen evolution reaction (OER), but the relationship between material properties and catalysis is still elusive. In this study, by regulating the distinctive geometric sites in spinel, Fe occupies the octahedral sites (Fe 3+ (Oh) ) and confines Co to the tetrahedral site (Co 2+ (Td) ), resulting in a strikingly high activity (η j = 10 mA cm −2 = 229 mV and η j = 100 mA cm −2 = 281 mV). Further enrichment of Fe ions would occupy the tetrahedral sites to decline the amount of Co 2+ (Td) a...

Oxide-derived copper catalysts have been shown to enhance CO2 reduction reaction (CO2RR) activity with high selectivity toward hydrocarbon products. However, the chemical state of oxide-derived copper during the CO2RR has remained elusive and is lacking in situ observations. Herein, a two-step process was developed to synthesize Ag nanowires coated with various thicknesses of a CuOx layer for the CO2RR. By employing in situ X-ray absorption spectroscopy, a strong correlation between the chemical state under reaction conditions and the CO2RR product profile can be revealed to validate another competing reaction (i.e., the spontaneous oxidation of Cu(0) in aqueous electrolyte) that significantly governs the chemical state of active centers of Cu. In situ Raman spectroscopy reveals the existence of reoxidation behavior under cathodic potential, and the quantification analysis of reoxidized behavior is revealed to indicate that the reoxidation rate is independent of surface morphology and strongly proportional to the electrochemically surface area. The steady oxidation state of Cu in an in situ condition is the paramount key and dominates the products’ profile of the CO2RR rather than other factors (e.g., crystal facets, atomic arrangements, morphology, elements) that have been investigated in numerous reports.

In the face of climate change and rising energy consumption, the electrochemical oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and electrochemical CO2 reduction reaction (CO2RR) are promising catalytic processes...