Probing the Crystal and Electronic Structures of Molybdenum Oxide in Redox Process: Implications for Energy Applications

Abstract

Knowledge regarding the phase and valence state evolution of molybdenum (Mo) and its oxides during the redox reaction is essential for advancing their energy applications (e.g., electrocatalysis), which unfortunately remains largely unexplored. Herein, the effects of atomic and electronic structures on the electrocatalytic performance of Mo/oxides core−shell structures are investigated on the basis of the combination of ex situ and in situ experiments. First, a two-step reaction pathway is revealed during the oxidation of nanoscale Mo: the formation of amorphous MoO 3 (A-MoO 3 ) shells followed by the nucleation of crystalline α-MoO 3 . It is shown that the electrocatalytic performance of A-MoO 3 is superior to that of α-MoO 3 , mainly due to more catalytically active sites in the former material. Furthermore, in situ transmission electron microscopy observations show that the A-MoO 3 shell can be rapidly reduced into metallic MoO 2 under reductive environment, which is likely to occur during the hydrogen evolution reaction measurement. Our in-depth characterization may contribute to the thorough and comprehensive understanding of the structural transition in Mo and its oxides during oxidative and reductive environments and thus serves as a reference for understanding the structure−property interplay for real energy applications.

Nanoporous Mo-Doped NiFe Oxide Nanowires from Eutectic Dealloying as an Active Electrocatalyst for the Alkaline Oxygen Evolution Reaction

“…Similar results were found in the NiFe 2 Mo 0.05 O 4 samples (Figure S6). In the Mo 3d core-level spectrum (Figure c), the peak position near 232.2 and 235.2 eV could be ascribed to Mo 3d 5/2 and 3d 3/2 , respectively, of Mo 4+ and that at 233.5 and 236.0 eV to Mo 3d 5/2 and 3d 3/2 of Mo 6+ , respectively. ,, The high-valence state of Mo was most likely caused by the oxidation of metastable Mo during the dealloying process. The Al 2p and Ni 3p peaks overlap in the spectra of Figure S7a, with the peak at around 74 eV attributable to Al 2p in the oxidized state and the peaks at around 68 and 70 eV attributable to Ni 3p.…”

α-MoO3 Micro- and Nanoparticles as Catalysts for Biofuel Production

“…Despite different studies describing the catalytic behavior of MoO 3 , especially for biodiesel production, few works focus on the structure−catalytic property relationship involved in MoO 3 . Peng et al 25 correlated the structural transition and the evolution of the Mo n+ valence state with the electrocatalytic performance of α-MoO 3 and MoO 2 oxides when the materials were subjected to oxidative and/or reductive environments. The structure−catalytic activity relationship of molybdenum-based materials has also been studied by Di ́az-Garci ́a et al 26 in palmitic acid hydrodeoxygenation tests.…”

“…The presence of catalytically active acid sites, ,,, structural phase transition, and the ability to form different intrinsic defects such as oxygen vacancies (V O ) and reduced Mo species (Mo 5+ and Mo 4+ ) are considered important for the understanding, design, and development of new potentially active catalytic materials. , In addition to the presence of ionic defects, knowledge about the crystal structure, especially the crystal orientation, is a fundamental key to understanding the reactivity of the heterogeneous MoO 3 catalyst. Despite different studies describing the catalytic behavior of MoO 3 , especially for biodiesel production, few works focus on the structure–catalytic property relationship involved in MoO 3 .…”