Time-resolved observations of water oxidation intermediates on a cobalt oxide nanoparticle catalyst

Abstract

In any artificial photosynthetic system, the oxidation of water to molecular oxygen provides the electrons needed for the reduction of protons or carbon dioxide to a fuel. Understanding how this four-electron reaction works in detail is important for the development of improved robust catalysts made of Earth-abundant materials, like first-row transition-metal oxides. Here, using time-resolved Fourier-transform infrared spectroscopy and under reaction conditions, we identify intermediates of water oxidation catalysed by an abundant metal-oxide catalyst, cobalt oxide (Co3O4). One intermediate is a surface superoxide (three-electron oxidation intermediate absorbing at 1,013 cm(-1)), whereas a second observed intermediate is attributed to an oxo Co(IV) site (one-electron oxidation intermediate absorbing at 840 cm(-1)). The temporal behaviour of the intermediates reveals that they belong to different catalytic sites. Knowledge of the structure and kinetics of surface intermediates will enable the design of improved metal-oxide materials for more efficient water oxidation catalysis.

In situ characterization of cofacial Co(IV) centers in Co 4 O 4 cubane: Modeling the high-valent active site in oxygen-evolving catalysts

“…In this regard, insights into the details of the OER mechanism in Co-OECs have been greatly aided by molecular model complexes. Complementary electrochemical studies of binuclear cobalt complexes and Co-OECs are consistent with the contention that OER occurs at a dicobalt edge site (23,(25)(26)(27). As illustrated in Fig.…”

Bio‐Inspired Leaf‐Mimicking Nanosheet/Nanotube Heterostructure as a Highly Efficient Oxygen Evolution Catalyst

“…Furthermore, the calculated work function ( W f ) of the Co 2+ O h structure is 0.46 eV smaller than that of Co 2+ T d structure, further indicating the higher capability of losing electrons from the O h structure than the T d structure. As the molecular mechanisms of water oxidation at Co sites involve reaction cycles among Co 2+ , Co 3+ , and Co 4+ oxidation sites,5, 16 the Co 2+ O h structure with a smaller energy barrier can significantly facilitate the electron transfer process for water oxidation reaction. Our XAS experimental results have shown the existence of Co 2+ O h , which are different from most of the previous reported OER catalysts with Co 2+ T d structures,37 thus providing an optimized electronic structure at the atomic scale for OER catalysis.…”

“…One of the most critical steps of water splitting is the oxygen evolution reaction (OER), 4 OH − + energy → O 2 + 2 H 2 O + 4 e − , which is a multistep four‐electron process and thus kinetically sluggish 5. Iridium and ruthenium oxides (IrO x , RuO x ) are regarded as pioneering OER catalysts with high efficiencies,6 while their prospect of large‐scale application is overwhelmed by their scarcity and the associated high cost.…”

Viewing the Valence Electronic Structure of Ferric and Ferrous Hexacyanide in Solution from the Fe and Cyanide Perspectives

“…The ferrocyanide anion, [Fe(CN)6] 4-, contains Fe 2+ with a nominally 3d 6 configuration, whereas the ferricyanide anion, [Fe(CN)6] 3-, contains Fe 3+ with a nominally 3d 5 configuration. Both complexes can be well described as having an octahedral Oh molecular structure (with a small Jahn-Teller distortion in ferricyanide).…”

“…In these systems the functionality is often governed by local changes of coordination, bonding, charge and spin state of the transition metal atom. [1][2][3][4][5][6] Particularly well suited for probing these local properties are X-ray spectroscopic methods due to their intrinsic sensitivity to the electronic structure in a local and element-specific manner. 7 Therefore, owning to the significant advance of related experimental technologies in recent years, X-ray spectroscopy techniques are becoming increasingly popular in the research of functional transition metal systems.…”