First turnover analysis of water-oxidation catalyzed by Co-oxide nanoparticles

Abstract

ARTICLE This journal isCo-oxides are promising water oxidation catalysts for artificial photosynthesis devices. Presently, several different proposals exist for how they catalyze O 2 formation from water. Knowledge about this process at molecular detail will be required for their further improvement. Here we present time-resolved 18 O-labelling isotope-ratio membrane-inlet mass spectrometry (MIMS) experiments to study the mechanism of water oxidation in Co/methylenediphosphonate (Co/M2P) oxide nanoparticles using [Ru(bpy) 3 ] 3+ (bpy = 2,2'bipyridine) as chemical oxidant. We show that 16 O-Co/M2P-oxide nanoparticles produce 16 O 2 during their first turnover after simultaneous addition of H 2 18 O and [Ru(bpy) 3 ] 3+ , while sequential addition with a delay of 3 s yields oxygen reflecting bulk water 18 O-enrichment. This result is interpreted to show that the O-O bond formation in Co/M2P-oxide nanoparticles occurs via intramolecular oxygen coupling between two terminal Co-OH n ligands that are readily exchangeable with bulk water in the resting state of the catalyst. Importantly, our data allow the determination of the number of catalytic sites within this amorphous nanoparti cular material, to calculate the TOF per catalytic site and to derive the number of holes needed for the production of the first O 2 molecule per catalytic site. We propose that the mechanism of O-O bond formation during bulk catalysis in amorphous Co-oxides may differ from that taking place at the surface of crystalline materials.

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

“…Such exchange coupling provides a mechanism for charge localization within cubanes, as shown here, and by analogy within the metalate clusters of Co-OEC. Isotope labeling studies of oxidic cobalt OER catalysts (23,24) and computational mechanistic studies of Co-OECs (42,43), together with model studies of dicobalt complexes (23), indicate that O-O bond formation requires an adjacent Co(IV) 2 active edge site; it is necessary that two Co(IV) centers localize to the edge site of a cobaltate cluster preceding turnover, as opposed to hole equivalents delocalized over the cluster active site. As we show here, antiferromagnetic coupling provides a mechanism to drive hole localization within the cluster core.…”

“…Electrochemical kinetics (19) and spectroscopic measurements (20,21) support a mechanism consisting of a minor equilibrium proton-coupled electron transfer process to generate effectively a Co(III)Co(IV) precatalyst, followed by a subsequent oxidation to generate a doubly oxidized state that drives the turnover-limiting O-O bond-forming step (22). Isotope labeling studies of active oxidic cobalt OER catalysts (23,24) establish direct coupling of oxygens on neighboring sites, thus identifying one path for O-O bond formation from a Co(IV) 2 state,…”

In situ/Operando studies of electrocatalysts using hard X-ray spectroscopy

“…Regarding mechanistic implications for amorphous Co oxides, the membrane-inlet mass spectroscopy (MIMS) experiments by Messinger’s group provided interesting insights of where the O—O bond formation occurs [25]. By following the time-resolved 18 O-labelling isotope-ratio with MIMS, they concluded that the O—O bond formation of the amorphous Co-oxide nanoparticles (Co/methylenediphosphonate (Co/M2P)-oxide) occurs via intermolecular oxygen-coupling between two terminal Co-OH x ligands, without the involvement of bridging oxygens.…”

Self‐Destruction of Cancer Induced by Ag2S Amorphous Nanodots

“…Currently, although amorphous bulk materials, such as rubber, glass, plastics, and asphalt have been exalted for many years, the in‐depth understanding of physicochemical properties and biological activities of amorphous nanomaterials (ANMs) is still critically lack because of the difficulties in preparation derived from their intrinsic metastable state . Recently, a few studies reported the extraordinary performances of ANMs, which were significantly superior to crystalline nanomaterials, such as catalytic capability and remarkable surface enhanced Raman scattering activity, which aroused great research interest in ANMs.…”

“…Currently, although amorphous bulk materials, such as rubber, glass, plastics, and asphalt have been exalted for many years, [1][2][3] the in-depth understanding of physicochemical properties and Studies on distinctive performances and novel applications of amorphous inorganic nanomaterials are becoming attractive. Herein, Ag 2 S amorphous and crystalline nanodots (ANDs and CNDs) are prepared via facile methods.…”