Photosensitized Water Oxidation by Use of a Bioinspired Manganese Catalyst

Karlsson, Erik A.; Lee, Bao‐Lin; Åkermark, Torbjörn; Johnston, Eric V.; Kärkäs, Markus D.; Sun, Junliang; Hansson, Örjan; Bäckvall, Jan‐E.; Åkermark, Björn

doi:10.1002/ange.201104355

Cited by 89 publications

(32 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…[18][19][20][21][22] The 2008 report 17 of the electrodeposited CoCat has spurred a wave of investigations on this material class. [18][19][20][21][22] The 2008 report 17 of the electrodeposited CoCat has spurred a wave of investigations on this material class.…”

Section: Introductionmentioning

confidence: 99%

Water oxidation by amorphous cobalt-based oxides: in situ tracking of redox transitions and mode of catalysis

Risch

Ringleb

Kohlhoff

et al. 2015

Energy Environ. Sci.

306

431

View full text Add to dashboard Cite

Water oxidation by amorphous oxides is of high interest in artificial photosynthesis and other routes towards non-fossil fuels, but the mode of catalysis in these materials is insufficiently understood. We tracked mechanistically relevant oxidation-state and structural changes of an amorphous Co-based catalyst film by in-situ experiments combining directly synchrotron-based X-ray absorption spectroscopy (XAS) with electrocatalysis. Unlike a classical solid-state material, the bulk material is found to undergo chemical changes. Two redox transitions at midpoints potentials of about 1.0 V (Co II 0.4Co III 0.6  all-Co III ) and 1.2 V (all-Co III  Co III 0.8Co IV 0.2) vs. NHE at pH 7 are coupled to structural changes. These redox transitions can be induced by variation of either electric potential or pH; they are broader than predicted by a simple Nernstian model, suggesting interacting bridged cobalt ions. Tracking reaction kinetics by UV-Vis-absorption and time-resolved mass spectroscopy reveal that accumulated oxidizing equivalents facilitate dioxygen formation. On these grounds, a new framework model of catalysis in the amorphous, hydrated and volume-active oxide is proposed: Within the oxide film, cobalt ions at the margins of Co-oxo fragments undergo Co II Co III Co IV oxidationstate changes coupled to structural modification and deprotonation of Co-oxo bridges. By encounter of two (or more) Co IV ions, an active site is formed at which the O-O bondformation step can take place. The Tafel slope is determined by both the interaction between cobalt ions (width of the redox transition) and their encounter probability. Our results represent a first step toward development of new concepts that address the solid-molecular Janus nature of the amorphous oxide. Insights and concepts described herein for the Co-based catalyst film may be of general relevance also for other amorphous oxides with water-oxidation activity. EXPERIMENTAL XAS measurements -in-situ experimentCoCat-coated electrodes were prepared by electrodeposition in a separate electrochemical setup before start of the in-situ XAS measurements from a solution of 0.5 mM Co 2+ ions in 0.1 M KPi at pH 7 (deposition of about 50 nmol cm -1 of Co ions, see ESI for further details). The in-situ XAS measurements were performed at the SuperXAS beamline of the Swiss Light Source (SLS) in Villigen, Switzerland. The excitation energy was selected by a double-crystal monochromator (Si-111, detuning to 50 % intensity, scan range of 7650-8400 eV) and used to irradiate the backside of the ITO/PET electrode at an angle of 45°. The spot size of the X-ray beam on the sample was 5 mm × 1 mm. Due to employment of a large spot size (defocussed beam) and a rapid-scanning mode, the influence of radiation-induced modifications was negligible, as verified in control experiments. The cobalt K-edge fluorescence was monitored perpendicular to the incident beam by a scintillation detector (19.6 cm 2 active area, 51BMI/2E1-YAP-Neg, Scionix), which was shielded by a 25 μm iron foil agai...

show abstract

Section: Introductionmentioning

confidence: 99%

Water oxidation by amorphous cobalt-based oxides: in situ tracking of redox transitions and mode of catalysis

Risch

Ringleb

Kohlhoff

et al. 2015

Energy Environ. Sci.

306

431

View full text Add to dashboard Cite

show abstract

“…1 top and an I2M mechanism is found when the favored species resemble those of the oxyl radical form depicted in the lower part of Figure 1 Recently several first row transition metal complexes have been reported as catalysts for the water oxidation reaction. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] While these catalysts are of interest because of their high abundance and low toxicity, their performance is much poorer than their Ru or Ir analogues, and in addition their mechanistic pathways are in most cases basically unknown. [28][29][30][41][42][43] We have very recently reported a new complex based on Cu, containing the amidate ligand OPBAN that can carry out the water oxidation reaction in a very efficient manner.…”

Section: Introductionmentioning

confidence: 99%

Single Electron Transfer Steps in Water Oxidation Catalysis. Redefining the Mechanistic Scenario

et al. 2017

View full text Add to dashboard Cite

show abstract

“…[1][2][3][4][5][6][7][8][9] The bottleneck in artificial photosynthesis is water oxidation (2 H 2 O!O 2 + 4 H + + 4 e À ), which can provide an unlimited source of protons and electrons for the production of solar fuels such as H 2 , CO (CO 2 + 2 H + + 2 e À !CO + H 2 O), or methanol (CO 2 + 6 H + + 6 e À !CH 3 OH + H 2 O). [16,17] So far a number of Co, [18][19][20][21][22][23][24][25] Mn, [26][27][28][29][30] Fe, [31][32][33] and Cu [34][35][36] WOCs have been reported. However, to be economically viable, the catalysts should be made from inexpensive, earth-abundant materials.…”

Section: Introductionmentioning

confidence: 99%

Efficient Chemical and Visible‐Light‐Driven Water Oxidation using Nickel Complexes and Salts as Precatalysts

Chen

et al. 2013

ChemSusChem

View full text Add to dashboard Cite

Chemical and visible-light-driven water oxidation catalyzed by a number of Ni complexes and salts have been investigated at pH 7-9 in borate buffer. For chemical oxidation, [Ru(bpy)3](3+) (bpy = 2,2'-bipyridine) was used as the oxidant, with turnover numbers (TONs) >65 and a maximum turnover frequency (TOFmax) >0.9 s(-1). Notably, simple Ni salts such as Ni(NO3 )2 are more active than Ni complexes that bear multidentate N-donor ligands. The Ni complexes and salts are also active catalysts for visible-light-driven water oxidation that uses [Ru(bpy)3](2+) as the photosensitizer and S2 O8 (2-) as the sacrificial oxidant; a TON>1200 was obtained at pH 8.5 by using Ni(NO3)2 as the catalyst. Dynamic light scattering measurements revealed the formation of nanoparticles in chemical and visible-light-driven water oxidation by the Ni catalysts. These nanoparticles aggregated during water oxidation to form submicron particles that were isolated and shown to be partially reduced β-NiOOH by various techniques, which include SEM, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, XRD, and IR spectroscopy. These results suggest that the Ni complexes and salts act as precatalysts that decompose under oxidative conditions to form an active nickel oxide catalyst. The nature of this active oxide catalyst is discussed.

show abstract

Photosensitized Water Oxidation by Use of a Bioinspired Manganese Catalyst

Cited by 89 publications

References 39 publications

Water oxidation by amorphous cobalt-based oxides: in situ tracking of redox transitions and mode of catalysis

Water oxidation by amorphous cobalt-based oxides: in situ tracking of redox transitions and mode of catalysis

Single Electron Transfer Steps in Water Oxidation Catalysis. Redefining the Mechanistic Scenario

Efficient Chemical and Visible‐Light‐Driven Water Oxidation using Nickel Complexes and Salts as Precatalysts

Contact Info

Product

Resources

About