Carbonate Ions Induce Highly Efficient Electrocatalytic Water Oxidation by Cobalt Oxyhydroxide Nanoparticles

Abstract

Synthetic models of oxygen evolving complex (OEC) are used not only to gain better understanding of the mechanism and the roles of cofactors for water oxidation in photosynthesis, but also as water oxidation catalysts to realize artificial photosynthesis, which is anticipated as a promising solar fuel production system. However, although much attention has been paid to the composition and structure of active sites for development of heterogeneous OEC models, the cofactors, which are essential for water oxidation by the photosynthetic OEC, remain little studied. The high activity of CoO(OH) nanoparticles for electrocatalytic water oxidation is shown to be induced by a CO cofactor. The possibility of CO ions acting as proton acceptors for O-O bond formation based on the proton-concerted oxygen atom transfer mechanism is proposed. The O-O bond formation is supposed to be accelerated due to effective proton acceptance by adjacent CO ions coordinated on the Co center in the intermediate, which is consistent with Michaelis-Menten-type kinetics and the significant H/D isotope effect observed in electrocatalysis.

Facile Templateless Fabrication of a Cobalt Oxyhydroxide Nanosheet Film with Nanoscale Porosity as an Efficient Electrocatalyst for Water Oxidation

“…has attracted much attention due to the leading catalytic performance and facile preparation ,. Recently, oxyhydroxide species such as amorphous CoO(OH), FeO(OH), NiO(OH) and CoFeO(OH) have been also proven as efficient catalysts for water oxidation ,,. In fact, Co−Pi and related catalysts are composed of small fragments/layers of CoO(OH) being responsible for water oxidation catalysis ,.…”

“…The other band (relatively weak) at 532.5 eV is attributed to the oxygen from the adsorbed hydroxyl contamination on the film surface. These XPS spectra in Co 2p and O 1s regions for the CoO(OH)‐NS film those were nearly the same as those for CoO(OH)‐NP film, (Figure S1a and b), ensuring that the chemical state of CoO(OH) is close between the CoO(OH)‐NS and CoO(OH)‐NP films.…”

“…This fabrication technique provides a stable and uniform porous film composed of interlaced CoO(OH) nanosheets and a facile control of Γ cov and thickness of the CoO(OH)‐NS layer deposited on the electrode. The nanostructure and electrocatalytic properties are characterized to demonstrate that the large accessible surface of CoO(OH)‐NS film improves the performance for electrocatalytic water oxidation relative to earlier reported CoO(OH)‐NP electrode ,…”

Promotive Effect of Bicarbonate Ion on Two‐Electron Water Oxidation to Form H2O2 Catalyzed by Aluminum Porphyrins

“…The effect of bicarbonate or carbonate ions in the four‐electron oxidation of water to evolve O 2 has been frequently studied over various oxygen‐evolving catalysts such as Ni complex, Ru‐sensitizer/IrO 2 (colloidal system), CuSO 4 / Na 2 CO 3 system, Cu complex, and CoO(OH)/indium‐doped tin oxide (ITO) electrode . The carbonate cofactor was found to have multiple roles in the water oxidation cycle, such as buffer anion, proton acceptor, non‐innocent anion binding with central metal ion, and so on, in enhancing the catalytic activity of water oxidation catalysts.…”

Modelling the (Essential) Role of Proton Transport by Electrolyte Bases for Electrochemical Water Oxidation at Near-Neutral pH

“…Thus, a high proton-transport capacity of the electrolyte is needed to prevent the formation of a local pH gradient. The choice of the electrolyte can strongly affect the catalytic performances [13] and has been the object of numerous literature studies [14][15][16][17][18][19]. In the Co oxide catalyst of the cobalt-phosphate type described first by Kanan and Nocera [20], we reported that the catalytic activity at high current density is proportional to the availability of unprotonated buffer molecules for a variety of tested buffer electrolytes [15].…”