Catalytic Oxygen Evolution by Cobalt Oxido Thin Films

Abstract

The contemporary demand to generate fuels from solar energy has stimulated intense effort to develop water splitting catalysts that can be coupled to light-absorbing materials. Cobalt oxido catalyst (Co-OECs) films deposited from buffered Co(II) solutions have emerged as arguably the most studied class of heterogeneous oxygen evolution catalysts. The interest in these materials stems from their formation by self-assembly, their self-healing properties, and their promising catalytic activity under a variety of conditions. The structure and function of these catalysts are reviewed here together with studies of molecular Co-O cluster compounds, which have proven invaluable in elucidating the chemistry of the Co-OECs.

Ambient nitrogen reduction cycle using a hybrid inorganic–biological system

“…S2B). As the AEM is not permeable to cations including Co 2+ , its use prevents the redeposition of adventitious Co 2+ onto the CoP i anode via self-healing, as we have previously described (24,26), emphasizing the importance of biocompatibility in our system.…”

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

“…High-resolution transmission electron microscopy of crystalline cobalt oxides in neutral and alkaline solutions reveals that the surface of the oxide is indeed an amorphous overlayer comprising the metalate clusters (15)(16)(17)(18). 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 Observations of Oxygen Evolution Cocatalysts on Photoelectrodes by X-ray Absorption Spectroscopy: Comparison between Cobalt-Phosphate and Cobalt-Borate

“…These data suggest that the Co-P i and Co-B i layers were composed of Co, P, K and O, and Co, B, K and O species, respectively, in good agreement with previous reports. 29,30 Additionally, the film thicknesses of the Co-P i and Co-B i cocatalysts were measured at the interfaces between the bare and Co-cocatalystmodified SrTiO 3 with a CLSM (Fig. 6), and were estimated to be approximately 100 and 220 nm, respectively.…”

“…In the present work, we focused on the differences in the reaction activities of Co-P i and Co-B i cocatalysts on photoelectrodes. In spite of many previous studies, [28][29][30][31][32][33][34][35][36][37][38][39][40][41] during photoelectrochemical reactions, using in situ Co-K edge XAFS, and subsequently discuss the functioning of these OER cocatalysts.…”

“…9,15,[21][22][23][24][25][26][27] Among these, cobalt-phosphate (Co-P i ) and cobalt-borate (Co-B i ) cocatalysts electrodeposited from a dilute Co 2+ solution containing phosphate and borate electrolytes, respectively, are known to generate highly active OER cocatalysts. [28][29][30][31][32][33][34][35][36][37][38][39][40][41] As an example, Nocera et al reported that a Si photoelectrode modified with a Co-P i cocatalyst exhibited high activity, with a solar energy conversion efficiency of 4.7%. 21 Domen et al also discovered that a Co-P i -modified Ba-doped Ta 3 N 5 photoelectrode had an efficiency of 1.5% using single-photon photoanodes system.…”