Light-Driven Water Oxidation with Ligand-Engineered Prussian Blue Analogues

Abstract

The elucidation of the ideal coordination environment of a catalytic site has been at the heart of catalytic applications. Herein, we show that the water oxidation activities of catalytic cobalt sites in a Prussian blue (PB) structure could be tuned systematically by decorating its coordination sphere with a combination of cyanide and bidentate pyridyl groups. K 0.1 [Co(bpy)] 2.9 [Fe(CN) 6 ] 2 ( [Cobpy–Fe] ), K 0.2 [Co(phen)] 2.8 [Fe(CN) 6 ] 2 ( [Cophen–Fe] ), {[Co(bpy) 2 ] 3 [Fe(CN) 6 ] 2 }[Fe(CN) 6 ] 1/3 ( [Cobpy2–Fe] ), and {[Co(phen) 2 ] 3 [Fe(CN) 6 ] 2 }[Fe(CN) 6 ] 1/3 Cl 0.11 ( [Cophen2–Fe] ) were prepared by introducing bidentate pyridyl groups (phen: 1,10-phenanthroline, bpy: 2,2′-bipyridine) to the common synthetic protocol of Co–Fe Prussian blue analogues. Characterization studies indicate that [Cobpy2–Fe] and [Cophen2–Fe] adopt a pentanuclear molecular structure, while [Cobpy–Fe] and [Cophen–Fe] could be described as cyanide-based coordination polymers with lower-dimensionality and less crystalline nature compared to the regular Co–Fe Prussian blue analogue (PBA), K 0.1 Co 2.9 [Fe(CN) 6 ] 2 ( [Co–Fe] ). Photocatalytic studies reveal that the activities of [Cobpy–Fe] and [Cophen–Fe] are significantly enhanced compared to those of [Co–Fe] , while molecular [Cobpy2–Fe] and [Cophen2–Fe] are inactive toward water oxidation. [Cobpy–Fe] and [Cophen–Fe] exhibit upper-bound turnover frequencies (TOFs) of 1.3 and 0.7 s –1 , respectively, which are ∼50 times higher than that of [Co–Fe] (1.8 × 10 –2 s –1 ). The complete inactivity of [Cobpy2–Fe] and [Cophen2–Fe] confirms the critical role of aqua coordination to the catalytic cobalt sites for oxygen evolution reaction (OER). Computational studies show that bidentate pyridyl groups enhance the susceptibility of the rate-determining Co(IV)-oxo species to the nucleophilic water attack during the critical O–O bond formation. This study opens a new route toward increasing the intrinsic water oxidati...

2D Network overtakes 3D for photocatalytic hydrogen evolution

“…Post-catalytic PXRD analysis of [Co-Ni] revealed that the 2D structure is retained S7e and f, ESI †). 33,34 Similarly, the FTIR spectra of [Co-Ni] (Fig. 3e and Fig.…”

Different Agglomeration Processes Induced by the Varied Interaction of Fe–Fe Analogues with Differently Charged Surfactants

“…8 Cyanide-based coordination polymers Co−Fe PB have better water oxidation activity than the ones with a pentanuclear molecular structure. 6 Highly crystallized Na 2−x Fe-[Fe(CN) 6 ] y shows better stability as well as higher battery capacity than the low crystallized ones. 9 Besides tuning the PBAs through regulating the synthetic strategies, 6,9,10 many efforts have been devoted to study the effect of surfactants on the structures and sizes of PBA materials as well as on the catalytic activity of the PBA-derived materials.…”

“…6 Highly crystallized Na 2−x Fe-[Fe(CN) 6 ] y shows better stability as well as higher battery capacity than the low crystallized ones. 9 Besides tuning the PBAs through regulating the synthetic strategies, 6,9,10 many efforts have been devoted to study the effect of surfactants on the structures and sizes of PBA materials as well as on the catalytic activity of the PBA-derived materials. 11−14 For example, it was found that the anionic surfactant sodium dodecyl sulfate (SDS) tends to adsorb on the (111) face of MnCo PB, which inhibits the decomposition of the (111) face and the growth of the (100) face, leading to the eventual formation of a hollow cube.…”

“…In the 1960s, the General Tire & Rubber Company discovered that Prussian blue analogues (PBAs) can catalyze the ring-opening polymerization of epoxy compounds with high activity . Since then, PBAs have been tested in various catalytic reactions, such as transesterification reactions, reduction reactions, − oxidation reactions, and so forth. PBAs stand out from other metal materials as catalysts due to their facile synthesis method, low-cost raw precursors, abundant transition metal in the framework, as well as controllable size and morphologies. , The controllable preparation of PBAs provides a possibility to reveal the relationship between the structures and the catalytic activity, which is very helpful for designing more efficient catalysts.…”

“…Since then, PBAs have been tested in various catalytic reactions, such as transesterification reactions, reduction reactions, − oxidation reactions, and so forth. PBAs stand out from other metal materials as catalysts due to their facile synthesis method, low-cost raw precursors, abundant transition metal in the framework, as well as controllable size and morphologies. , The controllable preparation of PBAs provides a possibility to reveal the relationship between the structures and the catalytic activity, which is very helpful for designing more efficient catalysts. For example, lattice volume has a significant effect on the ion storage capability of PBA cathode materials .…”