An Inorganic–Organic Hybrid Polymer Cocatalyst for Photoelectrochemical Water Oxidation with Dual Functions of Accelerating Kinetics and Improving Charge Transfer

Schiff Base Complex Cocatalyst with Coordinatively Unsaturated Cobalt Sites for Photoelectrochemical Water Oxidation

“…Therefore, the superior PEC activity of the BiVO 4 /MF photoanode should be ascribed to the decoration of MF complex to stimulate the charge carrier utilization with either effective photogenerated holes extraction ability or robust photoholes injection capacity, or both simultaneously. ,, To further gain more insights into the origins of the PEC improvement, the hole injection (η inj , Figure e) and charge separation (η sep , Figure f) efficiencies were measured in an electrolyte containing 0.5 M Na 2 SO 3 as a hole scavenger (Figure S29). ,, It is clearly revealed that the η inj and η sep of the BiVO 4 /MF photoanode are both significantly higher than those of blank BiVO 4 at the entire applied potential region (ranging from 0.6 to 1.3 V RHE ), confirming that the decoration of cobalt–organic complex is an effective strategy for the enhancement of charge separation and surface reaction. − …”

“…20 Figure S5 depicts that the characteristic −C�N groups peak is shifted to 1612 cm −1 because of lone pair density toward metal ions, evidencing that N atoms in imine groups are successfully coordinated with Co metal ions. 34 Besides, the characteristic peak of −OH groups is extraordinary shifted to 3640 cm −1 with negligible intensity (Figure S5), which is ascribed to another coordination of −OH groups in the ligand with metal Co ions. 35 The FTIR spectrum of BiVO 4 /MF is similar to that of the cobalt−organic complex (Figures 2d and S5), wherein the characteristic peak of −OH groups with more stronger intensity appearing at 3420 cm −1 , which probably indicates the formation of new bonds such as Co−O−Bi or/and Co−O−V (the latter will be excluded in following discussion) to release part of −OH groups without coordination.…”

“…With elevated coordination numbers and diverse coordination modes, Co 2+ metal ions can easily coordinate with ligands containing oxygen and nitrogen atoms. ,,, When the Schiff base ligand (structure is confirmed by 1 H NMR, see Figure S1) acts as an asymmetric unit (Figure a,b), Co 2+ metal ions cannot completely coordinate with ligands by virtue of the steric hindrance introduced by adamantane and 4,4-bipyridine groups to leave one or more coordination sites with solvent molecules as the end groups. − In the cobalt–organic complex with one-dimensional chain (Figure S2) and two-dimensional layer (Figure S3) structures configured by coordination-driven self-assembly process, these solvent molecules are discharged easily from the coordination skeleton and thus the coordinatively unsaturated sites are obtained. , The crystal structures of the pristine BiVO 4 and BiVO 4 /MF photoanodes were characterized by X-ray diffraction spectroscopy (XRD, Figure c). Except for the FTO substrate, all the characteristic diffraction peaks on the XRD patterns are consistent with the monoclinic phase BiVO 4 (JCPDS No.…”

“…14–0688) and no distinct diffraction peaks belong to the cobalt–organic complex are detected in BiVO 4 /MF. , Similarly, the Raman spectra for both BiVO 4 and BiVO 4 /MF are identical in Figure S4, with no significant difference in the Raman bands (see discussion of Figure S4). This is possibly due to the poor crystallinity of the cobalt–organic complex that is lower than the detection limit. , …”

“…To address these issues, exploration of organic–inorganic hybrid OECs possessing high chemical structure stability together with enriched catalytic active sites is necessary. ,,, Recently, transition metal–organic complexes have attracted much attention because of the combined advantages: (i) better stabilization than molecular OECs, (ii) rich accessible unsaturated metal sites, and (iii) no extra reconstruction or defects engineering process. − The crucial configuration procedure for effective metal–organic complexes is the design of organic ligands with integrated functional groups. − Therefore, developing organic ligands providing more possibilities for the construction of outstanding metal-based complexes of OECs are urgent. With a general formula of R-HCN-R, Schiff base ligands contain at least one azomethine or imine groups, which are one of the most active linkages in coordination chemistry. − Therefore, Schiff base ligands can incorporate catalytically active metals in a series of oxidation states .…”