Regulating the binding strength of oxygen intermediates with a conductive π–d conjugated metal-organic polymer CoTAA on BiVO4 photoanode for efficient photoelectrochemical water oxidation

Abstract

The slow charge transfer and sluggish water oxidation reaction kinetics represent the main obstacles in the advancement of efficient BiVO4 photoanodes for photoelectrochemical (PEC) water splitting. Herein, a conductive π-d conjugated metal–organic polymer composed of 1,4,8,11-tetraaza[14]annulene (TAA) and atomically dispersed Co sites (CoTAA) was developed as an efficient oxygen evolution catalyst (OEC) to overcome these limitations. In CoTAA, the highly delocalized π-d conjugation results in superior electrical conductivity, leading to improved charge transfer. Additionally, X-ray absorption fine structure (XAFS) spectra and theoretical simulations reveal that the atomically dispersed Co sites within CoTAA, configured as Co-N4, modulates the binding strength of water oxidation intermediates (*OH, *O, and *OOH), thereby decreasing the energy barrier and facilitating the water oxidation reaction kinetics. Consequently, when combining with ultrathin FeOOH withdrawing the holes, the optimized CoTAA/FeOOH/BiVO4 photoanode achieves a high photocurrent density of 4.97 mA cm−2 at 1.23 VRHE under one sun irradiation (100 mW cm−2). This photocurrent represents a 2.59-fold enhancement when compared to that of pure BiVO4. These findings demonstrate the tremendous potential of π-d conjugated metal–organic polymers as active OECs in enhancing the PEC performance of water splitting.