Enhanced charge separation and hole injection of Ti–Fe2O3 photoanode by ultrathin CoCu-MOFs for efficient photoelectrochemical water oxidation

Cobalt-based metal-organic frameworks (Co-MOFs) are considered excellent cocatalysts for improving the photoelectrochemical performance of photoanodes. Considering the boundedness of monometallic MOFs, introducing a second metal is an efficient method to enhance the activity and stability of Co-MOFs. In this work, Cu doped Co-MOFs was successfully decorated on Ti–Fe2O3 to prepare Ti–Fe2O3/CoCu-MOF. The photocurrent density of composite photoanode at 1.23 V vs. RHE reaches 2.06 mA/cm2, 5.5 times higher than that of Ti–Fe2O3, and the onset potential shifts 170 mV negatively. The results showed that CoCu-MOFs thin layer not only provided abundant active sites, but also effectively passivated the acceptor surface states of Ti–Fe2O3, thus inhibiting surface charge recombination. In addition, the introduction of Cu2+ can induce the generation of higher valence Co species, which significantly promotes the transfer of holes from Ti–Fe2O3 to the electrolyte. Our work demonstrates a new and promising photoelectrochemical cocatalyst, and provides a convenient method for the construction of other bimetallic MOFs materials.