Enhanced photoelectrochemical water oxidation activity of BiVO4 by coating of Co-phenolic networks as hole-transfer and co-catalyst

Bismuth vanadate (BiVO4) has been regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting owing to its low cost, and small band gap energy (∼2.4 eV). However, the achieved current density of the BiVO4 photoanode remains far below its theoretical value (∼7.5 mA cm−2) because of its severe surface charge recombination. Herein, a simple process is developed for preparing a new type of low-cost metal-organic coordination composed of tannic acid coordinated with Co ions (TACo) as an efficient cocatalyst to suppress the charge-carrier recombination on BiVO4 photoanodes. For the BiVO4/TACo photoanode, a high photocurrent density of 4.8 mA cm−2 was achieved at 1.23 V (vs. reversible hydrogen electrode (RHE), AM 1.5 G), which approximately 3-fold higher than that of bare BiVO4. Systematic studies reveal that the enhanced water oxidation performance of BiVO4/TACo photoanode can be ascribed to the synergistic effect of following factors: (i) For the thermodynamic process, the photogenerated holes are directly transferred to TACo layer; (ii) For the kinetic process, the transferred holes can directly oxidied Co2+ to generate Co3+ active sites, which could directly oxidize H2O to molecular O2. This work provides a new tool-kit for designing efficient water oxidation PECs.