Immobilization of cobalt-based polyoxometalates on titanium dioxide nanorod for enhancement in photoelectrochemical water oxidation

In this study, an effective hole scavenger layer of polyoxometalates (POMs) with excellent redox properties and high durability is coated on titanium dioxide (TiO₂) nanorods to enhance the photoelectrochemical (PEC) water oxidation activity. Nanocomposite films, composing of cobalt-based POMs (Co-POMs) and TiO₂ nanorod, were first fabricated by hydrothermal reaction, following by layer-by-layer (LbL) growth of Co-POMs on the TiO₂ surface. It can be observed that the onset potential of Co-POMs immobilized TiO₂ photoanode was lower and the induced photocurrent at the applied potential of 1.23 V vs. reversible hydrogen electrode (RHE) was almost two times that of pristine TiO₂ under neutral conditions. Co-POMs layers would retard the recombination of photoinduced electron-hole pairs by extracting and transporting the generated holes, thus ameliorate the overall PEC performance. There was an optimal number of Co-POM layers beyond which the produced photocurrent density started to decline. This work provides a facile LbL method to deposit Co-POMs layers on TiO₂ nanorod to promote PEC water oxidation under a neutral environment, which is proved to be more favorable for long-term application.