Tri-functional molecular relay to fabricate size-controlled CoOx nanoparticles and WO3 photoanode for an efficient photoelectrochemical water oxidation

Abstract

Heterojunction and element doping to couple light-harvesting semiconductors with catalytic materials have been widely employed for photoelectrochemical (PEC) water splitting. However, both suffer from serious electron–hole recombination, although the intimate interactions of the components is propitious for the charge transfer. In addition, the densely packed surface screens the active core from the catalytic media, leading to restricted performance. Here, a CoO_x-decorated WO₃ electrode (C-M2P-CoO_x/WO₃) was engineered via the organic linkage 3,3-diphosphonopropanate (C-M2P) for PEC water oxidation in a neutral medium. The C-M2P functions to control the colloidal CoO_x size and bridges the catalytic center and the WO₃ anode that allows an enhanced carrier density N_d to reach up to 1.9 × 10²¹ cm⁻³. Therefore, a strengthened charge separation was obtained and was further evidenced by the open circuit voltage decay (OCVD) measurements. The photovoltage decay revealed that the improved photoexcited electrons transfer could be attributed to the effective passivation of surface trap states. This brought about a generation of unexpected photocurrent as high as 3.5 mA cm⁻², and an incident photon-to-electron conversion (IPCE) reaching up to 71% under a combination of visible-light irradiation and applied bias. Together with the dramatically shortened charge lifetime and a large transient photovoltage on the assembled electrode, a proposed exciton transfer mechanism was established.