Delicate manipulation of cobalt oxide nanodot clusterization on binder-free TiO₂-nanorod photoanodes for efficient photoelectrochemical catalysis

Abstract

In this work, to probe the crucial role of photo nanosensitizer clusterization played in determining the performance of the photoelectrocatalytic process, an illustrative nano-regional heterostructure was constructed via novel in-situ loading ultra-small cobalt oxide nanodots (<3 nm) onto the surface of titanium dioxide nanorod array grown on FTO substrate. Photoelectrochemical studies showed that photocurrents of TiO2 nanorod anodes could be remarkably improved through loading with CoOx nanosensitizers, benefiting from the broadened light-responsive range and alleviated charge carrier recombination. For the first time, Förster-resonance energy transfer (FRET) assisted nanosensitizer re-excitation effect was observed. Beneficially, the lost energy through radiative-emission from TiO2 could be efficiently reutilized by adjacent CoOx, generating extra charge carriers on nanosensitizers for further improvement of photoelectrocatalytic performance. Importantly, we directly observed the strong clusterization tendency of CoOx and morphology evolution from sub-3 nm nanodots to clusters larger than 20 nm when their loading amount is slightly increased. Furthermore, photoelectrochemical (PEC) performance of photoanodes based on TiO2@CoOx hybrid structures underwent significant enhancement initially and sharp decline eventually. We reason it that the formation of large sensitizer clusters would severely block the charge carrier transfer from nanosensitizers to TiO2 nanorods and lead to exacerbated charge carrier recombination and photoelectrocatalytic performance.