Remarkably promoted photoelectrochemical water oxidation on TiO2 nanowire arrays via polymer-mediated self-assembly of CoOx nanoparticles

Abstract Water oxidation catalysts (WOCs) play an important role in performance improvement for TiO2 photoanode-based photoelectrochemical (PEC) water splitting, but their promotion effect is greatly restricted by the deep valence band of TiO2 and great challenges to maximize their electrocatalytic water oxidation activity and synergistic interaction with TiO2. Herein, we report direct growth of ultra-small, uniformly dispersed, and highly dense CoOx nanoparticles (NPs) on TiO2 nanowire arrays (NWAs) via polymer-mediated self-assembly, in which the polymer serves simultaneously as a linker, stabilizer, and reductant. The obtained nanohybrid arrays show a photocurrent density of 2.09 mA cm−2 and a photoconversion efficiency of 1.01%, which are 3.17 and 3.37 times, respectively higher than that (0.66 mA cm−2, 0.30%) of pristine TiO2 NWAs, and are among the largest reported for WOC-assembled TiO2 photoanodes. Further, their photocurrent density decreases only by ~11.81% while that of TiO2 NWAs decays by ~54.40% after 6900 s. The remarkable promotion effect of CoOx NPs is ascribed to their high intrinsic catalytic activity, ultra-small size, uniform dispersion, and high density significantly enhancing charge separation and hole injection and accelerating charge transfer and transport. This work not only creates a novel CoOx NPs/TiO2 NWA photoelectrode to significantly promote the PEC water oxidation performance of TiO2 NWAs and provides scientific insights into the enhancement mechanism, but also offers a general strategy for self-assembly of WOCs on various photoelectrodes with complex geometries for PEC water splitting.