Crystalline IrO2 nanoparticles decorated on TiO2 nanofibers as a robust water oxidation catalyst

Abstract

Photochemical water oxidation using solar light is an essential way to provide electrons for artificial photo-synthesis. To achieve an efficient artificial photosynthesis system, highly-active and robust water oxidation catalysts are critically required. Iridium oxide (IrO2) has been considered as a promising candidate material because of its low overpotential for water oxidation. In this thesis study, IrO2 nanoparticles decorated on nanofibrous titanium oxide (TiO2) scaffolds are synthesized as a water oxidation catalyst. Electrospinning technique was introduced to fabricate the nano-sized 1-D structure of TiO2 scaffolds. The IrO2/TIO2 hybrid nanofibers were prepared by mixing iridium nanoparticles and TiO2 nanofiber solutions, followed by heat treatment. The size and amount of IrO2 nanoparticles were controlled using the different concentration of iridium precursor solutions. The catalytic effect of IrO2/TIO2 hybrid nanofibers on water oxidation was confirmed using cyclic voltammetric analysis and oxygen evolution test. IrO2 nanoparticles with a diameter of 10 nm on the hybrid nanofibers showed higher turnover number (TON) than those of 30 nm-size IrO2 nanoparticles, and lower Ir contents on TiO2 nanofiber exhibited higher TON. The IrO2 nanoparticles on titanium nanofiber scaffolds could be used repeatedly without noticeable deactivation due to the high crystallinity of IrO2 nanoparticles on TiO2 scaffolds compared to IrO2 hydrate in a free solution. It was suggested that crystalline conjunction of TiO2 scaffolds and IrO2 nanoparticles facilitates the formation of high oxidation state on iridium oxide nanoparticles, which results in more efficient water oxidation activity of the IrO2/TiO2 hybrid nanofibers.