Surface Oxygen Vacancy-Dependent Electrocatalytic Activity of W₁₈O₄₉ Nanowires

Surface oxygen vacancies (SOVs) are the most relevant surface defects in metal oxides (MOs), and they participate in numerous physical and chemical reactions. However, information on the nature, distribution, formation, and reactivity of SOVs, as well as relationships among SOVs, is lacking. Investigating SOVs is difficult because of disturbance by the crystal phase, morphology of bulk materials, and synergistic effect between substrate and catalyst host. Herein, by clarifying the origin of SOVs and their distribution, one-dimensional (1D) tungsten oxide nanowires (NWs) with numerous SOVs were synthesized. Compared with the three-dimensional nanostructure, the high aspect ratio of 1D NW exposed the SOVs on the surface of the nanostructure rather than embedding them in the bulk. To investigate accurately the effect of SOVs on electrocatalytic activity, we clearly identified how SOVs of tungsten oxide catalyst regulate iodide reduction reactions in the solar cell by in situ filling of SOVs in electrodes and maintaining the crystal phase and morphology of NWs. Iodide reduction reaction activity was notably dependent on tungsten oxide catalyst SOVs, which serve as important catalytic site descriptors. These findings may clarify the fundamental features of SOVs on metal oxides and contribute to the rational design of efficient catalysts and supports.