Spatial Control of Oxygen Vacancy Concentration in Monoclinic WO<sub>3</sub> Photoanodes for Enhanced Solar Water Splitting
Heejung Kong, Haechang Yang, Ji‐Sang Park, Weon‐Sik Chae, Hee Yeong Kim, Jucheol Park, Jong‐Hoon Lee, Seung Yo Choi, Miok Park, Hyeonwoo Kim, Youbin Song, Hyunwoong Park, Junyeob Yeo
Abstract
Abstract Oxygen vacancies (OVs) are a mixed blessing for the photoelectrochemical (PEC) water oxidation performance of monoclinic tungsten trioxide (m‐WO 3 ) photoanodes. Although it is widely accepted that a moderate concentration of OVs is beneficial for the PEC performance of the m‐WO 3 photoanodes, this argument assumes a uniform distribution of OVs throughout the m‐WO 3 crystal. In this case, only the overall concentration of OVs needs to be considered. However, the spatial non‐uniformity of OV defects in m‐WO 3 photoanodes has not been thoroughly examined. In this study, by employing a m‐WO 3 nanorod array as a model photoanode, the aim is to show that a higher OV concentration near the surface of m‐WO 3 compared to that in the bulk is advantageous for the PEC performances of this material. In addition, a laser‐assisted defect control (LADC) process is employed to manipulate the spatial distribution of OVs in the m‐WO 3 photoanodes to achieve enhanced PEC performances. Moreover, a one‐step laser deposition process is introduced to obtain an ultrathin FeNi oxygen evolution catalyst overlayer on the defect‐controlled m‐WO 3 photoanodes, further improving PEC performance, photostability, and Faradaic efficiency.