W O bond shortening by doping of first-row transition metal ions that enhances its catalytic potency

Abstract Here, we report thorough spectroscopic characterization of tungsten oxide (WO3) nanoparticles (NPs) and WO3 NPs surface doped with transition metal (TM) ions (TM@WO3; TM = Cr3+, Mn2+, Fe3+, Co2+, and Ni2+) by using various surface analysis techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), high-resolution X-ray photoelectron spectroscopy (HRXPS), and extended X-ray absorption fine structure (EXAFS). At first glance, the morphologically distinct features were not perceivable across TM dopants. However, the detailed XPS analysis confirmed that the WO3 NPs doped with Cr and Fe ions formed a relatively large number of surface defects. Moreover, we found through EXAFS analysis that the chromium and iron ions doping on WO3 NPs promoted the dramatic shortening of the W O bond length as compared to pristine WO3 and other metal ion doped WO3 NPs. Much enhanced photocatalytic and electrocatalytic activities of Cr@WO3 and Fe@WO3, which relied on the different density of surface defects created by the charge and size of the TM dopants, were demonstrated in the photocatalytic degradation reactions of 4-chlorophenol and the electrocatalytic hydrogen evolution reaction. The present result can serve as a practical guideline for atomically precise control of oxygen vacancy toward the development of high-performance metal oxide photocatalysts.