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Han, Yujin,Choi, Keunsu,Oh, Hyeonmyeong,Kim, Chanseok,Jeon, Dasom,Lee, Cheolmin,Lee, Jun Hee,Ryu, Jungki Elsevier 2018 Journal of catalysis Vol.367 No.-
<P><B>Abstract</B></P> <P>Highly efficient water-oxidation catalysts (WOCs) were readily prepared through the simple heat treatment of cobalt-containing polyoxometalate [Co<SUB>4</SUB>(H<SUB>2</SUB>O)<SUB>2</SUB>(PW<SUB>9</SUB>O<SUB>34</SUB>)<SUB>2</SUB>]<SUP>10−</SUP> (POM). The annealing of soluble POM molecules at high temperatures in air led to the formation of insoluble nanoparticles, of which the crystal structure and catalytic activity can be controlled by the annealing temperature. POMs were converted to amorphous and crystalline CoWO<SUB>4</SUB> nanoparticles when annealed at 400 and 500 °C, respectively. Interestingly, amorphous CoWO<SUB>4</SUB> nanoparticles exhibited excellent catalytic activity near the neutral pH of pH 8.0, making them superior to both pristine POM and POM-derived crystalline CoWO<SUB>4</SUB> nanoparticles. X-ray absorption and photoelectron spectroscopies combined with density functional theory (DFT) calculations revealed that their outstanding performance was resulted from the generation of large amounts of oxygen vacancies upon annealing, leading to the optimum distance between the nearest Co ions for the Langmuir-Hinshelwood (LH) mechanism. Based on these findings, we could readily immobilize CoWO<SUB>4</SUB>-based WOCs on the surfaces of various electrodes for efficient electrochemical and photoelectrochemical water oxidation through the annealing of POMs pre-adsorbed onto the desired electrode surface. This study may provide insights not only for the synthesis of efficient electrocatalysts derived from POMs but also for their immobilization onto the desired electrode surface for practical applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> POMs were converted to CoWO<SUB>4</SUB> nanoparticles by annealing. </LI> <LI> POM-derived a-CoWO<SUB>4</SUB> exhibited excellent catalytic activity for water oxidation. </LI> <LI> Its catalytic activity was closely related to the formation of oxygen vacancies. </LI> <LI> It was readily integrated on a desired surface by adsorption and annealing of POMs. </LI> <LI> This enabled simple preparation of efficient (photo)anodes for water oxidation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>