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Water Oxidation Catalyst via Heterogenization of Iridium Oxides on Silica: A Polyamine-Mediated Route To Achieve Activity and Stability

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journal contribution
posted on 21.07.2016 by Nagaraju Shilpa, Joydeb Manna, Parasmani Rajput, Rohit Kumar Rana
Heterogenization of nanostructured iridium-based catalysts to simultaneously achieve activity and stability in the catalytic water oxidation with cerium ammonium nitrate (CAN) as the oxidant is reported herein. We demonstrate that a polyamine-mediated assembly process to disperse iridium species on mesoporous silica spheres facilitates the fabrication of nanosized iridium oxides under optimal thermal treatment. From comprehensive morphological and electronic structure studies including electron microscopy, UV–vis spectroscopy, XANES, and EXAFS, we show that the influence of polyamine is crucial in stabilizing catalytically active iridium oxides in the mesoporous silica matrix. While the functionalization of the silica surface with polyamine facilitates interaction with the negatively charged iridium precursor, the presence of polyamine further enables control of the dispersion and crystallization of the generated iridium oxides during the thermal treatment at 573 K. As a consequence, the catalyst exhibits enhanced activity with higher TON along with desirable stability to allow it to be recycled while keeping the activity intact. The activity and stability of the synthesized catalyst in comparison with those of IrCl3 and IrO2 reveal that balancing between the dispersion and crystallization of iridium oxides is crucial in heterogenization of the catalyst.