Role of the electronic state of rhodium in sodium borohydride hydrolysis

• In NaBH4 hydrolysis medium Rh/TiO2 catalysts were reduced.
• Electron-deficient rhodium particles were formed in the Rh/TiO2 calcined at 300 °С.
• The presence of these particles leads to enhanced decomposition of the BH4− ions.

The activity of Rh/TiO2 catalysts subjected to a thermal treatment at different temperatures prior to their reduction has been studied in a NaBH4 hydrolysis medium. It was found that the sodium borohydride hydrolysis rate increases with increasing the treatment temperature of unreduced catalysts. The state of rhodium in reduced Rh/TiO2 has been studied by a set of physical methods. In the catalyst calcined at 300 °С, nanoscale electron-deficient particles of rhodium were observed on the surface of titanium dioxide. The study confirmed that the decrease in the electronic density on the metal particles was due to interfacial charge redistribution between metal and semiconducting oxide. The presence of electron-deficient Rh particles on the catalyst surface leads to an enhanced decomposition of negatively charged BH4− ions and reduction of water to hydrogen proceeding by an electrochemical mechanism.

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