Hollow Ru/RuO₂ nanospheres with nanoparticulate shells for high performance electrocatalytic oxygen evolution...

This work shows that hollow Ru/RuO₂ nanoparticles having nanoparticulate shells (HN-Ru/RuO₂) can be prepared using hollow microporous organic polymers with Ru species (H-MOP-Ru) as precursors. Using silica spheres as templates, H-MOPs were prepared through the Sonogashira-Hagihara coupling of 1,3,5-triethynylbenzene with 2,3-ethoxymethylenedioxy-1,4-diiodobenzene. Acid hydrolysis of cyclic ethyl orthoformate protecting groups generated catechol moieties to form H-MOP-Cat. Then, H-MOP-Ru was obtained by incorporating Ru species into H-MOP-Cat. Heat-treatment of H-MOP-Ru under air induced the formation of HN-Ru/RuO₂ with a diameter of 61 nm and shells consisting of 6-7 nm nanoparticles. Due to the hollow structure and nanoparticulate shells, HN-Ru/RuO₂ showed a high surface area of 80 m² g^-1 and a pore volume of 0.18 cm³ g^-1. The HN-Ru/RuO₂ showed enhanced electrocatalytic performance for the oxygen evolution reaction (OER) with an overpotential of 295 mV @ 10 mA cm^-2 and a Tafel slope of 46 mV dec^-1 in alkaline electrolyte, compared with control RuO₂ such as commercial Ru/RuO₂ nanoparticles (A-Ru/RuO₂) and home-made Ru/RuO₂ nanoparticles (N-Ru/RuO₂) prepared via the same synthetic procedure as HN-Ru/RuO₂. While HN-Ru/RuO₂ inevitably contained Pd originated from coupling catalysts, it showed superior performance to Ru/RuO₂ nanoparticles with the same Pd content (N1-Ru/RuO₂), indicating that the efficient electrocatalytic performance of HN-Ru/RuO₂ is attributable to its hollow structure and nanoparticulate shells.